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LiIon, LiPo, NiCd & NiMh General General Battery Support


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Old 04-05-2008, 04:52 PM   #1 (permalink)
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Default Lipo Storage Voltage ????

Hi All

Just a quick question, I was wondering what voltage do your store your packs at in between use (say a couple of weeks).

I was allways under the impression that you would store at nominal voltage, eg a 3cell pack is 11.1V which is 3.7v per cell - so I have been storing at 3.7V this is what is written on the back of all my flightpower evo 20 packs - i have just read that all my new evo25 packs state that they should be stored at 3.4V per cell.

Does anybody now what is the correct storage voltage per cell.

Thanks
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Old 04-05-2008, 07:27 PM   #2 (permalink)
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3.4V per cell is way too low. Typical storage charge is ~ 50% capacity which is 3.85v per cell.
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Old 04-05-2008, 07:47 PM   #3 (permalink)
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Take a close look at the back of your Flightpower packs, I bet they all say 3.4 per cell like mine. I know everyone says that voltage is too low but if it is, why does Flightpower print it on the back of their packs???
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Old 04-07-2008, 11:03 PM   #4 (permalink)
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Quote:
Originally Posted by schwaggs View Post
Take a close look at the back of your Flightpower packs, I bet they all say 3.4 per cell like mine. I know everyone says that voltage is too low but if it is, why does Flightpower print it on the back of their packs???
Yes, and why do all new Flightpowers come out of the package at 3.8 volts??
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Old 04-11-2008, 08:33 AM   #5 (permalink)
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3.8 - 3.85 volts per cell.

And you will find that most every brand new lipo is at this charge level.
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Old 04-11-2008, 03:14 PM   #6 (permalink)
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I have contated flight power over here in the UK and they couldn't give me an answer as to why all the packs state store at 3.4V per cell - I am waiting for answer from them at the moment.

So most of you store your packs at 3.8V per cell for long term storage, do you guys do the same for short term, if you are using the packs regulary on a 2-3 day basis.
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Old 04-11-2008, 04:55 PM   #7 (permalink)
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The best bet is to charge them to 3.8v after use, and only top them off on the day you go out to fly. It probably would not hurt to top them off the night before though.

Flightpower will probably not respond regarding storage at 3.4v per cell because they are wrong.
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Old 04-15-2008, 07:33 AM   #8 (permalink)
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I have a triton charger, does anyone know how to select a specific voltage to charge to ?
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Old 04-19-2008, 06:58 AM   #9 (permalink)
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Can't do it with a Triton. You just have to watch it and stop the charge when the voltage is about 3.8 volts per cell.

The other thing to do, if you know you need to store the lipo, just cut your flight short. If you timer is set to use 80% of the pack, just cut the flight to 5/8s (62.5%) of the normal time. So if your timer is 6 minutes for 80% use, fly 3 minutes 45 seconds and you will be close to 50% charge, which is the storage level.
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Old 04-19-2008, 10:39 AM   #10 (permalink)
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Thanks pine this is very helpful....yet another reason why I should change my Triton LOL
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Old 04-21-2008, 09:01 AM   #11 (permalink)
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Quote:
Originally Posted by Pinecone View Post
Can't do it with a Triton. You just have to watch it and stop the charge when the voltage is about 3.8 volts per cell.
Wrong. For a Triton, charge your LiPo normally, then use a NiCD or NiMH discharge setting down to a bit below 3.8v/cell. Or go the easy route: put your LiPos in a plastic bag in the freezer while fully-charged, and take them out to warm up the night before you plan to go flying.

Anyway, yeah, with the Triton it's a little bit more involved than some other chargers, but it's still trivial to discharge to the correct voltage.

A LiPo naturally loses 2%-4% of its capacity per year even when left at "storage voltage" in room temperature. Cooling a partially-charged LiPo below 32F reduces that capacity loss to near zero. Cooling a fully-charged LiPo below 32F reduces its capacity loss per year to around 2-4%. Just don't charge a cold LiPo above 4.0v/cell! Note the actual battery chemistry itself does not freeze until around -20F (no water inside)...
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Old 05-01-2008, 03:57 PM   #12 (permalink)
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Not exactly, he asked about CHARGING to storage charge, and a Triton cannot do this.

Yes, it can DISCHARGE to a set voltage.

Not a good idea to put fuly charged lipos into the refridgerator or freezer. Below 55 dgrees, the max safe voltage of a lipo goes down, so your fully charged pack becomes over charged. You can chill partially charged packs, but not fully charged ones.
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Old 05-02-2008, 08:28 AM   #13 (permalink)
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Quote:
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Not a good idea to put fuly charged lipos into the refridgerator or freezer. Below 55 dgrees, the max safe voltage of a lipo goes down, so your fully charged pack becomes over charged. You can chill partially charged packs, but not fully charged ones.
You can chill fully-charged LiPos with little ill effect. Their voltage goes down substantially when frozen (break out your voltmeter and check, it's around .1v), and in fact if you have to store fully-charged lipos for any length of time, the only way to reduce the loss of battery capacity is to reduce their temperature. What's bad is CHARGING the LiPos while they are cold, because the usual 4.2v threshold is an over-charge. 4.0-4.1v/cell is normal below 55 degrees.

A frozen Lithium battery stored at full charge loses 2-4% capacity per year.
A Lithium battery stored fully-charged at room temperature loses 20%-40% capacity per year. At higher temperatures, it's worse.

I sometimes fly frozen LiPos (it's cold many months out of the year where I live), and now that I've learned their voltage characteristics, I've suffered no further ill effects. When I *charge* a LiPo to 4.2v/cell and it's well below freezing, the LiPo's useful life is less than 10 cycles. Treat ice-cold LiPos at around 1/4 to perhaps 1/2 their rated "C" rating or they are over-amped, and reduce flight times similarly.

If you like, I'll gladly provide some statistics of a stored-fully-charged-frozen LiPo versus one stored only at traditional room temperature. Unfortunately, that will need to be at end-of-season, but I have two new Loong Max LiPos I wouldn't mind endangering (heh) for the cause.
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Last edited by redgiki; 05-02-2008 at 09:52 AM..
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Old 12-20-2012, 09:28 PM   #14 (permalink)
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go for the powerlab8
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Old 01-04-2014, 02:20 PM   #15 (permalink)
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Always charge to a storage voltage of 3.85 balanced. and charge only before flying, and never charge or use cold packs, warm them if needed.. And you will get hundreds and hundreds of top quality flights out of your packs.. And if you have time always charge slowly. I charge my quality packs at 1c at home. 5c at the field..
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Old 01-04-2014, 02:25 PM   #16 (permalink)
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The longest I have had a pack sit was about six months and it was put to rest with 3.85 volts per cell and was 3.84 when I went to charge it six months later.
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Old 01-04-2014, 05:08 PM   #17 (permalink)
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+1 on That!!! always, store packs at 3.85v per cell and they will last for years and years and years! Thats all lipo packs, Doesn't matter the brand, only the battery chemistry.. I warm up my packs, (if it's cold) then charge right before flight, then charge/discharge to 3.85v storage voltage after flying for the day. even if I'm going to fly the next day. Since I started useing the PowerLab 8 and using this method my packs actually have been getting better with time, and the I.R. (internal resistance) stays low and gets lower with time.. had one pack that had a cell I.R. of 3.6-4.3-130.0!!! (brand new from factory). I have charged and flown with it about ten times now and the I.R. is down to 42.0 in the high cell that was 130.0 ohms..
My PowerLab 8 has taught me it's all in the charger.. And how you handle your packs... Hope this helps.. Your packs should last you many years of high power service then they start looseing capacity.. remember every once and awhile discarge your pack to 3.40v per cell and charge at a slow rate and see the MAh capacity of your batteries, You should get around 90% of the batteries capacity back in (i.e. 5000MAh battery should charge to at least, 4700 MAh in my opinion)..
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Old 01-04-2014, 05:59 PM   #18 (permalink)
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Quote:
Originally Posted by ukiah74 View Post
remember every once and awhile discarge your pack to 3.40v per cell and charge at a slow rate and see the MAh capacity of your batteries, You should get around 90% of the batteries capacity
I agree with everything else you're saying, but not this. That could potentially damage your packs performance, especially if your charger is capable of discharging at only a few amps. If you're discharging it at 40 amps, then that might be ok because the resting voltage will still be above 3.7v. If you discharge to 3.4v/cell at a slow rate you will fully deplete the pack, not good.
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Old 01-06-2014, 02:45 PM   #19 (permalink)
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on my charger 3.4v is 3.4 volts. It wont allow me to kill a pack.. safety features dont allow it.. you could go higher if you like but I hav hundreds of flights on my packs and they are almost like new.. the powerlab 8 cuts off before depleting a cell to far.. at least allways has for me.. the main thing is to leave at 3.85v per cell when not in use and your all good.
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Old 01-06-2014, 03:39 PM   #20 (permalink)
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I never said it would kill the pack, but it will damage its performance over the long run. I too own a PowerLab and am aware of what it can and cannot do. Just because it allows you to drop the voltage setpoint so low doesn't mean that you can apply it to any LiPo without any issue. I can see that voltage setpoint being used on other LiPo chemistries though, just not RC LiPo's.
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