Lithium Battery charging

[buckland]

This is probably a one up question.
Recharging my LiFePo4 battery to then balance the cells. It is on charger. BMS is balancing. Read out says 3.22 on each cell(4).
The question is the BMS % readout is 15%. This is real low though the Volts are 12.88v. What does it signify? (Time of photo it was 7%)

 

[Vic Harder]

Huh. Puzzler. The 82 mv number is the delta between highest and lowest cell. That works out to 2.54%, not 7%. A question for rando, methinks.

 

[rando]

The '%' value on the balancer display is just a guess at the SOC based on the battery voltage. For LiFePO4 batter 12.71 V is pretty much flat, the normal resting voltage is 13.2-13.3V, so an estimate of 7% SOC is pretty reasonable. Remember that for lithium batteries, using voltage for SOC is pretty much useless as the difference between fully charged (13.3V) and about 20% SOC (13.1V) is tiny.

 

[buckland]

Much appreciate that info. I was at a loss on it. The trickle charger has brought the cells up to 12.9 V Today I will put it on a regular 12 v charger for a few hours and see if it will go up to 13.5 V Thanks again.
Rob

 

[buckland]

I have a portable flex 100w panel and a spare controller. I wired it up to charge the packs and it is now finally increasing in % SOC. I think this is good however this morning all 4 packs were balanced... as the charging increased they went out with one very strong one. I intend to leave on the balancing after I get up at 100%. (Hopefully)

 

[buckland]

After two days on a 4amp charger, the BMS indicated a 60% charge and voltage of 13.33. Then hooked up a small inverter 150 watt and plugged in a 110 v fan to see what happens. After an hour on that load I took the photo below. Down To 33% and 13.19.
What this tells me I am not sure. I was wondering why the battery would not charge over 60%... and why it fell so rapidly. Individual bad cells in a pack (3)? Thoughts?

 

[CougarCouple]

Hi buckland
Was the charger still putting out to the battery? What was the voltage off the charger, amp output? If the charger was still charging the battery sound like it just needed more time.

I don’t know how long the charger you have would take to bring the battery up to 100%.

What you had plugged in sounds like you lost around 1/3 rd of a fully charged battery.

Russ

 

[PaulT]

I would be inclined to withhold judgement until going through a few charge/discharge cycles. It may be that the BMS will equalize the cells over several cycles And improve overall performance.

Paul

 

[buckland]

Russ, No that was with the charger off (when it was on it read 80%) soon as I took it off it dropped to 60%. Seemed no matter how long the charger was on 80% was max. That said ... it is sitting at 13.20 V at 35 % after using it to run a fan/inverter.
I could run it down a bit more and then put it back on the charger for a day. I was not aware that a few charge cycles could affect the performance.
Paul, Will run through a few charges and load this weekend and see if it affects the percentage.
Constantly learning
Thanks
Rob

 

[rando]

That looks really good to me, the cells are staying in balance both charging and discharging.

Remember, the display on the balancer is only guessing at what the battery SOC is based on the voltage it sees, which doesn't work very well on lithium to start with, and really doesn't work when the battery is not at rest. When you are loading it down with the inverter, the voltage drops, so the balancer display drops the SOC because it is only a linear function of the measured voltage. When you are charging the voltage rises, and all of a sudden the balancer thinks the SOC is high.

For now I would ignore the '%' number on the balancer, it is causing more confusion than it is worth. Either use a real current counting battery monitor, or the 'resting' voltage if you don't have a battery monitor.

 

[buckland]

Well that is hopeful news. The fan has been on for four hours and the cells are still balanced. I will let it run another two hours then plug in the 100 W panel to charge. I assume a controller that is not a mppt type (sunsaver 20) has a different way to handle the charge. Will see how this recharge goes. Thanks for the background explanation. It helps the understanding of what I am seeing.

 

[CougarCouple]

[Remember, the display on the balancer is only guessing at what the battery SOC is based on the voltage it sees, which doesn't work very well on lithium to start with, and really doesn't work when the battery is not at rest. When you are loading it down with the inverter, the voltage drops, so the balancer display drops the SOC because it is only a linear function of the measured voltage. When you are charging the voltage rises, and all of a sudden the balancer thinks the SOC is high.]

All that makes sense above.
Is the charger being used the problem?
What would be a reasonable time a depleted lithium battery take to charge to 100%.

The comment about cycling thru several charge cycles, what is the reason for that?

Thanks in advance
Russ

 

[Vic Harder]

All that makes sense above.
Is the charger being used the problem?
What would be a reasonable time a depleted lithium battery take to charge to 100%.

A depleted LeFePo4 100AH battery will charge as fast as you can feed it... Up to 1C or 100A) at the 4A that Buckland is feeding it, 25 hrs with no draw.

 

[buckland]

That makes sense... I appreciate your math in all your explanations... takes care of the "why?".

 

[Stokeme]

This is non scientific, but the one experience I had with a totally drained LFP4 system, (50w & 100w in parallel) which btw scared the crap out of me, was that it charged at a snail’s pace at the beginning, and as the voltage increased, the rate of charge seemed to slowly increase. The cells at higher voltage seem to release energy slowly & efficiently. They also charge effectively & evenly as well. But starting at very low voltage, as I watched charging progress with the internal Bluetooth modules, the cells were not as orderly, even or as efficient.
I used only my (240w) solar panels. It happened to be a uneven mix of clouds & sun all that week. It took 2 1/2 days to reach 99% SOC. I have a 20amp LFP4 Charger but I was curious how long only Solar would take to fully charge.
Throwing this out (sorry if superfluous) as one aspect I encountered with Lithium battery charging. Typically my System only drains 8 - 12% by next morning. By 1pm each day it’s back to 99% SOC.

 

[Vic Harder]

I got my dual 100AH BattleBorn's down to 8% SOC this week. Driving home today, the solar panels were putting 375W into the batteries. Might depend on the BMS of the battery?

 

[CougarCouple]

Morning Vic
Was that 375 watts just your panels, that looks pretty impressive to me.

Russ


ps thanks for the earlier response on time to charge battery.

 

[Vic Harder]

yup, just from the one panel. I was startled too.

 

[buckland]

Hello Vic
When you are able to get to the Canadian Maritimes you’ll get to appreciate Northeast weather! After a Covid test I was allowed to travel to Maine ... we are up on the Canadian border. Lots of bugs and rain. And now to the battery point. I have two canoes on the roof and it has rained solid for three days. The one Battleborn battery heroically has lasted but this evening I turned off the main camper electric knob as my Victron showed 11.85 V mighty low? We bought ice for the fridge.
When there was no juice from panels the Victron app stated that the charger needed 5volts higher than the battery to initiate charging. The panels suffered to be at 15 v. ( I have a portable 100 w panel and it could not produce that voltage due to clouds.
The second thought is about alternator charging. It seems it is not happening. I have a 2016 truck and being computer controlled I am sure it won’t reach 5 v over battery.
My truck battery indicates on the dashboard it goes on and off between 12.2 and 15 v almost in a computer generated on and off pattern.
Perhaps the Victron is not permitting alternator charging? Or is it the. Blue seas ACR thats is not allowing charge?
Electrical puzzles.
We are heading to a remote cabin for another week. Rain for two more days.) when we get there tomorrow I take off the boats and will also plug in additional panel to hopefully get the battery back up. Might have to consider a second battery.
Rob (aka Buckland)

 

[Vic Harder]

Hey Rob, yes... we are looking forward to a trip to the east coast. Not sure that will happen in 2020 because of Covid, but....

Re: canoes on top and rain. Yes, I experienced that this week too, hence the 8% battery SOC after 3 days of using our 1800W induction cooktop draining our 200AH of BBorn batteries. I was worried about the BMS putting the batteries in shutdown. That happened once already during testing. I had to disconnect the batteries for a few minutes to get them to reset and even accept a charge.

Regarding the 5 volt threshold for charging. PITA that, no?

To get more juice from your panels, you might want to consider going in series vs parallel. Or have you done that already?

Victron is only between PV panels and battery, so it won't be interfering with alternator charging. That's the Blue Sea ACR's job. Are you saying that on the truck dash you can see the truck battery oscillating between 12.2 and 15 v?