DIY 12V Lithium Battery Low Voltage while under light load

[wlfpck1]

My system is comprised of the following:
(2) 12V 100W panels wired in parallel
Renogy Wanderer 30A Lithium Charge Controller
300W Pure Sine Wave Inverter

Battery pack is a DIY 12V battery. (4) 3.2V 90aH lithium ion phosphate batteries in series w/ BMS. Varicore cells from AliExpress.

The battery voltage drops significantly even under super small loads. Under no load the battery voltage reads 13.09V, but once I start pulling 10 watts the voltage drops to 12.4V and keeps dropping after a few minutes. (picture below is with load and without load). All 4 cells are perfectly balanced while not under load (and mostly balanced while under a small load).
I do NOT have this issue with my small 12V 16aH lithium Miady battery from Amazon.
Any suggestions would be appreciated. It is very strange that if I am pulling a load during sunlight the voltage will jump all over, and if a cloud comes overhead the voltage drops considerably into the 12.6V range (even under small load like 15 watts).

 

[snoobler]

1) battery is not fully charged.
2) you have a loose connection somewhere.
3) you have high resistance in a cell or component (fuse/breaker)
4) you have bad cells.

 

[Bob B]

I'd bet on #2

 

[snoobler]

13.09 no load is a pretty low state of charge, so I listed it first...

 

[wlfpck1]

Thanks for the replies! Fully charged I am guessing I should be at ~14.4V?

 

[Bob B]

A good battery will drop back to 13.3 or a little less after resting if initially charged to 14.4

 

[snoobler]

A good battery will drop back to 13.3 or a little less after resting if initially charged to 14.4

I would expect to see nothing lower than 13.6V after a recent charge. I'm sitting next to two CALB 40Ah cells I haven't touched for a full year after a full charge. They're sitting at exactly 3.30V or 13.2V

 

[wlfpck1]

After redoing all the wiring I am still having trouble with the battery pack dropping voltage under light use.
It reads 13.1V under no load. When I pull 100 Watts with my 12V inverter the voltage drops down to 12.4V. How can I check the cells to make sure they are okay? Can I charge each 3.2V cell individually with my 12V SLA charger that plugs into the wall? I would like to get each cell up to 3.65V (I think that is full charge). Thank you! attached is battery parameters.

 

[Bob B]

Can you post a picture of your battery? What BMS are you using?

 

[wlfpck1]

Battery is (4) 3.2V 90AH lithium ion phosphate cells in series.
BMS is a Daly BMS 12V 100A.

Varicore Batteries:

US $234.0 22% OFF|3.2V 90Ah battery pack LiFePO4 Lithium phospha Large capacity 12V 24V 48V 90000mAh Motorcycle Electric Car motor batteries|Replacement Batteries| - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

tinyurl.com

Daly BMS:

US $38.22 16% OFF|Daly 3.7V 4S 12V 80A 100A 150A 200A 300A 500A Li ion Lithium Battery 18650 Board PCB BMS 14.8V Cell Charging Protecting Module|Battery Accessories| - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

tinyurl.com

Maybe I try and use the battery without the BMS to see if the BMS is causing the current drop? I am open to any troubleshooting ideas.
Thanks!

 

[Bob B]

When the voltage drops, I would check the voltage of the main battery plus and minus and see if it drops there .... If it does, check the individual cell voltages to see if one or more of them is dropping more than the others.

 

[wlfpck1]

When the voltage drops, I would check the voltage of the main battery plus and minus and see if it drops there .... If it does, check the individual cell voltages to see if one or more of them is dropping more than the others.

Just tired this. It seems the battery itself (and the individual cells) drop in voltage under small loads. Maybe bad bus bars? Bad cells/junk batteries? All cells are balanced before and during voltage drop

 

[Luthj]

You can find the voltage drop by probing both sides of each interface/connector with your meter.

You need to confirm the pack is charged as well.

 

[wlfpck1]

You can find the voltage drop by probing both sides of each interface/connector with your meter.

You need to confirm the pack is charged as well.

Yes, it seems the voltage drop is across all cells. Unsure what to do here, maybe the cells are bad? Maybe not fully charged? These are the settings for my solar charge controller.

 

[Bob B]

I would definitely not try to charge each cell individually with your SLA charger as you mentioned earlier .... but it would be good to try to charge the pack overnight with the SLA charger and see if you can get the resting voltage higher than 3.1.

Have you been seeing the 14.4 from the Renogy when you have full sun?

 

[wlfpck1]

I would definitely not try to charge each cell individually with your SLA charger as you mentioned earlier .... but it would be good to try to charge the pack overnight with the SLA charger and see if you can get the resting voltage higher than 3.1.

Have you been seeing the 14.4 from the Renogy when you have full sun?

I have not seen the full 14.4V after charging multiple days on my Renogy charge controller (with plenty of sun). Here is a picture of my Renogy charge controller settings. Maybe I set something wrong?
I have a BMS so maybe I put my Renogy settings as high a voltage as possible and let the BMS cut off the charge to the battery?

 

[Bob B]

I don't see anything in the settings that would keep the battery from being charged ....but personally don't like the high voltage settings that high.

I would be troubleshooting the charge circuit. Measure the voltage you are getting into the charge controller at full sun and measure the output voltage.

Give us more info about your SCC and panels .... if you can get a picture of the panel specification and post a link to the model of your SCC.

Trying to charge it overnight with the SLA charger would be a good way to troubleshoot and see if the SCC is the problem.

 

[wlfpck1]

I don't see anything in the settings that would keep the battery from being charged ....but personally don't like the high voltage settings that high.

I would be troubleshooting the charge circuit. Measure the voltage you are getting into the charge controller at full sun and measure the output voltage.

Give us more info about your SCC and panels .... if you can get a picture of the panel specification and post a link to the model of your SCC.

Trying to charge it overnight with the SLA charger would be a good way to troubleshoot and see if the SCC is the problem.

This is the SCC: https://www.renogy.com/wanderer-li-30a-pwm-charge-controller/
The panels are 2 100W Panels. This setup has all worked perfectly with a flooded lead acid battery, just having trouble since switching to these new lithium cells. See attached panel specs.

 

[wlfpck1]

This is the SCC: https://www.renogy.com/wanderer-li-30a-pwm-charge-controller/
The panels are 2 100W Panels. This setup has all worked perfectly with a flooded lead acid battery, just having trouble since switching to these new lithium cells. See attached panel specs.

I am thinking it's the SCC settings that are limiting the battery from getting up to 14.4V. I am thinking I need to bump up the setting but am worried about over charging the battery (I think my BMS would cut off the charging if it got dangerously high).

 

[Bob B]

The charge and float are both set to 14.4 ..... That should charge the battery fine, but wouldn't be good for the batteries long term. Once you get things working properly, I would set the float voltage quite a bit less.
Doesn't seem like you should be having problems achieving the charge voltage with 2 100 W panels.

I keep stressing .... use a different charger to see if the problem is with the charger or the pack.