I'm into RC airplanes and helicopters and I need a power source for my charger to recharge my lipos at the flying field which has no power. I keep looking at generators but only one I like are the expensive honda since they are so quite. Looked at regular deep cells but they cant handle the 52amps I pull from my powersupply when I parallel charge all 4 lipos at once with my two chargers. So I keep looking at the lifepo4 batteries and figure I need an 80ah-100ah and a 4s would work since my chargers are rated for up to 16vdc input.
I have (4) 6s 3600mAh 30C lipos that I run (2) at a time on my large heli and that is what I'm wanting to recharge. I did the math and it goes like this:
Assuming I want to leave 25% in the charging battery, that gives me 60 amps of usable charging power out of an 80ah battery. I leave 30% in my lipos so I only recharge (3.6x0.70) 2.52 amps. So 4.2 (volts per cell)*6 (cell) x 2.52 (amp to recharge lipo)= 63.504 watts /12 (battery voltage) = 5.292 amps taken from it for each 6 cell 3.6 amp lipo I recharge. Then add about 15% for charger overhead and I need 6 amps per lipo to recharge. So 6(2) is 12amps I need after each heli flight. 60/12= 5 flights which doesn't sound like a lot but it is. I go to the field with all 4 charged and usually I'm done after 3-4 flights later when I hookup to a friends honda generator. I could get the field, fly twice, recharge them 4 times, and still have plenty to recharge my little 3s 2200mah lipos I have for my smaller stuff.
After looking around on ebay and other sites it looks like the best price for (4) 80ah lifepo4 cells is about $350-$400. Anything cheaper or any other ideas?
