LiFePo Batteries Draining Overnight Without Any Major Draws

ToroPower · August 2023

Hello again from latitude 9.5N.

This is an inherited system consisting of 16 old 100watt panels, two FX80 controllers, an FX2524 inverter/charger and six BB10012 batteries in series/parallel for 24 vdc. Granted, the equipment is +20yo however the batteries are 2yo, connected as directed by BB and Outback. No, I do not have bus bars, nor do I have bus bars on my house system which is 8 10012s in s/p for 48 volts. This system has been fine for over four years.

The 24 vdc system with FX units has begun eating batteries. This began after new tenants moved in and started using the system like they were connected to the grid. He had to start using the generator too often. I brought all six BBs back to my home and carefully charged them individually, balancing and then load testing with a coulombmeter I just received. All passed with flying colors, taking almost six hours at 16-17 amps to discharge but never have I seen them go to LVD (10v BB says). Needless to say, this took almost two weeks.

Back in service, they would be as high as 29vdc on a good solar day but quickly discharge at night. Now he must run the generator two times through the night. Each time I check, I see no excessive current draw during the day with my amp clamp. The MATE shows no faults. I even had him turn off the controllers at night just to eliminate them as the cause. No change.

Here's the kicker: It is always the three POSITIVE ones in parallel that drop to below 12vdc. The negative ones are always above 13vdc. I have swapped their relative positions (I've numbered them) and tested for voltage drop through ALL the cables (same cables as on my 48vdc system). It's difficult to get a proper technician/installer to come all the way out here.

24v 300ah 1pdf - Adobe Acrobat Reader DC 32-bit 9_28_2021 2_31_28 PM3png

The crux of the problem is the constant drain that occurs when there is no sun at night. I admit, I have never done a current measurement at night as I don't live there. Perhaps I may have to sleep by them. It's almost like he's running a 1000 watt heater but it's too hot for that.

Have any of you seen this phenomenon where the positive side drains down but not the negative? I suspect the 20yo FX inverter, FET or PCB but I don't want to just "throw parts at it."

This beyond my pay scale. Any input is greatly appreciated.

Saludos!

PS The "You need to confirm your email address" box is still on the screen. ??

ToroPower · August 2023

Addendum: I neglected to mention that while the tenants wife was away, he tested the system at night by turning off the house breaker box. It is not a draw from any circuits in the house.

By the way, there seems to be an age old question as to which way electrons flow, from - to + or + to -. Seems the consensus is it flows from out from the negative and back to the positive.

Any other questions?

ToroPower · August 2023

OOPS!

I may have found the weak link. The positive terminals one a couple of the BB10012s were overheated and were loose where they join the positive bus bar inside the battery. I suspect he tried to force too much amperage into them. The one read '0' volts until the terminal was pushed to one side, then it read 13.2vdc.

Note the terminal bar is insulated from the bus bar with a plastic strip, the current flows through the charred, loose bolt as it overheated from too much amperage. He must have tried to force more than 50 amps into it. I will report back once they are in service again. I'm confident this was the problem.......................ineptness, not the FX inverter.

ToroPower · August 2023

Update:

Last night he reported the four BB10012s were at 26.9 and this AM 25.2vdc. I am charging/balancing the other two that were next to the one with the loose/burnt terminal.

Hope to have all six on-line tomorrow.

BB. · August 2023

Sounds like a manufacturing (or possibly design) issue. Loose/dirty connections--Mfg. issue. "Too small" of bus bar/connections can be a design issue.

The BMS for these batteries are typically designed to shut off the battery if you draw too much current.

-Bill

ToroPower · August 2023

BB. said:

Sounds like a manufacturing (or possibly design) issue. Loose/dirty connections--Mfg. issue. "Too small" of bus bar/connections can be a design issue.

The BMS for these batteries are typically designed to shut off the battery if you draw too much current.

-Bill

Thanks Bill. I find it odd this terminal is not butted against the bus bar. BB really emphasizes clean, tight, proper connections for the terminals outside the battery but have this weak link inside. This may be on purpose. As per the photo above, the current goes through the bolt and the two lock nuts look like they were hit with a welder.

However, after cleaning and resurfacing the terminal and nuts at the bus bar, it charged fine and is resting at about 14vdc. I charged it gradually to 14.6vdc and witnessed the charging amps dwindle to 0.12adc.

Thanks again for you input.

BB. · August 2023

You do need to look at the installation carefully. There can be an interconnected precision shunt resistor somewhere to measure the current (and Amp*Hours used/charged).

But in your case, it sounds like a mfg. process issue. There is no reason for "loose bolted connections" in any electrical circuits.

"We" are used to 10-20 amps flowing through our house wiring... But with low voltage DC battery banks, the equivalent power of 10 amps @ 120 VAC==For example:

P=V*I
P=120 VAC * 10 Amps = 1,200 Watts
P=12 VDC * 100 Amps = 1,200 Watts

Or roughly 10x more current at 12 VDC vs 120 VAC... So having wiring designed to support 100-300+ Amperes is pretty standard in the Off Grid DC power world.

-Bill

ToroPower · August 2023

I don't think they were loose during assembly. I think the dude in my rental overcharged them and that plastic liner of course softened, the bolt lost its grip, heat made it worse, then arcing ruined the connection.

SteveK · August 2023

Doesn't BattleBorn give a 10 year warranty?

ToroPower · August 2023

I'm not within the US of A. Still struggling.

LiFePo Batteries Draining Overnight Without Any Major Draws

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