Cutoff Voltage

[pdonahue]

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!!!

[pdonahue]

You are correct Roberto!!!   

[Mordaz]

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!

[myelectricbike]

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...!  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... 

[Mordaz]

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

[myelectricbike]

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???

[mustangman]

WOW, That is some impressive set of numbers!!!  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 Keep up the work and post the final results !!! 

[myelectricbike]

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.   

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))?

[pdonahue]

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  . 

Have a great day.

Pete

[pdonahue]

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 

[Mordaz]

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  . 

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

[pdonahue]

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  . 

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 

[pdonahue]

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

[myelectricbike]

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.

[pdonahue]

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