SoaringDude's blog View Details
Archive for May, 2014
Posted by SoaringDude | May 09, 2014 @ 12:17 PM | 12,961 Views
This is a follow-up to my blog post "Protective fuses for your servos" immediately preceding this one. While the micro fuses in that post would do a good job protecting your plane from a potentially catastrophic servo short circuit, using a resettable "polyfuse" is even better since it never needs to be replaced if it ever trips. I owe Mike Wilson the credit for suggesting this alternative.

The resettable fuse part number: TE Connectivity p/n RUEF110 1.1A 30V, Mouser p/n 650-RUEF110, $0.32/ea in qty 10. These devices are low cost and small (14x7mm) "radial" package devices that look like capacitors and should be soldered directly into your harness in front of each servo you want to isolate for short circuit faults (described later in this post).

How they work

If you're electronically curious you can read how these resettable fuses work here. The basic idea: current that exceeds the rated trip current causes the polyfuse to heat up and increase its resistance thereby reducing the current to safe levels until either the short circuit terminates or until the fuse is reset via a power cycle.

Bench tests

To test this device I used a Hyperion 2S LiFe 1450mAh battery, a 68 ohm 1 watt resistor to simulate a 100mA average servo load, and a 1ohm current shunt that allowed a digital storage oscilloscope to display the current flowing through the servo load during short circuit conditions. Two types of tests were performed: a continuous...Continue Reading