My imax b6 charger states 50W maximum output.

So if you are doing true solar charging then you are a few watts short.

However a 2000mah 3s is charged at 2A to about 11.1V (well, lets use 12V for simplicity) for 24W + the load of the charger.

Switch it around and a 18AH power sport battery is 18,000mah, or theoretically enough to recharge the previously stated 2000mah battery 9 times (excepting the load of the charger), so maybe the one panel would be enough to keep the battery from depleting too fast so you can keep flying.

I charge off my car and don't worry about it.

You can also look into a battery charging relay and put a second battery in the trunk charged off the engine, but isolated from the electrical system. (boating stuff)

Phil

This is an interesting thread.

Interesting because when I do the math I come up with the answer "don't use your car batteries to charge your LiPos -- you'll suck them dry".

Yet, when I fly RC electric I charge from my car all the time (and it's a little car with a little battery), and there's people here saying that's what they do, too, and I see other guys at my RC field with MUCH BIGGER PLANES (4500mAh, 7-cell packs) charging from their trucks.  So -- I'm confused, in a mathematically-oriented, engineering-ish sort of way.

If the "7 watts per ounce" rule is correct, then a 59 ounce plane uses about 150,000 Joules per flight.  If you assume near-perfect efficiency, that rounds to about 3.5 amp-hours (3500 mA-h) from your car battery per charge.

I did a quick check on car batteries; the first one that I found that would fit my 2000 Escort ZX2 had a 12 amp-hour capacity.  Which says that charging after just one flight would suck more than 1/3 the capacity of the battery.

Yet, when I fly electric RC, and per the testimony of the group, this can be done.  Maybe the one battery that I found was really wimpy, or had a very conservative amp-hour rating??

I think if you really wanted to be safe you should find a deep-discharge battery with 3.5 amp-hours per charge you intend to pump in.  Then charge it with solar or your car or whatever, but don't try to pull enough power directly from the sun to charge your LiPos, unless you're patient.

If you want to contribute to the group, poll your RC friends about what works, or toss some jumper cables into your car and go charge batteries at the field, then report back.

I have not managed to kill the car battery charging at the field  I did have the minivan battery die suddenly at an early age - reading here about how easy it is to actually stress-out a car battery makes we wonder if thats that happened to me.

The econoboxt has no place to carry a deep discharge marine battery.  An all solar rig is too big to be easily portable.  The idea of using a solar make-up charger as a hedge against injuring the normal battery sounds like a viable compromise.

Bob: thanks for tip on the RC field set-up.

Hi Tim,
0.6 to 0.7 Watt-hours per ounce ... maybe?

Regards,
  Dean