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Old Dec 18, 2004, 09:14 AM
A man with too many toys
United States
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End of Day LiPo Recharge

After the last flight of the day should I recharge my LiPo batteries or just let them set until the next flying day?


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Old Dec 18, 2004, 09:19 AM
Southern Pride
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Haralson County GA. USA
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Depends on how much charge remains and when they will be used next.
Best stored at 40%-50% charge and at cool temp.
http://www.batteryuniversity.com/partone-19.htm


Charles
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Old Dec 18, 2004, 09:41 AM
A man with too many toys
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That is interesting but I have no test equipment so I have no idea of what the voltage is.

The voltmeter on my Triton is kind of strange because when I first start a charge the voltage will first drop a little then start to rise. Which voltage is correct or is that the way LiPo’s charge?
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Old Dec 18, 2004, 10:27 AM
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A simple meter can be purchased for as little as a few dollars. Using Li cells without having a meter to check them is not safe. Periodically measuring Li cells with a meter can help prevent loss of an expensive Li pack, and possible venting with flames that could start a fire.

It's normal for the charge voltage to drop at the beginning of a charge. The 40-50% charge is only required for longterm storage, i.e. weeks or months. There's no problem leaving Li cells full charged for days at a time. If they are stored at full charge for longer periods, the cells will gradually lose capacity.

Li cells are not plug and play. They require extra care and attention in order to be used safely. For the safety of themselves and their families, anyone who is not willing to take the time for this extra care and attention should stick with NiCd and NiMH.
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Old Dec 18, 2004, 10:43 AM
Southern Pride
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Haralson County GA. USA
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Quote:
Originally Posted by RC Man
That is interesting but I have no test equipment so I have no idea of what the voltage is.

The voltmeter on my Triton is kind of strange because when I first start a charge the voltage will first drop a little then start to rise. Which voltage is correct or is that the way LiPo’s charge?
Not strange ,voltage rises during charge and decreases during discharge.

Dave's post is correct. Lipos require more than just a casual relationship.

You can check the pack voltage with you Triton Charger.
Set to proper cell count voltage 11.1 for a 3 cell pack , set to Discharge at 0.1 A rate. This will show the packs voltage under a very light load which will be close to a no load voltage.
40% charged would be 3.9 V per cell or 11.7 v for 3 cell pack.A full charged 3cell pack would read approx. 12.40-12.50.

Charles
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Old Dec 18, 2004, 09:16 PM
BEC
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If you expect to fly again in a reasonably short time (say, within a few weeks) just charge 'em up. They'll still be charged when you go to fly. If not, then all the makers recommend storing them for long periods at about half charge as the other guys have pointed out.

I almost always just recharge after coming in from a flying session (as I am doing right now). That way, I'm ready to go fly (presuming charged transmitters ) just about at any time.
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Old Dec 18, 2004, 10:47 PM
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Quote:
Originally Posted by RC Man
That is interesting but I have no test equipment so I have no idea of what the voltage is.

The voltmeter on my Triton is kind of strange because when I first start a charge the voltage will first drop a little then start to rise. Which voltage is correct or is that the way LiPo’s charge?
Nothing strange, the Triton measures the pack voltage before starting the charge to determine if the settings are correct. It will try charging at 0.1A for a bit and than stop and measure the voltage. You know this is happening when the current reads 0.0A. It might do this a couple of times before it starts charging at the inputed level.
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Old Dec 18, 2004, 11:01 PM
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I believe that lipos are safer when they are discharged. They are less likely to vent with flames from being dropped, left in a hot car, etc. I leave my batteries discharged after flying, and recharge them the morning before I fly.

Dan
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Old Dec 19, 2004, 06:12 AM
A man with too many toys
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Quote:
Originally Posted by Dan Baldwin
I believe that lipos are safer when they are discharged. They are less likely to vent with flames from being dropped, left in a hot car, etc.

Is that really true?

How about some other opinions.

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Old Dec 19, 2004, 10:43 AM
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Quote:
Originally Posted by Dan Baldwin
I believe that lipos are safer when they are discharged. They are less likely to vent with flames from being dropped, left in a hot car, etc.
The problem with this line of reasoning is that while it sounds logical, it has not to my knowledge been proven. Someone reading this might get the idea that it's safe to leave discharged LiPos in a car parked out in the sun on a hot day. This would not be good.

I would run this theory by some true LiPo experts before putting any faith in it.
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Old Dec 19, 2004, 12:31 PM
Motors beat engines!
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I always recharge after flying, the exception being if It'll be a long time, ( months?) till I'll use them again.

Since I'm not waiting for the next flight, I'll usually also charge them at a very low rate as thats supposed to be less stressing on the cells, and seems to allow a slightly higher ending resting voltage than if I charged at a higher rate.

BTW, I also use a kokum safety guard while charging. Pretty much impossible to overcharge while these are in the circuit.


Dean in Milwaukee
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Old Dec 19, 2004, 01:01 PM
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Quote:
Originally Posted by DeaninMilwaukee
BTW, I also use a kokum safety guard while charging. Pretty much impossible to overcharge while these are in the circuit.
That would be true only in the case of balanced packs. Since Kokam SGs only limit total voltage to the pack and not individual voltage to cells, they cannot prevent individual cells in an out-of-balance pack from being overcharged.
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Old Dec 19, 2004, 01:10 PM
Motors beat engines!
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True Dave, but overcharging a individual cell is a problem any charging scheme other than charging each cell individually would run into.
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Old Dec 19, 2004, 02:14 PM
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Right, Dean. The only reason to be picky about how this is stated is that someone reading this thread might get the idea that the SGs protect against overcharge in all situations, including unbalanced packs, which they do not. As you note in your last post, pack balance must be checked in order to assure maximum safety from overcharge event whether using SGs or not.
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Old Dec 19, 2004, 08:06 PM
PGR
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The idea that discharged LiPo cells are safer than charged ones may have some validity. One of the problems that can occur with LiPo and LiIo cells is a phenomenon often referred to as thermal runaway. I don't profess to understand the dynamics of this phenomenon but I do know that it is typically triggered by extreme discharge rates like dead shorts. This is why it is strongly recommended that a LiPo pack be immediately moved to a safe location and monitored for at least 30 minutes if the leads are shorted even momentarily.

Thermal runaway requires energy and a fully-charged cell obviously possesses more energy than a discharged one so in that respect, a discharged cell could be considered safer than a fully-charged one. But thermal runaway isn't something that happens spontaneously. It requires a trigger event like the previously-mentioned dead short and it's not real likely that a pack stored with even the most rudimentary level of protection will suffer such an event.

So the bottom line (at least in my book) is that if you are in the habit of storing your LiPo packs on your work bench or somewhere where they can be hit by falling objects or have things accidently set on them then you may want to consider leaving your packs discharged until you need them.

I prefer to keep my packs charged because I can never tell when a rare (this time of year) opportunity for an after-work flight might present itself and there's nothing worse than having such an opportunity but no charged battery packs. I don't leave my packs just laying around, though, so the state of charge that I store them in is a moot point.

Pete
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