Fuses on the panel, or not

More air flow can fan or extinguish a fire.

In his shoes, I'd have stepped over the side. I'd really hate to have a
major part of the glider burn away while on final approach!


"son_of_flubber" wrote in message
...
On Tuesday, October 15, 2013 11:39:59 AM UTC-4, 7C wrote:
If you can't physically isolate then you are stuffed when you are
flying... Bet you can't land quickly enough

Someone told me a story about bad smoke developing in the cockpit of a
glider. The pilot ejected the canopy. At that point the increased airflow
stoked the smoldering fire and something burst into flames. Story goes, he
landed and the fire went back to smoldering.

Does this sound plausible or is it yet another BS story?

A couple of comments about circuit protection some of which has been covered before in other threads;

- Pete Purdie's comment above about undersized wiring is on target. Bigger is better (within reason)! If you saw smoke you probably do not have Tefzel wiring. Get some!
- Fuses are great as they are cheap, fast acting and have ZERO voltage drop across its terminals. Cons are that they are more difficult to replace in flight and somewhat fragile (glass type).
- Breakers are great as they are easy to reset in flight. Cons are that they are expensive, somewhat slow acting and will cause a voltage drop across its terminals. This voltage drop effect is worse at small breaker values, you can loose 1/2 volt or more. That is fine for ships with generators but lousy for gliders.
- Put a FUSE on each battery at the terminals. This is the absolute minimum circuit protection you MUST have.

So if you really want separate protection for each of your devices, then use small value fuses rated just above the maximum current for each piece of hardware. Otherwise go with a large value single breaker to protect the entire system.

As to the use of different types of fuses (glass versus blade type) this relates more to what your IA will sign off. Blade type are certainly more robust and I saw them in lots of experimental airplanes at Oshkosh. But the FAA is a strange and demanding mistress. ;-)

My $0.02. Good luck.

- John

Please don't install glass fuses, because they are prone to:
- blowing under vibration (like, rolling during launch)
- even more prone to blowing in gas-powered motorgliders
- corroding and introducing voltage drop at the (non-gas-tight) ends
The voltage drop breakers introduce can be significant and can cause problems.
Use blade types inline (not on the panel!) and avoid these problems...
Hope that helps,
Best Regards, Dave "YO electric"

I have just finished designing my new panel and will now place all fuses behind the panel. The reasons are 1) I want a very clean panel and 2) in the past 600h of flight i never had to reset a fuse, and i wouldn't do so if it blew. The only thing you must make sure is to have a possibility to shut off power in case of smoke/fire (master switch).

....And be sure to have an appropriate sized fuse as close to the battery
terminals as possible.


wrote in message
...
I have just finished designing my new panel and will now place all fuses
behind the panel. The reasons are 1) I want a very clean panel and 2) in the
past 600h of flight i never had to reset a fuse, and i wouldn't do so if it
blew. The only thing you must make sure is to have a possibility to shut off
power in case of smoke/fire (master switch).

Regarding mini-blade type fuses, my searching has yet to locate a reasonable sized mini-fuse block as well as not being able to locate mini-blade fuses in low amp values. IMSMC, 2 amp was the smallest value I could find cataloged from DigiKey or Mouser.

I would appreciate a steer to any small mini-blade fuse blocks or low amp mini-fuses.

On Friday, October 18, 2013 11:23:28 AM UTC-4, wrote:
Regarding mini-blade type fuses, my searching has yet to locate a reasonable sized mini-fuse block as well as not being able to locate mini-blade fuses in low amp values. IMSMC, 2 amp was the smallest value I could find cataloged from DigiKey or Mouser.



I would appreciate a steer to any small mini-blade fuse blocks or low amp mini-fuses.

Take a look at these motorcycle fuse blocks- http://www.easternbeaver.com/Main/main.html

On Friday, October 18, 2013 11:23:28 AM UTC-4, wrote:

I would appreciate a steer to any small mini-blade fuse blocks or low amp mini-fuses.

https://www.google.com/search?q=1amp...ient=firefox-a

My preference is for individual equipment CBs to be on the panel
and visible (rather than hidden fuses or CBs) to help with in flight
diagnosis in the event of an instrument or equipment power loss.

In some cases I might try a reset - I did so succesfully once when
the turbo pylon CB popped with the engine half retracted. I
would probably reset a bugwiper CB too. Delicate intruments -
not so likely. Nor if the cockpit were to be getting smokey.

John Galloway

At 21:49 16 October 2013, wrote:
I have just finished designing my new panel and will now place
all fuses
be=
hind the panel. The reasons are 1) I want a very clean panel
and 2) in the
=
past 600h of flight i never had to reset a fuse, and i wouldn't do
so if
it=
blew. The only thing you must make sure is to have a possibility
to shut
o=
ff power in case of smoke/fire (master switch).

Some dumb questions, but these things sometimes don't work like I imagine they would.

Say I have a 3 amp fuse at the battery and a 1 amp blade fuse in series and the one amp feeds power to a single instrument. (with other 1 amp fuses going to other devices)

Is there a scenario where a 1 amp blows and the 3 amp does not? I figure that most shorts will draw more than 3 amps and blow both fuses. Do devices develop "partial shorts"?

Is there a scenario where both fuses blow?

Would it make sense to make the 3 amp "slow blow" and the 1 amp "normal blow"?

What am I missing?