Faulty Lifepo4 pack..can the gurus help?

[benjy_a]

My Cellman Lifepo4 A123 pack seems to be dying.

It's a 16S 6P A123 pack which is now just over a year old with 3-400 cycles on it. It has suddenly lost about 30-40% capacity.

Any thoughts? Faulty cell? Badly balanced?

Thanks in advance,
Ben

 

[cwah]

Hello Benji,

Both are possible.

You need to open your pack and check individual cell voltage and look for voltage discrepancy.

Post your results here

 

[benjy_a]

Scary stuff, it's all vacuum wrapped, wish me luck taking this thing apart!

When I check cell voltages can I just do that with them all still all connected up to the bms?

I'm not a complete technophobe but I've never messed around with packs of 96 cells before!

If there is a faulty cell I'd be happier to try to remove a whole bank and go to 16S 5P at full capacity.

 

[benjy_a]

D8veh, am I right in remembering that you are in Bristol? Would it be a massive imposition to ask if you would in any way be able to give me some guidance with this? I'm in Bristol next week for a few days. Slightly concerned about either blowing myself up or destroying a £500 battery!

 

[cwah]

You should be able to check the voltage directly with the bms plugged. But be careful if the 2 pins touch each other while you check the voltage, you create a spark.

I found it simpler to disconnect the JST plug out of the bms

 

[averhamdave]

I think D8veh is in Telford

 

[benjy_a]

Ah, why did I think Bristol? Shame

 

[Deleted member 4366]

I'm in Telford, not Bristol.

You have to peel back the heatshrink to get to the BMS.

Unplug the multipin connector, then measure the cell voltages. Each adjacent pair is one cell. If you only have 16 pins, the last cell is between the lowest pin and the thick black from the cells or the highest and the thick red from the cells.

Don't worry, you won't blow anything up.

 

[cwah]

Makes me think cellman pack wasn't better than my victpower pack?

 

[benjy_a]

Haaaaa, don't rub it in! I'm waiting for a response from cellman about this!

 

[benjy_a]

I'm in Telford, not Bristol.

You have to peel back the heatshrink to get to the BMS.

Unplug the multipin connector, then measure the cell voltages. Each adjacent pair is one cell. If you only have 16 pins, the last cell is between the lowest pin and the thick black from the cells or the highest and the thick red from the cells.

Don't worry, you won't blow anything up.

Ok thanks for this, I will have a look when I'm off work next week and report back!

 

[benjy_a]

One more question before I embark on this, should I be testing when the pack is fully charged, or when it's at the point the bms cuts off?

 

[cwah]

Ideally I'd advise to try on cut off point, but if you have BMS failure you'll just loose more cells....

So check voltage while fully charged and see results

 

[benjy_a]

Here is the advice from Cellman;

> I suggest you get access to the BMS balance plug, then measure the voltage on the balance plug to the BMS after the pack has been fully discharged and also after a full charge. Measure the voltage on adjacent pins, don't measure everything back to the ground wire. If you can record the voltages and let me know, we will have a better idea what the problem could be. Also, let me know the layout of the pack, or at least the dimensions of the pack.


Can anybody decipher this for me as somebody who has never even seen a BMS? Where exactly am I measuring voltages?

 

[cwah]

BMS looks like one of these:
http://bestechpower.com/512v16spcmbmspcbforlifepo4batterypack/

Just unplug the little wires where you see them to measure the voltage. You should see 16 of them.

Be careful to remember their exact position when you put them back because if you mix wires around you could short your BMS.

 

[Deleted member 4366]

The balance wires from the cell should all be in a bunch to one 16 or 17 pin connector. The connector will be plugged in to the BMS. You just pull it out. Normally there's small slots on one side with metal strips in where you can poke your meter probes. All what you've been told will make more sense when you open it up. Here's a picture of a 13 cell BMS. Your circuit board might be different, but it should have a similar connector:

 

[benjy_a]

Ok thanks for this...I'm trying to understand it conceptually before taking things apart.

The 16 wires going into the bms must connect between banks of 6 cells in parallel? Basically measuring between these should identify the problem group of 6 cells together is that right?

 

[Deleted member 4366]

Just like that schematic except you have 16 cells not 6.

 

[banbury frank]

Hi Found this Charger to charge LIfepo4 battery cells 3.2 volt 10Ams £ 22.95 + delivery UK supplier


Single Cell 3.2V 10A LifePo4 Battery Charger
Frank

 

[benjy_a]

Just like that schematic except you have 16 cells not 6.

Ok so 16 batteries, each consisting of 6 cells in parallel.

Thanks for the link to that charger Frank. I am concerned that all the cells in my pack are spot welded together so I'm not sure how I will be able to balance individual cells if that is the issue. I'm guessing that I may be able to balance each batch of 6 cells together, ie, all 16 'batteries'?