LifePo4 Battery BMS issues

[gwalarnyacht]

Hi everyone,

I’m a beginner with DIY solar setups and could use some advice. I recently bought a 150Ah LiFePO4 12V battery from a vendor in China, but it’s been giving me issues. After some sudden voltage drops, it no longer provides enough power to my small sailboat.

When I opened up the battery, I found 24 cells at 3.2V, 25Ah each, arranged in a mix of series and parallel connections (see attached pic). The BMS is labeled “ShenGu Technology Co., Ltd., DMO-JL-0002-4S 4-series lithium iron, 200A, DM020190624001,” but I can’t find any information about it online.

Here’s what I’ve tried so far:

• Checked voltage before the BMS: 13.3V
• Checked voltage after the BMS: 3.2V
• Ran my 12V fridge directly from the battery terminals (bypassing the BMS) for two days without problems; voltage dropped only to 13.0V.

My questions:

1. Is it likely that the BMS is faulty?
2. Can I test the BMS somehow to confirm this?
3. If I need to replace it, what type/specs should I look for in a new BMS for this battery setup?

Thanks in advance for any advice or tips!

 

[PaulRainbow]

Oh dear. That is nasty, it doesn't have cell balancing, so anyones guess what the BMS is doing, if it is a proper BMS. Because of the way the cells are connected you cannot balance all of the cells, the best you could do is to balance them in the groups of 6 cells that are connected in parallel. That's far from ideal. I wouldn't want it on my boat.

 

[geem]

Not that it is much help for the OP but it's a good post to demonstrate why you don't want such a battery on your boat, as Paul says.
A BMS must include a balancer, especially on cheap cells as these are the cells that really do need a good balancer. Active balancers give approximately 10 times the balance current of passive balancers so are far more effective.
On a good battery, Bluetooth would show individual cell voltage. This can give you a warning that something is amiss with the battery. A battery that doesn't have this and is not configured as a simple 4S for 12v, or 8S for 24v can't show individual cell voltage. I would stay clear of such a battery.

 

[Sea Change]

The OP could buy two 4S BMSs and rebuild the battery as two 75Ah packs. Quite a lot of work for two very small batteries though!

 

[PaulRainbow]

The OP could buy two 4S BMSs and rebuild the battery as two 75Ah packs. Quite a lot of work for two very small batteries though!

How would that work ?

 

[geem]

The OP could buy two 4S BMSs and rebuild the battery as two 75Ah packs. Quite a lot of work for two very small batteries though!

Not easy to see from the photos but it looks like welded busbars. A nightmare to pull the pack apart if it is

 

[geem]

Not easy to see from the photos but it looks like welded busbars. A nightmare to pull the pack apart if it is

I have just had another look at the photos and I think it's welded busbars. If that is the case, then I am afraid the battery is likely to be scrap. If it has conventional threaded terminals, you could remove the bms and add a JK bms. The jk bms has a balancer but you would not be able to balance every cell. You would have to balance in groups of cells which is far from ideal.
I would buy 4 new cells and a jk bms and build my own replacement battery. Total cost about £400 for a 280Ah battery with decent cells and bms

 

[kwb78]

Are the 4 small wires going to each group of cells not balancing wires (a fifth one appears to have become detached on the right side, you can see the white insulation in the spiral wrap - this could actually be the fault causing the BMS to trip out)? I would try reconnecting it and testing whether the BMS wakes up again. If not, you should be able to solder the balancing wires for a new BMS to the same points. The 6 cells in parallel will balance with each other anyway, so it's only the 4 sets of cells in series that need to be balanced with each other. If the cells themselves are OK, which they appear to be from OP being able to run his fridge from them directly, then I don't see a problem with continuing to use them.

 

[Neeves]

Hi everyone,

I’m a beginner with DIY solar setups and could use some advice. I recently bought a 150Ah LiFePO4 12V battery from a vendor in China, but it’s been giving me issues. After some sudden voltage drops, it no longer provides enough power to my small sailboat.

When I opened up the battery, I found 24 cells at 3.2V, 25Ah each, arranged in a mix of series and parallel connections (see attached pic). The BMS is labeled “ShenGu Technology Co., Ltd., DMO-JL-0002-4S 4-series lithium iron, 200A, DM020190624001,” but I can’t find any information about it online.

Here’s what I’ve tried so far:

• Checked voltage before the BMS: 13.3V
• Checked voltage after the BMS: 3.2V
• Ran my 12V fridge directly from the battery terminals (bypassing the BMS) for two days without problems; voltage dropped only to 13.0V.

My questions:

1. Is it likely that the BMS is faulty?
2. Can I test the BMS somehow to confirm this?
3. If I need to replace it, what type/specs should I look for in a new BMS for this battery setup?

Thanks in advance for any advice or tips!

I wondered what motivated you to buy a battery direct from China? Most people would go to a local vendor - as it gives them consumer rights. You say you are a novice - but are able to take the battery apart and know what everything does?

I did a quick google search and came up with:

Shen Gu Technology Company - Google Suche

But the company seems to be involved with consumer electronics, phones, no mention of batteries. But there is an indication you could go into communication with them - and raise a warranty issue (though taking the battery apart might void any warranty).

Sending them a copy of this thread might motivate them to take you seriously.

Jonathan

 

[B27]

Are the 4 small wires going to each group of cells not balancing wires (a fifth one appears to have become detached on the right side, you can see the white insulation in the spiral wrap - this could actually be the fault causing the BMS to trip out)? I would try reconnecting it and testing whether the BMS wakes up again. If not, you should be able to solder the balancing wires for a new BMS to the same points. The 6 cells in parallel will balance with each other anyway, so it's only the 4 sets of cells in series that need to be balanced with each other. If the cells themselves are OK, which they appear to be from OP being able to run his fridge from them directly, then I don't see a problem with continuing to use them.

View attachment 184772

In as much as we can tell from photos, I'd agree with this.
I suspect the BMS is just shutting down due to seeing the wrong voltage on the disconnected wire.
I'd be tempted to re-connect it and see what happens.

Usual caution about potential for fire and all that....

 

[jakew009]

Cells in parallel will self balance, there is nothing fundamentally wrong with that and millions of batteries are made in exactly that way.

But the build quality of that battery is diabolical and frankly dangerous.

 

[Neeves]

I still wonder.

Knowledge of Lithium is low, there are a few experts - but they urge caution and belt and braces with everything they say. Here we have a member who has a problem. He buys a battery from an unknown source in China - they are not cheap and he will have received documentation on his battery, but we have not been told who he bought from (the company mentioned built the BMS not the battery). The first thing he does is take his battery apart, then joins YBW - and then asks for advice.

How many here would take their Lithium battery apart?

It appears the battery manufacturer is one to avoid - but we don't know who

Hoping the OP will return

Jonathan

 

[geem]

.......

Cells in parallel will self balance, there is nothing fundamentally wrong with that and millions of batteries are made in exactly that way.

But the build quality of that battery is diabolical and frankly dangerous.

When you have high quality grade A cells, placing them in parallel works. When you don't have grade A cell it is far better to have cells in series only and have individual voltage readings for each cell. With a balancer, you can correct cell voltage as it varies. The worst combination is poor quality cells in parallel with no balancing or individual voltage read out. This is how this battery is configured. In my opinion, it is not suitable for a boat.
If it was configured with Winston cells, it would probably work perfectly