Be cautious ordering generic blue wrap LFP cells

[john61ct]

dupe

 

[john61ct]

oops

 

[hour]

It sounds like that one cell may have significantly higher resistance. I hope its just first cycle variance.

I hope that too, and maybe there's actual hope since the first full charge had two cells doing this, and now only one is.

Maybe just pack-level charge, disable balancing with the hobby charger.

Just use the Deligreen balancer, and watch the cell voltages manually to ensure not going too high.

If balancing still takes a long time, tune the current input lower so it's just enough, the Deligreen can keep up redistributing.

Can do, will do. I still have no way of measuring this, but I am skeptical as to whether the deligreen balancer can keep up. Even though one cell is at 3.45v now (0.9a charge current to pack) and three cells are at 3.58 at this low of a charge current, the active balancer is still going to take hours to straighten out. Going on an hour and a half with the active balancer connected and the variation from high to low cell is still averaging 0.160. It was averaging 0.180 initially. It's already been mentioned how a balancer that says 6 amps / 10 amps peak may do very little work if the variation isn't extreme, but 0.160 is extreme to me and I'd fully expect this thing to let the high cells shoot to 3.75+ and still be doing little work. Obviously not supposed to be used without a BMS as it has no protections, but damn do a little more would ya?!

Going to remove balance leads from hobby charger now and restart charging at a lower (but higher than 0.9a) current. Will monitor highest cell voltage like a hawk.

 

[john61ct]

Do **not** allow any cells to go above 3.60V, 3.65V absolute drop-dead maximum

am skeptical as to whether the deligreen balancer can keep up.

Check to see at various sources for that model, if it says (in chinglish attempt anyway)

actual balance current goes up if the voltage difference is greater, less current as the voltages get closer

There are other, more expensive balancers that let you set the balancing current, and specs state

balance current does not depend on voltage difference


Yes anything over 0.1V is a high delta

> Going to remove balance leads from hobby charger now and restart charging at a lower (but higher than 0.9a) current. Will monitor highest cell voltage like a hawk

Good.

Plan B, break the pack, wire in parallel, sit a while, charge at 3.6V, hold CV a while, let sit a while, rewire for serial.

Tedious I know

 

[hour]

Going to remove balance leads from hobby charger now and restart charging at a lower (but higher than 0.9a) current. Will monitor highest cell voltage like a hawk.

Well, it was a nice thought. Without the balance leads connected and charge set to 3.6Vpc on a manually set 4S pack (since it can't calculate that without balance leads of course), the charger instantly throttled because overall voltage reading was getting to where it needed to be. Highest cell shot up to 3.65 in about 30 seconds at 1.4 amps (though it maintains 3.58-3.60v at 0.9a with whatever bleeding is occurring) and I instantly stopped the process

Gonna just have to let it sit and hope the equalizer does its thing eventually. In looking at the hi-lo min-max on an RC monitor in real time (same thing I had on my tv yesterday but a different screen), I can see the high cell is shifting every second between 1, 2, and 4. 3 is the low one, so that's obviously remaining the lowest cell on the display.

So maybe that's the result of the equalizer. But maybe that's also slowing down the equalizer when it too senses another cell is now highest and starts supplying cell 3 from it. Can't lock on to a high cell long enough to get rolling? Might not be how they work though, theories..

 

[john61ct]

The bleeding balance method (most BMS / hobby chargers) does **not** transfer energy, just stops charging while burning off the high cell(s) energy to heat via resistors.

Then charge all cells, then stop & bleed, loop.

Maybe the Junsi charger coming does it better faster.


______
A completely different approach, charge through balance leads, each cell gets an independent "node charger"

RadioLink CB86-Plus

Balance charger - RadioLink Electronic Limited

Balance charger radiolink

radiolink.com.cn

BC168 (discontinued)

UN-A6 Plus, aka UN-A6PLUS+
(also A9)

ANGO iC8S

Unique "hybrid"
CP620

 

[hour]

The bleeding balance method (most BMS / hobby chargers) does **not** transfer energy, just stops charging while burning off the high cell(s) energy to heat via resistors.

Yeah, speaking of the equalizer. It still appears that it's alternating the high cell it's transferring energy from every second, to supply the low cell. And this makes sense, 3 cells at identical voltage - take a little from the highest of the three and it quickly becomes the lowest of the three, so a new high cell is identified to transfer to the lowest cell.. interrupting the process? Hell, that's just as fast as the little RC cell monitor updates, it could be happening much quicker.

Interesting with individual cell charging, but how in the hell can they deliver any meaningful current through the 22ga or whatever balance leads? I'd understand if it had screw terminals that you could install larger wire in to, and larger balance leads. Very much dislike balance leads for big packs. Puny and all of them are designed for small cell groups so you pretty much have to solder extensions to reach everything. And you'll probably still end up using a JST extension

Getting in to the 0.13X range of variation, so things are happening, slowly. Next full charge will absolutely be equalizer connected when it's nearing the top - and yea disconnected for discharge and initial charging bit to make sure I'm not counteracting the top balance.

 

[luthj]

A typical LFP setup where the cells are within 5% resistance of each other, will not need any balancing for hundreds of cycles at fractional C usage, and even then when it needs it, it will be on the order of 100-500mA. High C rates will need more, or for poorly matches cells.

 

[john61ct]

Interesting with individual cell charging, but how in the hell can they deliver any meaningful current through the 22ga or whatever balance leads?[/B]

Yes, 6A I think max

The old BC168 did 8 or 10 but pulsed I think.

For a big bank, not used for the big-bulk main charge process up to say 3.50Vpc, just the final balancing, from there up to 3.60V

Ideally only needed occasionally

but for an unmatched or aging bank, at least get the job done quicker without the (I think) much higher cost of the other dedicated balancers that push higher balance current independent of voltage delta.

 

[hour]

Yeah... think something is fucky with cell 3. All cells balanced to 1mv earlier - the iCharger unit arrived (X6) and it is ************.

First thing to note, with the equalizer connected the balancing of the hobby charger (also connected to its own balance leads) terminates prematurely. It holds 3.6Vpc for a whopping 30 seconds or minute and then enters sustained balancing mode. If I disconnect the equalizer and charge up again moments later, it takes an hour to round things out using the iSDT equalizing methods.

That means if you equalize with the Deligreen and a hobby charger delivering charge current, you'll still likely be squirrely. If you let the iSDT do the final phase and enter its sustained balance routine without active balancer aid, it will take longer but achieve greater similarity. You're just getting yourself closer to iSDT balance territory with the equalizer.

So anyway, I let the iSDT take it to 3.6Vpc and then enter sustained balance for an hour. Then I replaced it with the iCharger and let it run a balance-only routine. This got it to 1mv difference. Ok so now I'm at 3.6Vpc confirmed by iSDT and absolutely confirmed by superior iCharger.

Hit pack with 160w load. Cell 3 drops to 200mv below highest cell. Keep it going for 29ah discharge and the thing is basically 200mv below other cells the entire time, from start to calling it quits at 30ah discharged.

Disconnect load and things IMMEDIATELY rebound to 1mv difference.

Start charging at 11.4 amps (set to 25 but unit throttles) because that same damn cell jumps to 3.6V immediately.

If I didn't know any better, I'd say cell 3 is an oddball and will ******** with this pack for an eternity.

I provided these findings, the steps to get to it, and screenshots to the seller who said "I get back to you later". One of these things is not like the other, same ******** with my existing house battery comprised of decade-old cells. One is far from the others and it throws a wrench in the gears.



Discharging mismatch. Cell was immediately 200mV below highest the second load (~160w) hit. This picture is after consuming 29ah of battery at 160w. Consistently out of whack the entire time.



1 second after shutting off load, the pack is back in extreme balance at 2mV. Meaning cell 3 is taking a lubeless butt ************** because 1 second earlier it was 200mV down at 160w raw.



another few second later, charging it back up (so my process was discharge 29ah and see 200mv difference entire time, suspend discharge for a second and see immediate harmony, then initiate charge and see immediate 200+mV spike on that one oddball cell).

Something is definitely fucky with #3. I do know I can get no less than 150ah (and likely much more) ah out of the pack and that makes this process and learning experience completely worth it. But I'm still in the ******** boat floating down ******** river wondering if one cell is raping itself or not - thus my situation (er peace of mind) hasn't really improved much over my 57ah usable decade old lifepo4 pack.

 

[john61ct]

Yes, if this were a western company and shipping it back were reasonably priced, I'd expect satisfaction.

Worth trying I suppose just to see, but personally I'd wait for a decent load test result on a good cell to see if you have more ammo, before pushing hard.

If 3/4 are say 175Ah and that weaker one is 150Ah, that's a different convo from all being further under spec.

Use the Junsi to do the per-cell testing.

_____
Setting that aside, if you can find a way to get it back to top-balanced each cycle in an automated stress-free way, you may get years of service out of it at a reasonable cycling capacity.

Like living in a home with one dodgy stair, once you know it's there maybe just work around it.

 

[hour]

Yes, if this were a western company and shipping it back were reasonably priced, I'd expect satisfaction.

Worth trying I suppose just to see, but personally I'd wait for a decent load test result on a good cell to see if you have more ammo, before pushing hard.

If 3/4 are say 175Ah and that weaker one is 150Ah, that's a different convo from all being further under spec.

Use the Junsi to do the per-cell testing.

_____
Setting that aside, if you can find a way to get it back to top-balanced each cycle in an automated stress-free way, you may get years of service out of it at a reasonable cycling capacity.

Like living in a home with one dodgy stair, once you know it's there maybe just work around it.

Very true. All of it. I just need to figure out how to do a meaningful 1S discharge on the iCharger. I see discharge kits available on eBay up to 30some amps. Time consuming, a little more money, but would provide the smoking gun.

Working around it isn't difficult at all with 4x my daily capacity on reserve. But it still makes me nervous every day in my existing setup at least, knowing things can go sour towards fully charged - and complicated by the fact that a 70+w fridge load may connect or disconnect at any given time and PV input can fluctuate by the minute. I ordered two bluetooth BMS units last night that I'll write software for. I've heard they can log charge cycles but I'll be able to graph (and allow others to graph) super useful information for non-drop in replacement packs in the near future for months worth of data.

Testing ongoing, have several days until the ammo can and PowerPole circle mount connectors arrive. Still hoping it snaps out of its Thunberg syndrome before then. But I can make this work somehow.

 

[john61ct]

how to do a meaningful 1S discharge on the iCharger.

Googling with the site: keyword on RCGroups forum should get details

> complicated by the fact that a 70+w fridge load may connect or disconnect at any given time and PV input can fluctuate by the minute

I think you won't see any problems like those unexpectedly, your testing will tell in advance.

The balance issue is only at the top/bottom, middle range should be OK

 

[hour]

Googling with the site: keyword on RCGroups forum should get details

> complicated by the fact that a 70+w fridge load may connect or disconnect at any given time and PV input can fluctuate by the minute

I think you won't see any problems like those unexpectedly, your testing will tell in advance.

The balance issue is only at the top/bottom, middle range should be OK

So if one cell is appearing to get hammered and reading 200mv below highest cell, don't worry because it's only under load? And more than 2x the normal load I'd be experiencing on average, dead of night (fridge brief turn on at ~60*F temps)

They certainly flattened out during the low end with 150ah consumed yesterday. Less variation at even higher consumption. But still kind of irks me. How the hell are drop in replacement mfgs accomplishing this stuff? Esp lower end. This supplier apparently supplies Bieonno Power (with what I do not know)

 

[john61ct]

I would think big buyers would have QA go/no-go testing before it even leaves the factory.

Individual buyers with little recourse more likely to get the dregs