Underrated C cells, bad cell in a battery and conductor size (power cables).
As an electrician I get a real giggle out of the RC world how they can have huge current draw on shoe string cables. As a comparison a house point of attachment rated for 100amp has a conductor size of 16mm minimum depending on the wiring installation. I see many copters including the first tri I built pulling in excess of 100amp on supply cables that are smaller than 2.5mm building wire (rated for 18amp). I'm surprised that the wire insulation has not melted off a few copters
Agreed! And if we didn't keep the flight times down, we'd have more trouble.
Chatting with a guy last weekend who owned a dual ducted fan ME-202 -- he said the plane pulled anywhere between 80-120 A, and was grounded until it got a badly needed rewire. The stock plane came with deans(the nice ones are rated to 70A burst), and though he didn't mention the AWG run for the wires, he said they too were badly undersized.
The point it dawned on him when he opened the canopy after a long flight and saw the foam had melted away from the power lines and the connector was too hot to touch. quick IR reading showed he was about to reflow the solder on the connectors. He felt lucky -- If they had, at best he'd have a ball of foam to pick up off the ground . . . at worst a flying lipo fire.
At 40-60A per motor, each separate harness may have been fine for short flight times, but the stock design had one pack and a really weak link, right at the Y.
