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        Help! Should I or shouldn't I charge

#1 Turbopropdrive Nov 07, 2012 04:54 PM

Should I or shouldn't I charge
 
Hi,

I just got a Radio Shack 22-813 model Digital multimeter. I have a bunch of 1s lipos that I have not used for a while. While checking the voltage of each one with my multimeter in the 9v range, they show between 3.8 and 4.1 volts. However when I connect them to my micro rc receivers they simply can not power the motor or the receiver led blinks rapidly. Should I recharge them this time in parallel? ;How can I tell if they have or not reached lowest cutoff voltage ?
Am I doing something wrong?

Thanks for your shared wisdom.

:confused:

#2 356Jim Nov 07, 2012 05:47 PM

It's best to charge them individually. If you connect them in parallel, differences in terminal voltage will cause the higher voltage cells to discharge into the lower voltage cells, confusing the charger.

Once the individual cells come off the charger, each one will be at the same voltage (e.g., 4.2 vdc). But after each use, especially in 1s applications, they will all be different voltages again.

#3 slipstick Nov 07, 2012 05:48 PM

Fully charged is 4.2V so it sounds like they could do with charging. But leaving lipos almost fully charged for "a while" can seriously reduce their capacity so you may have ruined at least some of them.

Steve

#4 nemoskull Nov 08, 2012 12:51 PM

lipo storage is said to be at 3.9 volts, or 50%. lipos do wear out and hold less charge.

#5 Turbopropdrive Nov 08, 2012 03:19 PM

Ok, Thanks a mill for your replies. Now If I am not confused,and hoping that these lipos still take a charge, If they are above 3.8 but below 4.2, can I still charge them or should I scrap them and get fresh ones?

Thanks again.:)

#6 Turbopropdrive Nov 08, 2012 03:22 PM

Also, if they still hold above 4.0 volts, without being used for a while, why then, if they still show this voltage they can not power with enough punch the receiver/motor?:confused:

#7 Petefoss Nov 08, 2012 04:59 PM

As batteries age the internal resistance goes up. When that happens you end up with a battery that looks fine unloaded, but when you try to draw current out the voltage drops very quickly.

#8 slipstick Nov 09, 2012 03:18 AM

Quote:

Originally Posted by Turbopropdrive (Post 23218552)
Also, if they still hold above 4.0 volts, without being used for a while, why then, if they still show this voltage they can not power with enough punch the receiver/motor?:confused:

As Pete says, because the voltage you measure with no load on the battery doesn't tell you very much about how it will behave when you ask it to deliver current to a fairly heavy load (like a motor). What happens is the voltage suddenly drops much lower....and the reason it's easy to get confused is because when you take the load back off and try to measure battery again the voltage will have bounced back up to something that looks quite reasonable :(.

Steve

#9 rhodesengr Nov 09, 2012 11:20 AM

you can also try to cycle them. If you charger has a discharge mode, run them down and recharge a few times. If they get too low where you get a low voltage error on your charger, you can charge them as an NiMH to get the voltage up.

If you cycle them, and they still don't power your model, then you can declare them shot.

#10 Petefoss Nov 09, 2012 11:44 AM

I would cycle at 1C discharge.

#11 coriolan Nov 09, 2012 06:16 PM

Quote:

Originally Posted by rhodesengr (Post 23225699)
you can also try to cycle them. If you charger has a discharge mode, run them down and recharge a few times. If they get too low where you get a low voltage error on your charger, you can charge them as an NiMH to get the voltage up.

If you cycle them, and they still don't power your model, then you can declare them shot.

Cycling doesn't revitalize dead Lipo, and charging as a NiCad/Nimh will produce the magic smoke real quick:eek: As Petefoss noted, Lipo which have been stored fully charged degrade chemically and seems to have very low capacity because of higher internal resistance.
http://www.rcgroups.com/forums/showp...23&postcount=1

#12 rhodesengr Nov 09, 2012 06:23 PM

Quote:

Originally Posted by coriolan (Post 23228711)
Cycling doesn't revitalize dead Lipo, and charging as a NiCad/Nimh will produce the magic smoke real quick:eek: As Petefoss noted, Lipo which have been stored fully charged degrade chemically and seems to have very low capacity because of higher internal resistance.
http://www.rcgroups.com/forums/showp...23&postcount=1

well I guess everyone is entitled to their opinion but cycling helping a new battery that I bought that didn't work right as received. Worked fine after cycling.

Also, I used the NiMH trick just the other night on a small 1S battery I hadn't used in a while. I have it a few seconds in NiMH mode and then it charged fine in LiPo mode. Obviously you need to be careful doing anything with batteries but the trick does work if you accidently over-discharge a LiPo and your charger gives you a low voltage error and won't charge it.

#13 Turbopropdrive Nov 09, 2012 07:05 PM

Gentlemen!!

Thanks for your advice, I will use my B6AC charger to try to recycle them (BTW can 1s lipos be recycled in parallel? Just asking!), and see what happens. I will then keep you posted and also get prepared to purchase new 1s lipos from HK and this time, if I will store them I will only charge them for storage capacity.
:cool:

#14 rhodesengr Nov 09, 2012 10:35 PM

Quote:

Originally Posted by Turbopropdrive (Post 23229088)
I will use my B6AC charger to try to recycle them (BTW can 1s lipos be recycled in parallel? Just asking!), and see what happens

You could cycle them in parallel but it will be harder to tell if you have improved a bad one. The way you'll gauge improvement is to either time how long a discharge cycle takes or look for an increase in the total mAh during a discharge. The test before and after must be with a single battery. Start fully charged and your charger will stop when it reads a preset voltage. Probably 3V or 3.3V for a 1S. Hopefully your charger reads out time, total mAh, or both for a discharge.

#15 Turbopropdrive Nov 10, 2012 10:24 PM

Will do,

Thanks again and I will keep you posted. I will take some time since the next few days I am on reserve. But I will follow your advise on my days off and give you the feedback on how the lipos are behavin'

Take care and thanks.:cool:


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