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LiPo question - 6/25/2008 6:52:18 PM   
spiral_72



Posts: 511
Joined: 3/7/2007
From: Chesnee, SC, USA
Status: offline 		Q&A seems to be a catch-all, so here it goes.

I've got a single cell LiPo, unkown manufacturer, with what looks like a serial number on it. The serial number seems to be useless for information about the battery.

I've got a Triton Jr, voltmeter and several other electric/tronic tools. Can you think of a way to judge it's capacity? If it makes any difference the cell is about 1/4" thick, probably 2" square.

I've been treating it like an 800mAh battery, but I have a feeling this is very conservative because it handles that charge a little too well. I've also discharged it and other batteries, but generally the total current discharged seems to have little to do with the pack's actual "rated" capacity. I'm a little cautious about dumping a huge current into the battery to see what happens. I haven't experienced this, but supposedly LiPo's are pretty volital(SP?)

Oh, it's going on a hacked and modified CVS camera.

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RE: LiPo question - 6/25/2008 6:58:52 PM   
Nathan King



Posts: 1468
Joined: 5/29/2007
From: Omaha, NE, USA
Status: offline 		You'll have to charge it to 4.15 volts and put the battery under a known load until the battery empties. Once you have the discharge time and known load you can easily figure out capacity.

For example, you load the battery with a 400mA load for 2.2 hours. The battery has a capacity of around 880mAh.

< Message edited by Nathan King -- 6/25/2008 7:02:29 PM >


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RE: LiPo question - 6/26/2008 5:40:30 PM   
spiral_72



Posts: 511
Joined: 3/7/2007
From: Chesnee, SC, USA
Status: offline
Thanks, I wasn't sure how the 3.0 minimum voltage would figure into that, because supposedly bad things happen when you drop below 2.9V.

If it takes 2hours to discharge from 4.15 to 3.0 at 400mA, what does that tell me?

< Message edited by spiral_72 -- 6/26/2008 5:42:23 PM >

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RE: LiPo question - 6/26/2008 6:00:42 PM   
ampeater


 

Posts: 144
Joined: 6/13/2005
From: Burlington, NJ, USA
Status: online 		That would be 400 mA X 2 Hr = 800 mAHr. But that's not necessarily the capacity of the battery, it may be just how much you had put back into it.

If you put it on a LiPo charger (as a single cell, slowest charge rate to be safe) in line with a WattsUp meter, it will charge until the voltage gets to 4.2, then hold it at 4.2 while dropping the current until fully charged. The WattsUp meter will tell you exactly how many mAHr went back into the pack. The good thing about the WattsUp is that it integrates the amp-hours over the course of the charge, rather than trying to calculate it.

Enough people have these chargers and meters nowadays that you should be able to find a friend with them if you don't already have them.

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RE: LiPo question - 6/28/2008 2:03:49 PM   
Stick 40


 

Posts: 262
Joined: 6/7/2003
From: quincy, MI, USA
Status: offline 		I am getting into the li-po's now and was told not to discharge a li-po down below the S1 voltage level or 3 volts for a one cell li-po.

In fact I just recieved two 3 cel li-po's and the instruction state " DO NOT DISCHARGE A BATTER TO A LEVEL BELOW 3 VOLTS PER CELL UNDER LOAD". For mine is would be 9.9 volts for three cells.

From what I am learning li-po's are a lot different than our other batterys. While flying I plan to fly enough to take them down to about 11 volts for the 3 cell pack and then recharge them.

I think you will be alright with the regular charger, as you don't have more than one cell to charger . BUT you need to charge to the voltage level for the batter and at a current rate for the battery. The current (or amp's ) are important.

LI-PO'S CAN CATCH ON FIRE IF NOT HANDLED PROPERLY!!!!!!!!!!!!!!! Try to charge them on cement out in the open etc. I have a old 1 sq. Ft. safe I use in the basement on the cement floor.

My new ones are 1900 mA which means I can charge them at 1.9 Amps untill the voltage gets to (3*4.2)= 12.6 volts. A one cell pack should not go over 4.2 volts at what ever amp's the battery calls for.

If yours is 800mA then you would not want to charge over .8 Amps and only charge it untill the voltage reaches 4.2 volts.

To tell you the truth, this is helping me to understand this.

< Message edited by Stick 40 -- 6/28/2008 2:40:52 PM >

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