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Old March 8th 05, 10:06 PM
ContestID67
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Default Fuses versus Breakers

I have some fuses in my glider. One is on the main battery itself.
The other fuses are in the instrument panel and are for individual
devices (radio, computer, vario).

I got it in my head that I should replace the panel fuses with
breakers. There are several advantages, like being able to reset the
breaker in flight and being able to "pull" the breaker.

I have been told that all new breakers must be able to be manually
pulled (tripped) in case of emergency. Older breakers could be reset
but not pulled. Obviously fuses can be pulled also but I have an image
of my fumbling the loose glass fuse in the cockpit which isn't a pretty
picture.

Looking at a particular brand of breaker, the Texas Instrument Klixon
7277 line (http://www.ti.com/snc/products/controls/acb-7277.htm) from
Aircraft Spruce, I found that at low current draws you can loose a volt
or more from your primary.

1/2A 2.00 Vdc drop my vario
3/4A 1.45 Vdc drop
1A 1.10 Vdc drop my computer
2A 0.70 Vdc drop
3A 0.33 Vdc drop my radio
4A 0.30 Vdc drop
5A 0.25 Vdc drop

This is not good. It got me thinking that a glass fuse isn't too bad
after all especially considering a fuse is $1 each and the breaker is
$25 each.

The question is, what is the typical forward drop of a fuse? Also, why
does the breaker have such a high forward drop at low amperages?

Thanks, John