Fuse block, in flight accessible?

Brian Vickers · #1 06-14-2007, 09:55 AM

I have started the panel in my RV4 and was planning to use an Aero Electric recommended fuse block. My airplane and panel is ultra simple. I have seen various references to making the fuse block accessible in flight. This makes perfect sense but I don?t have a good place to do that because the connecting wires fan out on both sides. For aesthetics I was hoping not to look at a fuse block while piloting. I am using so few fuses that I?m rethinking this and considering going with panel mounted fuse holders (screw type). My panel is so bare that I could actually mount it right there if desired (kidding). What have other fuse block users done? Suggestions or comments, about anything fuse block related? Go with panel mount screw in fuse holders?

Sincerely,
Brian Vickers, RV4 project now past a decade but still creeping along

Kevin Horton · #2 06-14-2007, 10:22 AM

If your fuses are properly sized, the only thing that should cause a fuse to blow is a short in the wires. If this has happened, do you really want to be replacing the fuse and feeding current to the short again in flight? This is an activity better attempted on the ground.

Some people argue for fuses that you can replace in flight because the fuse feeds some vital system. Well, if you have a system that is so important, you really need to have a second backup system, as systems can fail for many, many reasons that don't involve a fuse blowing.

Do you have any electrically powered systems that would prevent a safe landing if the system failed, or the fuse blew?

My recommendation is to do the research to figure what what size the fuses need to be so they don't blow unless there is a wiring problem. Then make sure the wiring is hefty enough to handle the fuse's rated current. Put the fuse block out of reach of the cockpit, as troubleshooting an electrical failure is an activity that really should be done on the ground, not in flight.

bsacks05 · #3 06-14-2007, 10:23 AM

I went with the fuse block because my panel is very simple also. The block is totally inaccessible in flight (and barely accessible on the ground!) My only breaker is for the alternator and it is mounted on the panel. I followed 'lectric bob's logic that so long as there are no "safety of flight" related components being affected, there is no reason to have access to the fuses in flight. And, if a fuse does blow, it probably means there is more of a problem than simply changing it out and a proper diagnosis would be done on the ground.

After 100hrs there have been no issues with my fuses, or anything else for that matter.

videobobk · #4 06-14-2007, 10:38 AM

In time, your panel will probably fill up, and you may need more fuses. While I'm not all that familiar with the 4 panel, I put my fuse block (-9A) under the center of the six-pack, hinged so that it folds up out of sight. Hit a lever and it drops down between my knees. No panel space taken, very accessible in flight and not obvious. I have the fuse location chart as a page on my Dynon checklist, so if a fuse blows (as it just did last week) I can drop the fuse block, bring up the list and change the fuse. Of course it didn't fix the problems last week, but it did work as planned. Finding the short in the panel lights fixed the problem.

Bob Kelly

jcoloccia · #5 06-14-2007, 10:40 AM

Quote:

Originally Posted by Kevin Horton

If your fuses are properly sized, the only thing that should cause a fuse to blow is a short in the wires. If this has happened, do you really want to be replacing the fuse and feeding current to the short again in flight? This is an activity better attempted on the ground.

<snip>

100% right on the money. Given the seemingly chronic fuse blowing/breaker popping that happens in experimentals, I have to think that most people undersize their wiring. When is the last time you or someone you know blew a fuse in your car for absolutely no reason at all. Honestly, I can't even remember the last time I blew a fuse at all.

dan · #6 06-14-2007, 10:42 AM

Quote:

Originally Posted by videobobk

In time, your panel will probably fill up, and you may need more fuses. While I'm not all that familiar with the 4 panel, I put my fuse block (-9A) under the center of the six-pack, hinged so that it folds up out of sight. Hit a lever and it drops down between my knees. No panel space taken, very accessible in flight and not obvious. I have the fuse location chart as a page on my Dynon checklist, so if a fuse blows (as it just did last week) I can drop the fuse block, bring up the list and change the fuse. Of course it didn't fix the problems last week, but it did work as planned. Finding the short in the panel lights fixed the problem.

Bob Kelly

When in heavy turbulence, sometimes my legs get bounced around. If my fuse block was hinged up above my knees, there's a very good chance I might have "taken out" my whole electrical system on occasion.

Just playing devil's advocate about the "above your knees" location.

szicree · #7 06-14-2007, 10:50 AM

I bolted my fuse block to the left side skin up near the firewall. The bolts are hidden by the cowl cheeks. I've got no electricals that are mission critical so I don't need to access them in flight. I also agree that trying to troubleshoot such a failure in flight seems like a bad idea.

ccarter · #8 06-14-2007, 12:18 PM

As I read through Bob's "AC Book" I really identified with his focus on low cost "less is more" philosophy. The EBuss provides essentials in a power problem. Steam gauges cover me in the event of a serious failure, the Dynon and GPS have their own internal batteries. Breakers cost much more in time and money to implement. If I encounter an open fuse, I'll wait till I'm on the ground to shoot it.

Chris...
http://www.n212s.com
RV-7, IO-360, Garmin Stack, 496 GPS, LightSpeed IGN
(Finishing, FWF,Wiring)

ABRV4 · #9 06-15-2007, 06:45 AM

My electrical system is also pretty simple and is intended for VFR flying. I put the 8 circuit fuse block to my RV-4 vertically on the right bulkhead just below the panel and right next to my knee. I also have a small Radio Shack LED next to each fuse that will light if the fuse blows. It was all very cheap and will give me some additional information should something go wrong plus I can easily cut a circuit should I need to work on something. I can replace the fuses in flight. However, I agree that messing with the electrical system while flying is probably a poor idea and most likely I will not replace a fuse in flight unless absolutely necessary.

Alan
RV-4

gmcjetpilot · #10 06-15-2007, 05:23 PM

I hesitate to say anything but the "philosophy", is based on you don't reset any fuse in flight.

In other words: YOU DON'T RE-SET FUSES IN FLIGHT, BECAUSE if it blew the fuse you should (consider) not re-setting it, per this "philosophy". It should not be critical item. You should be able to finish the flight safely and live (fly) with out it.

If it's an item that is critical and you can't live (fly) without it, consider a resettable CB or at least a switch to provide a secondary power supply (the so called E-buss or emergency buss).

One cool idea I saw on one of Van's prototypes was having the fuses exposed in the panel, using the standard car ATC style blade mini fuse holder/boxes. It was not one of the monster 20 circuit ones but a smaller compact 6 or 8 circuit size I estimate.

At least you have the access and the practical option to reset the fuse if you have spares, but don't forget a plastic fuse puller / tweezers (probably steal one from your car). Those little buggers are hard to get out with finger-nails only.

So think about every independent fused circuit and if you can live with out it. If you can't, than have a way to reset the fuse/CB or power it alternatively.