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.

[phemens]

So, for shore power I think I have it figured out.
Similar but different issue - I have 2 victron MPPTs going directly to battery bank (from different arrays). In bulk charge they work fine, I get to 100% (14.4V). However they then go into standby waiting for the voltage to drop to the threshold to kick back in on bulk charging, which you guessed it is when I'd hit around 20% SOC (12.8V), I don't want to draw that far down.
Any harm in setting float voltage on the MPPTs to something rather high (say 13.5V or even higher?) to keep the batteries topping up during the day. This obviously would not be a problem after sunset, and would give the batteries a chance to draw down overnight. ?

[phemens]

I did try the AC for a few seconds, it started up but the voltage started dropping below 13V, and I think the inverter was signalling an overload (which makes sense as it's 3K).
Read an interesting article on Lithium battery charging with parasitic loads:
Link to article

[steveh27]

My invertor is only 400 watts, so I'll not be having a huge draw, but will have much more usable power. I'll try to attach a pic. It's not pretty, but it's working.

[Itinerant1]

I can see the smile on your face while you did the testing. Roughing it off the beaten trail just got quieter. 😉

[phemens]

I think you'll like your batteries. I just did a test running the microwave, fridge on electric and coffee maker, my voltage dipped all the way down to 13.1V 😉

[steveh27]

I just installed my 2 Lifepo4 batteries, each 100 ah to give me 200 ah in my very small space battery box in my Class B. They have BMS which I cannot see or change. I have the PD4635 charger and they told me to just keep it in boost mode while charging. I have Trimetric 2025 meter & they gave specs for me to use:
For Lithium LFP batteries, the changes needed are as follows:
P1 - 14.4 Volts.
P2 - 2% of P3 (battery bank capacity)
P3 - Battery Bank capacity in Amp-hrs
P7 - L3
P10 - 98%
P14 - 0.00 hrs

When pugged in all went well with these settings. I now have it unplugged. Probably will not boondock until October 20. That will tell me a lot.

[phemens]

They are not Battleborn, it's a manufacturer new in market operating out of Canada. He's an electrical engineer by trade, he spun this business out of another one, started out building them himself and just recently outsourced manufacturing to China. He's been very responsive in helping me get set up.
Samlex recommended 6 minutes for Absorb exit, why would you say 1 hr? The Samlex setting to clarify dictates the time to hold at Absorbtion voltage before stopping bulk charge.

[LittleBill]

phemens wrote:
The battery guy gave me what he admitted were conservative numbers for the Samlex since he wasn't too familiar with the unit. I will be bumping up float to 13.6, absorb to 14.4, float exit to 13.6.
Absorb time I assume is time at voltage before cutting out bulk?

float exit should be lower 13.4, are these battleborn battery's?

absorb time should be higher , set it at an hour and go from there.

[dave17352]

The new trilliums have a state of charge monitor on the battery themselves.

[phemens]

The battery guy gave me what he admitted were conservative numbers for the Samlex since he wasn't too familiar with the unit. I will be bumping up float to 13.6, absorb to 14.4, float exit to 13.6.
Absorb time I assume is time at voltage before cutting out bulk?

[phemens]

Itinerant1 wrote:
phemens did you get the soc % figured out between the bmv-702 monitor & the batteries display, you mentioned that in the other thread?

I spoke with Victron, Samlex and the battery mfg. The BMV-702 is accurate for amps out, pretty much every other reading I figure is useless (SOC on BMS I was informed is not extremely accurate, the BMS uses voltage only for protection). So now I will use only the 702, and get over my inherent paranoia over SOC 😉

[LittleBill]

if your using battleborn its pretty easy, 13.6 float, bulk 14.4 equalization off or 14.4 as well.

looks like they are design to work with normal chargers, since they have a bms in front of the charger, and reading u can go to 0 on DOC so it doesn't matter

your settings are off.

i would change float to 13.6 equal/absorb to 14.4, float exit to 13.5

not sure i understand absorb time.

you should be asking your battery mfgr for their numbers, not the charger mfgr.

to be honest, unless you can control the BMS, you can't control their charge state, im pretty sure the bms decides the final output of the cell voltage regardless of the input voltage from the charger. i assume the only reason they give you different voltages is for float and bulk is simply so the charger puts out more amps in bulk mode. i highly doubt the cell final voltage changes regardless of the input voltage. you would need to change the bms charge setting to do the 80/20 split if that's your goal, thats something u need to ask the Battery mfgr.

[Itinerant1]

MEXICOWANDERER wrote:
Not only a meter with that resolution is needed a processing core and both kinds of memory are needed to analyze a reasonable sampling rate.

i.e.

If this is this and that is that then "X" must conclude as being.....

Includes high-resolution voltage, real-time WATTAGE and time-analyzed WATTAGE HOURS.

This is one area outside the realm of simple addition and division. It is utterly comparitive based. If this exceeds a person's ability do not knot your knickers over it. It's entirely the responsibility of nerd engineers like me. Practicing the written formula is basically an utter mental overload of few other uses.

Outside the realm of equipment us poor slobs are using. It will be awhile before my battery bank gets gets shut down and torn apart for a check of cell capacity lose.

[Itinerant1]

phemens did you get the soc % figured out between the bmv-702 monitor & the batteries display, you mentioned that in the other thread?

[MEXICOWANDERER]

Not only a meter with that resolution is needed a processing core and both kinds of memory are needed to analyze a reasonable sampling rate.

i.e.

If this is this and that is that then "X" must conclude as being.....

Includes high-resolution voltage, real-time WATTAGE and time-analyzed WATTAGE HOURS.

This is one area outside the realm of simple addition and division. It is utterly comparitive based. If this exceeds a person's ability do not knot your knickers over it. It's entirely the responsibility of nerd engineers like me. Practicing the written formula is basically an utter mental overload of few other uses.