Cutoff Voltage

[myelectricbike]

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?

[weiser]

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).

[myelectricbike]

...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 90^c 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.

[erdurbin]

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.

[myelectricbike]

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.

[erdurbin]

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.

[myelectricbike]

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? 

[erdurbin]

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

[movintoelectric]

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 )

[myelectricbike]

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.

[pdonahue]

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

[pdonahue]

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

[OneEye]

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

[mustangman]

 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.

[OneEye]

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.