LIFePO4 batteries - interesting challenges

[phemens]

In another thread I detailed what I was doing to upgrade batteries to LIFePO4. Thought I'd raise a new thread for some challenges I'm facing in case someone searches on it in the future.

I have 4 100AH LIFePO4's (1 more on the way), with a Samlex 3012 charger inverter and a Victron BMV 702 monitor (and 2 Victron MPPT solar controllers, not central to discussion, but FYI).

One of the 'interesting' issues is that since the batteries hold their voltage all the way down the SOC ladder, I'm finding it challenging to figure out how to get the charger to kick on in a way that balances keeping the batteries charged with not always keeping them topped up.

Initially, the Samlex rep told me to set the charger to 2 stage charging profile, and to set the Reset Voltage (kick in Bulk) to 12.6V. I tried this and left everything alone for about a week. Checked back and SOC was at 40%, but voltage still above 13.1 V.

Here are some of the settings I have set on the 3012 (based on input from the battery manufacturer):

Battery type=Lithium
Charging profile 3=2Stage Type 1
Absorb exit amps=0A
Absorb time=1min
Floating exit=12.00V
Equalize-4Stages 0=No
LV cut off time=1200sec
LV detect time=10 sec
Batt low voltage=12.00V
Low volt alarm=11.50V
Reset voltage=12.60V
Batt over volt=14.40V
Compensate=4mV/C/C
Floating voltage=13.00V
Equalize voltage=14.00V
Absorb Voltage=14.20V

I realize the Samlex 3012 is not a true Lithium charger, but it's what I got and I don't see changing it any time soon. I'm not an electrical engineer (duh!) so I'm looking for some advice on how to debug this - how to get the charger to kick in when needed while on shore power. I spoke with the battery guy, he said it would be fine to keep the batteries at full charge for a few weeks at a time (but not say over winter). I do have a spare charger (Boondocker) that I could hook back up for this purpose, but I'd rather find a decent balance with the Samlex if possible. For now I've got the solar turned back on in the driveway to keep the batteries charged while I figure this out.

[Itinerant1]

Mex here are readings from Sept 21st of last year. LFP voltage so flat.
When the batteries are full as phemans is seeing/ learning the SoC drop compared to voltage is so little you can only see it if you have a meter with xx.xx v.

Here is a typical day that has been going on for the past 3.5 years everyday on my bank and mainly being charged by solar (99% of the time). SoC, Voltage, discharge/ charge amps are read of the EMS display for the LifePo4 batterys (500ah). The next columns are from the Magnum inverter display.



As you see until there is a heavy draw item then you see some temporary voltage drop but even still this is at 37% SoC (185ah) or 63% DoD.

I could show higher SoC readings but the voltage move is very minimal.

[MEXICOWANDERER]

This is a comparative analysis question.

As analyzed, does lithium slump the same as L/A, when amp-hour analysis is compared to state of charge? This is a sampling technique in which actual ampere hours is compared to theoretical amp hours remaining.

[BFL13]

You are now off the hook for between trips on shore power and keeping them full instead of 80%. If "winter" is more than a few weeks (unlike here 🙂 ), you can still disconnect them at a chosen SOC and leave them to sit until camping starts again. (Boondocker for 12v for when disconnected)