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Archive for April, 2014
Posted by SoaringDude | Apr 29, 2014 @ 11:12 PM | 11,846 Views
May 9 2014 update: I just added a new blog post "Resettable fuse isolation for servos" that describes an even better servo fuse solution than the one described in this post.

A recent RCG thread related how a plane that was being bench tested all of a sudden experienced a servo short circuit failure that quickly melted a servo connector, harness wires, and even some of the plane's wing skin. Had this happened in the air the plane would have lost control as soon as the battery was drained, which would not take long with a short circuit in progress.

One of the posts by Tuan (RCG: fnnwizard) suggested a fuse for each servo as a protection mechanism so I did a bit of research and found a nice submicro fuse that can be directly soldered into your harness for each servo you want to protect. These are Littlefuse sealed micro slow blow fuses, $1.11/ea in qty 10 and in stock at mouser.com.

1.5A fuse: Mouser p/n 576-047301.5MRT1L, Littlefuse p/n 047301.5MRT1L
2.0A fuse: Mouser p/n 576-0473002.MRT1L, Littlefuse p/n 0473002.MRT1L
2.5A fuse: Mouser p/n 576-047302.5MRT1L, Littlefuse p/n 047302.5MRT1L
Manufacturer datasheet
Construction: molded epoxy + axial solder leads. Dimensions: 3.4mm x 7.1mm (small!)

Comparison of times/currents to fuse blow:
1.5A fuse: 2.7A in 100sec, 3.1A in 10sec, 4A in 1sec, 5A in 0.5sec
2.0A fuse: 3.5A in 100sec, 4.3A in 10sec, 6A in 1sec, 7A in 0.5sec
2.5A fuse: 4.2A in 100sec, 5.0A in 10sec, 7A in 1sec, 8A in 0.5sec


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