Low voltage with load

[rcjokibbe]

Hi,
I have a 100ah lithium battery that is having an issue. With no load the multimeter reads 12.68. With a load (connecting my solar charge controller) it climbs from .1 volts and stalls around 2 volts. I put a multimeter on each cell with no load and it reads: 3.64, 3.46, 3.47, 3.46.

Why does the voltage drop so low with a load?
Why would the total volts of the cells not equal the volts read from the battery's terminal?

What else can I do to troubleshoot this battery?

Thanks,
Courtney

 

[Rednecktek]

I have a 100ah lithium battery that is having an issue. With no load the multimeter reads 12.68.

Ummm... that's pretty dead for a LFP battery. It should be at least 13.5-14v if it's anywhere close to full. Get a charger on the battery and get it topped up without a load and see where it sits, then throw the load on there and see what your drop is.

 

[mikefitz]

The BMS is in protection mode due to over voltage in the high cell, the one showing 3.64 volts. Once the cell volts falls below the recovery voltage things will return to normal. Put a real load on the battery , greater than 2 amps.

The cell volts Indicate a fully charged battery. It's showing a low, 12.68, voltage, due to the voltage drop across the BMS.

It may be your charge voltage is too high, what are the settings you used?

Mike

 

[Ampster]

I agree with @mikefitz that it is probably the BMS being in protection mode. I do not think it is a dead battery. Try lowering your charging voltage until that one cell gets balanced with the other cells,

 

[rcjokibbe]

My solar charge controller is from Rich Solar. Up until a week ago, it was using the default Li settings. I recently changed it to settings found by other members of this forum with Renogy/Rich scc:
High Voltage 14.4 was16.0
Charge Limit Voltage 14.2 was 15.5
Equalize Charge Volt 14 was 14.4
Boost Charge Volt 14 was 14.4
Float Charge Volt 13.8 was 14.4

For clarification, this battery was one of two in parallel. When the second battery is removed, the problem battery can not power up the scc. I believe the scc needs 9 volts to power up. So, I'm not sure how to lower the settings and let it balance without being able to power the scc.

Put a real load on the battery , greater than 2 amps.

I have a spare water pump that is supposed to draw 7 amps. When I connect it to the problem battery the pump will run for less than a second and quit. I wait a few seconds and it does the same thing. I'm not sure how to get it below the recovery voltage. Should I continue doing this?

 

[rcjokibbe]

Correction, I tried it again and the pump is running continuously. Not sure what I did differently to get the pump running.

 

[rcjokibbe]

Hey, the multimeter on the battery terminals is now reading 13.something volts. It can also power up the scc too! Although the pump was starting and stopping, those few moments must have taken the BMS out of protection mode. Thank you for your help with this.

I am thinking of putting this battery back in the trailer's electrical system without the second battery. Check it later to see if the cells have balanced and then add the second battery in parallel. Sound good?

Do those scc settings look good?

 

[mikefitz]

From your measurements the high cell over volts was triggered by a charge voltage just over 14.0 volts.
The cells have a slight inbalance that should correct over time with BMS balancing
I suggest lowering the charge voltage, boost voltage . Try 13.9 volts. As things improve increase the charge voltage.
Float at 13.8 is too high, set to 13.5 volts.

If there are other charge devices in your trailer set.to over 14 volts they will cause BMS protection shut down.

Mike