I have not seen the "resettable fuses" that SH is using. However, I
have been using resettable fuses in my line of glider power supplies for
several years. The ones I use are mounted 'thru-hole' on a circuit
board, but they could be put into basically form factor. _Many_
manufacturers make them. You can find them through any of the major
electronics suppliers... Allied Electronics, Newark, Mouser, etc. What
do the ones look like that you are referring to?



When you look for a resettable fuse, you need to look at 3
specifications: the maximum voltage, I(trip), and I(hold). The maximum
voltage is self explanatory. I(trip) is the current at which the unit
is guaranteed to "trip" or "open" and stop the current flow. I(hold)
is the current at which the unit is guaranteed to hold. Current between
these two values is in an ambiguous area... it might trip or not. Once
"tripped", usually you must remove the load completely from the circuit
in order for the unit to reset itself. In essence, it has to cool off
until the molecules of plastic have shrunk enough to allow the current
flow again.



You have touched on a _very_ important point. ABSOLUTELY fuse the
battery... at the battery!!! What you need to do is to protect the high
current portions of the wiring from smoke or fire in case of a profound
short. I have seen the results of a short in the power wiring in a
glider. It happened on the ground but could have been disastrous while
flying. An enormous amount of smoke was generated almost immediately.
I typically suggest a 5 amp fuse at the battery.



Which brings me to another point... Have a qualified person check your
glider to be sure that your wiring is up to snuff. If you have
conventional wire, I suggest changing it out to Tefzel (high temperature
Teflon coated) wire. This stuff doesn't burn and outgas like
conventional wire does in the presence of heat.



Larry Goddard

01 "zero one"









" wrote in
message news

1) Don't use multiple small breakers for each item. Rather use one
large single master breaker (like a 5A or larger) as you can probably
afford to loose that 0.25Vdc.


The downside to a single large device is that if you have a short in
wiring to one component (it's not likely to be a failure within the
device) then with #1 above you have now lost power to ALL your instruments.

I would suggest that a single large device SHOULD be mounted directly on
the battery, (preferably right next to the negative termanal) but it
should have a high interrupt load - 10 amps or even more. If you have a
short in the wiring between the battery and the rest of the panel, this
will keep a short from making a mess (possibly behind the seatback or
even under the seat). If you do have a short, a 10 amp fuse will open
very quickly.

Meanwhile, back to the original request. SH is outfitting new gliders
with these neat little "resettable fuses". I'm still curious if anyone
has seen something similar in the US???