Schneider LiFePo4 Build

[MisterSandals]

Let your charger top it off. Your BMS may readjust 100% with cell overvolt.

How many battery cycles are shown? Any?

Your cells are well balanced at mid-voltage, hopefully good as you go over 3.4V. That is when you will need to be attentive the first few cycles.

 

[flpilgrim]

Let your charger top it off. Your BMS may readjust 100% with cell overvolt.

How many battery cycles are shown? Any?

Your cells are well balanced at mid-voltage, hopefully good as you go over 3.4V. That is when you will need to be attentive the first few cycles.

5 cycles as of today

 

[MisterSandals]

Max volts recorded?

 

[flpilgrim]

Max volts recorded?

56.69 a couple days ago, neither of my chargers have ever been set that high.

is there a way to reset it to keep it from wigging out like its doing in the above screenshot?

 

[n2aws]

ok. so are you saying i should ignore the warnings, go back to charging at 55.2 across the board and wait for the bms to do its job? as in, it may take a few cycles for that to happen? I reduced my chargers settings down to 54.4 because i thought my battery was feeling "triggered" lol.

Close, but not quite.

if you drop the "take a few cycles" and replace with "leave it in high SOC until they balance and show 100%" then, yes

After your initial balancing, recharging them to full regularly, will *maintain* it, but if they are imbalanced enough to be showing cell overvoltage alarms, I suspect you need to give it some time and get a good, solid topbalance in once. *then* you can cycle it

 

[flpilgrim]

Close, but not quite.

if you drop the "take a few cycles" and replace with "leave it in high SOC until they balance and show 100%" then, yes

After your initial balancing, recharging them to full regularly, will *maintain* it, but if they are imbalanced enough to be showing cell overvoltage alarms, I suspect you need to give it some time and get a good, solid topbalance in once. *then* you can cycle it

ok ill do that. the bms cell voltage readings match my voltmeter readings but should i be worried about that giant discrepancy in the screenshot above?

98% at 52.29v ?

 

[400bird]

Ok, I'm just trying to understand, what harm will starting balancing at 3.2 do to my Overkill or my battery? Not trying to be difficult, those little tidbits of info help me understand other things usually.

The cell that is actually more charged (and needs to burn off energy/be balanced) isn't necessary the highest cell at 3.2 volts. I've seen it with my own eyes. If this is the case on your pack, you can cause it to be more out of balance by having the balance turne on at such low voltage.

I keep getting cell overvolts on cell 4 at the top end of my absorb cycle, not even into float yet. It seemed to follow in my brain that if things were more balanced before i got to 3.4 it might help prevent some of that.

If cell 4 is still getting balanced at 3.2 volts, you probably can leave it for now, but eventually you really should adjust it back to 3.4

 

[chrisski]

If you’re balancing a single cell in the Overkill with 3.4 v and above, recommend leaving always balance on, not while charging only.

The Overkill spends so little time charging above 3.4 to full SOC, it’d take too many cycles to balance only done while charging.

 

[flpilgrim]

If you’re balancing a single cell in the Overkill with 3.4 v and above, recommend leaving always balance on, not while charging only.

The Overkill spends so little time charging above 3.4 to full SOC, it’d take too many cycles to balance only done while charging.

done, thanks.

does anybody have any experience with soc discrepancy above? anyone?

 

[n2aws]

done, thanks.

does anybody have any experience with soc discrepancy above? anyone?

This is likely going to be specific to your BMS, that I'm unfamiliar with. but many will "calibrate" SOC, after a few cycles when it can guage what your capacity actually looks like.

 

[flpilgrim]

This is likely going to be specific to your BMS, that I'm unfamiliar with. but many will "calibrate" SOC, after a few cycles when it can guage what your capacity actually looks like.

cool, it was just reading normal until today, seems like i might have fucked something up unknowingly.

 

[42OhmsPA]

That model of BMS will not ever tell it is at 100% until it has had a cell hit High Volt Disconnect. This is a KNOWN issue... It's not unique to JBD/Overkill either.

This has me confused, I simply adjusted my 100% voltage setpoint and have no issues getting to 100%.
I will say the SOC estimate in them is crap based on my experience but I'm running 3 packs in parallel so they frequently see very low currents.

LFP has TWO Voltage Ranges like all other chemistries and THAT is where everyone falls over...
1) The Allowable Voltage Range. This is the safe voltages that will not harm the cells. This is NOT for regular usage. (2.500 - 3.650)
2) The Working Voltage Range. This is the range that actually delivers the rated Amphours. (3.000-3.400)
Most will allow cells to go down to 2.800 Volts before low volt disconnect but that does not give much extra.
LFP has a Very Flat curve 3.0-3.4 mostly below 3.0 it is a cliff fall, and above 3.4 is a rapid climb.

I used this info as well as the settings from @SupraSPL in another JBD thread and things seem to be working well with my attached values.

@flpilgrim you may find them helpful. I would run the balance start a little higher once the packs get better.
If you hold them at 54.4V for a day or more with them your deviation / balance will get much better.

Edit to add I thought I still had balance at 3.39v. You'll need 54.6 - 54.8V with those settings.

 

[chrisski]

My two overkill BMS show different SOC. One is accurate; the other even when fully charged show a SOC of 70%.

It’s been installed two years now, so not going to correct itself. I find no way to adjust on Blue Tooth.

There is another thread that discusses buying the usb adapter card, disconnecting WiFi, and now the SOC can be adjusted.

That thread was just active a couple days ago.

 

[SupraSPL]

@chrisski The Overkill Android Bluetooth app will allow you to adjust the SOC/voltage figures on each BMS to match. Maybe that is an old version of the ap?

I'm still trying to get mine dialed in but it's getting better.

 

[chrisski]

@chrisski The Overkill Android Bluetooth app will allow you to adjust the SOC/voltage figures on each BMS to match. Maybe that is an old version of the ap?

I'm still trying to get mine dialed in but it's getting better.

I am going to adjust those this weekend when I'm in the RV.

Right now, each of the BMSs has the exact same parameters. At least I think so. If not, I will be a bit embarrassed.

What I think I need is a "Synchronize SOC to 100%" button like Victron has. Until the shunt gets dialed in, the numbers tend to drift.

 

[flpilgrim]

Thanks again all for chiming in...maybe the bms soc is right, ive pulled hard on the thing today and have barely used a tenth of a volt

 

[n2aws]

Thanks again all for chiming in...maybe the bms soc is right, ive pulled hard on the thing today and have barely used a tenth of a volt

It's possible. Thats what we mean by the voltage curve being pretty flat from 20-80% SOC. during the "flat" part, the cell could be 25%, or 75% SOC. It's nearly impossible to know.

Let us know how top balancing goes. Make sure when you do it, that you don't have any loads on the batteries. let them balance out until they are all balanced really closely (mine will get to .01v difference). Once you have a good top balance, you can excercise them and as long as you top them off regularly, they should *stay* pretty healthy and balanced.

 

[400bird]

Above 3.4 volts. When you can get all the cells bunched close together around 3.45 to 3.65 volts together with a small voltage delta. Then it's balanced.

 

[n2aws]

Above 3.4 volts. When you can get all the cells bunched close together around 3.45 to 3.65 volts together with a small voltage delta. Then it's balanced.

Oh, piggybacking on this.. I forgot to mention...


When you get your cell overvoltage warning, set your charger to maintain that voltage. don't try to pump more energy in. STAY at that voltage until they balance, and let the error clear. Then bump the voltage back up in maybe 0.5v increments, rinse and repeat the process until you hit whatever pack voltage you actually want these batteries to live at. Once you are at that voltage and they are balanced, you are good to go.

 

[flpilgrim]

Oh, piggybacking on this.. I forgot to mention...


When you get your cell overvoltage warning, set your charger to maintain that voltage. don't try to pump more energy in. STAY at that voltage until they balance, and let the error clear. Then bump the voltage back up in maybe 0.5v increments, rinse and repeat the process until you hit whatever pack voltage you actually want these batteries to live at. Once you are at that voltage and they are balanced, you are good to go.

awesome, just so im crystal clear:

my cell target full charge with no load should be 3.4-3.5v

unlike with lead acid batteries i don't need my charger setting 2 volts above my pack target to get there---ie---my absorb/float setting (for this one time at least) should be 54.4v.

If i set my chargers at 54.4 and im still getting cell overvolts, reduce my charger setting to whatever the battery reading happens to be when the event occurs and maintain that till my delta reaches 10 mv or below, then creep up to 54.4 in .5v increments.