Defective BMS?

Hi,
I have a Scream Power 12V 100AH battery which I bought 2 years ago. I used it 2 times in the past for a fishing trip of 4 days. The fish finder draws 1.7A. Both of these times it worked properly but it did not get discharged much.
This year I went on a trip that was 7 days long. At 48% battery capacity left (determined with a Renogy battery monitor) and 11.9V the battery shut off. It did charge up and was fine for the remaineder of the trip.
When I got home, I fully charged it. I then put the same load on it and again it shut off at 11.9V and 48% capacity left.
Seems to me that the BMS is set to turn off the battery at 11.9V which is incorrect. Am I right? Or is something else going on?
I have of course filed a warantee claim with the company. And of course, the company has not responded. So thinking of three scenarios:
1) File a claim with Visa...might not work since it was purchased through Amazon.
2) Buy another piece of that junk then take the old battery, put it in the box and return it to Amazon. Might work, I'll fight them if they try to charge me through my credit card. It would serve the company right for not responding for the warantee claim.
3) Buy a BMS and try to repair it.
Is it the BMS? If one cell was bad would it not show a lower voltage?

Thanks for your help.
Tom

tomb18 said:

Hi,
I have a Scream Power 12V 100AH battery which I bought 2 years ago. I used it 2 times in the past for a fishing trip of 4 days. The fish finder draws 1.7A. Both of these times it worked properly but it did not get discharged much.
This year I went on a trip that was 7 days long. At 48% battery capacity left (determined with a Renogy battery monitor) and 11.9V the battery shut off. It did charge up and was fine for the remaineder of the trip.
When I got home, I fully charged it. I then put the same load on it and again it shut off at 11.9V and 48% capacity left.
Seems to me that the BMS is set to turn off the battery at 11.9V which is incorrect. Am I right? Or is something else going on?

Click to expand...

tomb18 said:

3) Buy a BMS and try to repair it.
Is it the BMS? If one cell was bad would it not show a lower voltage?

Click to expand...

11.9 volts is not 48%
No where near it.
11.9 volts is an average of 2.975 volts/cell. Basically dead.

You probably have a imbalanced pack, weak cell, something wrong with set set up of the battery monitor, or something similar. If your battery doesn't have Bluetooth or a removable lid, you are short on options inside the battery, but you could investigate the battery monitor.

How did you determine it was fully charged?

During charging the battery voltage reached over 14V and then the charger shut off. After a while the battery voltagew was at 13.6V When the 1.7A load when on it went to 13.3V and stays there for hours.
It acts the same with two different chargers, a 6amp and a 20A.
The battery monitor is a Renogy. When charging is done it is set to100% (100A). I also followed it manually, time vs current. The manual checks agree with that of the monitor.
I guess then a cell is defective?

tomb18 said:

I guess then a cell is defective

Click to expand...

Perhaps, but more likely the cells are out of balance. Idealy, connect a power supply, or configure a charger, set to just below you noticed the charge cut off, say 13.8 volts. Apply this for a day ot two and carry out your capacity test again.
It's possible it's just a bad battery and never had 100Ah from the start.
It takes a great deal of optimism to buy a battery with the name Scream Power.

lol...at the time, there were not too many options out there.
I do have a lab grade power supply. What should the current be set at?
Thanks

tomb18 said:

What should the current be set at?

Click to expand...

Set the volts before connecting and current limit to 5 amps, leave for a few days and test, if an improvement, repeat.

Ok, so I am using a Silgent bench power supply. I set the voltage to 13.8V and the current to 5A. The power supply will indicate the actual current draw and voltage as well.
When I first connected this, it reads the full 5 amps. Slowly the amperage decreased until it reached 0.5A and then slowed more. Now, two hours later, the power supply is indicating that it is outputting 13.8V but the current draw is now 0.00A. Would this not mean that it is now fully charged and balanced?
I tried increasing the voltage by a couple of tenths and then the supply indicates the full 5 Amp output. However, I suspect that what is happening at this stage is that the BMS has actually disconnected the battery from charging.
Is this true? Is the battery fully charged now? I am going to leave it for 24 hours as suggested but if the power supply is no longer giving any output is there a point?

13.8 is only 3.45 volts per cell and we don't know the balance specs on that BMS.

I'd go up to 3.6/cell or 14.4 volts.

Balance current could be very low, possibly low enough to now show on the power supply.
Zero current could be either an open BMS because of high cell voltage or a fully charged pack. Discerning between those two is tricky. I'm not sure I'm up to describe the difference.

tomb18 said:

voltage by a couple of tenths and then the supply indicates the full 5 Amp output. However, I suspect that what is happening at this stage is that the BMS has actually disconnected the battery from charging.

Click to expand...

If the battery took the 5 amps then the BMS is still allowing current.

tomb18 said:

is there a point

Click to expand...

The point is to apply a voltage below BMS cut off so the balance process can act, but higher than the voltage where balance takes place. Typically this will be over 3.4 volts per cell and charging. The cell bleed off current is low, a few 10s of mA, thus it will take a long time even for a 1% differential in cell capacity.
The most probable cause of protection cutting charge current is cell overvolts, as the process is based on cell balance issues

Thanks for all your help.
Ok, I will charge the battery, then set my power supply to 14.4V and let it sit.
I do believe I already tried this, but seeing a current of 0.000 amps I thought it was not operational. Does this mean that the BMS was shutting off?

tomb18 said:

Does this mean that the BMS was shutting off?

Click to expand...

Yes.
You may get more balance time with the charge voltage set just below the cut of volts, it depends how the BMS was configured. Some balance regardless if the cell volts are higher than 3.40, others balance only if charging and cell volts are above the threshold.

I guess I am just not getting this or maybe I am....
So the battery was charged to maximum. I waited a little while then I attached a bench supply set at 14.4V 5A.
Immediately the supply indicated it was outputting 5A and then the current started dropping. The power supply indicated that the voltage reached 14.4V and 0.000 amps.
However, I also have an inline current meter (4.5 digit Fluke) and I now measure a fluctuating current from t 0.05mA to 2ma. So something is happening. Does this seem right?

If you have an inline meter then measure how much you put in from the charger when it gets to 11.9V and then see if at amount is about what your battery capacity is or measure how much is drawn from full to empty. It isn't clear how much you are drawing other than you expect more out of it. There may not be an issue with the battery at all.

@hardtop: I have a battery monitor on it. I know what it is drawing and for how long. Always stops at 47% and 11.9V

Well after 36 hours there was no change at all.
The whole thing is moot now. I decided to open it. Went well, but as i was
pulling the cells out, one of the cells burst.
SMoke everywhere....What a stench. Took about 1 hour to finish smoking with the help of a steady stream of water.
Thias was the second cell in the battery. The first pouch, is now hot to the touch and bulging alot.
Time for a new battery.

Yikes, there was always the chance that a cell was failing. I didn't expect that!

tomb18 said:

@hardtop: I have a battery monitor on it. I know what it is drawing and for how long. Always stops at 47% and 11.9V

Well after 36 hours there was no change at all.
The whole thing is moot now. I decided to open it. Went well, but as i was
pulling the cells out, one of the cells burst.
SMoke everywhere....What a stench. Took about 1 hour to finish smoking with the help of a steady stream of water.
Thias was the second cell in the battery. The first pouch, is now hot to the touch and bulging alot.
Time for a new battery.

Click to expand...

That sounds scary. Did you bring it outside and point the garden hose on it? I'm not sure what I would do if mine caught fire seeing how I'm out in the country.