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Old Jun 20, 2014, 07:58 AM
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How To Determine When It's Time To Take A Lipo Pack Out Of Service?

What methods are used to determine when it is prudent to take Lipo packs out of service from a safety (fire) and/or performance perspective?

Thank you.
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Old Jun 20, 2014, 08:03 AM
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When you start noticing an unacceptable drop in flight performance or the low voltage cut-out starts activating early. This will depend on application, a battery that is unacceptable in a high demand application might be fine in another less demanding model.

Or I guess if the pack is badly puffed and looks like it might burst or has other serious physical damage.
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Old Jun 20, 2014, 09:37 AM
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Or if the internal resistance (IR) is getting high(er) it can be an indication that the LiPo battery has seen it's better days. Some chargers can display IR when charging LiPo batteries. It can be good to keep track of IR values so one can see over time if it change to higher values. In practice You will notice decreased performance from the LiPo battery at high throttle and sooner or later it's time for recycle bin for a LiPo, it is only a matter of time for all LiPo. But one want to have as many cycles as possible but still good performance out of LiPo packs. Very cheap LiPo packs maybe have less chance to achieve that but You never know. Same for expensive and supposed to be "quality" packs, maybe they will last longer but one never know.
In my competition F3A models I use ThunderPower LiPo (G8, 25C) and they seems to cope with many cycles, still give good performance and have still rather low IR.
Last time I checked IR on one of my 5 cell LiPo packs 5000 mAh (TP G8 Pro Lite+, 25C) the IR was between 2.5 and 2.9 milli Ohm and it had about 20 charge cycles so far on it.
But low C rated battery will have higher IR then high C rated LiPo.
For every day flying maybe ThunderPower Lipo is on the expensive side but they are usually rather good.

/Bo
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Old Jun 20, 2014, 09:48 AM
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I gather that all lipo cells will gradually develop higher internal resistance with use/abuse. Nowadays, I try to store packs at 3.75 to 3.85 volts per cell and not over discharge them to the point where packs become hot vs barely warm.

When they finally puff up and lose their punch, I set them aside and eventually discharge and dispose of them.
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Old Jun 20, 2014, 10:59 AM
A man with too many toys
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Quote:
Originally Posted by itsme2 View Post
What methods are used to determine when it is prudent to take Lipo packs out of service from a safety (fire) and/or performance perspective?

Thank you.
I use IR.
When the IR gets to double of what it was on a new pack it's time to retire it. It pays to keep records of your batteries. I test all new batteries and check about every 20-30 cycles.


Note:
IR changes with charge and temperature so try to take readings at the same charge state and temperature.


.


.
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Old Jun 21, 2014, 11:50 AM
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Quote:
IR changes with charge and temperature so try to take readings at the same charge state and temperature.

Seems some of the experts disagree and have posted that state of charge has little to no effect on IR.
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Old Jun 21, 2014, 12:02 PM
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Quote:
Originally Posted by everydayflyer View Post
Seems some of the experts disagree and have posted that state of charge has little to no effect on IR.
I'm no expert but yes, i used to think that charge had an effect but after testing I can confirm it doesn't, at least nothing significant.
Temperature on the other hand has a big effect and heating during charging or discharging can fool you into thinking that the change of charge state has decreased IR, when in reality it's almost all caused by increase in internal battery temperature.
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Old Jun 21, 2014, 05:11 PM
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Originally Posted by RC Man View Post
I use IR.
When the IR gets to double of what it was on a new pack it's time to retire it.
Can I have your 'retired' packs? I'll pay shipping!
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Old Jun 21, 2014, 08:10 PM
PGR
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I fly battery packs until they change dimensions or they'll no longer deliver the performance I need. My "testers" are the planes I fly them in and a noticeable drop in performance isn't necessarily grounds for retiring packs as long as they haven't changed dimensions. Sometimes I simply don't perform maneuvers as close to the ground as I would with a healthier pack and sometimes I fly weak packs in less-demanding planes.

And sometimes I re-purpose weak packs for other things like external power packs for my video camera or photo strobes. I used an old pair of TP2100-3S (8C) packs for several years that way and that was after flying planes with them for nearly 4 years. I'm currently using some old TP3300-3S ProLites to power my FPV video RX and monitor and they still do that just fine after flying planes and multirotors for 4+ years.

I don't even care what the capacity or IR is. If packs do what I want them to for as long on a charge as I expect them to without changing dimensions, then they pass all the tests that matter to me. The reason I'm comfortable with that practice is I fly a premium brand of LiPo packs and they aren't known for sudden failures. They wear out, but they do so in a predictable manner.

Pete
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Old Jul 01, 2014, 08:01 PM
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When the IR is 25 milli ohms per cell I take them out of service or use them for other purposes
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Old Jul 01, 2014, 09:13 PM
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Originally Posted by Ermilo View Post
When the IR is 25 milli ohms per cell I take them out of service or use them for other purposes
Keep in mind that IR is inversely proportional to capacity so 25mohm might not be so bad for really tiny packs while it would be really bad for high capacity batteries.
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Old Jul 01, 2014, 09:17 PM
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And it depends on what is used to measure the IR.
With my method, 25mohms is great.
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Old Jul 05, 2014, 02:35 PM
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I thought I had this issue worked out, now I see that is more complicated. I use my icharger to test my IR. As close as I could get to an answer as to when I should retire a battery was 25. Now I am back at square one. Any electronic engineers out there?
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Old Jul 08, 2014, 09:04 AM
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Do you mean 25mohms per cell?
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