Can you charge lipoly batts through a wattmeter? - RC Groups
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Aug 31, 2003, 11:13 AM
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slammin's Avatar

Can you charge lipoly batts through a wattmeter?

I need a charger for my lipoly batteries, and would rather not spend the money for something like the trition with a built in display, so I'm wondering if you can charge lipoly batts on a cheap charger, through a wattmeter, to see how many mah has been put into them. I have heard of people doing this with nickel batteries, but those have a peak detection, not a constant current/constant voltage charge like lithiums do. Anyone done this or have any thoughts?

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Aug 31, 2003, 12:04 PM
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sheerLuck's Avatar
Yes, I do it. I don't think the WhattMeter knows or cares what chemistry the batteries use...

Aug 31, 2003, 01:31 PM
Registered User

How many cells are you running in your battery pack? If it is the typical 2 cell, then look into using a cell phone charger specifically made for Lithium batteries.

All you need to do is put an appropriate connector on it to charge your expensive cells with safety and next to zero risk....after all, they are made with the lowest common denominator intelligence level end user in mind that will accidently leave the battery on charge for 2 weeks while they go on summer vacation!

I have had great results using them on LiPoly cells, and if you know one end of a soldering iron from the other and have a voltmeter, just find the positive and negative feeds and connect it up.

The cell phone industry is changing from using 2 cells to a single cell, so make sure the charger is for an older, 2 cell phone. Mine cost $1.99 on sale, so price is sure not a factor. There are many after market manufacturers of cell phone chargers that will work nicely.

The one I use was originally made to charge a Motorola model SC-3100 phone.

Lee Smith
Last edited by Lee Smith; Aug 31, 2003 at 01:33 PM.
Aug 31, 2003, 02:59 PM
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slammin's Avatar
I do use a couple of cell phone chargers currently, but it would still be nice to know how much energy it is putting into the packs. I would also like a charger that does the proper constant current/constant voltage charge, as opposed to the constant voltage charge of cell phone chargers. It would also give me some more performance, since the cell phone chargers have to cut out at a lower voltage.
My conern is what the voltage loss through the wattmeter might do to the charge cycle. Correct me if I'm wrong, but for nickel chemistry batteries, the charger is looking for a peak. Even with the voltage loss through the wattmeter, it can still see a peak, and it would then stop charging. For a lithium cell, the charger is looking for a certain voltage, correct? So would the voltage loss through the wattmeter cause the charge to stop early? Or is the voltage loss through a wattmeter so small that it really doesn't matter?

Aug 31, 2003, 03:42 PM
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WJ Birmingham's Avatar
Yes, you can use a Whattmeter to monitor battery charge. I do so on every pack I charge.

The Whattmeter consumes 17milliamps for power, so it's really a non-issue for power consumption during charge or discharge.
Aug 31, 2003, 06:29 PM
Radix malorum est cupiditas
radix2's Avatar
As the batteries become fully charged, the charge current drops to nothing - therefore, there will be virtually no drop across the wattmeter as the charge is completed - and no error to be concerned with.
Sep 01, 2003, 01:30 AM
Flys with Thumbs
Danal Estes's Avatar
See this thread, scroll down to photo:

The black square on the edge of the fire safe, in line in the wiring from the constant current / constant voltage power supply to the battery, is a whattmeter.

Didn't realize it was face down when I took the picture...

So, the answer is: I use a CC/CV power supply + a whattmeter to charge LiPos. More description on the Power Supply technique here: