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Old Aug 19, 2011, 12:28 PM
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Idea

3s Lipo battery Charger with MCP73831 IC


Hi, I have been trying to make a simple 3s lipo battery charger and I came upon this 1s lipo charger from sparkfun. http://www.sparkfun.com/products/10217. I have this idea that I can hook up three of these in series to charge a 3s battery with an input voltage of ~16V. I know that the Chip itself can only handle a max voltage of 6V but since there will be 3 chips in series; the voltage drop across each board is 1/3 of the input. I am also worried about not having enough current being sent to the battery.
I haven't bought the parts yet but would like to have your opinions on if this would work.

Thanks for the help.

This is what I had in mind (copy&pasted from sparkfun)
I may be connecting the reference voltages of each circuit wrong
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Old Aug 19, 2011, 01:12 PM
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I am curious what made you want to do this?

I imagine a standard 3s 2200mah battery would take about 2 hours to charge... what size 3s batteries are you planning on using?

Even then I am not sure they would balance charge evenly; but I must admit this is not my area of expertise so I could be completely wrong.

The best thing I ever did for my self in this hobby was invest in a decent charger and Tx. I am currently using the Hyperion Super Duo 3 and I love its features; especially its ability to charge two batteries simultaneously at 20-Amps each (only with newer nano batteries). That puts my total charge time for one 3s 2200 battery around 8-10 mins for a completely balanced charge from 30% capaciity.

It changed the way I spended money in the hobby as well since now I can go to the field with 2 batteries and fly nonstop all day long. My batteries have remained healthy after hundreds of cycles; I could not say that when I was using lesser quality chargers.
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Old Aug 19, 2011, 02:20 PM
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Yeah, I just had this idea because I need a small charger to integrate into my RC boat. The capacity of my lipo ranges from 1.3AH to 5AH. I am cool with this trickle charging the lipo at 0.5A or a little less. (I'm a very patient guy )
I guess that since the voltage at each lipo changes; this changes the reference voltage at each chip and battery. I think that this would make them still charge correctly. I could be looking at this completely wrong.
Old Aug 19, 2011, 03:08 PM
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Your guess at it is as good as mine.

I will say, the price is right; at $9 each, it is a very economical way of getting a 3s charger.

For my stuff, I guess I have shifted more to a mindset of battery maintenence and less about only caring about the charge... After using a poor quality charger for years, I went through countless batteries and they never seemed to have a long lifespan. At the time, it was before HK came on the market too so I was spending $50-$70 per battery. Since switching to a quality charger, I have not had to replace one battery (except for crash damage) in over a year!

For me, although it was a $300 investment in the charger, I am confident I have made up for that expense by not having to buy near as many batteries. I do not have more than 2 batteries per plane anymore and I can fly all day long without waiting on charges.

I am curious to hear more of your boat project. With the 3 1s chargers wired together onboard the boat, what are you using as a power supply for the chargers?

Also, I am curious what was the inspiration for installing it on a boat. I am curious, what are you trying to recharge while you are on the water?
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