Help & Advice with Batteries

[ecycler]

Do the following before you do anything else:

1. Unplug the white connector from the BMS.
2. Put the negative end of your multimeter on the D- point
3. Measure and record the voltage at each of the pins on the white connector successively
4. Post the numbers up for us so we can better advise you on the condition of the battery and how to proceed

It will look something like:

1 - 3.11V
2 - 6.21V
3 - 9.47V
4 - 12.58V
etc.

The final number should be the same as what you are measuring for the total pack voltage.

Make sure you do not bridge any of the pins by accident or you will toast wires/connections. These things can be dangerous, so be very careful and deliberate about what you are doing. The battery getting too hot to touch while or after charging is NOT a good thing. You never want a lithium battery to get that hot, as at the very least you will degrade the capacity.

 

[d8veh]

I think that P+/P- connection must be the battery positive connection.

What are you writing?
P+ is positive, P- is negative. They cannot be connected together.

The photo of the BMS seems to show no B- connected. It cannot work like that. The cell-pack negative must be connected there.

 

[Suggs]

I think that P+/P- connection must be the battery positive connection.

What are you writing?
P+ is positive, P- is negative. They cannot be connected together.

The photo of the BMS seems to show no B- connected. It cannot work like that. The cell-pack negative must be connected there.

I think that was my fault as I initially had a typo in my post which flangefrog quoted. I meant to type P+/B+ but originally typed P+/P-

 

[Suggs]

Do the following before you do anything else:

1. Unplug the white connector from the BMS.
2. Put the negative end of your multimeter on the D- point
3. Measure and record the voltage at each of the pins on the white connector successively
4. Post the numbers up for us so we can better advise you on the condition of the battery and how to proceed

It will look something like:

1 - 3.11V
2 - 6.21V
3 - 9.47V
4 - 12.58V
etc.

The final number should be the same as what you are measuring for the total pack voltage.

Make sure you do not bridge any of the pins by accident or you will toast wires/connections. These things can be dangerous, so be very careful and deliberate about what you are doing. The battery getting too hot to touch while or after charging is NOT a good thing. You never want a lithium battery to get that hot, as at the very least you will degrade the capacity.

Thanks ecycler, it's very much appreciated. I'll do as you suggest and post back. Unfortunately it won't be for a week or so :-(

 

[flangefrog]

I think that P+/P- connection must be the battery positive connection.

What are you writing?
P+ is positive, P- is negative. They cannot be connected together.

The photo of the BMS seems to show no B- connected. It cannot work like that. The cell-pack negative must be connected there.

As suggs said it stemmed from a typo - I meant the connection where the red and yellow wire is. If you look closely you can see a cell tab is connected to B-

 

[ruralrider]

if you can obtain a Variac unit to plug into your LITHIUM charger then by lowering the mains voltage with the knob you can set the output of the charger to the correct voltage. installing an ammeter with a scale reading 0-3 amps would allow you to see the current cutoff at full charge ( at full charge the ammeter reading will drop to ZERO ), at this point unplug the charger - the charging is complete.

 

[flangefrog]

if you can obtain a Variac unit to plug into your LITHIUM charger then by lowering the mains voltage with the knob you can set the output of the charger to the correct voltage. installing an ammeter with a scale reading 0-3 amps would allow you to see the current cutoff at full charge ( at full charge the ammeter reading will drop to ZERO ), at this point unplug the charger - the charging is complete.

Good idea but most chargers are switchmode regulated and their output voltage is not proportional to the input voltage.

 

[Golden Motor Canada]

That is definitely a golden motor 48v12ah battery. I recognize it easily from the bms and the cells. These batteries were a nightmare with a real high failure rate. It seems the experts here know much more about it than I do so certainly listen to what they have to say. You should stop using that 60 volt charger immediately though. If you do have success with that pack I do have end caps that are new or some used ones from spent packs that have the plugs still in them. All though they all look the same there are slight size differences in the shells and end caps so some exact measuring would be required.

Gary

 

[Suggs]

Thanks Gary, great input. Although it doesn't sound good about the actual batteries with the high failure rate
I'll measure up and let you know the sizes of the aluminium case I have.

 

[Suggs]

if you can obtain a Variac unit to plug into your LITHIUM charger then by lowering the mains voltage with the knob you can set the output of the charger to the correct voltage. installing an ammeter with a scale reading 0-3 amps would allow you to see the current cutoff at full charge ( at full charge the ammeter reading will drop to ZERO ), at this point unplug the charger - the charging is complete.

Good idea but most chargers are switchmode regulated and their output voltage is not proportional to the input voltage.

Thank you both. I'll do some reading up on your suggestions.

 

[ecycler]

I would not follow ruralrider's advice.

 

[Suggs]

Do the following before you do anything else:

1. Unplug the white connector from the BMS.
2. Put the negative end of your multimeter on the D- point
3. Measure and record the voltage at each of the pins on the white connector successively
4. Post the numbers up for us so we can better advise you on the condition of the battery and how to proceed

It will look something like:

1 - 3.11V
2 - 6.21V
3 - 9.47V
4 - 12.58V
etc.

The final number should be the same as what you are measuring for the total pack voltage.

Make sure you do not bridge any of the pins by accident or you will toast wires/connections. These things can be dangerous, so be very careful and deliberate about what you are doing. The battery getting too hot to touch while or after charging is NOT a good thing. You never want a lithium battery to get that hot, as at the very least you will degrade the capacity.

Ok, here are the results following your advice above:

1 - 4.02V
2 - 8.17V
3 - 12.30V
4 - 16.40V
5 - 20.5V
6 - 24.6V
7 - 28.7V
8 - 32.8V
9 - 36.9V
10 - 41.1V
11 - 45.1V
12 - 49.2V

The voltage across P+ and D- is 53.3V

 

[Suggs]

This is the inside of the charger. Can't see a potentiometer

 

[ecycler]

1 - 4.02V
2 - 8.17V
3 - 12.30V
4 - 16.40V
5 - 20.5V
6 - 24.6V
7 - 28.7V
8 - 32.8V
9 - 36.9V
10 - 41.1V
11 - 45.1V
12 - 49.2V
The voltage across P+ and D- is 53.3V

Okay, so here are the voltages of the cell strings:

1- 4.02
2- 4.15
3- 4.13
4- 4.1
5- 4.1
6- 4.1
7- 4.1
8- 4.1
9- 4.1
10- 4.2
11- 4.0
12- 4.1
13- 4.1

So, from looking at these voltages of your cells after charging and then resting things don't look too bad. It appears none of your cells are internally shorted which was the fear - you would see 0V or close to it on those strings by now. It also appears none of them got waaay too overcharged. The #10 may have been the one giving off the heat because it got a little overcharged and you pulled it just in time before things got really bad.

It is impossible to say without load testing how varying the capacities may now be. Bad cells could be the ones that have higher voltage than the rest (2, 3, and 10) and/or lower than the rest (1 and 11) but I would not treat the pack like a ticking time bomb anymore - just keep an eye on it when charging. You definitely need a charger that takes your pack to 54.6V or your BMS will never be able to balance them. In it's current state you perform a poor man's load test and take it for a 1.5mile ride. Upon returning measure all the voltages again immediately and see how far off the average they are again. That will give you some idea for how healthy the cells are based on how far off they are from their previous voltages compared to the others.

Do not follow the earlier posted advice of tweaking the input AC voltage to your charger to try to change it. That could be a fire hazard. Just order an adjustable kingpan and be done with it. Make sure you use some quality wire terminations on the charge and output cables from the battery to the controller. If you are still confused about which to use for which just post back. Hopefully this helps shed some light on your battery and how to better understand/measure its health!

 

[d8veh]

There's no pot on that charger that I can see.

One cell is missing from your measurements. You have given only 12. There should be 13. The 13th is sitting either between the black cell-pack wire and pin 1 or between pin 13 and the red battery wire. There's probably nothing wrong with it if you charge it to the correct voltage. The heat could have been coming from the bleed resistors doing their job.

 

[Suggs]

If you do have success with that pack I do have end caps that are new or some used ones from spent packs that have the plugs still in them. All though they all look the same there are slight size differences in the shells and end caps so some exact measuring would be required.

Gary

Hi Gary.
The case has the following dimensions:

Overall aluminium case length: 295.5mm
Cross sectional dimensions of end (outer): 72.5mm x 150mm
Cross sectional dimensions of end (internal): 68mm x 145.5mm

End screw hole centres: 72mm x 141mm

Aluminium case thickness: 2mm

Photos below. Note the 1 end cap I do have has been taped up. I assume this is where the two connectors came out.

 

[Suggs]

Okay, so here are the voltages of the cell strings:

1- 4.02
2- 4.15
3- 4.13
4- 4.1
5- 4.1
6- 4.1
7- 4.1
8- 4.1
9- 4.1
10- 4.2
11- 4.0
12- 4.1
13- 4.1

So, from looking at these voltages of your cells after charging and then resting things don't look too bad. It appears none of your cells are internally shorted which was the fear - you would see 0V or close to it on those strings by now. It also appears none of them got waaay too overcharged. The #10 may have been the one giving off the heat because it got a little overcharged and you pulled it just in time before things got really bad.

It is impossible to say without load testing how varying the capacities may now be. Bad cells could be the ones that have higher voltage than the rest (2, 3, and 10) and/or lower than the rest (1 and 11) but I would not treat the pack like a ticking time bomb anymore - just keep an eye on it when charging. You definitely need a charger that takes your pack to 54.6V or your BMS will never be able to balance them. In it's current state you perform a poor man's load test and take it for a 1.5mile ride. Upon returning measure all the voltages again immediately and see how far off the average they are again. That will give you some idea for how healthy the cells are based on how far off they are from their previous voltages compared to the others.

Do not follow the earlier posted advice of tweaking the input AC voltage to your charger to try to change it. That could be a fire hazard. Just order an adjustable kingpan and be done with it. Make sure you use some quality wire terminations on the charge and output cables from the battery to the controller. If you are still confused about which to use for which just post back. Hopefully this helps shed some light on your battery and how to better understand/measure its health!

Thanks very much, really appreciated

 

[Golden Motor Canada]

Hi Gary.
The case has the following dimensions:

Overall aluminium case length: 295.5mm
Cross sectional dimensions of end (outer): 72.5mm x 150mm
Cross sectional dimensions of end (internal): 68mm x 145.5mm

End screw hole centres: 72mm x 141mm

There are slight differences in case size for various packs. I measure the screw holes on the new lifepo4 packs at 73x139mm center of hole to center of hole. So I don't think they would fit unless you want to glue or duct tape them on. I may have some older ones around but I will have to do some digging.

As for the cells, the number do seem encouraging but I would take the advise of those that posted here as their knowledge certainly exceeds mine.

Gary

 

[Suggs]

I'm trying to find a relatively cheap charger suitable for these batteries. These look suitable but there are a number of different wattage versions available. Do I need a specific wattage? Does the higher wattage just charge the batteries quicker?

http://www.greenbikekit.com/battery-charger/120w-lifepo4-li-ion-battery-chargers.html

 

[ecycler]

The correct voltage and chemistry: Lithium Ion 54.6v

watts = volts x amps (look up Ohm's Law to learn more about the basics of electricity, it will really help you understand some of these things we regularly discuss with ebikes)

Your assumption is correct, higher wattage just means it will charge the battery faster. The one you linked to should charge around 2amps at 54.6v (there are some losses between its rating and actual output) so if your battery holds 10ah and you run it to 60% DOD (depth of discharge) you will need to put 6ah back in it. In theory the charger you linked to would take a little over 3 hours to charge it, but in reality it will take longer since it should lower the current at the end of the charge as it nears the desired voltage and also you have an old battery pack in unknown condition that may take some time for the BMS to balance it where it may need to charge then stop charging to balance then charge again, etc. You should definitely plan on your first charge taking at least overnight and monitoring the voltage of the low and high cells we identified earlier in the process to make sure your BMS is operating correctly and they all end at 4.2v. The voltage will immediately drop a bit when unhooked from the charger. We call this HOC (hot off charger) voltage and then it will drop again a bit when you put the first load on the battery. It should then stay fairly stable as you run the bike except for voltage sag when it sees a large load from full throttle (especially going up hills) until the batteries have given most of their charge up. You should also keep your first 5 charge/discharge cycles very shallow until you can measure and see how things are working out, so ride only a mile or two. Your numbers are right on the verge of where one might recommend you individually charge some of the strings manually before hooking it up to a bulk charger.

 

[ecycler]

Also, I should say, stick with that charger. It will require a little more patience with the slower charge rate, but it is the best thing for you and your batteries to start with.

 

[Suggs]

Thanks Ecycler, great advice. Would it be worth paying a few more £ for a higher wattage charger?

EDIT: I typed that whilst you were sending your second message!

 

[Suggs]

Would a XT90 connector be ok for the charger? I've ordered a XT90 anti spark connector to use between charger/battery and battery/controller.

 

[ecycler]

Yes, from an electrical perspective it is overkill (which is great) as that connector is capable of handling 90amps and your charger will only be pushing 2a, your controller is likely in the 20-30a range. It is a great choice though as you will be physically connecting and disconnecting it a lot and it will hold up well over time to the abuse. If you want to save a few quid you could get away with an XT60.

 

[Suggs]

Hi Gary.
The case has the following dimensions:

Overall aluminium case length: 295.5mm
Cross sectional dimensions of end (outer): 72.5mm x 150mm
Cross sectional dimensions of end (internal): 68mm x 145.5mm

End screw hole centres: 72mm x 141mm

There are slight differences in case size for various packs. I measure the screw holes on the new lifepo4 packs at 73x139mm center of hole to center of hole. So I don't think they would fit unless you want to glue or duct tape them on. I may have some older ones around but I will have to do some digging.

As for the cells, the number do seem encouraging but I would take the advise of those that posted here as their knowledge certainly exceeds mine.

Gary

How much would a new case cost me Gary?