Problem with LiFePO4 battery bms or charger?

mwinschel · Jul 4, 2015

New Bafang system purchased from elifebike with battery and charger. Only about 50 miles of use. Noticed what appeared to be charger not working properly after a few uses. Battery seems to operate unit fine however upon hooking charger to battery the charger tells me immediately that the battery is fully charged without ever going into a charging state. Problem was intermittent at first and I thought I might going crazy. I just ran the pack until cutout on my unit and plug in the charger and it lights full charge instantly again. Was assuming this was a charger issue but not sure how bms functions and wondering now if that might be the problem before I buy another charger. I thought that I remembered the charger with no connection to the battery originally showing a charging state if turned on. It now shows full charge if connected or not connected to the battery upon startup. Taking the fuse out shows full charge also. Checked fuse a while bag and it tested okay. I was wondering if it was a voltage sensing issue with the charger so for grins and giggles I tried to connect it to a lower voltage battery and two instantaneous tests had it starting to try to charge so I am at a loss as to the source of the issue not knowing how these systems function.

Can anyone help point me to the problem or something to test before I start randomly buying new things?

dnmun · Jul 5, 2015

do you have a voltmeter? measure the voltage at the charging port of the battery.

999zip999 · Jul 5, 2015

Little more info on battery ?
An ebike needs a multi meter. Cheap they start at 5.00usd or free with Harbour Freight coupon and comes with a 9v battery. Free.

dogman dan · Jul 6, 2015

Intermittent at first is the key tip off.

Somewhere there is a bad connection. Green light on the charger means charged, or it means un plugged.

If you don't find the problem on the plug itself, on the charger or the battery, look next inside the charger, where the DC output wire attaches to the board. if not that, then the problem will be on the connection to the bms inside the battery.

90% of the time though, it's just a bad solder on the plug.

mwinschel · Jul 6, 2015

dogman dan said:
Intermittent at first is the key tip off.

Somewhere there is a bad connection. Green light on the charger means charged, or it means un plugged.

If you don't find the problem on the plug itself, on the charger or the battery, look next inside the charger, where the DC output wire attaches to the board. if not that, then the problem will be on the connection to the bms inside the battery.

90% of the time though, it's just a bad solder on the plug.

So far I have verified the charger works. I ran it for an hour on the "run" cable for the battery bypassing the bms. Charge is showing and matching on both the charge set of cables and the run set of cables. I think i cut the charger out at 51 Volts plus or minus. Seems to be something with the BMS I am guessing that seems to think the battery is charged?

mikebikerad · Jul 6, 2015

I think you have the correct thinking in targeting the BMS charge circuitry being shut down. This can happen for various reasons...unbalanced pack, fully charged cells, low cells, circuit board component failure, etc etc. You might want to get a replacement BMS coming from elifebike asap since it is a cheap part that they should send to you express no questions asked and relatively easy to replace if you can do some basic soldering.

dnmun · Jul 6, 2015

usually the reason that the BMS turns off or appears dead in your case is because one of the cells in the battery pack is already overcharged. so when you bypass the BMS the cell that was overcharged is charged even more.

mwinschel · Jul 12, 2015

I opened the battery pack up to look at it. Each cell is balanced and showing 3.294 volts and 52.7 across both the charge and run wire. I forgot the charger out of town, do not have it right now but I could charge through the run cable. Is it safe to assume that the BMS card is bad?

Also there appear to be three circuit boards as part of the BMS package. Would purchase of the BMS typically be all three? Dont know if these are kind of standard but it appears there would be a few plugs to pull and three leads to solder for replacement?

dogman dan · Jul 12, 2015

It does appear that way, if the bms is shutting off charging when none of the cells is overcharged.

Bitch at the vendor for a new bms. Too bad it wasn't the simple fix, a bad solder on the plug.

dnmun · Jul 12, 2015

there does not appear to be anything wrong with the BMS. if you charge through the output then you have no protection against overcharging and destroying the battery.

not sure why you decided to do this without having a charger designed for the battery. it is not the seller's fault when you damage the battery playing cheap like this and using something other than the correct charger. that BMS is built so cheaply. has only 3 or 4 mosfets instead of the 20 it should have. it is limited to 30A.

999zip999 · Jul 12, 2015

GET A VOLT METER. # 1. A multi meter can check voltage. Set voltage on MM higher than voltage testing. Plug probes in charger report back with charger voltage. We need to know if the battery is 16s or ?
1. Check charger voltage
2. Check battery voltage
3. Check per cell voltage and post like

1. 3.28v
2. 3.65v
3. 2.95v

16. Xxx volt
Report back for next steps. Did you contact supplier ? Yes a plug or two and three or four wires to replace bms. Now back to testing first.

mwinschel · Jul 12, 2015

dnmun said:
there does not appear to be anything wrong with the BMS. ( What basis is this statement made on? I have established that the charger does work and that all cells are balanced and below full charge, it would appear that is the only item left?)

if you charge through the output then you have no protection against overcharging and destroying the battery. (understood, this was done to verify that the charger was not the functional issue, with two engineering degrees and an area to contain the possible fourth of july fireworks I accepted the risk for the purpose of elimination in absence of any other obvious methods).

not sure why you decided to do this without having a charger designed for the battery. it is not the seller's fault when you damage the battery playing cheap like this and using something other than the correct charger. (please stick to the facts, especially if you wish to berate me. I have never and had no intention of blaming anyone, just trying to determine what the problem was and fix it, and I used the charger supplied by the battery manufacturer).

that BMS is built so cheaply. has only 3 or 4 mosfets instead of the 20 it should have. it is limited to 30A. (Thats fine, I am trying to determine the problem and fix it accordingly. Are the mosfets in the battery supposed to be in addition to the ones in the motor controller? ).

mwinschel · Jul 12, 2015

999zip999 said:
GET A VOLT METER. # 1. A multi meter can check voltage. Set voltage on MM higher than voltage testing. Plug probes in charger report back with charger voltage. We need to know if the battery is 16s or ?
1. Check charger voltage
2. Check battery voltage
3. Check per cell voltage and post like

1. 3.28v
2. 3.65v
3. 2.95v

16. Xxx volt
Report back for next steps. Did you contact supplier ? Yes a plug or two and three or four wires to replace bms. Now back to testing first.

I left the charger at the beach house, cant get that right now. Voltage was the same as when it was originally supplied to my recollection. The battery is a 16 cell (assuming 8 series/2 parallel). Individual cells all report 3.294 volts and 52.7 across both the charge and run wire

Problem with LiFePO4 battery bms or charger?

mwinschel

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dnmun

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999zip999

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dogman dan

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dnmun

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mwinschel

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dogman dan

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dnmun

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999zip999

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mwinschel

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mwinschel

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