Feb 12, 2003, 12:38 AM
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billystiltner's Avatar

DIY simple lipoly charger


i put together a charger from radio shack parts .
you can get the schematics and info on how to modify it for your cellpacks here.

i used the simple design and measure the voltage with a voltmeter while charging so i dont overcharge.

my charger has been modified for a single cell 145mah lipoly
the values i changed are as follows
R1 = 5 ohm(i used two 1/4watt 10 ohm in parallel)
R3 = 1000 ohm (this lets you charge a single cell the original circuit was for charging 2 cells)

construction took about an hour and a half most of the connections between parts can be done with the component legs i had to use 2 wires and none of the connections overlap so all the soldering can be on 1 side of the board.

for the 12 volt supply i used a spare computer power supply.
for the heatsink i used a peice of aluminum soda can folded all up.

i will post a graph or just the actual numbers of the voltage and current vs time after i drain and recharge my battery.

here are some pics.

Last edited by billystiltner; Feb 12, 2003 at 12:41 AM.
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Feb 12, 2003, 12:55 PM
Registered User
Hi! I have built 2 li poly chargers with Shdesign 's scheme and I can say that they work wery well and are cheaper!
Feb 12, 2003, 03:06 PM
Embedded Systems Engineer
MX's Avatar
I built one too and it works very well. I made mine with switches
to select 1 or 2 cells and 560mAh or 1020mAh capacity.

Feb 12, 2003, 04:25 PM
Foam Flyer
Depdog's Avatar
MX, thats EXACTLY what I want to do (I am electronics challenged) never took it in school, got a crash course from a friend, I know how to solder and read a schematic (mostly). Do you have a circuit schematic on yours with the mods?

Feb 12, 2003, 04:30 PM
Thats NOT indestructible
j8m8l's Avatar
Hi All

I need to make a charger for some LiPo's.......

....is there any way to make it "time out" when 4.2v has been reached, coz i dont like having to stand over the charger


Feb 12, 2003, 04:45 PM
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Depdog's Avatar
The one he talks about above, the SHDesigns one. If you do the advanced version, it has an led that goes out when its fully charged. The circuit is set for 8.4 volt duel cells as it sits, but he also tells you how to convert it to single 4.2 volt cell charging.

Feb 13, 2003, 12:56 AM
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billystiltner's Avatar
here's an excerpt from the shdesigns page about the charger

Panasonic recommends charging at a constant current of 0.7C until 4.2V/cell is reached. Then constant voltage (CV) is to be used until current drops to 0.1C. At that time, the charging should stop. The circuit follows this recommendation exactly. However it does not turn off the charge. Testing has shown that the current drops to almost zero anyway.

The circuit simplifies this by limiting the charge voltage to 8.4v. When the battery reaches 8.4v, it will no longer draw current. The charger is also current-limited. Below about 75% charge, the limit current is reached. After about 80% charge, the current decays toward 0. At about 95% charge the current drops to only a few milliamps. In theory, the battery will never finish the charge, the closer it gets, the less current it draws. If left on the charger for 2 hours or so it will reach near 100% charge. But, 95% can be reached in less than an hour in most cases (assumes discharged to 50% or so.)

then later on he says you shouldnt leave the cells on charge for more than a few hours with the improved led indicator version.
Feb 13, 2003, 05:45 AM
Thats NOT indestructible
j8m8l's Avatar

I think that i am gonna do the LED one, more snazy

I am gonna do it for a 1020mah 2 cell pack, for running a DX-A

Cant wait (i am too cheap to buy a charger !)

Feb 13, 2003, 11:34 AM
Registered User
billystiltner's Avatar
keep us updated.
Feb 13, 2003, 11:40 AM
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senor_paco's Avatar
I'm gonna put a bunck of LEDs on mine, they do absolutely nothing, but make it look Buck Rogers-ish. anybody remember him? from the 30's, not that 70's monstrosity (though Erin Gray, mmmm... but now she's old).
Feb 13, 2003, 01:31 PM
Propellers are cool.
propfan's Avatar
Thanks for posting this! I have to build one with a green or blue LED and a black case Now that will be cool.
$10 charger and $20 for 2 1020s - NiCds must be getting pretty worried
Feb 13, 2003, 01:49 PM
Registered User
Is this a better DIY charger than the one using a LM3420 regulator chip?
Feb 13, 2003, 02:51 PM
Embedded Systems Engineer
MX's Avatar
Originally posted by Depdog
MX, thats EXACTLY what I want to do (I am electronics challenged) never took it in school, got a crash course from a friend, I know how to solder and read a schematic (mostly). Do you have a circuit schematic on yours with the mods?

Here's the changes I made. These are just made using the
notes on the web page that tell which resistors to modify for
different cell sizes and number of cells. I actually tweaked the
resister values a bit while using a meter to get things exact.
I mounted mine in a nice black case with the switches
labeled, an illuminated power switch, and banana terminals
for input and output.

Last edited by MX; Feb 13, 2003 at 02:59 PM.
Feb 13, 2003, 06:25 PM
Registered User
billystiltner's Avatar
here is the data
the calculated current i reckon comes from V/R=I
in this case thats vR1/R1=iR1
R1=5.5ohm which gives me .8C
as you can see somewhere between 1h 20m and 1h 24m the charge current dropped below .1C (.0145ma) thus being fully charged.
on kokams curve at .7C a full charge should occur at about 1 hour and 15 minutes or so.

the voltage fits pretty close to kokams curve.

t------ vBat -- vR1 - iR1(calculated)

4:14 - 3.33
4:18 - 3.77 - .56 - .101
4:22 - 3.83
4:26 - 3.87
4:30 - 3.89
4:34 - 3.91 - .55 - .1
4:38 - 3.92
4:42 - 3.94
4:46 - 3.95
4:50 - 3.97
4:54 - 3.99
4:58 - 4.01
5:02 - ? missed it
5:06 - 4.05
5:10 - 4.07
5:14 - 4.1
5:18 - 4.15
5:22 - 4.19 - .36 - .065
5:26 - 4.19
5:30 - 4.19 - .17 - .03
5:34 - 4.19 - .11 - .02
5:38 - 4.19 - .07 - .012

i had left the cell plugged into my rx prior to charging
and had it driving a motor that was drawing way too much current. i run the motor for a second and noticed the battery was drained.
it had went down to 1.8V. i should have trickle charged it but wanted to see how it will affect the performance of the battery.
in the instructions Scott says to use a 10 ohm resistor in place of
R1 to make a trickle charger. with 1 145mah cell would this 10 ohm be sufficient or should i use a 50 ohm?
Last edited by billystiltner; Feb 13, 2003 at 06:30 PM.
Feb 13, 2003, 06:38 PM
Registered User
billystiltner's Avatar
you are welcome
i had seen a link to this somewhere else and had seen a few other diy chargers. i choose this one because of the amount of info that came with it fro modifications. and scott answered an email i sent so i figured if i had any problems building it he would help. there are simpler diy chargers out there. but i like this one for some reason. ablue led on this thing would be cool. i put mine in a snuff box today. i thought it was cool but i showed my girlfriend and she looked at me like it was weird.

i am not sure.

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