My Headway LiFePO4 battery won't charge? fault finding tips?

[callagga]

Oh dear - my Headway LiFePO4 10AH battery suddenly is not charging anymore Any help re how to fault find what the problem may be would be appreciated.

Some details:

• Headway LiFePO4 10AH 36V battery
• About 2 years old now - so have been using it 2-3 days a week on average
• I think what happened is after the 2nd last ride it may not have charged, & I just took it out for the last ride & pretty much had drained the battery before getting home before I realized it
• When I try to charge it, by "Watt's Up" meter highlights it getting the expected voltage applied to it, however the currently flowing is really low, in fact this morning when I tried again it wasn't registering any current flowing
• I'll put some pic's of the battery below

Any tips on how to fault find, for example:

• is there a way with a multi-meter to go through cell by cell to try to tell if one cell is dead?
• how to tell if it's the BMS (e.g. so batteries ok but BMS not) - should I try charging directly to the cells bypassing the BMS? (note I charge via the BMS but discharge directly, as the BMS was hitting a safety cutover when it shouldn't be whilst I was riding - have been doing this for years)

 

[dnmun]

post up a list of the cell voltages. sounds like you over discharged one of the cells and killed it. count from the bottom 1through 12.

 

[callagga]

So just leave everything wired up and put the voltmeter across each cell separately I assume?

 

[dnmun]

yes, or measure at the base of the sense wire plug on the BMS. just don't short the pins to each other with the voltmeter probes. you should have been monitoring this all along since you were using the pack without a BMS to discharge.

you want to check the voltage on the gate of the charging mosfet too to see if it is turned on, but sounded like it took charge, just slowly, so i expect the charging FET is on, but you just have a buncha cells that are now dead.

 

[callagga]

ok - so here are the voltages measured - kind of displayed in a table that mimics the batteries:

2.49, 2.9, 3.11, 3.16
3.05, 2.95, 3.07, 2.95
3.07, 3.07, 3.02, 3.15

I'm not sure what the expected range is, however that first one is low no?

Also measured voltage across all cells I note are 33.2V...

 

[dnmun]

not too low, unbalanced but is this after charging? do you know how to find the gate leg of the charging FET? follow the trace of the negative charger lead around the end of the BMS pcb and you will see where it goes to the source leg of the charging FET. that is the right leg on the mosfet, the middle leg is missing, and the left leg is the gate, measure that voltage against the battery negative, ground.

 

[callagga]

not too low, unbalanced but is this after charging?

It was after I "tried" to charge it, however the issue is when I put it on the charger I don't get any/much current flowing (I have a WattUp meter). So if there's an issue in the BMS preventing charging occurring properly then I guess it's not after charging, if you know what I mean.

do you know how to find the gate leg of the charging FET?

do you mean whilst not charging? anyway there are 4 big transistor looking things each with 3 legs and attached to the heat sink. These are the largest transistor looking things on the board. Just now (not during charging) the voltages across the outside legs is 11.1V.

Also noted that my wattsUp meter doesn't register any voltage from the batteries. The digital multimeter seems sensitive enough to pickup and register a voltage, however the WattsUp meter doesn't even turn on, just blank. I took the battery back to the garage and put it on the charger to prove the WattsUp meter itself is ok, and it came to life fine after this, registering around the 43V I think it was...but no current flow...

 

[Spacey]

Does sound like a charging FET has broke.

 

[callagga]

what do you think re way forward? can you buy a new BMS? not sure how much these cost versus the cost of the whole battery?

 

[dnmun]

do you have a jumper with alligator clips? you can try jumping frm the charging lead directly to the black wire going to the pack.
see if current flows.
you should be able to see where the trace on the board runs from the charging lead C- to one of the mosfets. i cannot tell in your picture, and it seems like you still have it taped onto the pack so i don't know how you can even examine it, but you need to find the gate of the charging FET and measure that voltage.

 

[markobetti]

Okay. So maybe i can help. My headways didnt charge also . The volt meter gave in a pack of 24 all cells are well over 2.3 but one of the cells that is actually 2.5 v when bms starts to work drops to almost 1.0v or even less. That strange behavior cell was replaced and bms started to balance perfectly .. So try to give each cell a small load. If voltage drops instantly below 2.0 the cells wont charge since bms dont function bellow .. Anyways that was my situation.. Maybe it help before you start blaming bms or charger or whatever ..

 

[dnmun]

we never got that far. if we knew there was voltage on the gate of the charging mosfet, then we could look for some reason it will not take charge. if the gate voltage is off then it may be off because of a low cell and come back on when he charges bypassing the BMS. i wondered where he was too.

 

[callagga]

markobetti/dnmun - just back on line - Jim from headway is going to give me some advice (which is great)...will let you know how we go...