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Old Oct 30, 2014, 12:11 AM
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Storing LiFe batteries...full or half charge?

Hey folks, I searched all over the web, with no answers. Is it safe to store LiFe batteries at full charge?

I have been using lipo's for years, and always store them at a storage charge. Well, I replaced my Nimh pack in my Transmitter, with a LiFe pack, and bought a spare LiFe pack for it as well. As a spare, it would make sense to have it charged, and ready to swap in if need be. Is storing a LiFe the same as storing a LiPo? I sure hope not, since that sort of makes a spare pack, only a half charged spare pack, if needed in a hurry.
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Old Oct 30, 2014, 04:25 AM
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LiFe batteries are much safer than LiPos in that they can take much more abuse without going up in flames. I've been using A123 for several years now as main power batteries, and I always store them at full charge so that they're ready to go.

One disadvantage of LiFe is that their voltage changes so little between 100% charge and 20% charge that it's difficult to measure accurately what % remains. And then at a certain point (I don't know exactly what it is) the voltage will suddenly drop drastically, and not recover when the load is removed. I'm not sure how that will work out with your transmitter's low-voltage alarm.
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Old Oct 30, 2014, 10:51 AM
Southern Pride
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Haralson County GA. USA
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LiFePO4 left at full charge is not really an issue and fact is that LiPolys used in low discharge rate applications such as RC transmitters or receivers are not an issue either.

Comparison graph LiFePO4 and LSD NiMH from just over 4 years ago.

http://www.rcgroups.com/forums/showp...&postcount=172


Charles
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Old Oct 30, 2014, 11:02 AM
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Thanks guys. I guess my main issue, was if it was safe to keep my spare LiFePO4 transmitter battery at full charge, for several weeks, while waiting for it to be needed. I know that would be a no no with LiPo's, as the voltage tends to climb a bit when stored at full charge, for more than a few days, and they can puff if left at full charge.
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Old Oct 30, 2014, 12:09 PM
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The voltage tends to climb when stored at full charge?

Where did you read that?
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Old Oct 30, 2014, 12:59 PM
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Originally Posted by hoppy View Post
The voltage tends to climb when stored at full charge?

Where did you read that?
I have read that LiPo's (but my question is about LiFeP04 batteries) will do that, and especially if in a warm environment. I will try to find a link...........
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Old Oct 30, 2014, 01:22 PM
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Originally Posted by everydayflyer View Post
LiFePO4 left at full charge is not really an issue and fact is that LiPolys used in low discharge rate applications such as RC transmitters or receivers are not an issue either.

Comparison graph LiFePO4 and LSD NiMH from just over 4 years ago.

http://www.rcgroups.com/forums/showp...&postcount=172


Charles
NIce graph, Everydayflyer! What would be a safe voltage to run my 1500mah LiFePo4 battery down to in my DX7? I have been using it quite a bit on its first charge, and it still reads 10v on the transmitter's meter (it is acurrate, I double checked with a cell checker). I would hate to be flying, and think its good to go, and have it peeder out at say, 9.9v. I was thinking recharge after it gets down to 9.9v on the meter, to prevent the TX from going down during a flight.
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Old Oct 30, 2014, 01:33 PM
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Originally Posted by hoppy View Post
The voltage tends to climb when stored at full charge?

Where did you read that?
Concerning LiPo's (and not LiFeP04), maybe it was the internal resistance of the cells that increases, when stored fully charged. I thought the voltage could climb too with LiPo's, but don't have time to search right now. See post #13 by everydayflyer here: http://www.rcgroups.com/forums/showthread.php?t=403523
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Old Oct 30, 2014, 01:43 PM
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That post states it causes their IR to increase faster which it does but as I posted above tnat is not an issue for low drain applications. A LIPoly used in a transmitter is most likely discharged at 1/10C or less . Most LiPoly used to power a motor for flight is discharged at 10C or greater or 100 times higher discharge rate.

Charles
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Old Oct 30, 2014, 01:46 PM
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Haralson County GA. USA
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NIce graph, Everydayflyer! What would be a safe voltage to run my 1500mah LiFePo4 battery down to in my DX7?
Best to test.

Turn on the transmitter and note times and voltage write them down and post in / on transmitter. I do this all of the time.

Note I do not use LiFePO4 in transmitters due to their extremely flat line discharge. Eneloops or other high quality LSD NiMH cells give a much easier to follow discharge curve .
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Old Yesterday, 12:10 PM
Howdie Doo Dat ?
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The RDS8000 has a system timer to use for timing such batteries. Set it to zero and check it when you feel or need to.
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Old Today, 12:42 PM
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Originally Posted by Jimbo45 View Post
Hey folks, I searched all over the web, with no answers. Is it safe to store LiFe batteries at full charge?

I have been using lipo's for years, and always store them at a storage charge. Well, I replaced my Nimh pack in my Transmitter, with a LiFe pack, and bought a spare LiFe pack for it as well. As a spare, it would make sense to have it charged, and ready to swap in if need be. Is storing a LiFe the same as storing a LiPo? I sure hope not, since that sort of makes a spare pack, only a half charged spare pack, if needed in a hurry.
I've done a LOT of testing with those LiFe, A123 and Nih battery packs. As for transmitter use, IMHO, it's a pretty even trade off, all work rather well.

But, for receiver/servo use, it is a much different matter. Your transmitter pulls a fairly constant discharge current, with rather low currents involved.

Much different on your receiver battery, where the current pulled can vary from a few dozen milliamperes to a measured peak current of 14 AMPS on my giant Bigstick model with its seven Hitec 645MG servos.

The LiFe and A123 battery packs can handle 14 Amp peak currents without an issue. These two type batteries can be topped off after a day's flying, and they are ready to go for the next day of flying, no matter if its later in the week, or a year later. They hold over 90% of their charge while on the shelf for a year.

They are also quite efficient in the charging process, around 95% or so. So, if your battery takes 1145 Milliampere Hours to recharge it, your radio used 1145 * 0.95 or 1087 Mah for your days flying. Not being able to measure voltage to determine level of charge really isn't an issue. Just top off your battery after a day's flying, and you'll be just fine.

As you've asked, these LiFe or A123 packs can be stored at full charge, half charge, doesn't matter much.

As an added note, a two cell LiFe or two cell A123 battery pack is a direct drop in for replacing a five cell Nih battery pack. The voltage level of these two batteries is nearly identical at low currents. Much different at 5 or 10 Amps or more. The 2300 Mah A123 receiver battery will still have 3.3 Volts per cell or so at 10 Amps, where a typical 2000 Mah 5 cell "AA" sized Nih battery will drop down to the four volt range.

I've personally seen two cases where the battery connector of a 2300 Mah A123 receiver pack got shorted out. The battery lead burned up, welding the receiver on-off switch contacts together. The A123 pack survived just fine. (Yeah, I did one of them!)

Here is a LOT of reading material on this subject:
http://hangtimes.com/a123_batteries_for_giants_faq.html
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Old Today, 01:01 PM
Howdie Doo Dat ?
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I've been using Energizer NIMH 2300's in my transmitter and when it gets down 40F or lower that cold knocks my use time to just over an hour. I just ordered an LiFePo4 transmitter battery. The NIMH's droop too much and I never got a full run of expected time out of them.
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