Be cautious ordering generic blue wrap LFP cells

[john61ct]

they were all pretty much equal.

Equal voltage at zero SoC means nothing if top-balancing is the goal.


> hobby charger that drops current and begins to siphon power (waste to heat) when one cell reaches the set voltage (which I set to 3.6v)

Set that to start much lower, that way you can sit at just over that for days without overly stressing the cells.

So, set to 13.8V pack CV, balancing starts at 3.4Vpc, total current just enough to match the charger's balancing current x4.

190Ah ÷ 13A rate is 0.07C, not "too low" but yes very very slow.

Better to get on mains power for this commissioning stage stuff, working at 0.2-4C will be faster.

Otherwise could easily take many days

 

[ShamusTX]

Did your cell bulging reduce after the overnight charge? When I built my box for the CALB's to store in the ammo can, the cells required to be numbered to fit into specific slots. However once I got them charged with 140+Ah back in, they fit loosely in the slots now. Basically the batteries were shipped with about ~20% SoC. Which makes sense as when I was researching batteries, I looked at shipping batteries UPS and other shippers requires them to have an SoC of no greater than 30%. So yours were probably shipped with very low SoC, which could be why they were bulging.

 

[luthj]

If the cells were very low, some bulging is possible. You may check again not that they are fully charged.

 

[hour]

Equal voltage at zero SoC means nothing if top-balancing is the goal.


> hobby charger that drops current and begins to siphon power (waste to heat) when one cell reaches the set voltage (which I set to 3.6v)

Set that to start much lower, that way you can sit at just over that for days without overly stressing the cells.

So, set to 13.8V pack CV, balancing starts at 3.4Vpc, total current just enough to match the charger's balancing current x4.

190Ah ÷ 13A rate is 0.07C, not "too low" but yes very very slow.

Better to get on mains power for this commissioning stage stuff, working at 0.2-4C will be faster.

Otherwise could easily take many days

Guess I missed that in battery building 101. I thought the only point of paralleling cells destine for a series setup was to get them to match voltage wise, so that they could then be connected in series. Too much deviation for even connecting in parallel, then manually discharge the high cell to be within the paralleling ballpark, then connect in series after they've been paralleled for a while. Never knew there was a need if all the cells are nearly identical in voltage?

The chargers balancing current is like 1 amp at best (same with almost all hobby chargers) so that doesn't give me much current, 4 amps? Hopefully that won't take an eternity though since the cells are already resting at 3.3X. Maybe I can up that when I throw the active equalizer in the mix tonight?

What do you mean mains power? I have a dumb PSU that has a pot I can adjust and outputs a max of 360w, so I could calibrate that to 13.8v and babysit. It's currently feeding my hobby charger's DC input - but again that's capped at 13 or 14 amps. Next week I'll have a 600w meanwell driver and iCharger X6 - capable of 30amps charge current.

Still expecting the whole thing to take days

 

[luthj]

I would do any balancing with the cells in parallel. Set the voltage supply to the desired top balance voltage, connect it up, and watch it very closely. The current will taper as it approaches the desired voltage. When it tapers down to 1-2% of C, they should all be full.

 

[hour]

Did your cell bulging reduce after the overnight charge?

I'll have to check them out when I get home. That'd be exciting if they unfk't themselves. Never knew that was a thing...

 

[luthj]

Part of the reason that cells need to be firmly clamped is that the movement of lithium ions out of the graphite anode causes the cell to swell slightly. Mechanical restraint prevents possible resulting damage. To a certain extent this swelling can be reversed by recharging the cell. Ideally with a firm and flat clamping. Doing this over several cycles sometimes helps.

Extensive swelling may also indicate electrolyte breakdown and gas buildup (balloon like swelling results usually). I have seen a few events where overcharging caused significant swelling. Interestingly, other than some capacity loss, the cells survived often.

 

[john61ct]

Bulging will not subside.

Does not mean damaged if slight, but do get them compressed before inflicting high temps or high C-rates.

I thought the only point of paralleling cells destine for a series setup was to get them to match voltage wise, so that they could then be connected in series.
…
Never knew there was a need if all the cells are nearly identical in voltage?

Yes but you are top-balancing, so counter-productive to balance at any other SoC.

This is hopefully a one-time "commissioning" deal, only,

Get them as balanced as you can, ideally within 5mV 0.005V at as high a voltage as possible at least 3.55?

Then paralleled to settle down to resting together, since you don't have a 1S input right? If you did, then parallel charge at 3.55V, later up to 3.6V, seeing how they settle to resting after each new plateau.

Many ways to skin the cat, make do with what you have.

Then in 4S, do some cycling, capacity load testing, confirm your hobby charger is doing its job balancing at the top, then just Bulk charge no balance leads, confirm your BMS is balancing at the top.

In future bump up the start-balance V back up a bit at a time on the BMS, but for now, starting earlier will help speed things up.

You can then choose which to use in normal cycling, one or the other.

> Hopefully that won't take an eternity though since the cells are already resting at 3.3X. Maybe I can up that when I throw the active equalizer in the mix tonight?

I'd set that aside for now, first see which works better, charger vs BMS.

Later on compare with that gadget.

Just for giggle, links to each of these?

> What do you mean mains power?

aka shore, AC 120V or 240V from the electric company


> I have a dumb PSU that has a pot I can adjust and outputs a max of 360w, so I could calibrate that to 13.8v and babysit.

Yes, good for bulk charging at higher speed, but yes watch it and shut off when CV acceptance gets much under 10A (0.05C) , certainly before 5A

> Still expecting the whole thing to take days

Keep plugging away.

The true capacity number will be the next important data point.

 

[hour]

Then paralleled to settle down to resting together, since you don't have a 1S input right? If you did, then parallel charge at 3.55V, later up to 3.6V, seeing how they settle to resting after each new plateau.
I guess I do, the hobby charger i'm using is 1-6S and can charge without balance leads plugged in, you can define how many cells when you leave it disconnected. So I could parallel the cells when I get home and try to charge up to 3.55 or whatever, and then series later and try to get them to play nice together.

Just for giggle, links to each of these?
I don't know what specifically we're talking about so here's a dump:

Existing hobby charger I've been using (ISDT Q6 Pro, 13a, 1a balance, can't fully control Vpc)
Existing PSU I've been using (360w 12v, bought many years ago for something else)

New hobby charger (iCharger X6, 30a single output, 2a balance, apparently free range of cell voltage instead of presets, balances at any voltage)
New power supply (600w 24v Meanwell$)

4S equalizerbalancerwtf (Deligreen/QNBBM/? 6/10 amp balancer)
4S BMS (Deligreen 80amp flavor)

I'll have to wire up the inline meter I have to do any charging with the power supply by itself (the 12v 360w one, does like 12-14.8v adjustable). Would much rather offload that responsibility to the new iCharger X6 when it arrives but if I get impatient I'll go this route.

 

[john61ct]

OK, so you can do 1S paralleled, that's great.

But **much much** slower, check your amps rate.

So serial balance charge to 14.2V (3.55Vpc) for speed, then

parallel for the last push to 3.6

then let sit overnight.

Done with initial balancing.

For test cycling fastest is the raw PSU at 13.8, then when you want / need to balance use the hobby charger.

Unless the BMS works well, then just increase voltage on the bulk charger just above the start-balance setpoint.

 

[john61ct]

All good quality gear.

Go to rcgroups.com about the X6, not as familiar.

 

[hour]

So serial balance charge to 14.2V (3.55Vpc) for speed, then

Yeah that's the thing, I couldn't get two of the cells to even 3.45v while the other two were 3.55-3.6. They were certainly higher this morning than they were when I went to bed (like 3.41 to 3.43-3.44 or something) but the other two cells were still hanging out practically at 3.6v and the charger had barely cut current (13a to 10a) in that time span. So yeah they were increasing, but I have no idea what was happening to those other two cells that were being forced to hang out on the high end. You indicated that they were probably cooking their lifespan away, so I don't know if 3.55Vpc is achievable at this time.

Just got home and all cells were still balanced at 3.33v resting for half a day. For some reason the supplier sent me four bus bars so it doesn't look like I can parallel all four together at once. Need to make another two bus bars I guess, have some aluminum flat stock or some copper pipe I can hammer flat (used that for bus bars on my existing house battery DIY). Or I could connect all the positives together with the bus bars I have, and then run four 10 gauge wires with ring terminals from each cell to a bluesea negative distribution block thing. Any thoughts?

And should I expect spark connecting these 3.2v in parallel? I'm used to it when paralleling 12v. Just kidding, I'm not used to it. It scares the ******** out of me every time.

 

[luthj]

If the batteries are all within 50mv of each other, there will be no "force" to drive big currents (voltage difference) so you should see zero or very tiny sparking.

 

[john61ct]

Yeah that's the thing, I couldn't get two of the cells to even 3.45v while the other two were 3.55-3.6. They were certainly higher this morning than they were when I went to bed (like 3.41 to 3.43-3.44 or something) but the other two cells were still hanging out practically at 3.6v and the charger had barely cut current (13a to 10a) in that time span. So yeah they were increasing, but I have no idea what was happening to those other two cells that were being forced to hang out on the high end. You indicated that they were probably cooking their lifespan away, so I don't know if 3.55Vpc is achievable at this time.

I did not realize they were on a balance charger, should be safe.

But the bleeding/resistance they use can be **so** slow, sure see how you go paralleling from where they are now all the way up to 3.55V

Then maybe test the balance charger.

Really doesn't matter long as you get there, all good experience building too.

BTW make sure your V&A measuring tools are accurate, never trust the charge source alone.

The intra-bank wiring should all be the same, gauge, resistance, lengths.

Marine quality wiring & ring terminals are just fine.

genuinedealz.com will make them up for you if you don't have access to good crimpers.

 

[hour]

Yea, I know the bleeding they do in the home stretch (combined with reducing current) can make it take forever, I was anticipating that last night. But I didn't really have any solid indicator that it was ever getting to that point other than the drop to 10 amps from the set 13 amps, after eons of charging at full blast.

Just connected everything in parallel after hacking some things together, no spark (thanks luthj). Plugged in the hobby charger which read a simple 3.4v, so I did go through with connecting the balance leads just for a single positive and the negative. That let the hobby charger print out a more accurate reading of 3.34v starting with the cells paralleled. They're now charging at a whopping 35w and I had to set it to 3.6v because there's no lesser option for any chemistry supported by the charger.

I'll check it periodically tonight and if I get above 3.55v (in what I'm guessing will be hours upon hours), I'll disconnect, let rest, connect in series, shoot for 3.55+Vpc and hope that balancing was achieved. I guess this is all alien to me since I did bottom balancing on my existing 90ah pack, and hobby balance charger top balanced (without any issue like I experienced with these blue cells) on my portable 26650 packs.

Part of me wishes I had left it chugging along all day at work in series, since current had dropped to 10amps and something was changing. I surely would have crapped bricks from a mid-day John post though, until I read the last comment that it was probably safe since they were on a balance charger. Doh.

Thanks guys