Powering SG90 servos with lipo and BEC

Hi there,

I'm building a robot with 15+ SG90 micro servo's.

To power it, I've bought a 2C lipo battery, and a 5/6 volt BEC.

I've hooked up the BEC's 5v (red) to all the servo's red, and the BEC's ground to the servo's ground, as well as some arduino grounds (that control the servo).

The BEC has an on/off switch.  When the BEC is switched to off, and I plug the battery into the BEC, a surge of current flows through to the motors.  They all "twitch" very rapidly, and I've had some wires melt/smoke.

My questions are:

1) Are BEC's supposed to behave this way? It seems like plugging the battery (even with the switch to off) might fry my robots motors and/or arduino's

2) Is it safe to power my robot in this way? The BEC is capable of many amps, but I figured that those micro servo's would only draw what they need





I powered servos in this way many times and had no troubles.

If the circuit is ok, no shorts or wrong connections, looks like your BEC is defective. it should not power anything when switched off even when batteries are connected.

Use a meter and check the circuit and separately measure BEC+accu.

Good luck

With the BEC power turned
With the BEC power turned off, electricity still flows through but at the original voltage. So your pumping all of 7.4v through it.

Also what amperage rating does your bec have. You will need at least 6a to keep it from draining your battery too fast. I use a 9amp with my servos. Take a look at pololu. They have a wide variety of bec’s in different amperages.


That would be a very weird circuit. I find the term BEC less than enlightning as it is just a voltage regulator. Most modern units employ switching a regulator for efficiency. Please post the model number and a circuit diagram.