New Power Cable in the Sabre

The setup for the Sabre has always been that the BEC was powered by the flight battery's balance plug. I’ve never had any issues, however, after a friend brought it to my attention, I decided to do some investigation regarding the current draw of my servos on the Sabre.

The concern is that the balance plugs (JST-XH) are rated for low current (2 or 3 Amps, according to the internet) and if my setup is drawing more than that, then eventually something in the connector could heat up enough to cause a failure, resulting in loss of power to the servos, and therefore loss of control of the airplane.

I hooked up my ammeter in series with the BEC and powered the airplane on. At idle (that is, all servos powered but not moving (representative of straight and level flight in smooth air)), it pulled about 1.8A. Cycling the sticks while deploying flaps would pull 5 – 6A, and cycling the sticks while loading servos could spike to 8 – 9A. Granted, this is worst case scenario, and it is only for short periods of time, but this was enough to make me uncomfortable with keeping the balance plug as the input power source for the BEC.

For my reassurance, I built a new power cable that powers the plane (through the Vector’s Power Supply Unit (PSU)), as well as a second set of wires which will power the BEC. The micro Deans connector is what will plug into the BEC now, and these connectors are rated for 10A continuous. With this upgrade, the entire airplane will be powered just by plugging in the flight battery’s Deans plug into this adapter, but I will still be able to power just the BEC for servo checks, just by unplugging the Deans from the PSU.

The New Cable. (The small connector is what is new, compared to the old one)

New (Top) vs. Old (Bottom) Connector