still burnin

I know you see this asked all the time, but I can't figure out the formula for charging batteries. I have a dragonfly heli. I don't know what kind of batt. it has but the batt. is 650ma and the charger has a 300ma output. I am wondering how to figure out how long to charge a dead batt.
Thanks,
Matt

tanasit

The charger has 300 ma output so it will put out 300 ma per 1 hour, so if your pack capacity is 650 ma it will take about just over 2 hours if your pack is fully discharged. But say if your pack is half full or about 300 ma left, then the same charger will take only 1 hour to fully charge it.
Think of it as you fill your car gas tank, but it take one hour for the capacity of the charger to put out that much.
The basic formula will be: Time to fully charge (in hour) = Batt capacity (before charging) in amp / The charger capacity in amp
That's why many prefer to discharge the pack before charging.

puble23

My Feedback: (1)

so wait, since my charger has a 350 mA output and my batterys are 700 mA that means i only have to charge my batteries for 2 hours? Becuase someone told me that they must be charged for 4 hours. And thats how long i've been charging them for since i got them.

ChopperMike

If your battery is 700 mAH and the charger puts out 350 mA, then yes, 2 hours will fully charge it. 350 mA x 2 hours = 700 mAH. This being the case you definitely don't want to charge for more than 2 hours (I'm assuming your charger is not the automatic cutoff, peak detecting type). When charging at the overnight rate, or 1/10 rate (charge rate = 1/10 of the capacity) you normally charge for at least 10-12 hours. At this low rate you could leave the battery on the charger for a couple days without hurting anything. At higher charge currents, the battery can't tolerate as much overcharge. At the 1/2 rate you're using I wouldn't charge more than a few percent over.


Mike