Newbie question

I have a simple question about electric flight: where is the fuse (or
fuse-equivalent)?

Long, long ago I learned that the purpose of a fuse (the thing that
melts when too much current goes through it, not slang for "fuselage")
was to protect the wiring in a circuit, not the device at the end of
the wire. That makes sense.

Now let's look at a typical setup:

Bat --- ESC --- Motor

where of course there's another branch, too:

ESC --- Receiver --- Servos


Suppose that something goes wrong at the motor -- your anti-noise
capacitor gets shorted, for instance. Suddenly you've got a large
potential current draw at the motor, and it seems like a good chance
to melt the motor wires, the Bat <-> ESC wires, or both. If the
ESC has some sort of over-current protection, you're probably
OK...but if not, you're headed for a fire.

This isn't entirely hypothetical, of course -- while flying with
my kids, with a 700mAh Lipo powering a J250 motor, this is just what
happened to me. The time between "hunh...something's wrong here...
the prop isn't turning when we goose the throttle" to "there's a smell
of melting/burning insulation" was about 6 or 7 seconds, tops. By
the time I grabbed things and ripped them apart, I had a couple of
pieces of burning insulation and an ESC that looked like a small
roman candle. (Ammazingly enough, the plane -- fanfold foam -- was
undamaged. Damn. Why couldn't the $.50 plane get wrecked and the
$15 ESC be saved?)

So...should I henceforth solder in a fuse in the battery-to-ESC
wire? Something like 7A fast-blow should do the job, since that's
the top discharge rate for my 10C lipo, right? At the cost of a few
grams, I'll feel a lot safer...

--John

.

Relevant Pages

  • Re: Throttle/pitch mixing help
    ... I don't know what current that your motor and ESC draw, ... The fuse should be placed in series with the positive ESC lead. ... This worried me for a newbie and proved rightly because the heli flipped ...
    (rec.models.rc.helicopter)
  • Re: REQ:Breaker Maximum...6AL...?
    ... The device on the end of the wire also has nothing to do with the fuse rating. ... In general the wire has to have a rating 125% of the motor rating. ...
    (alt.home.repair)
  • Re: Hot wires powering blower motor
    ... the wire being cool enough but the switch ... BUT the wire itself being cool...) ... The fuse does not limit the current, ... > Assuming my motor works with the original fuse, ...
    (rec.autos.tech)
  • Re: Newbie question
    ... | I have a simple question about electric flight: where is the fuse (or ... and weight to the plane, ... If you have a brushed motor, the best place for a fuse is between the ... ESC and motor -- that way, the BEC still provides power if the fuse ...
    (rec.models.rc.air)
  • Re: Hot wires powering blower motor
    ... too hot indicates switch-problems. ... BUT the wire itself being cool...) ... The fuse breaks the circuit when the current is too big. ... Assuming my motor works with the original fuse, the current is not too big. ...
    (rec.autos.tech)