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Old 01-20-2013, 10:02 PM   #1
farkas
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Default lipo charging storage limits

can anyone advise on this, once fully charged - what is time limit discharge batteries. can u charge night before flying? I charged up 4 6S packs to fly Friday and it ended up being too cold. can I leave the packs charged for a day? two days? is there a short term storage limit? what is the proper cell storage voltage 3.7? is it acceptable to store slightly higher?

I'm sure this is covered somewhere.....don't want to mess up my packs but on the other hand, don't want to over think it.

Thanks,
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Old 01-20-2013, 10:04 PM   #2
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A weekend is fine, a week may be too much. 3.80-3.82 is storage charge.
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Old 01-20-2013, 10:17 PM   #3
farkas
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awesome, thanks
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Old 01-21-2013, 03:27 AM   #4
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It is also dependent on temperature, charged and warm is worse than charged and cold (not frozen). Storage charge and cold is best. Fridge is ok, Freezer is not.

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Old 01-21-2013, 01:39 PM   #5
RocketSled
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Quote:
Originally Posted by farkas View Post
can anyone advise on this, once fully charged - what is time limit discharge batteries. can u charge night before flying? I charged up 4 6S packs to fly Friday and it ended up being too cold. can I leave the packs charged for a day? two days? is there a short term storage limit? what is the proper cell storage voltage 3.7? is it acceptable to store slightly higher?

I'm sure this is covered somewhere.....don't want to mess up my packs but on the other hand, don't want to over think it.

Thanks,
It's covered many places.

You can leave your fully charged LiPos fully charged for quite some time. The thing you need to understand though is that LiPos degrade as a function of how long they're asked to hold a charge. The effect is slow, but it's generally not considered to be a good idea to leave a fully charged pack fully charged for more than a week or so. Many chargers include a "storage charge" function that typically charges or discharges to about 3.8V. A tenth or a volt (or two) in either direction won't matter much. Lower voltage is better, but LiPo cells self discharge over time and if you're going to leave them parked on the shelf for a long time, you don't want to start them off at 3.3V or they might over-discharge and be ruined because of that.
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Old 01-21-2013, 03:23 PM   #6
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FWIW, I've heard the damage is cumulative. So they're not going to fail after a week or anything. But 3 days here, 4 there, a week some other time, etc, and it all slowly adds up.

I choose to bring mine down to storage that night if I don't get to fly them. If I was flying the next morning, maybe I'd leave them charged, but I choose not to leave them charged for a day or two.

I've heard that higher-performance, higher-C-rated batteries degrade more quickly when they stay charged.

I typically use my charger's discharge function. But that's only 20W. For 6S, that's under 1A, so it takes a while.

So I built an external discharging load, with about $8 of power resistors, bolted to a piece of aluminum, to act as a heatsink. They are a pair of 2 ohm resistors, each rated to 100W (this is important), connected in series, for 4 ohms. With 6S, ~25V, they will flow about 6.3A, and dissipate 160W (80W each). I keep a fan blowing across them. I connect the parallel board's bullet plugs to the female bullets I soldered to the resistors. And I connect only the parallel board's balance plug to my iCharger. I use the charger's Monitor function to sound the buzzer when it reaches, say, 3.80V/cell. No current actually flows through the charger.

There are also other ways to do this, but this method is very simple. You just need to manually unplug the resistors at the target voltage, or the packs will keep going to 0V. Some people use halogen light bulbs, that works too. Resistors means you don't light up the room

The nice thing is that this method is cheap. And you can use more/bigger resistors for more current, if you want. A friend just made a version for his 6S packs with 4 of these resistors, two sets of mine in parallel with each other, for 2 ohms, 12.5A, 320W, still 80W/resistor.

It makes discharging a pretty quick/painless process, rather than waiting several hours for my 20W-discharge charger to do it
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