I recently took my ePPG to its first 3-day fly-in. I wanted to see how quick and easy it was to charge the batteries on a portable generator and maximize my flight time. Here’s some observations:
8 Bonka 22Ah batteries
3 Dual-Channel Battery Chargers
-2 Polaron EX (400 Watt per Channel)
-1 HT700 Duo (350 Watt per Channel)
1 1500 watt Power Supply (for the Polaron’s)
If you could charge a LiPo at 1C from 0% to 100% it would only take 1 hour. In practice, topping off the battery (the last 20% or so) uses significantly less amperage to prevent taking the cells over 4.2V. I believe the average LiPo takes 1.5 hours to charge from 0% to 100% at 1C.
In my case, 400 Watts gives me about 22 Amps (1C) for just a few minutes, but as the voltage climbs, my Amperage drops. Plus I always do a balance charge, which adds time as well. I average 2 hours for a complete charge, (and I typically see the Bonka batteries give a full 22Ah).
I also have two other limiting factors, my power supply is only 1500 Watts, so charging 4 batteries off of the one power supply gives me about 350 watts per channel (with overhead wattage for the actual chargers). With all three chargers running, I am pulling more than a standard 20 amp AC circuit can deliver, and it pops the breaker (in theory I should be under the 2400 Watts for the circuit- but I’ve tested on several circuits at my house and at another house, and they always pop).
Knowing all these factors, I tried a Honda 2200 generator, but it couldn’t handle the load, so I ended up using an older Champion 5000 Watt generator with 2 20amp outlets and it worked great!
Best case scenario would be to start each morning with fully charged batteries, do one flight then start charging the first 4 batteries, and then do a second flight (on the other 4). After the second flight start charging 2 more batteries. An hour and a half later the first 4 would be done then add the last 2 batteries. Then another flight and 2 more batteries on the charger. Before mid-day a last flight with 6 batteries, then charge everything back up and repeated the process in the evening.
So 8 flights in a day is best case, which sounds like a good day, but it would really only be a little over 2 hours total time in the air. During the test, I spent a significant amount of time swapping batteries back and forth, and of course, waiting…