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Home made Lithium Ion battery charger

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Home made Lithium Ion battery charger

Old 02-18-2004, 12:40 PM
  #26  
vicman
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Default RE: Home made Lithium Ion battery charger

Why not use a cell phone bat and the charger?
Old 03-29-2004, 08:58 PM
  #27  
ashamans
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Default RE: Home made Lithium Ion battery charger

i have some li-ion batts that have electronis on them for charging, i think that you just need to put some dc power to them, is this right for chargeing?

any help pls
Old 03-29-2004, 09:52 PM
  #28  
urbnsol
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Default RE: Home made Lithium Ion battery charger

there is a very complete discussion about making your own li-poly charger at:
http://www.rcgroups.com/forums/showt...hreadid=130567

the scott henion design is listed farther down in the thread, but i like the electron_head design better, its is simpler with fewer parts and less chance for error with the switches on the henion design, which of course is similar to the less expensive commercial designs with jumpers or switches.

also, it is mentioned in the other board, but the lm317 is rated for 1.5A, the lm350 is rated at 3A, and the lm1084 at 5A with an even lower dropout voltage than the 317 or 350. just in case you want to charge those 2000/2100mah packs, or parallel a couple of smaller packs and still have the quicker charge times.

im getting ready to build one of these myself with the optional charge complete indicator circuit.

anyone who is thinking about building a charger should read the rcgroups thread and/or the scott henion page about safety and such, and while it is a bit long (270+ posts) there is a lot of good info on the rcgroups thread.
Old 03-29-2004, 11:00 PM
  #29  
ashamans
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Default RE: Home made Lithium Ion battery charger

thanks man, got a question though, i have 4 cells, they all have some kinda of chip on them, what does that do?

also, so i could hook all of them like i want to for a 7.2v 1260mah batt pack and just charge of the last leads

lastly, you say li-po, those will work li-ion too right?

thanks
Old 03-30-2004, 08:19 AM
  #30  
urbnsol
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Default RE: Home made Lithium Ion battery charger

i dont know what the chips are for, i havent gotten my packs yet, and im not getting single cells, im getting a kokam pack.

as to charging, you can charge them series-parallel, but it isnt always recommended.
also, the cells have to be the same ratings, ie all 700mah, or all 350mah, you cant mix and match cells, 350mah+700mah to make a 1050mah pack.
THAT COULD BE DANGEROUS!
i dont know exactly what would happen, but i wouldnt want to find out.
if you had 4 350mah cells, you could make 2x2s packs and put them in parallel with an adapter board to fly, that would give you a 7.2v 1400mah arrangment

li-poly and li-ion are the same basic chemistry so you can use the same charger, just dont exceed the charge rate of the pack, ie 1c=1xcapacity= no more than 750mah charge for a 750mah pack.
can always charge at less than capacity, but not voltage, it just takes longer.
Old 03-30-2004, 04:55 PM
  #31  
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Default RE: Home made Lithium Ion battery charger

What do you think about this one?

Before connecting the cells to the charger the max charging voltage has
to be set by adjusting P1 (2k potentiometer).
The max charging voltage must not exceed 4.2V per cell (Kokam), e.g. 8.4V for
two serial connected cells. It is recommended using a digital voltmeter.
The max charging current is set by choosing the value of Rx.
Rx = 0.6 / max charging current

For example, for a max charging current of 600mA, Rx should be 0.6 / 0.6 = 1ohm,
while for a max charging current of 1.2A it should be 0.6 / 1.2 = 0.5ohm.
The dissipated power on Rx at a charging current of 1.2A is:
P = V x I = 0.6 x 1.2 = 0.72W

The dissipated power on the LM317 IC is:
(Vin - Vout) x Charging Current.
It's advisable to use a heatsink to prevent the IC from getting too hot.
Notice that the IC's metal package or tab also carries the Vout, so it's necessary
to use isolating washers in case you attach the heatsink to a metal case.
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Old 03-30-2004, 05:28 PM
  #32  
ashamans
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Default RE: Home made Lithium Ion battery charger

i think the chips are for charging since the batt pack sthat i have seen dosen't have chips on them, just a battery and since a charger is really simple

i'm going to talk with a EE on this one

i have 4 3.6v 630mah batts, there really small and can fit perfectly in my 1/28 xmod

thanks
Old 04-01-2004, 09:05 PM
  #33  
urbnsol
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Default RE: Home made Lithium Ion battery charger

ORIGINAL: adam_one

Before connecting the cells to the charger the max charging voltage has
to be set by adjusting P1 (2k potentiometer).
The max charging voltage must not exceed 4.2V per cell (Kokam), e.g. 8.4V for
two serial connected cells. It is recommended using a digital voltmeter.
The max charging current is set by choosing the value of Rx.
Rx = 0.6 / max charging current

For example, for a max charging current of 600mA, Rx should be 0.6 / 0.6 = 1ohm,
while for a max charging current of 1.2A it should be 0.6 / 1.2 = 0.5ohm.
The dissipated power on Rx at a charging current of 1.2A is:
P = V x I = 0.6 x 1.2 = 0.72W
i dont have enough knowledge to evaluate a circuit, but i would only point out what was brought up on the other forum i posted earlier:

having an adjustable output makes error more likely, also, pots can have a tendency to drift if they are not a high quality, linear taper one, which can be expensive, making it less attractive to build.

another problem a couple of people ran into was using inexpensive multimeters to measure the voltage and current, leading to inaccurate reading, which as anyone who is thinking about building a charger for li-poly _should_ already be aware of, this can be EXTREMELY DANGEROUS.

the lm317 is rated at 1.5A so anyone should be aware that is isnt the chip of choice for high current charging. the lm350 is rated at 3A and the lm1084 is rated at 5A.
also in the other design, the regulators get rather warm so good heatsinks are a necessity to get the full potential from the charger.
the 317-350 are bulletproof in that they are not supposed to be able to melt down, they have a built in protection circuit, and they will power down as they approach the rated thermal limit.
Old 04-02-2004, 05:32 AM
  #34  
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Default RE: Home made Lithium Ion battery charger

ORIGINAL: urbnsol

having an adjustable output makes error more likely, also, pots can have a tendency to drift if they are not a high quality, linear taper one, which can be expensive, making it less attractive to build.
Yes, there's always a compromise between quality and price in everything you buy or build.
If you don't feel comfortable building and/or understanding electronic circuits, you are not advised to build this battery charger.

As for the cell's max voltage measurement accuracy I refer to Using LI Po Batteries Safely by Fred Marks somewhere else in this forum:
If, say, a Li Po cell is charged at six to seven volts, well above the nominal 4.2 V limit, the electrolyte can begin to “boil” and develop voids as temperature rises above about 180 degrees F. If this abuse continues for, say, ½ hour, the electrolyte, being organic, can eventually ignite.
http://www.rcuniverse.com/forum/Usin...1238924/tm.htm

So, a multimeter with an accuracy of about 2% will do just fine.

But I agree, there's a risk charging Lithium batteries as well as there's a risk flying models using Lithium batteries, as they may catch fire in event of a crash.
However, one may always take preventive measures, such as having the batteries on a non-inflammable place while charging them (a box with sand is a cheap fire extinguisher) and never charge batteries unattended, regardless you're using a homebuild charger or a commercial one.
Old 04-03-2004, 08:05 AM
  #35  
ReallyUglyStick
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Default RE: Home made Lithium Ion battery charger

one thing that hasn't been said (i don't think it has, anyway) is that li-ion packs such as cell phone packs and the cheap bulk rate ones, aren't high discharge packs. They are ok for small electrics that have low current draws (sub 5 amps) but if you try to use them in high amp applications you will smoke them and maybe your plane. That's the reason irate, etec, and the others can charge so much for their batteries...the $2 cells aren't rated for 7+ amps.

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