Over-discharge protection not working for amazon battery

[finangler]

The manufacturer claims the battery has a BMS with "over-charge and over-discharge protection". I connected a 15A load when the battery was at 13.3V. I expected it to turn off automatically at around no-load 10V. It kept discharging until I removed the load and checked the no-load voltage at 9.57V.

This is my first LiFePo4 battery so I want to make sure I'm interpreting this correctly. Do BMSes stop discharge at 10V if they are working correctly?

 

[gnubie]

It should disconnect the load at what ever the low voltage cut off is. If it does cut off if you remove the load and check the battery with a digital multimeter you can still read voltage, maybe 9V but there will be no current to back it up, ie any sort of load at all will cause the voltage to go to near or actually 0.

Does the information for the battery tell you what the cut off voltage is? There has been mention of a battery that was set to cut off at 2.0V. 2.5V is generally considered the lowest point for a 12V battery these days.

 

[Gazoo]

It would help if you would post a link to the battery?

 

[finangler]

Its this one: https://www.amazon.ca/gp/product/B08G89TJX8/

 

[gnubie]

Another scream power battery was mentioned on the forum, see this post. This model had an alleged 10V cut off. If you want detail it seems you'll have to contact the seller.

Scream Power LiFePO4 12v 100ah

Does any one here have any experience withh is brand from Amazon? I am trying to decide if I want to DIY or buy this one. Thanks.

diysolarforum.com

 

[gnubie]

Googling turns up screampower on dhgate. It's a generic fill in the blanks type page with a 24V battery on it, but the specs down the bottom of the page are for a 12V battery. 10V cut off is stated there too.

Oh dear. They don't even print labels for each battery configuration by the looks of it. One generic label with tick boxes next to each specification. That isn't exactly assuring of a quality product.

 

[Gazoo]

Its this one: https://www.amazon.ca/gp/product/B08G89TJX8/

I would contact the seller and ask them why the BMS is not working as advertised. The BMS should have cut off before you reached 9.57V. But I wonder about the accuracy of the built in meter. It should be accurate enough, but did you measure the voltage at the terminals with a DVM?

 

[finangler]

Yep. measured everything with my trusty multimeter.

 

[finangler]

9.57V was the voltage across the terminals after I switched off the load. While the load was still connected, it read 9.13V. The battery's own voltage indicator is incorrect as well. It was showing 8.9V across the terminals when the multimeter was showing 9.57V.

Overall, I don't trust this battery anymore.

 

[Gazoo]

9.57V was the voltage across the terminals after I switched off the load. While the load was still connected, it read 9.13V. The battery's own voltage indicator is incorrect as well. It was showing 8.9V across the terminals when the multimeter was showing 9.57V.

Overall, I don't trust this battery anymore.

Sorry you had a bad experience. But it's good you shared your story. It will be helpful to others thinking about buying Scream Powers.

The difference between the reading on your multimeter and the battery's voltage indicator is terrible. I am really surprised by that.

Hopefully you can resolve this with the seller.

 

[finangler]

When I try to charge the battery using the charger that came with it, it doesn't charge beyond 10.2 V. Is there any way to revive the battery?

 

[Darrenm01]

Based on your posts, it sounds like you were able to charge the battery (at least once) and the voltage was 13.3.

But now when you plug in the charge, it doesn’t charge the battery and the voltage doesn’t go above 10.2.

I recently bought the same battery as you have - Scream Power LiFePO4 12v except the 120 Ah model.

I didn’t test to see if the BMS would shut the battery down. When I did the capacity test, I saw the voltage dropping, but I unplugged everything at 11.1 v. I didn’t think lower than that was high enough to run my AC inverter, and didn’t think to test that part of the BMS.

When I plugged in the included charger, fortunately my battery did recharge. The light on the charger was red while it was charging and it has a small fan built into the charger that ran quite a bit. It is a 10 amp charger, so I think I let it sit overnight to finish charging.

Anyway, when I got up the charger light had switched color - green. When I disconnected the charger and checked the voltage at the terminals, it was 13.5 v.

 

[Steve_S]

I don't know what kind of BMS is in there, I would not expect any Stellar by any means.

Any BMS that does it's job would cutoff the battery the moment ONE Cell hit's 2.50V (which is 0% SOC on LFP). The cutoff is based on Cell status, not the complete battery pack's status. This is to protect the cells, otherwise, the battery may read as 12.0V because 3 of the cells are higher voltage and one is dropping below 2.50 and damaging itself.

An LVD cutoff triggers a Safe Mode as such. Some BMS' can auto-recover by using a sensing pulse looking to see if there is + voltage incoming. Other BMS' require manual intervention which can be flipping a switch or shorting one of the "specific leads" to trigger a reset. THAT IS BMS SPECIFIC - DO NOT EXPERIMENT !

Unless the vendor gives you very specific instructions for the enclosed BMS and how to get it to reset and accept charge your up against a wall.

Options:

• Crack open the box, hopefully the BMS has a label/brand model number which can be tracked down and a manual/doc obtained.
• Crack it open and replace the BMS with a Known Good Unit (the one in there is obviously "dubious" at best). At least cracking it open you could see what the cells are and if it is actually put together properly... Boy have we seen some doozies ! At least you did not get a ShunBin ! (a box of nightmares)
• Open a Claim for a defective battery - a mystery thing... a "few" vendors have been good and do the right thing, others not at all.
• HINT, if you paid with a Credit Card or PayPal a dispute may be another option IF you are within the timeframe window. That actually works better for those who ran into problems with a dubious or borked product.