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Old Sep 11, 2004, 05:02 AM
Registered User
Manila, Philippines
Joined Jul 2004
1,203 Posts
DC to DC converter Module/no need for balancing circuit to charge Multi-Lipoly.

Have you tried a DC to DC Converter module, to created an Isolated DC power supply connected to the INPUT of a LIPO battery charger, with this setup you can make 3 identical single cell LIPO charger to charge an individual cell of a LIPO battery that connected in series, with this configuration all individual charger will charge a single cell, and no need for a balancing circuit.

3 units Converter 3 units Charger 3pcs Lipo
connected in series
12V---Dc to DC converter-----Lipo Charger------Lipo cell
12V---Dc to DC converter-----Lipo Charger------Lipo cell
12V---Dc to DC converter-----Lipo Charger------Lipo cell

all 12V input is connected in parallel

DC to DC converter is 12Volts in and 12Volts out 50 watts converter.

the Lipo charger is just a LM317 (constant current) and another LM317 (constant voltage)...or any single charger you prefer.

Lipo cell battery can be of different capacity. you can mixed 1000, 1500 or 1200....just assume its the lowest capacity available for the whole pack.

some of you might say that brand new DC-DC is expensive, but you can check at surplus store, its really cheap about 5 doller only.

I am sure it will work cause the output of the DC-DC converter is totally isolated, just imagine its a separate 12 volts battery on the output of DC-DC converter, in fact you can create a 24 volts power supply by connecting the negative of the output to the positive of the input.

if you can get lucky, you might find a Li-ion battery sell for less than 1 doller.....the Lithium-Ion has a low discharge rate, so I use 2S6P thats equivalent to 8400MAH 7.2 volts, I use it on my electric Speed boat, can run it for more an hour.
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Old Sep 11, 2004, 03:28 PM
Dimension Engineering
Akron, Ohio
Joined Jan 2002
1,705 Posts
Gotta be careful with that. SOME dc-dc converter topologies are isolated (forward,flyback, SEPIC) but the more common ones (buck, boost and buck-boost) are not. Also, there are few topologies that can give you 12v out with a 12v input.

Now, if you were custom building the DC-DC supply then you can certainly do it, but buying a dc-dc converter surplus and assuming it will be isolated is a good way to kill some batteries.
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Old Sep 13, 2004, 02:51 AM
Registered User
Manila, Philippines
Joined Jul 2004
1,203 Posts
Comatose, Thanks for the Info....I check the website for the manufacturer of the Dc-Dc converter before using it, 1st I saw it, it did'nt make sense for 12 input and 12 output....I never thought its Isolated, after checking the Website, I just realize there lots of application, you can even connect it in parallel to increase its current....I have also bought a 12 in to 5 volts out, there also an trim input, that you can lower the voltage, I was able to trim the 5 volts out into 1 to 2 volts, by just adding a single Potentiometer, and use this to power the GLOW IGNITER....I was thinking of using the 12/12 converter to make a charger, to charge my RC starter battery from my car battery, use the dc/dc to produce 24 volts and using a LM317 linear regulator to drop it to 13.8 volts to charge the battery.....or using 12 volts and 5 volts (trim to 1.8 volts) connected in series to produce 13.8 volts......brand of DC/DC module is VICOR, www.vicr.com I know this really an expensive module, it so happen I just got it cheap.

for you who plan to use it at home, Just use a regular transformer with diode and capacitor, in place of a dc-dc converter, I guess it simple to contruct.

I was able to get an HP laboratory Power supply with a 4 digits mechanical thumb dial from 0.000 to 19.999 volts and an adjustable current 0 to 1 amps, I guess it more than 30 years old, but it works I use it to charge my Lithium-Ion battery just set it to 4.20 volts per cell....it so cheap got it for only 20 dollar.....its a big power supply size of a shoe box, using discrete component, I guess this whole power supply, Is equivelent to a single LM317...the 4 Digits Mechanical switch is just a series of Precision resistor connected in series.

Guys sometimes its cheaper just buy one than making one, suggest visit you suplus shop.
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Last edited by lazy-b; Sep 13, 2004 at 03:08 AM.
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Old Sep 13, 2004, 03:06 PM
Dimension Engineering
Akron, Ohio
Joined Jan 2002
1,705 Posts
Usually its cheaper to buy things than make them, the people who hang out here are masochists. I wasn't saying DC-DC wasn't useful, they're great to have in your arsenal. I was just urging a bit of caution, thats all.
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Old Sep 13, 2004, 03:10 PM
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Dan Baldwin's Avatar
United States, CA, Norwalk
Joined Apr 2004
2,713 Posts
masochist?! You're calling me a masochist?!?!.

Well, yeah. Maybe a little.

Dan
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Old Sep 13, 2004, 03:12 PM
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Dan Baldwin's Avatar
United States, CA, Norwalk
Joined Apr 2004
2,713 Posts
BTW
Buying a DC-DC converter for each cell to be charged, then building a charger for each cell just to eliminate a $5.00/cell balancer sounds like stepping over $1.00 to pick up a nickle.

Dan
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