out of ballance

[alan c]

Hi can anyone tell me what causes lipos to go out of ballance. I have 24s 2p zippy 16 ah and charge with 2 hyperion 1420i chargers at 10 amps ballance charged every time. I have noticed the last 2 times I have charged them they were way out of ballance 0.036. I have checked that none of the cells have puffed they have about 300 cycles on them. Today I pulled the whole pack apart measured every cell, Batt 1 1st cell 3.96 2, 3.96 3, 3.96 4, 3.94, 5,3.94 6, 3.96 batt2, 1st cell 3.96, 2, 3.96 3, 3.96 4, 3.94 5, 3.94 6, 3.96 batt 3, 1 3.95 2, 3.94 3, 3.96 4, 3.95 5, 3.95 6, 3.95 batt4 all cells3.95 that is the 1st 12s pack the 2nd 12s pack is notbad it seems to stay within o.oo8 and will ballance to about 0.004. it seems to have happened after my son rode my trike he had the throttle wide open and had got to about 30 kph when he hit a stick with the front wheel and it flicked into the backwheel on the tar and locked up with wot smashed my rear rack only bent 1 spoke but it nearly pulled the nipple through the rim .Batts are 30c running 40 batt amps never been bellow 3.8v per cell

 

[amberwolf]

Hi can anyone tell me what causes lipos to go out of ballance.

Several threads discuss that, mostly in people's battery repair threads or build threads, but there are a few reasons:

factory-defective cells

overcharge

overdischarge

charge/discharge under extreme temperature conditions

physical damage

age

etc.


For RC LiPo packs, 300 cycles is pretty old if they're deeply cycled.

 

[SamTexas]

What did I miss? For an RC LiCo (LiPo) pack with 300 cycles, your pack looks very good. What "out-of-ballance" are you talking about?

 

[alan c]

Hi Samtexas not sure but they used to stay within 0.008. When should I worry

 

[SamTexas]

I would not. If I read your numbers correctly, the largest difference between any two cells is 0.02V, right? Not a single thing to be concerned with.

 

[alan c]

No worries Sam. Thanks I was just concerned because on my charger it says o.o36 and it used to read 0.008mv difference. Thanks

 

[TMaster]

What you really need to do is check the cells when they are drained. Run them down to 50% and check, Run them down to 25% then check. Down to 10%, be very carefull with taking them down; if you have some weak cells that have lost capacity the voltage of those cells will go lower then the others in the pack and you might puff them. You will be able to tell when you check the voltages on the drained side and you see some big differences. I have no idea how far you have been taking down the capacity under normal use.

I didnt ride my ebike for 4 months once, and I was cycling the batteries, and found 2 bad cells out of the 69 I have. Turns out the 2 cells were about half the capacity as normal. In my 3P setup, normal would be 6.9Ah total(2.3ah x 3). With the 3P on the bad cells I had 5.8Ah (2.3,2.3,1.2Ah). I then replaced the cells and cycled the packs and the other 2 cells paralleled were ok, even though the bad cells voltage had dragged the good cells down. This is Lifepo4's though, A lot more tolerant to abuse. You do this to lithium polymers, and bad things will happen.

300 cycles I'd say you got your money's worth, and you have treated the cells well. 1. Don't peak charge the cells, 2. don't drain them down to the LVC. They will last longer.

 

[wesnewell]

No worries Sam. Thanks I was just concerned because on my charger it says o.o36 and it used to read 0.008mv difference. Thanks

Reseat your balance plugs. That may be the reason the reading is off a bit. But I wouldn't worry until you can't get it to balance better than .06V difference or you get a puffed cell.

 

[dogman dan]

I doubt I have any tools in my house that really measure voltage that accurately, including my dvm's. For damn sure my charger is not that accurate.

I call out of balance worth worrying about when it approaches .1v out of whack. Measuring with my cellog 8's, and given the variations in contact in jst plugs, I'm confident that when it's that bad, it's real.

Balancing them every charge may have helped your pack last, but in general the way you keep any battery balanced is by practicing a fairly conservative depth of discharge. I find that more than 80% discharged definitely increases their tendency to get inbalanced. Discharging at moderate c rates seems to help as well. Cut all c rates in half is my motto when choosing a battery size with low c rate stuff.

Without knowing, I can safely guess you may have been doing that ( moderate dod's), since you have a pack in pretty good shape at 300 cycles. Mine are not as good at that, but my lipo use is nearly 100% high performance riding, so lots of harsh amp spikes the whole ride.

 

[NeilP]

Yep as dogman says, you are lucky if yo can measure accurately to the levels you are worrying about.

If you are using Battery medics, they are all out to a dregree any way.
Celllogs the same but to a much lesser extent
If you are measuring with a DVM, just touching the probes to the JST connectors can induce the amount of error you are seeing.

I have a good quality multi $ Fluke meter, and even that gives slightly different readings as you see when measuring the same pack again and again.
The terminals on the JST connectors are only crimped on and can and do come loose,

0.1 volts and more then worry...your packs look nicely in balance

 

[Ykick]

Resting voltages only provide a partial glimpse into pack balance. Logging cell voltages while delivering 20-40A at the "near empty" cliff is what will reveal lowest capacity cells.

How much Ah/Wh a cell delivers when compared to others in the pack is what "balance" is really all about.

Often, a cell with lower resting voltage will actually have more capacity than the cells that tend to measure higher resting voltages. Trouble is, you can't really tell until you take 'em down close to the cliff using significant load.

This is where CellLog 8S comes in handy for my battery arrangement. I can easily visualize the lower capacity cells under working load conditions.

 

[alan c]

Thanks guys for all of your replies I guess I will just stop worring so much. This is my 1st lipo pack and I was just concerned because it has just started acting funny and I dont want to burn down my garage

 

[SamTexas]

You are welcome.

Stop worrying so much as you said is right. But don't stop completely, after all you're still dealing with RC LiCo, one of the most temperamental chemistry. So relax a little but still be careful.

 

[dogman dan]

Agreed, the reason I don't worry about less than .1v out of balance is that less than than can be dealt with fairly easy by running a regular balance charge. Any more, and you might want to start doing single cell charges to get back in balance because it's faster.

If you are running very deep discharges though, even beautifully balanced packs can still get overdischarged. The main thing to worry about is overcharge, overdischarge, puncture.

You are doing a great job if you get to 300 cycles without doing any of those things, give yourself a pat on the back. Stop worrying, but do keep monitoring.