GoldenMotor.com Forum
General Category => General Discussions => Topic started by: OneEye on July 11, 2007, 11:52:54 PM
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Is the low voltage cutoff on the controller adjustable? (so you can change it based on which battery chemistry is being used)
What is the factory setting? (even if not adjustable)
-Mike
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I asked Philip Yao for a schematic diagram of the controller several months ago. Maybe if you ask him too he will provide us with one.
The cut-off problem involves not just the lowest voltage but how long the cut-off voltage is surpassed. The duration setting, when using lead acid batteries, may be even more important than the voltage level since even a half discharged lead acid battery pack can dip below full discharge of 10.5 volts and then come back up to 12.5 when the load is reduced or removed.
This morning I connected three good batteries and one bad one in series to my 48 volt controller. The bad one has a dead cell so I got a good feel for where the cut=off voltage is on this controller. I saw total voltage go as low as 40 volts in just a flash before the controller cut-off but it also cut=off at voltages as high as 44 volts. My meter only read in half second intervals so the actual momentary voltage low and long enough to trigger the cut-off seemed to average around 42.5 volts. Divide by 4 and guess what? You get 10.625 volts. Since full discharge is 10.5 volts my theory is that the controllers are intended to cut off below 10.5 for any duration more than half a second. That means 31.875 should be the expected cut-off for a 36 volt controller. Fortunately I took my 36 volt controller along and when there was not enough power left in the dead cell to keep the pack above 42.5 volts I switched to the 36 volt controller and maintained 40. volts the rest of the way home, hitting 38 volts only once on the next to the last hill climb.
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Too bad it is not a programmable or adjustable voltage cutoff. Depending on the cell count, LiFePO4 or other lithium chemistries can have a lower cutoff voltage and still not kill the battery by over discharging them.
I've been reading a lot of success stories from folks grabbing the DeWalt 36V tool batteries and using them as-is in their e-bikes (heinzmann, wilderness electric, and Crystalyte motors for the most part). The packs have a much lower end-of-discharge voltage, about 22V. If the controller cuts out at 31.5 volts you may be missing out on a significant chunk of the cells available energy.
Some remote control aircraft enthusiasts have been putting the lithium cells from the DeWalt packs through their paces and have run them at 30A through more than 1000 discharge cycles (to 100% depth of discharge) and they still had almost 80% of initial capacity. That makes it sound like they will really stand up to a beating.
As with all Lithium ion batteries, the packs are a bit expensive (going rate on ebay is ~$105 shipped). They deliver 2.3Ah each, so about 57.5Wh through 100% discharge. A pair should give around 6 or so miles of motor-only range. If someone actually continues to use their e-bike over the long haul they are probably 1/3 the cost of lead-acid batteries. The lithium batteries are also much lighter, about 2.5lbs for each DeWalt pack.
On another forum, someone mentioned there is a way to replace resistors on a different controller (Crystalyte, I think) to change the cutoff voltage. Maybe with the controller schematic we could figure out how to do a similar thing. I'm guessing it would involve placing a lower R on a pull-up line.
The LiFePO4 packs GoldenMotor sells probably have enough cells to match the low-voltage cutoff of 31.5V at nearly 100% depth of discharge.
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The solution I discovered this morning for a single dead cell should be applicable for batteries where full discharge is a much greater percent of full charge. In other words I lowered my cut-off voltage by switching to a lower voltage controller instead of racing home I got home at normal speed with plenty of reserve due entirely to the good cells remaining in the bad battery. Another option I'm looking at in line with this idea is to use single cell (2.1 volts) SLA/AGM batteries intended for portable high current electronic devices. It might also be a lot cheaper in the end in regard to replacement than having to throw away a battery with 1 bad and 5 good cells.
However, I think the fuel cell may be the answer since its output is nearly the same as the line powered charger depending on what happens with cost for the unit and for the hydrogen and whether or not you can make your own since the storage system is hydride which I do not think is pressurized although I would prefer a fusion reactor. ;D
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They also have fuel cells that run on liquid methanol. I believe they have some that run on about 500mL per hour for 500W continuous output.
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I've been to a web site of a company either in Denver or Provo that has a whole range of outputs and fuels including Methane and Methanol but the smallest output is 1,000 watts and it is too big and expensive for an ebike. Company did not respond to numerous emails requesting more info regarding fuel cells for ebikes.
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Does anyone have a schematic of the controller yet??? I'd like to adjust the high voltage cutoff of my 36V controller for use with a 48V battery.
Pete
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I am having the same problem using the Nimh packs, the cutoff is set too high so I am only getting about 30-40% from the packs before the controller starts to shut down the motor, looks like its back to SLA :(
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Anyone with a controller can start on a schematic by scanning their circuit board at high resolution and posting it. We can do circuit traces and find out what most of the components on the controller are. If we compare to other controller schematics (I believe there is a crystalyte schematic on the endless sphere forums) we may be able to figure out where the voltage reference / sense is, and perhaps someone who is good with electronics can recommend a modification to change how that is read. I am told you can do a resistor change on a crystalyte controller to change the low voltage cutoff. The same is likely to be true of this controller.
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Not necessarily. The new regen controller has a micro controller chip and the only stuff on the board is what's necessary to support the interface with the mosfets. Before you go tearing your controller apart you might want to just write down all the part numbers and then look them up. Some companies, however, use parts with assembly labels so in that case forget abut even looking up the parts. Hate to disappoint. :( :'(
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I found the low voltage cutoff for the 36V controller... I'll try to post a pic this evening when I get home... Basically if you take a look at the edge of the board on the opposite side from the FETs there is a location that is marked (on the silkscreen) as a resistor, but is actually just a small piece of metal soldered in place. To raise the voltage cutoff (i.e. for 48V operation) you can just add a resistor inplace of the wire. (3.5K for approx 42V cutoff) To lower the cutoff it should be possible to just replace the 11K resistor next to it with a slightly smaller one.
If anyone has found a way to disable the high voltage cutoff it would be most appreciated. I tried e-mailing goldenmotor to find out how to order a 48V controller but there is still no response.
Pete
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Most controllers will have a micro chip, this drives the PWM on the fet's to control the motor. You can sometimes guess about which pins serve which functions by comparing to similar models. Admittedly it isn't a sure thing.
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It's quite easy to trace back the Hall inputs and the FET outputs. Also the LM56 temperature sensor. I still can't figure out the over voltage cutout though.
Pete
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You can find out which chip they are using for the microcontroller, and see if it has an internal voltage reference in its specification. Occasionally the voltage comparison will be tied to a specific pin on the microcontroller. Otherwise you would use another chip to serve as the voltage reference and it would provide a high-low signal to one of the microcontroller's I/O pins.
Of course EE is well outside my area of practice, so everything stated above is highly suspect.
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You guys are not hearing what I am saying... microcontroller means microcontroller as in software. Yep, that's right. Software to control both the low and the high (is there really such a thing?) cutoff. Of course there could be a dedicated onboard cutoff that's part of an overvoltage/undervoltage protection circuit but my guess is that for things like different type batteries or hookups its all controlled by the software.
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I am keenly aware the microcontroller uses software to makes decisions based on what it senses. There are occasionally ways to change what the microcontroller is actually sensing, which could have the effect of perhaps lowering or raising a cutoff voltage.
For instance:
1. If the microcontroller is using an external chip for its voltage reference signal (ie it gets a TTL high or low from an external chip based on when the voltage moves out of 'spec') you can change or replace the voltage reference chip to change the thresholds where it signals a bad voltage condition.
2. If the microcontroller uses an internal voltage reference (the specs on the specific microcontroller can help in this regard), it is sometimes done through a serial resistor that scales the actual voltage to the sensed voltage. Changing the resistor can adjusts the scale so the desired cutoff voltage is now sensed as though it were the stock cutoff voltage.
This has been done on other controllers. A schematic is (obviously) extremely helpful.
It is obviously a warranty voiding experiment, and chances of success are limited. It would be neat if the controller had a software setting to change the cutoff voltage to different values, but that is obviously asking a lot. If all else fails you can always buy a 3rd party controller that has the right voltage cutoff (or a programmable cutoff) as a feature.
Oh well, wishful thinking.
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Let me back up here a minute... Atmel makes a dandy 3 phase microcontroller (http://http:/www.atmel.com/products/AVR/) that you can power with an external voltage regulator from most any supply level above TTL. It may even offer sin wave output!
You merely need to write a program to set the operating range (top and bottom cut-off) based on input from a supply voltage sensor. The two operating range criteria are then, 1.) preventing deep discharge, and 2.) not exceeding the mosfets maximum power rating.
With large enough mosfets, top cutoff might not even be an issue, which leaves only deep discharge a concern. It probably would not be to difficult to construct a cutoff circuit for each battery in the pack so that this problem is solved.
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True, that would be a good approach. Essentially you always feed the microcontroller pin responsible for voltage sensing with the "right" signal and then offload the low-voltage cutoff elsewhere.
In effect you remove the controller from the voltage cutoff part of the equation and use a different method to protect the battery system. Some of the lithium chemistry battery packs already have low-voltage protection in their BMS (to prevent voltage reversal in a cell = dead cell, and possible thermal runaway)
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DIY motor controller (http://www.youtube.com/watch?v=4FZoaqAqRtQ&mode=related&search=)
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The 36V controller uses a PIC16F72.
The pins are (as far as I can tell):
1: not MCLR (drag low to reset the processor)
2: ???
3: Measure input voltage for low voltage cutout
4: ???
5: Throttle input
6: Brake input
7: ???
8: GND
9: Oscillator
10: Oscillator
11: ???
12: ???
13: ???
14: ???
15, 16, 17: Hall sensor inputs
18: Green LED
19: GND
20: +5V
21: ???
22: ??? (connected to the LM356 op-amp chip)
23, 24, 25, 26, 27, 28: Outputs to the FET gate drivers.
If anyone has more info please share.
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Did you scan or take a photo of the circuit board while it was out of the extrusion case? (both sides)
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Here's the datasheet for the microcontroller: http://ww1.microchip.com/downloads/en/devicedoc/39597b.pdf
Pin 3 can serve either as a TTL I/O port, or as an analog/digital converter. That still leaves it somewhat ambiguous what is triggering the low voltage cutoff.
More information is needed:
1. Follow the trace from pin 3 to see what other components are feeding the signal to it.
2. Put a voltmeter on it in operation as the battery voltage drops below 31.5V.
If the voltage on that trace goes from ~5V to ~0V, this would indicate a TTL I/O port, so a separate component is providing the voltage sensing logic.
If the voltage on that trace goes from ~0V to ~5V, it would also indicate a TTL I/O port, but the controller is looking for a positive "bad voltage" signal. In that case, cutting the trace might disable the low voltage cutoff.
If the voltage on the line doesn't show a sharp transition, it would indicate the pin is being used as an A/D converter. The A/D inputs can use either supply voltage or voltage on pin 5 as a reference. Pin 5 is noted by pdonahue as being the throttle input, so if it is being used as an A/D converter it must be comparing the voltage on pin 3 to VDD. In a way that's too bad, if it had been using pin 5 as the voltage reference we could just play with the voltage provided to pin 5 (a diode on the line to drop the voltage?) in order to make the controller think the voltage on pin 3 was a bit higher.
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myelectricbike said:
DIY motor controller
There is also the Open Source Motor Controller (OSMC) as an option. Definitely only for someone who knows a lot about electronics design though.
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I suspect that the low voltage cutoff is under software control, however I think the high voltage cutoff must be implemented using some sort of latching hardware (that then feeds into a digital I/O pin on the MCU) since doing a processor reboot doesn't reset the high voltage cutout. The only way I have found to reset the high voltage cutout is to remove power, wait for the caps to discharge, and then reconnect the power.
Pete
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Thanks for all the info you are putting up, pdonahue. Does the 11k resistor on the trace from pin3 go directly to the supply voltage? If so, you're probably right about changing out the resistor to give a higher sensed voltage for the low voltage cutoff. I should go find a circuit simulator to play around with the numbers and see what would change the low voltage cutoff to ~22V. You mentioned in that post that you took a picture. Can you post it for us?
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Did you read the note on page 2 for the PIC16F72...? The PDF file will not even allow it to be copied...
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The 11K does in face go directly to the supply voltage, but it is also connected to GND by a 1.2K resistor forming a voltage divider such that the actual voltage at the pin is:
Vpin = (Vin) * (1200 / (11000+1200))
I think I am recalling the resistor values correctly, but I'll check this evening. The original cutout is at around 31.5 volts (3.1 volts at the pin).
Changing the 11K to a 7.5K would set the cutout to the correct value, but that would make the pin voltage ~5.8v for a fully charged battery. I doubt that the PIC will appreciate having any of its pins that high.
A compromise would be to try a 9K resistor so that 42v input gives close to 5v at the pin and the cutoff is around 26v.
As for the picture, I don't have my flash card here so I'll have to try to remember to post it tonight.
Pete
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Which "note" are you referring to?
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Actually, that 7.5K resistor should be just about perfect for using DeWalt batteries. Right off the charger they are 36V and drop quickly down to 33V and lower. At 36V, the pin voltage would be just about 5.0V. The input pins will take VDD+0.3V if they are being used as A/D inputs. I'm assuming VDD is somewhere near 5.0V.
At low voltage, 22.5V will show as 3.1V on the pin, which would be the same as an SLA setup at 31.5V.
If I remember my physics of electricity and magnetism correctly, paralleling a 24K resistor with the 11K resistor will give you an effective resistance of about 7.5K.
Thanks pdonahue!
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right click on the link and "save target as..." if you want to save a local copy.
I'm glad these are bikes and not medical devices.
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Which "note" are you referring to?
The note to the OEM about the security of the micro-code... Think I'll look at using a dedicated 3 phase BLDC PM chip, hopefully with sin output, so that trying to figure out the micro-code will not be an issue or even in the way.
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Which "note" are you referring to?
The note to the OEM about the security of the micro-code... Think I'll look at using a dedicated 3 phase BLDC PM chip, hopefully with sin output, so that trying to figure out the micro-code will not be an issue or even in the way.
Actually, I havne't even tried reading the code. Anyone know if the protection bits are set or not?
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Good thing we can just alter the way the chip sees the world and not mess with the on-board firmware.
On a different note, I wonder if the high voltage sense pin is on a trace paralleled with a capacitor. If a high voltage condition ensues, the capacitor will maintain the overvoltage condition on the pin as the leakage current on an I/O pin is relatively small. That could explain why the overvolt condition lasts a long time, even after the microcontroller reboots.
Could a diode on the high voltage sense line drop enough volts to keep the controller from overreacting to 50.5 volts while still keeping it from allowing say 65 volts? Of course, that assumes someone figures out which pin is used for overvoltage sensing.
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My SLA batteries come of the charger and settle to 53.6 within an hour. I've never had any problem with cutoff. Someone familiar with the mosfets told me at one time they believed that the mosfets in the 36 volts standard Golden controller were capable of handling 58 volts so that I could power a standard 36 volt controller with 31 to 58 volts.
However, the 48 volt controller handles the extra power much better than the 36 volt controller. Acceleration is faster and top end is higher, etc. so for $78 it costs it seems like modding a 36 volt controller to do the job or a 48 volt controller is an awful lot of work for nothing, especially when it is the motor that needs help. Right now I'm putting the extra effort into upgrading the materials so I can rewind and rewire the motor.
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My plan is still to buy the 48V controller, but I figure it's going to be at least a few weeks until I get a response from sales@goldenmotor and then another few weeks to ship it to Canada. I'd like to get the 36V controller working in the meantime...
Pete
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Well certainly as back up its good to be able to have a 36 volt controller with you just in case you discover miles from home a dead cell in your 48 volt pack, etc. I'm just saying that its not the optimal plan to put it into service except as a standby unit - but then the effort might also pay off in finding out how to lower the bottom cutoff for the 48 volt controller so that you might not need to take a 36 volt controller along.
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Here is the pic of the controller. This site limits the size to 128kb so I had to shrink it down. I'm trying to track down the rest of the pin functions and hopefully figure out how to stop the controller from cutting out.
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Hummm... Since I no longer use the power cutoff breaks I'm thinking of mounting an old fashioned keyboard lock on the end of the controller to deter theft. Do you know the the green LED is for? I can see all sorts of potential for circuit add-ons and modifications.
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Re: Green LED
My guess would be that it is a status LED.. Just after power up with nothing connected it flashes 6 times then pauses, then repeats.
Pete
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Humm... a POST for a microcontroller? Humm...
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Probably not a POST... More likely used for debugging and trouble shooting during actual operation... I've used a single LED for debugging on a few PIC projects that didn't have a serial interface or a LCD.
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There is no software High Voltage Cutoff!!! It turns out that it's actually the KA7915 voltage regulator that doesn't like the higher voltage. It's connected to V+ via a 150 ohm resistor. It feeds directly into the 5V regulator to feed the PIC and low voltage circuitry on the board. The 150 ohm resistor is sized such that the voltage drop under normal conditions (i.e. Vin ~ 36V) the actual voltage that the 7915 sees will be OK. When larger voltage is applied, the 7915 can't handle it. It works for a few minutes then overheats. It ends up putting out about 5V in the fault (overheated) condition. With the voltage drop of the 5V regulator that means that about 3.2 volts ends up being applied to the 5V logic and the controller cuts out. You then have to wait for the 7915 to cool down (not wait for the caps to discharge as I has originally thought) before the controller will work again. I added 2 4.3V 5W zener diodes in line with the 150 ohm resistor and now the controller no longer cuts out. I've only taken it on a short run (~5km) so far, but I'll let you know tomorrow if I make it all the way to work (15km) and back with no problems!!!
Pete
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Inline like this...?
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Inline like this...?
Probably not... I guess he placed the zener where you placed the resistor (in your picture). The catode goes to the 7915 in, and the anode goes to the +B.
pdonahue, do you confirm this?
[]s
Roberto
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No, not like that.
Basically replace the (150 ohm resistor):
--- (150 ohm resistor) ---
with a series combination of the zeners and resistors:
--- (Controller V+) ==> (150 ohm resistor) ==> (4.3V zener) ==> (4.3V zener) ---
See the zeners in the attached pic.
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I'm not sure if I got the direction right in the pic, but the cathode (banded side of the zener) is toward V+ such that there is a 4.3v drop across it. The whole purpose of the zener is to drop some of the voltage that the KA7915 has to handle so it doesn't overheat. I'm off to bed. Good night and I'll let you know tomorrow if I make it all the way to work!!!
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You are correct Roberto!!! :) :)
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You are correct Roberto!!! :) :)
No, I'm not!!! I meant one thing, but wrote the opposite. Yes, the cathode is actually the banded side of the zener:
K ---|<|---- A
I must be tired... Sorry for that!
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Everything on my board is lacquered over so I can't read even the indent markings on the PIC. Where is the 7915? ...or did you mean the 7815?
Humm... ...seems like the resistor goes to an empty trace maybe for a 7915... but no 7915... which your photo shows as well...! ???
Hey... there's a red led... boy, this is getting exciting...! :D I wonder what those thing-a-ma-bobs over there on that piece of aluminum do... :-\ Maybe if I moved those leds to a couple of holes drilled in one of the end plates I could see what they were doing while I was riding... boy, this is getting exciting... :P
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Everything on my board is lacquered over so I can't read even the indent markings on the PIC. Where is the 7915? ...or did you mean the 7815?
Both are fixed 15V voltage regulators. 7915 is a negative voltage regulator and 7815 is a positive one. These are very commonplace.
I just noticed Peter mentioned a 7915, not a 7815. From his schematic, it must be a 7815 (it's referenced to ground and its input is tied to battery +V).
Don't get too excited about these LEDs. Sometimes they're just used as very low voltage zeners.
Roberto
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Too late! I've already remounted the circuit board from the level indicators to the same end plate on the controller where I'm remounting the LEDs from inside the controller. The level indicators look like they use zeners to set the voltage level.
The P75NF75's though are what I'm really excited about... they are rated at 75 volts instead of 58 volts ...and 80 friggin amps.
Schematic??? What schematic???
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WOW, That is some impressive set of numbers!!! :o :o I wonder how fast you can push this controller (mph/kph) over stock?? Do you need to improve the heat sinks if you push up the voltage from stock 36 volts ??? If you guys are this successful with 36 volt controller , I wonder what the 48 volt controller is capable of ??? :D :) Keep up the work and post the final results !!! :) ;D
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I'll have to open the 48 volt controller before I can see what the differences are. I suspect for one thing that the mosfets are spaced further apart rather than anything else being much different. Hard to guess without opening her up.
OK, I finished the LEDs. I grabbed the wrong hookup wire - telephone wire with the hot melt glue strands wrapped in a thin foil of copper. How I ever got it soldered to the LED stub leads or to the traces on the board I'll never know but sure enough the green one flashes when the throttle is disengaged and the red one must be a power indicator to let the assembler/repairman, etc. know that there is power to the board. Anyway it was a lot of work but now I have 5 different blinky or whatever LEDs shining on one end of the controller. :P ;D 8)
Do you have to increase the resistance to 266 ohms to limit current to 240mw when you apply 48 volts or is 320mw OK? ...and do the two zeners drop the zener output voltage to the 7815 from 48 volts to 39.4 volts (48-(2*4.3))?
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It makes sense that it should be a 7805. The output is definitely 15V w.r.t. GND, not 15V below V+. It's hard to see the markings on the case.
I doubt that the zeners need to be 5W. That just happened to be what I had in my junk drawer. If I were actually buying parts I would probably replace the resister with a single 12V-5W zener since I doubt that the current draw of the MCU is more that 0.25A. In any case, I'm at work and got here without any problems!!! My average speed was a little over 40kph and the max was over 50kph (steep downhill). Probably could have gone faster but my fear of death kicked in and I applied the brakes ;D.
Have a great day.
Pete
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You are correct Roberto!!! :) :)
No, I'm not!!! I meant one thing, but wrote the opposite. Yes, the cathode is actually the banded side of the zener:
K ---|<|---- A
I must be tired... Sorry for that!
That makes two of us!!! You were correct on where I had placed the zeners though :)
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My average speed was a little over 40kph and the max was over 50kph (steep downhill). Probably could have gone faster but my fear of death kicked in and I applied the brakes ;D.
What about your uphill speed? And how steep is it?
I have pretty steep hills in my area -- did not measure them, but most cyclists get off their saddles and walk them up. My main ride is a recumbent (no power-assist yet) and, being a lazy rider, I never get off my seat. I climb these hills at speeds as low as 5 km/h (it's that hard - guess I'm not that lazy at all), but I do it as a workout anyway.
What impressed me the most about the hub motor on the front 20" wheel of my delta trike is that I can climb these hills with no pedalling at all. I don't think I would be able to do that on a 26" wheel.
This trike is kinda heavy. If I stop or slow down in the middle of an uphill, the low-v cutoff comes in. My battery pack probably have a large internal resistance and drops its voltage significantly under high-current, but I think the controller is too conservative. I think I'll lower this threshold a bit.
Roberto
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My average speed was a little over 40kph and the max was over 50kph (steep downhill). Probably could have gone faster but my fear of death kicked in and I applied the brakes ;D.
What about your uphill speed? And how steep is it?
I have pretty steep hills in my area -- did not measure them, but most cyclists get off their saddles and walk them up. My main ride is a recumbent (no power-assist yet) and, being a lazy rider, I never get off my seat. I climb these hills at speeds as low as 5 km/h (it's that hard - guess I'm not that lazy at all), but I do it as a workout anyway.
What impressed me the most about the hub motor on the front 20" wheel of my delta trike is that I can climb these hills with no pedalling at all. I don't think I would be able to do that on a 26" wheel.
This trike is kinda heavy. If I stop or slow down in the middle of an uphill, the low-v cutoff comes in. My battery pack probably have a large internal resistance and drops its voltage significantly under high-current, but I think the controller is too conservative. I think I'll lower this threshold a bit.
Roberto
Hi Roberto,
There is only one very steep hill on my way home from work. It's a granny gear climb for sure. About as steep a hill as would be allowed for a public road. (I've done a cycle tour across Canada and this hill is on par with the hills in costal cities like St. John's and Halifax). When I first got the motor I tried it out and I made it to the top, but I was steadily slowing down from about 32kph at the bottom to 16kph at the top. It was around then that my 20A fuse blew. Luckily I was almost to the crest of the hill so I managed to gear down and pedal my way to the top. Now I always pedal with the motor going up it. With pedaling I can maintain about 30kph on 48V (used to be about 25kph on 36V). On normal inclines (around 7% grade) the motor is fine and can maintain 35+kph on its own, but the energy usage goes to ~1100 watts. My whole bike including motor and battery is around 90lbs and I'm a 200lb rider.
Pete
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Do you have to increase the resistance to 266 ohms to limit current to 240mw when you apply 48 volts or is 320mw OK? ...and do the two zeners drop the zener output voltage to the 7815 from 48 volts to 39.4 volts (48-(2*4.3))?
The resistor does not function as a current limiter. The current is completely determined by the draw from the 7805. The idea is that the current will average 30mA or so which will result in a voltage drop of around (.030*150)=4.5V across the resistor. So for a 36V battery (42v peak): Vin to the 7815 is 42-4.5=37.5. At that point the resistor is dissipating about 135mW. For 48V operation (54V peak), it is possible to put in a larger resistor (500 ohm) to decrease the voltage more:
(0.30*500)=15V to give 54-15=39V which should still be ok, but the resistor will be dissipating about 450mW.
Using the zeners as I have, the resistor will continue to dissipate 135mW, and each zener will dissipate 130mW. That means the the 7815 will have about 260mW less energy to dissipate and thus it should no longer overheat.
The actual voltage that the 7815 sees when the battery is actually at 48V is ~(48 - (2*4.3) - 4)= 35.4
Note that the extra 4 volt drop is the approximate drop across the resistor and will change depending on what the MCU is doing. i.e. it will be slightly hight when the MCU has the Green LED turned on and slightly lower otherwise.
Pete
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Thanks for this reply. I was not sure how to include the voltage drop of the resistor or the current draw of the 7815/7805 and MPU. So what will the voltage drops be if you then drop back to a 36 volt pack using this zener circuit?
Also I suggest the 36 volt or 48 volt regenerative controller for any kind of hilly area - especially steep hilly areas.
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Thanks for this reply. I was not sure how to include the voltage drop of the resistor or the current draw of the 7815/7805 and MPU. So what will the voltage drops be if you then drop back to a 36 volt pack using this zener circuit?
The voltage drop will be the same (~13V) so Vin to the 7815 will be:
42-13=29 at full charge
31-13=18 at full discharge
It may be a little higher or lower depending on the current draw. There won't be any problems until it drops to around 8 volts, at which point the Vin of the 5 volt regulator will be at around 6.? and the output of the 5V regulator will start to drop below 5V.
Pete
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There won't be any problems until it drops to around 8 volts,...
...which won't happen unless you lower the low voltage cutoff on the controller to something below 31 volts which would be in deep discharge territory and a bad idea ...right?
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The P75NF75's though are what I'm really excited about... they are rated at 75 volts instead of 58 volts ...and 80 friggin amps.
Don't get too excited, simplisticly the pwm controller + motor act as a buck converter. In other words, when going slow at full throttle, the voltage on the motor side pretty much drops to the motor's EMF, and the amps go up to make up for it, so you can end up with say 3-4X more A or so in the motor phase wires then what you get out of the battery.
Still I've managed to pull peaks of 60A's with P75NF75's, haul ass uphill at 40A. It worked for a few weeks, then one of the fets shorted. But this was under 36v, with 48 there's likely to be more amps still. However it should be possible to find fets close enoufgh to work but say, with twice higher ampacity, and lower on resistance (less waste heat).
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...amps from Counter EMF would better explain why the insulation is melting and the windings overheating. Never thought of that. This is my 4th or 5th rewire - this time to test 14 AWG with 90c temp insulation before using my last bit of Teflon 16AWG. If it's from Counter EMF then I'l have to develop a power absorption circuit.
When I was looking around inside the controller for neat stuff to do I found a lot of solder splashes which might explain the short you found.
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I checked my battery after it started cutting off on my way back from lunch today.
22.5 volts
How could I still be running on 22.5 volts if the cutoff it 31.5?
I could not give it full throttle at all without it completely cutting out, but about 1/4 throttle got me up the last hill (6mph).
It sure is hot here, 98 F. Kentucky is not supposed to get this hot for this long!
3 - 12volt 12 ah SLA in series for 36 volts is my battery setup.
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Since 10.5 volts is considered full discharge for any 12 volt lead acid battery (3 times 10.5 volts is 31.5 volts) and any lower reading means your batteries are in deep discharge.
I have measured cutoff on my controller at ~31.5 volts with two good batteries and one with a bad cell. If your controller is not cutting off at 31.5 volts then you should not use the controller because it will put your batteries into deep discharge, which will dramatically reduce battery life.
I do not repair controllers (yet) but I will test yours free of charge if you are willing to pay for shipping both ways. Let me know.
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I just got my kit a month ago, there should not be anything wrong with it.
Update:
I just checked my charger and it is only outputting 25.5 volts.
It is supposed to output 42.4 volts.
How do I get a warranty replacement on my charger.
I know it was charging with 42.4 when I first got it, I checked it with a meter.
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Have you ever plugged the charger into the line voltage and then connected it to the battery or disconnected the charger from the battery and then disconnected the charger from line voltage?
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Update:
I was using a meter from my supervisor at work and am not sure if it was off or what.
I used my meter at home and everything seems fine now. The batteries are charging to 43 or so volts before the charger cuts out.
I am not sure what was causing a false reading, but the charger puts out the exact 42.4 volts now
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Has anyone found a solution to using 36 volt DeWalt Li Ion Battery packs with the 36 volt controller? Apparently the controller cuts out at 31.5 volts drastically limiting the range that the packs can provide.
Has any one tried the solution that pdonahue suggested and oneeye added input to for using Dewalt packs? (Refer to “Cutoff Voltage” posts #26 and #28)
Would it be correct to add a 24K resistor at location R4 ? (Refer to “Cutoff Voltage” post #36 )
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You might ask zane@FoxxPower.com, the guy mustangman referred us to as a potential LiPo and LiFePo4 source. Since I need the cutoff to stay at 31.5 volts for my SLA/AGM batteries I have not even thought about circuit changes except to compare what was done in the new regen controller.
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Has anyone found a solution to using 36 volt DeWalt Li Ion Battery packs with the 36 volt controller? Apparently the controller cuts out at 31.5 volts drastically limiting the range that the packs can provide.
Has any one tried the solution that pdonahue suggested and oneeye added input to for using Dewalt packs? (Refer to “Cutoff Voltage” posts #26 and #28)
Would it be correct to add a 24K resistor at location R4 ? (Refer to “Cutoff Voltage” post #36 )
In my original post I suggested changing R73 to a smaller value to lower the cutoff, but it probably makes more sense to increase the 1.2k resistor instead (just to keep the current through the voltage divider roughly the same as in the original circuit). Changing it to a 1.5k should give a cutoff value of around 25.8v. The 1.2k resistor is located just to the right of where the arrow is pointing in the picture in my earlier post.
The cutoff is activated when pin connected to the voltage divided reaches about 3.1v, so the cutoff voltage can be found using:
Vcutoff = 3.1 * (R73 + R4 + Rsmall)/ Rsmall
Rsmall is the 1.2k resistor. I don't have the board here to see the number.
The factory setting is:
R73=11000
R4=0
Rsmall = 1200
To move the cutoff to around 42V for use in a 48V SLA setup, changing R4 to a value between 3500 and 4000 works well. (cutoff is around 40.5V for 3500 and around 42V for 4000)
To move the cutoff down to 26V, chance Rsmall to 1500 to give a cutoff of 25.8.
Note: I haven't actually tried moving the cutoff down, only up since I'm running a 48V SLA, but it should work. If anyone tries it and finds that it does work, please post.
Pete
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I just read back over my post after I posted it... Sorry about the spelling/typos... I haven't had my cappuccino break yet...
Cheers,
Pete
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Listen to Pete, he obviously knows more about electronics than I do.
My suggestion was to parallel a 24K resistor with R73. Adding the resistor at R4 would series them, so your cutoff voltage would shoot up really high (the low voltage cutoff condition would be triggered at anything less than 93V!)
I wouldn't worry too much about the line current after any changes, it doesn't change too much. The total resistance of the series between positive and negative after the modification would be 8.7K, so about 4 mA current would be flowing through the trace. P = (I^2) * R = 0.149W. Without the modification, total resistance is 12.2K, about 3mA, P = 0.106W.
You may want to research what the recommended low voltage cutoff is for the 10 cell series in the DeWalt packs. I was under the impression 22.5V was a good number, but I can't figure out how I came up with that number. I thought it was published somewhere, but now I can't find it, so it might be something I invented. I know the cells can go down to ~2.0V, but you want some cushion when you have a bunch of cells in series so you don't risk pushing a weak cell much below that value. One way to check would be to find out what low voltage the charger balks at. I'll post again if I find anything definitive.
-Mike
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May I suggest a switchable cutoff to take advantage of different battery chemistries. The default setting would be 36V SLA, then 48V SLA, 36v - 48v NiCd, 36v - 48 LiFePo4 ,this could be accomplished with a daughter board with a DIP switch or some similar method.
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A 1p6t rotary switch with the right resistors wired in place of R73 would do the trick. You could then have an arrow on the knob that points to the different options. Unfortunately there are probably too many different combinations to be practical, so everyone will need to do their own mod to what they are using.
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You can also use on-off and on-off-on switches in a matrix of resistors to provide the cutoffs you'll need.
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If you design it and build it, I would buy it! :)
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Thank you all(myelectricbike, pdonahue, oneeye, and mustangman) for your input. When there is time I will add a resistor to lower the cut-off voltage and then monitor battery voltage with a voltmeter as I ride. The whole world is waiting on good batteries at a reasonable price and efficient solar cells at a reasonable price to charge them. Who ever can get a good handle on either of those will be the next Bill Gates.
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I don't know if anyone is reading this string yet, but I can share some info on my e-bike project.
I have a 36V front hub motor kit. I live 12 miles from work.
I bought 120 NiMH AA cells for my battery pack. (2600mHR cells by T-energy ~$1.20 each.)
you can find these cells at www.all-battery.com.
They are arranged as 4 sets of 30 cells in series, housed in eight ~2' lengths of 1/2 Sched 40 PVC from menards.
I use B360B schottky diodes to tie the 4 sets together to make one 36V 10.4 AHr pack.
In the beginning I wasn't able to reverse engineer the charger and limit the charge current. As a result, I used resistors in series to limit the current. (messy) I also switched to 28 cells in a string (112 total batteries) because the pack voltage was too high for the charger. I now have the charger modified to 1A current limit (250mA in each string) and got rid of the resistors.
With the 28 cell configuration, due to cuttoff voltage, I was not able to deliver more than 5A to the controller
I also discovered R71 and change it so cuttof should be 29V, but haven't tested it.
I am now in phase 2. I'm making a 'smart pack' of 120 cells. I monitor each pair of cells (60 voltages) using 8 MSP430F2012 uP's. (each uP has 8 a/d inputs) If any cell goes to 0V, I can signal the controller to stop draining power by connecting the brake input to the 430's. (Ultimately I want to be able to switch out the string and run on the other 3 until they go as well.
If anyone is considering alternatives to Lead Acid, I'd consider NiMH cylindrical cells.
If you're willing to work with AA's (lowest cost) I paid ~$140 for 36V @ ~10AHrs. (This included 60 AAA's @ 1AHr as a bonus) and free shipping!
all-battery also offers D cells (10AHr) You could get 30 for ~$225, which isn't but probably the best deal you can get. This would simplify the design (only 2 MSP430's required!) but I don't know if there is a common PVC size that would fit the D cell.
I will keep posting on how well they hold up, but 500 cycles should be realistic, especially if my 430 protection design works.
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I use NiMH AA cells for things like mice and cameras and portable power for home made electronics projects, flashlights and all the rest so further investment in the technology is a possibility for me.
My only complaint so far is that of the 10 or so 4 battery per packs I recently purchased 4 have only held up for 20 to 30 cycles at the most and neither Wal-Mart or Target will take open battery packs or light bulbs that pop on the first day back.
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Here is a datasheet of a NiMH cell very similar to the ones I use:
http://www.all-battery.com/datasheet/2300mah.pdf
It gives a nice curve on capacity vs cycles if you properly charge/discharge the cell.
Perhaps the reason NiMH didn't work out is that your devices are expecting alkaline voltages (1.5V) and NiMH is 1.3V at light currents and 1.2V when discharging at C.
Recharging can also play a big role. This website has been very helpful in understanding batteries:
http://www.powerstream.com/
Click on Technical Resources, then "How to charge NiMH batteries"
If you want to see what I am trying to do with my MSP430 voltage monitoring,
http://www.powerstream.com/
Click on Technical Resources, then "Special Design Rules for Large Battery packs"
The device pictured at the bottom of this page is very similar to what I am planning to make for my e-bike. With active monitoring like this, the probability of getting 500 cycles should be rather high.
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Since the stated cycle life of NiCad is double NiMH why do you prefer NiMH, if cycle life is of concern?
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I would have gone with NiCd if I could have found a source for cylindrical cells at a good price.
With my NiMH selection from all-battery: $1.20/cell where each cell is 1.2V@2.6AHrs, thats $ 0.384 /watt*hour.
If I could find a NiCd battery that would beat that, I'd switch. (They are lighter to boot! BTW, my pack weighs 10.5lbs with PVC)
Of course this is with an unproven vendor (T-energy) so I've risked $140, and
all I have is a datasheet for a 'similar battery' that tells me I should still have 80% of capacity after 500 cycles.
Time will tell if I made the right choice.
One cool thing about my 'multiple strings of monitored cells' approach is that if later on I decide I want to add new cells to the pack, or even cells of a different chemistry, I can just switch out dead strings made up of old cells as they die early and let the newer cells keep trucking, or biking in this case.
Have you found any good sources for cylindrical NiCd's?
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Its been several months since I did my last search. To be honest my doctor has order me off the ebike until I loose 20 lbs. I never considered that gaining weight might be an ebike hazard. I've tried to stay with lead acid and pedal a lot using my regen controller but to be honest again I am a pitifully lazy creature. ;D
Actually, I can not recall where I found the best price with the greatest possibility of quality assurance but the total price was well above the price of either the Golden or the PowerStream packs and Golden may no longer sell the Ni Cads. http://www.goldenmotor.com/batterypack.htm (http://www.goldenmotor.com/batterypack.htm)
If you do a search on this site there have been a fair amount of posts suggesting the cheapest source of Nickle based battery technology may be from used Toyota Prius packs recovered from disabled vehicles.
Otherwise its the LiFePo4 technology everyone here seems to be eying. If you check the batteryspace.com site and search for LiFePo4 you will find a lot of information but no cells with more than 2 amp hour capacity whereas cells with 10 to 30 amp hour capacity are needed unless you design a circuit to cut in new strings when the current string is discharged.
Also the forums.batteryspace.com has a moderator that will answer most any tech or sales related question except something like asking how fragile lead acid batteries are.
If I do a price search in the next few days I will post it here just in case I find something with better quality assurance if not lower price.
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I bought 30 T-Energy F Size 14000mAh NiMH cells from All-Battery. They seem to have some of the best prices. My bill was $335, not dirt cheap, but it’s a good cell and packs a hefty punch. I broke my pack up into three 12 volt sections which get charged simultaneously with separate peak chargers. The power plug is then jumpered to connect them in series. The pack is fixed into a trapezoid shape 10.5” long by 7” wide by 2.25” thick.
mn_engr
Did you solder your batteries end to end or do you rely on a compression contact inside the tubes?
I like your micro control scenario. I bet it looks like an atomic device when you are done. I’m working on a datalogger, based on a basic stamp, to monitor the three 12 volt packs. It’s not as sophisticated but should help me identify problems before too much damage occurs. I could easily rig a similar 1 volt/cell/pack cut off circuit, it’s a great idea.
Andy
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30 T-Energy F Size 14000mAh NiMH cells from All-Battery are now $403.50 so that must have been a seasonal thing. 25 are listed as $335, however. If the only and best requirement for battery management is a circuit to monitor each battery and cutout at 1 volt then I would use the no tab batteries with a 2 layer piece of circuit board between each battery to facilitate both monitoring and switching. That way if you have a few extra cells than needed and one goes down you can replace it instantly without shutting the whole pack down.
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Nickel prices have been doing wierd things over the past few years, driving the cost of Ni based batteries higher. Recently the metal cost started falling though. Hard to say whether that will translate to Ni battery prices falling or not.
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If its anything like coffee the higher the highest price the higher the recovery price will be. We were at $5.89 at th end of February, $9.19 all Spring and half of the Summer and now at $7.33.
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That is why we need the LiFePO4 technology to level the playing field on pricing.
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Humm... don't suppose the battery industry might be raising the price of Nickle based technology so they can maximize the volume starting price of LiFePo5...?
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Ooops, I did not think of that scenario. Maximumizing profit ratio on new technology. ;D
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There is a site somewhere I've run into in the past couple of days that starts with meta something or another that has brief commentary on stuff like subway musicians go to Korea or overlimit credit card charges that were followed by 3 to 10 followup offers for more credit cards.
Recently in fact my power company began sending out billing notices that instead of taking you to the "View your bill" customer login page took you to the home page where a "Pay your bill" was the only link. It took you to a page where you either could pay your bill online for an additional charge of $4.99 or to sign up for ebill which if you had already signed up for took you back to the home page. Why, I wondered?
Turns out that customers where unwilling to pay their bill without viewing it first so that by the time they finally got through to customer service or got a paper bill sent to them in the mail they had exceeded the deadline for payment and were given the option of having their power turned off until they paid the $35 turn on fee or to just pay the turn on fee and not suffer through having their power turned off.
Moral: The world is full of schemers. The ones you see in the tabloids are the ones who have gotten caught doing what the big utility companies and other corporations get away with doing all of the time. If someone is not scheming to find a way to maximize profit on battery technology then there minds are at work scheming to find a way to maximize profit on something else. Wal-Mart's scheme of low price and return anything including dead batteries and light bulbs without a receipt with grandmother types to greet you when you enter and to check your receipt when you leave plus handing your kid a smiley plus whatever else they do seems to be the best scheme yet.
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ahend:
I am using a compression spring from menards in each tube. It is about 1" long, and I compress it about 1/2", so it has a relatively strong force.
My strategy was to keep everything as repairable as possible, that way if the monitoring circuitry tells you that a particular cell (or pair of cells in my case) is always going dead first, you can disassemble that tube, replace the cell, and even test the cell in question in the lab to determine why it discharges so early.
I thought about other sizes, but I also presumed that AA cells, since they are so common, would give the lowest cost/W*Hr. Plus, if I had to abandon project due to infeasibility, I could always use AA's, I have few devices that use anything else.
However, after 3 hours on the bench today, I've been having second thoughts about buying 10AHr D cells like these instead, which would decrease circuit complexity by a factor of four.
http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1878
Four sets of these cost $184, plus you get 2 extras for backup. That's only $40 more than my 120 AA's, and basically the same capacity. As far as I know, this deal is still good if anybody wants to play with 30 T-energy D cells.
MyElecBike:
As for the PCB between each cell, that was my original idea. However, in the end I used steel wire through a small yet oversized drilled hole in the PVC. When I drill the holes, I use a spacing jig. When you compress the cells, you have to make sure you don't have any misallignment issues.
Everbody:
BTW, as I develop this 'active monitoring' circuitry futher, if any are interested, I will share technology. (a phrase from my playing Civilization days ;) If it works out, it would be a shame for me to spend all this time just to make a smart battery pack for myself... You need to be handy, and it does take some perserverence...
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Sounds Great, You could even build a few to sell to some of us who are not able to make it.(minus the batteries) :)
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don't mean to double post but here is some more info on batteries:
http://hardware.slashdot.org/article.pl?sid=07/09/06/0431237
One post here mentions the A123 battery and there is a IEEE Spectrum article on the company:
http://spectrum.ieee.org/sep07/5490
On page 3 they talk about calendar life for Lithium cells. The article states some Li-Cobalt chemistries lose 20%/year in capacity, just sitting on the shelf. (Not LiFePO4 chemistry, but the article leads you to think the effect is still there but perhaps reduced?)
I suspect this will be a big factor in acceptance of these cells, although as an engineer it will be difficult to access this risk when designing your product.
Besides not having a shelf life capacity reduction issue, NiMH and NiCd cells can be stored at partial/full discharge and not risk losing cycles. This was one of the biggest reasons I want to make NiMH (or NiCd) work.
Since I live in MN, I expect I'll only be able to get 100 rides to work per year. If I get 500 cycles out of my cells, my optimistic side tells me I can make these cells last 4 years, maybe more. However, if there is a cobalt lithium effect going on, that would put a significant dent in that number.
I don't know what the best chemistry is out there for transit, but whoever gets it right will be famous. Somedays I wish I was a ChemE rather than EE. At work, I do a lot of testing of Energizer L91 primary AA's. (LiFeS2 chemistry) This battery is spectacular, to say the least but it's a primary. I remember reading somewhere (can't find a reference) that this chemistry is also rechargable, but only at high temperatures (250C or something like that.)
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30 T-Energy F Size 14000mAh NiMH cells from All-Battery are now $403.50
Just an FYI . . .
All-Battery has an eBay store where they sell quite a few items. In that store they are still listing 30 F sized 14Ah cells for $335. This is where I picked up mine. It is in contrast to their website so it might not be bad to check out if your in the market.
Andy
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Andy,
How many cycles do you have on your T-Energy pack?
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How many cycles do you have on your T-Energy pack?
About 10, too early to give me any warm fuzzies about the decision. I was a bit worried about heat damage as I did some heavy duty soldering, both end to end, and tabbing with beefy battery bars.
Andy
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Check out missbattery on ebay, they have some good prices on LiFePO4 batteries. They don't mention shelf life but do mention cycles and being good for 3 to 5 years.
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So has anyone been able to actually accomplish a real life working lower voltage cut off controller? Did I miss something?
Thanks! :)
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The theory and resistor locations are all worked out, but I haven't heard of anyone actually implementing it. Look through this thread for pdonahue's posts. He cracked the code for lowering or raising the low voltage cutoff, and also found out what needs to be done to raise the operating voltage to 48V.
If anyone implemented this with good results please post your results.
-Mike
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The theory and resistor locations are all worked out, but I haven't heard of anyone actually implementing it. Look through this thread for pdonahue's posts. He cracked the code for lowering or raising the low voltage cutoff, and also found out what needs to be done to raise the operating voltage to 48V.
If anyone implemented this with good results please post your results.
-Mike
I did implement it when I first went to 48V, but I put it back to the regular cutoff value so I could use my 36V battery as well when my 48 is drained.
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With my nickel batteries 42 volts seems to solve the problem. I had to add a 4 cell nimh pack in series with my 36 volts. Seems to work great.
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What is your range?
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I did the mod, now r73 is 10000 ohm and the cutout is 29.22. It works awesome, see attached pics!
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Sorry myelectricbike, I just noticed your question about range. I pedal alot so my average is 25-30 km from about 5-11ah of assist. Today I went out and rode 40km on 10ah.
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The cutoff voltage is the electrode voltage value that reduces the dependent variable of an electron tube characteristic to a specified low value.
_________________
Thermostat (http://www.prothermostats.com/)
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Guys, please answer this (stupid??) question:
Is the cut off voltage formula 3.1*(R73+R4+R11)/R11 valid for both controllers, 36V & 48V?
I have a 48V controller and a cut off problem, I will try the Resistance solution according your answer.
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Guys, please answer this (stupid??) question:
Is the cut off voltage formula 3.1*(R73+R4+R11)/R11 valid for both controllers, 36V & 48V?
I have a 48V controller and a cut off problem, I will try the Resistance solution according your answer.
Sorry myelectricbike, I just noticed your question about range. I pedal alot so my average is 25-30 km from about 5-11ah of assist. Today I went out and rode 40km on 10ah.
The cutoff voltage is the electrode voltage value that reduces the dependent variable of an electron tube characteristic to a specified low value.
_________________
Thermostat (http://www.prothermostats.com/)
You do realise this thread is 3 yeasrs old. The controllers these gents were chatting about I believe are phased out some time ago and replaced with the Magic controller. and the batteries run different chemistry since then too.
The Magic controller can have setting like voltage and amount of current changed via a Computer>USB>Controller connection cable and software interface purchased from Golden Motor.
The problem is that one need to be able to alter these settings to a set figure input to work happy with other devices.
The Magic controller will only allow three voltage choices based on GM'S packs requirments and specifications. 24v, 36v, and 48v
If youre using SLA batts it might be wise to set a 48v pack to 36v or a 36v pack set to 24v. Then purchase a cycle analyst and mod it to regulate LVC for you on the Magic controller. Though I think you need to mod the CA to work properly with the Magic controllers throttle controll interface.
The way the CA does LVC current controll or speed controll is pretty neat, Instead of cutting the supply to the controller like a BMS and some controllers will do. The CA will limit the amount of throttle, disallowing the rider to pull the pack voltage down below the settings.
Instead of go and stop LVC its Go and slow LVC. I have this Go and Slow LVC on one of my brushed bike controllers with SLA's. Even if I make my pack really flat, if there is anything to had at LVC voltages, I can still get it.
The Cycle Analyst LVC can be set to any voltage.
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LOL and to think I nearly started reading the whole thing!!
Thanks Les ;)