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]

12v 500ah (4s5p)

[LittleBill]

Itinerant1 wrote:
Mine are not dropin but GBS Elite power solution prismatic cells. Which have these connected between the 20 cells that connect to the CPU/ EMS...



When a sense board is installed correctly the green led will light up. There is also a red LED on the sense board, which indicates cell balancing is occurring. This led will light up any time the cell voltage is 3.55V or higher.

Note: not by a certain battery voltage but by a cell voltage. Yes some cells climb faster in voltage than others.

well its battery voltage divided in series etc. all the balancer cares about is when it individually gets over 3.55

appreciate the photos

why 20 cells what voltage are u running?

[Itinerant1]

Mine are not dropin but GBS Elite power solution prismatic cells. Which have these connected between the 20 cells that connect to the CPU/ EMS...



When a sense board is installed correctly the green led will light up. There is also a red LED on the sense board, which indicates cell balancing is occurring. This led will light up any time the cell voltage is 3.55V or higher.

Note: not by a certain battery voltage but by a cell voltage. Yes some cells climb faster in voltage than others.

From reading different manufacturers and surfing different forums most "suggest" 14.4-14.6 for both the resetting of the SoC % capacity and to balance the cells.

[LittleBill]

Itinerant1 wrote:
I believe he means balancing.

do you have to reach a certain voltage for balancing to occur? i though the balancers worked continuously? not sure how the bms in them work

according to the battleborn faq need to be over 14v


"A passive balancing process is activated by the BMS at the top of each charge cycle, when the battery voltage exceeds around 14V. This ensures that all the cells remain at the same state of charge, which helps for pack longevity and performance"

[Itinerant1]

I believe he means balancing.

[LittleBill]

what exactly do they mean by the cells reset?

[phemens]

LittleBill wrote:
i am going to back peddle on my comments.

my comments were mostly around li-ion which is what i use. looking at how life are composed the final voltage does matter, there is no charge controller inside most of these battery types simply a balancer lvc etc..

14.4 puts u at about 3.6v per cell which is max.

13.6 puts you at 3.4.

if you didn't want to run max somewhere around 14.0-14.2 i would go( really depends on if you need the higher capacity)

SOC is practically impossible from what i am reading, the voltage drop curve is practically straight

you would be better off basing it on AH removed and using that for SOC, instead of voltage. this is done by running down to LVDC.

sorry the misdirection earlier, we all learn something new every day.

link on DOD cycle life

Thanks for the info, I am definitely learning as I go! I am indeed basing off the amps out/in, as you say voltage is essentially useless. I have bulk set to 14.4 but may ease off to 14.2 as I don't need the extra oomph and I don't think it gives me much.
I got the discharge curve on my LIFePO4's, they run straight until you hit about 20% SOC remaining @ 12.8V, at which point it tails off pretty quickly (12V @ 10%, then precipitously steep decline from there).

[phemens]

Itinerant1 wrote:
My gear is all Magnum (inverter/ charger & PT100 controller. The controller follows the same settings as the IC.

This is how I have mine set..
The following parameters are for programming the ME-ARC Version 4 advanced control.

LBCO Setting: Volts = 12.0
Battery Type: = Custom
Absorb Volts: = 14.2
Float Volts: = 13.6
EQ Volts: = 14.2
EQ Done Time: = 0.1 (I don't use EQ)
Absorb Done Time: = 0.1(I can't turn this off)
Max Charge Rate: = 100%
Final Charge Stage: = Float

I have not gone over 14.2 on my setup the % capacity resets/ balances the cells at that voltage.

Most drop ins require 14.4-14.6 occasionally to reset the % capacity/ balances the cells.

For your summer style with the camper I would use these but you can go with a bit less but you will have use 14.4 occasionally.

The battery guy said I was fine at 14.4, the cells reset at 14.6. Thanks for the info.

[phemens]

steveh27, the SOC on the Victron works fine. Initially I was trying to reconcile it with what the BMS was showing me, but the battery mfg said the SOC measurement on the BMS should not be considered accurate.

The battery guy got back to me and said that floating the batteries at 13.6 during the day on solar was fine, since they would draw down at night. This will let me leverage solar all day to run the fridge on electric with the excess.
His only concern was extended periods of floating voltage on shore power, but my Samlex is set not to do that, so we're good there.

[steveh27]

SOC seems to work OK with the Trimetric and my lifepo4.

[phemens]

Sorry, DODC?
Support from the various sources has been good (Samlex, Victron, Battery mfg), but I am assembling the overall system myself, I like to build things and figure it out. Not disappointed at all, I knew what I was getting into.
In this case I guess the complexity is in the various systems together and the specific use. It’s funny how little literature there is out there on subjects like dry camping with LIFePO4 and solar and parasitic charges and optimizing battery cycles and... 😉
What can I say, I find this stuff interesting, I’d almost swear I like it better than actual camping!

[LittleBill]

i am going to back peddle on my comments.

my comments were mostly around li-ion which is what i use. looking at how life are composed the final voltage does matter, there is no charge controller inside most of these battery types simply a balancer lvc etc..

14.4 puts u at about 3.6v per cell which is max.

13.6 puts you at 3.4.

if you didn't want to run max somewhere around 14.0-14.2 i would go( really depends on if you need the higher capacity)

SOC is practically impossible from what i am reading, the voltage drop curve is practically straight

you would be better off basing it on AH removed and using that for SOC, instead of voltage. this is done by running down to LVDC.

sorry the misdirection earlier, we all learn something new every day.

link on DOD cycle life

[Itinerant1]

My gear is all Magnum (inverter/ charger & PT100 controller. The controller follows the same settings as the IC.

This is how I have mine set..
The following parameters are for programming the ME-ARC Version 4 advanced control.

LBCO Setting: Volts = 12.0
Battery Type: = Custom
Absorb Volts: = 14.2
Float Volts: = 13.6
EQ Volts: = 14.2
EQ Done Time: = 0.1 (I don't use EQ)
Absorb Done Time: = 0.1(I can't turn this off)
Max Charge Rate: = 100%
Final Charge Stage: = Float

I have not gone over 14.2 on my setup the % capacity resets/ balances the cells at that voltage.

Most drop ins require 14.4-14.6 occasionally to reset the % capacity/ balances the cells.

For your summer style with the camper I would use these but you can go with a bit less but you will have use 14.4 occasionally.

[LittleBill]

the less DODC the better, bring them right to 13.6, doesn't matter the charge source at all.

for the amount of money you dropped, I'm disappointed no one has pointed you in the proper direction when you ordered the stuff, unless you just bought it all yourself.