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

ContestID67 wrote:
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.

In 5000 hours of flying gliders, I've only had to replace a fuse once in
flight (fuse actually went bad), and disconnect only one fuse (gear
warning going off at the wrong time). I think electrical problems where
a breaker would be handy are so rare, I like to keep it simple: I have a
master switch to disconnect the battery if there is smoke, and then just
fuses on the usual things. I carry a fuse of each type in a little
baggie in the pocket so I can replace fuse if I need to.

The engine controller on my motorglider does have a circuit breaker that
is used as a switch for the Ilec controller. It came that way from the
factory.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

X-no-archive: yes
In article , Eric Greenwell
writes
ContestID67 wrote:
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.

In 5000 hours of flying gliders, I've only had to replace a fuse once in
flight (fuse actually went bad), and disconnect only one fuse (gear
warning going off at the wrong time). I think electrical problems where
a breaker would be handy are so rare, I like to keep it simple: I have a
master switch to disconnect the battery if there is smoke, and then just
fuses on the usual things. I carry a fuse of each type in a little
baggie in the pocket so I can replace fuse if I need to.

That may be so Eric, but breakers stop the incorrect value fuse being
used if it is the only one available.

One option worth considering is the use of Self Resetting Fuses. These
electronic devices work like breakers but reset themselves when the load
is removed.

Tim Newport-Peace

"Indecision is the Key to Flexibility."

Generally, you size a breaker several times the normal operating
current. So if your vario draws 0.1A a 0.5A breaker would be a good
choice. The voltage drop is proportional to current, so at 0.1A it will
be less than 0.4V. This should be of no consequence to your vario. A
fuse will have a lower voltage drop, but isn't resetable.

While a fuse is highly reliable, it isn't perfect. And you can be
assured that if it does fail it will be at the worst possible moment.

Tom

Reset-ability is a two edged sword. I was just reading the review of a nice
Russian amphibian aircraft. The circuit breaker panel is in the back of the
aircraft so that the pilot cannot reset them during flight.

From a safety standpoint, when a fuse blows or a circuit breaker pops, it is
telling you that probably there is problem. Although it can be a simple
matter, it can also be telling you there is an electrical failure that could
start a fire in flight, or cause smoke problems.

I am sitting on the fence as I have a few fuses in my panel and a few
circuit breakers. The fuses were there and are not essential to flight.
One is for the vario. And, who needs that? If the radio circuit breaker
goes out, I will get the handheld out and not turn the main radio back on
until on the ground. The nice thing about a glider is that the electrical
stuff is not essential, so fly the glider down and park it, then fix the
problem.

My electrical engineer friend says the fuse is designed to protect the wire
from overcurrent and properly designed equipment should be protected itself.

Just wanted to complicate something that ought to be simple.

Colin

ContestID67 wrote:
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

Warning! Circuit breakers may well not have a suitable response time to
protect some of your valuable devices.
Save a fuse- lose an instrument.
UH

I have installed a 1 amp version breaker of this type for my sn-10b. I
checked the voltage as reported by the sn-10 and only saw a .3 volt
drop from measuring directly at the battery.

Regards,

John

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

Don't know about what is typical, but look at it this way. A breaker
trips because there is a bimetalic resistor that heats up when current
flows through it. If you have resistance you get heat and a voltage
drop. Stick in Ohm's law and you can probably get an answer to your
question.

BTW - Breakers and fuses are there for one thing only. They keep a
shorted wire from turning into a foam cutter. Components are usually
protected by an internal fusable device. Always size the breaker for
the wire.

writes:

Generally, you size a breaker several times the normal operating
current. So if your vario draws 0.1A a 0.5A breaker would be a good
choice. The voltage drop is proportional to current, so at 0.1A it
will be less than 0.4V. This should be of no consequence to your
vario. A fuse will have a lower voltage drop, but isn't resetable.

No, you should size a fuse acording to the WIRE! So if you wire is
rated for 5A, then fit a 5A fuse. Be sure to check inrush current
and fit a `slo blo' if needed.

While a fuse is highly reliable, it isn't perfect. And you can be
assured that if it does fail it will be at the worst possible
moment.

The best way I know of to increase fuse reliability is to replace
them every few years. Or it is for 3AG or the like.

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.

There are components which are not fused internally (i.e. T/S indicators,
Colibri etc).

Bimetal breakers are disastreous in this case as they are very slow and will
ultimately less pass about 10 times the nominal value before cutting off.
This winter I was loocking into replacing my fuses by breakers, and I
decided that I didn't want to have this crap in my gliders. The breakers to
use are magnetic ones which are pretty fast - but the price tag is very
different... so finally I kept going with fuses.

--
Bert Willing

ASW20 "TW"


"Don Hammer" a écrit dans le message de news:
...

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

Don't know about what is typical, but look at it this way. A breaker
trips because there is a bimetalic resistor that heats up when current
flows through it. If you have resistance you get heat and a voltage
drop. Stick in Ohm's law and you can probably get an answer to your
question.

BTW - Breakers and fuses are there for one thing only. They keep a
shorted wire from turning into a foam cutter. Components are usually
protected by an internal fusable device. Always size the breaker for
the wire.