left lipos for 3 years charged up...

[RVD]

i know you're supposed to put lipos in storage mode when leaving them in storage...but a few years ago i moved and most of my stuff was in storage. life got really busy (new city, new job, more kids, etc.) and to make a long story short, i am only now getting to my lipos.

most of these lipos were stored at around 3.9-4.0v and it's been around 3 years since they have been charged. a few were brand new at the time so they were shipped from hobbyking and haven't been touched since.

i checked the voltage of the cells via the balance tabs and it looks like most of these cells are still charged up.

my plan is to run each of these lipos through about 3 cycles of discharge/charge at 1c and observing the cells throughout the process to ensure that there isn't any odd behavior. this will happen per cell in the fireplace for safety. if i deem the lipo good, i'll use it but keep a close eye on it.

does that sound like a good approach? or is this a futile effort and should i just get rid of all of them and buy new ones?

i did find one brand new 4s 5ah turnigy hardcase that had one bad cell (0.7v). i was thinking of taking that one outside onto the cement and slowly charging it up at 0.1a to see what happens...is that really stupid?

RVD.

 

[Ykick]

Measure IR (holler if you need a link) plus smell and look for visual signs of trouble.

IMO storage voltage is more myth than reality. At least for RC Lipo sitting around 4V and below.

Oh, and I don't bother with cells that have been much below 2V. Sure, give it a try in a safe place but mark it up well and keep a close eye on it if you attempt to use it.

 

[dnmun]

if you have a single cell charger then charge the one that self discharged up to match the voltage of the others in that pack and then put it on the balancing charger. if it continues to self discharge at a high rate then you should allow it to self discharge and see how low it drops in voltage over a few days or weeks. then let us know how low the voltage drops.

you can use a cell phone charger to push current into it if you don't have a single cell charger but watch it during the charge to make sure it ends up identical in voltage to the others in the pack before putting it on the balancing charger.

there is no need to worry about internal resistance now. that is more of an aging phenomena and if these are never used that should not be an issue for them.

 

[dogman dan]

Wrong, just sitting there, especially your storage place was a bit warm, can result in a higher internal resistance, which translates to a very low capacity if you discharge them very fast. That was my experience anyway. For me, the packs were used, but ones with 200 cycles performed about the same as those with 20, by the third year. Mine simply aged out in storage, fully charged.

But as said above, only testing them will show how they do. Some of yours were not really that full, so that may have helped a lot.

The one with a 0v cell, I would not bother to charge it and revive it. IMO, doing that makes it dangerous. Leave it at or near 0v, and move the discharge wire to make that pack into a 4s, then you can use it.

Or remove that cell completely, then do fun experiments with it.

 

[RVD]

Ok thanks for the info. I have not measured IR before but did a few searches on Youtube to see how other folks do it. It looks like some people measure voltage with a multimeter (which i have so that's good) and then run some load on it (with light bulbs or whatever) and then measure the voltage drop and then use ohm's law to measure resistance?

RVD.

 

[Ykick]

Ok thanks for the info. I have not measured IR before but did a few searches on Youtube to see how other folks do it. It looks like some people measure voltage with a multimeter (which i have so that's good) and then run some load on it (with light bulbs or whatever) and then measure the voltage drop and then use ohm's law to measure resistance?

RVD.

Yep, that's pretty much it. Realize that it's milli-Ohm value (well below 0) returned, not the meg-Ohm often found with high value resistors.

Good, stiff, RC Lipo cells would be under 15mOhm per cell. Or if doing the entire series string, divide the result by the number of cells in the string. But, you're better off measuring voltage drop and thus IR of each cell.

Much above 20mOhm, I cull 'em out for eBike duty. Some folks parallel and run them to 30-40mOhm but I've got plenty and I don't like excessive voltage sag.

 

[RVD]

I'll report back with some numbers but I usually ride at around 14s (52v) 10ah rarely pulling more than 40 amps so I don't think I'm as aggressive as others with batteries so I might be ok with some sag but we'll see. Thanks for the info!

RVD.

 

[neptronix]

Oh, that ain't fully charged. 3.9ish is a safe storage voltage long term. I keep my lipos right around there long term.
I've got lipos that are almost 5 years old now that have tolerated that very well.

 

[dogman dan]

True, mine were stored full as they could get, his were not completely full. So test and see.

The ones I talked about were in the 50's for resistance. I used them for another 2 years, for extra capacity on longer tours. But I pretty much had to parallel them with better batteries, or they'd only deliver 50% capacity. I could still get about 70%, if they were run in parallel with good cells.

So even if they are bad, they might still be useful in some way. But not likely to run a bike well in less than a 20 ah pack by themselves, if they are high resistance now.

 

[RVD]

i was out of town most of the weekend but got back last night and spent a few hours working with these batteries.

well, one of the 6s packs is puffed so i put that one aside (it's outside on the cement along with my 4s that has one bad cell). the rest of these batteries seem ok...i took them all down from around 3.9-4.05 down to around 3.83 and they handled that ok. i'm going through them one by one to do a charge up to 4.10 (where i usually charge up to) and then back down to 3.83 again and then back up to see how balance is maintained. it's time consuming since i'm doing them one by one and the first 6s5ah battery that i did performed well. i am also watching these batteries like a hawk. i counted battery packs last night and i don't know why i have such a big (at least for me) lipo stash...12x6s 5ah packs, 4x4s 5ah packs and 4x2s 5ah packs. this is going to take awhile...

i'll try to set up an IR measurement process today (need to get the light bulb things, etc. set up) to measure IR.

 

[dnmun]

will you charge up the cell that self discharged to .7V so that it reaches the same voltage as the others in the pack and then charge up the entire pack together to full charge?

make sure they all reach the 4.20V level and then let it sit and measure the rate at which the voltage drops.

see if that cell has an observable higher rate of self discharge than the other cells.

 

[John in CR]

Be sure to mark any that were significantly lower than the others cells. Otherwise I'd consider the others to be good as long as they're not puffed, because they stood the test of time, and important one AFAIC. Balance them and run them through a a handful of moderate cycles to wake them up, and look at balance, IR, and capacity. I for one wouldn't hesitate to put packs on a bike if they sat unused for a few years and still maintained voltage, balance, and showed no swelling. I wouldn't make permanent strings until they've gone thru some cycles and I capacity matched them. I wouldn't be surprised at all if yours still had over 90% of their original capacity.

 

[dogman dan]

True, any not puffed or discharged by now are defect free.

But they could still be rock hard, take a full charge, and balance nice, and still have a resistance in the 40 or more ballpark.

 

[Ykick]

i'll try to set up an IR measurement process today (need to get the light bulb things, etc. set up) to measure IR.

I discovered it takes a bunch of lightbulbs to create significant load. I'm much happier using old/junk heater elements from toaster ovens, ranges, space heaters, etc.

Here's one example I'm kinda proud of it's funkiness -

120VAC 1200-1500W heaters tend to draw about 5-7A on my 60-67V packs which seems to be enough to get a pretty good idea of discharge IR for RC Lipo.

 

[RVD]

i'm still working on building an IR resistance setup. i bought a small light bulb socket and hooked that up to my lipo but the amp draw is really low (~0.2?) even though i put in a 60 watt bulb. my guess is that this socket is set up for 110v. when i put in a 22v 6s lipo, the light bulb is really dim. when i put in a 44v 12s lipo, the light bulb is brighter but still not 60 watts.

i'll try buying a 50 watt bulb with 2 leads on it instead.

as for my 6s and 4s, i checked on them today (they are both outside on my cement patio) and both batteries were puffed. the 4s is in a hardcase so it's harder to tell but even the hardcase is a bit puffed.

i was going to try trickle charging the 4s (with 1 0.7v cell) but i don't have a way to charge just that cell. i was going to try slowly charging the entire lipo (since other cells are at 3.8) up to around the point that the other cells get to 4.15 and by then see what happens to this one but i didn't get that far. charger wouldn't accept the charge since i put 4s and it detected voltage for a 3s. i guess i could force it to but didn't want to do that as it was starting to get a little dark and i wasn't sure how long i'd be able to watch this thing...

maybe another day.

 

[izeman]

you need 12v light bulbs (for cars eg) if you want to measure small packs. for a 6s lipo i recommend 6x 12v 100w light bulbs. 3x 2 in series for 24v and 300w. this would give you a decent load of around 12a. good enough for internal resistance measurement. i bought them on ebay/aliexpress for cheap.