LiPoly Battery charger schematic - RC Groups
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Jul 09, 2002, 01:58 PM
Registered User

LiPoly Battery charger schematic

Does anyone has a schematic to build a simple battery charger for the Lithium Polymer cells?....They require 4.2 volts at 140ma
This should not be difficult...
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Jul 09, 2002, 02:02 PM
13brv3's Avatar
Good timing. I just read the info at the following web site, and it should give you a real good overview of what you need, though he stresses that his experience is with Lithium "Ion".

I actually bought a supply from WildRC, but HL seems to sell the same supply. Both are in the mid $20 range, and handle 1 or 2 cells.

Good luck,
Jul 09, 2002, 03:06 PM
Registered User
Dave Wulff's Avatar
If you have access to RC MicroFlight there was an article on Li cells and a charger schematic. It was around the beginning of the year. I emailed the author for some advice on altering the design for different size and number of cells but got no reply.

Dave W.
Jul 09, 2002, 04:25 PM
Registered User
jberg's Avatar

this is a circuit like I use. The first LM317 works as a constant current source. The second one works as a voltage regulator. Charging termination has to be done by hand when the current has gone back to 0.05-0.1C (see cell manufacturers specs). So don't go away while charging. This is the drawback for the circuit being so cheap and easy.

The resistor values:

R1=1.25V/Icharge (~3.3Ohm/1W for 830's Qualcomm, ~8.2Ohm/0.5W for 140's)

R4=2.5kOhm spindle trimmer

Use a good (exact) voltmeter to adjust the output voltage to 4.2V without load. Don't charge more than one cell at a time with this simple design, as there is no security against charging the cells unbalanced.

You may burn down your house if overcharging Li-Ion cells, so if you don't know exactly what you are doing, don't do it. I am not responsible for any harm or damage happening with this circuit. People who know what they are doing will know which pins of the LM317 to use where.

Remember, charging termination has to be done by hand when the current meter in line with the cell shows a value below 0.05-1C (dependent on cell manufacturers steps). So don't go away when charging.

People who want automatic termination should buy a ready-made charger.
Last edited by jberg; Jul 09, 2002 at 04:57 PM.
Jul 09, 2002, 05:16 PM
Hmm, kerosene... :)
NightSwan's Avatar
the charger at can also easily be
modified for 4.2V (single cell) and less amps.

To lower amperage, increase the value of R1.
R1 = 0.65V/max_current (approximately)

Adjust the values for the potentiometer and resistors in series with it to
lower the output-voltage.

The charger works great on my qualcomm 2-cell packs.
For a charge-graph see my post in the modelling-science section :

Total cost of the charger should be under 5 bucks.
Jul 10, 2002, 12:34 PM
Registered User

Battery charger schematics

Hey..thanks for the help.....i also found some schematics while i was looking for some lectronic components....if you take a look ant the datasheets of this operational amplifiers you'll find some charger designs in the application notes...just download the datasheets for the following OpAmps. LM350 & can find them in the National Web

This designs are very simple...and they do work....i found also that there are specific IC to charge Lithium Ion batteries..and they cost only 2 or 3 can find them in National too...
Jul 29, 2002, 10:54 PM
Grand Poobah of Nothing
Trizza's Avatar
I built a charger from the schematic NightSwan suggested, seems to work fine. I use it for my Kokam 140 Li-polys

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