Should I need to top balance again after cells sitting for ~7 weeks?

blutow

Solar Addict
I did all my final top balancing and pack testing back in April and then broke down the batteries while I was finalizing my battery boxes and working on other things.
I reassembled them this week and charged each pack back up in series (but did not top balance). One of my batteries had a runner that caused high voltage disconnect and I had a cell in another pack sitting quite a bit lower than the others at full charge. I had not seen any of that behavior from those cells in past testing. I'm at least going to pull the packs apart and clean connections, but wondering if a top balancing is needed again if some cells are self-discharging at different rates. They were just sitting loose for the last ~7 weeks at around 3.3v, not connected in any way. I was charging them around 80a for 272ah cells in 12v packs, which is a bit higher than I was previously testing at, but still a pretty low C rate for that size cell. Should a top balance be needed after only sitting a couple months or is this more likely another issue?
 

snoobler

Solar Honey Badger
Yes. This seems common with the "cheap" commodity cells.

Cells have slightly different self-discharge rates, and even very very small deviations in SoC (0.1%) can cause runners.

Rather than going through the effort of re-paralleling them, you can just hit each cell individually with the 10A supply until it hits 3.65V.
 

Hedges

I See Electromagnetic Fields!
During a build, having to top-balance again is a one-time bother.

Once assembled, if used seasonally, would be nice to avoid. Does BMS provide some degree of balancing? If so, can your charge controller be set to a voltage that will keep high cell from hitting disconnect and allow balancing to be performed?
Possibly the limit on voltage difference between cells would need adjustment.

Lower charge rate might help. Differences in IR drop would contribute to creating apparent runners.
 

blutow

Solar Addict
Thanks for the responses. I'll go ahead and top balance the 2 problem packs. Maybe just do all of them for good measure. I've got some little jumper connections to allow top balancing without pulling the cells out of the enclosures, so it shouldn't be too big of a deal. I ran the packs down a bit overnight and recharged all 4 of them together this morning and had the same issues on those 2 problem packs. I was charging at 100a (only ~25a per battery), so the lower c rate didn't seem to help with the runner.
 

Just John

Photon Sorcerer
Probably more trouble than it is worth, but I have used 10 gauge wire with ring connectors and an Anderson plug (the cheaper 45 amp rated) on each cell. This allows me to easily plug in a power supply for each cell without disassembly, no worries about polarity, etc. If it (different self discharge rates) becomes a significant problem, it might be worth the time, effort and expense. All it really takes to justify the effort and expense is a couple of times to make it worthwhile for me.

Of course everyone has their own price/pain threshold to work with. I love my Ridens, just set 3.65v and let it go.


These are rather expensive, cheaper to make your own if you have the proper crimp tool. I do, and make my own for much cheaper. So I haven't tried these.

 
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MisterSandals

Participation Medalist
I'll go ahead and top balance the 2 problem packs.
You have an opportunity to match your cells if you do this. Put the stronger ones all together and the weaker ones together in the other battery pack. This will match the cells with similar characteristics - it works really well.
You did label your batteries and take good notes right?
 

blutow

Solar Addict
You have an opportunity to match your cells if you do this. Put the stronger ones all together and the weaker ones together in the other battery pack. This will match the cells with similar characteristics - it works really well.
You did label your batteries and take good notes right?

I went ahead and top balanced all 4 packs. Since I had some jumpers made previously, I didn't have to take apart the packs and it didn't really take any time. It was pretty quick pulling bus bars and leads and just sticking the jumpers on. It was just getting over the mental hurdle of pulling things back apart - I thought I had done my final assembly, got my terminals nice and clean, final polish on the bus bars, applied my oxidation stuff, etc.

I've been running the packs all week in a variety of tests and they are working very well together. I still have a single cell in one of my packs that doesn't like to sit above 3.5v (it drops into the 3.4's pretty quick after charging while the others sit at 3.5x for quite a while). It's always dragging behind the others a bit while charging once I getting into the upper knee. It's not causing any issues and it's not a low cell during discharge. I individually capacity tested all my cells and that one was solid (not the highest, not the lowest). Nothing weird with IR. I'll keep an eye on it, but it doesn't seem to be affecting any performance.

I guess the real test to see if they stay in balance "on their own" is to let them sit idle for a bit and see if anything gets out of whack. My van is outside with solar, so having them sit idle is not something I ever anticipate. After I stop playing around with them, there will be days with just minimal draw and I guess that will be a good test over time to see if they stay in balance.

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MisterSandals

Participation Medalist
That is a GREAT looking setup. Are you designing battery racks for Victron? Those are sweet. I see why you did not want to break down cells!

Why do you have 2 Orions? Do you have 2 alternators?

I had to look long and hard to find anything I didn't love but there are a couple finger smudges on your battery covers. :*)
 

Hedges

I See Electromagnetic Fields!
Nice fat battery cables.
Is there a battery fuse concealed under a cover somewhere?
Or is it just fuses on each load inside Lynx?
 

blutow

Solar Addict
That is a GREAT looking setup. Are you designing battery racks for Victron? Those are sweet. I see why you did not want to break down cells!

Why do you have 2 Orions? Do you have 2 alternators?

I had to look long and hard to find anything I didn't love but there are a couple finger smudges on your battery covers. :*)
Thanks. 2 Orion’s because I wanted more charging amps and those are the biggest Victron makes. I thought about going with a sterling, but saw some negative reviews with those running hot and not hitting the rated capacity. I just have the stock alternator, but it’s 250a
 
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