I am doing a glow to electric conversion of an airplane I've had for 20 years. The motor is a Hacker C50, ESC is a Hacker Opto77, and power is from 3 3s2p LiPo packs wired in series. I've made my own series harness and it includes a high voltage UBEC to power my receiver and servos. With the batteries connected to the harness, my Whattmeter measures 38VDC. So far, so good. My next step is to program up the Opto 77 with the Hacker Master Programming Box. I have a separate receiver pack hooked into the Programming box as well as the ESC signal cable. When I try to plug in the ESC to the battery harness, I get sparks (enough to startle me). There are no stray wires, solder splashes, or any other type of visible short sources.

I removed the ESC from the system and simply plugging in the final battery also caused sparks (again, enough to startle me).

I now have one of the UBEC input leads cut, so it's out of the system. I still get sparks when plugging in the ESC.

The only common denominator is my harness, but I measure the proper voltage at the output end. The harness uses Deans connectors and it is pretty easy to see that there are no shorts anywhere.

Has anyone had a similar experience with high-voltage systems and know this to be "normal"? Personally, I don't think so, but I am not omniscient. Note that the Whattmeter plugs in without any issue (but there's nothing on the load end either).

Thanks,
JK