How much does it cost to replace a fuse?

So about a month ago I had a failure of my 430 where I could not transmitt. Receive ok, but on transmitt, the tx light would come on but no one could hear me.

I tried everything (well obviously not). I stuck the 430 in a Bonanza and it worked. I ran new coax, new connectors, new thru tray bnc's, sent in audio panel for repair, rewired audio panel to comm. I spent a rediculas amount of time trying to find the problem.

It was with great dissappointment that I had to take a day out of work and fly the plane to Stark Avionics. I bought 2 planes worth of Avionics from them. I wired both myself and as a homebuilder, this was my last recourse and I absolutely HATE taking my plane to someone to work on.

I spent 5 hours there with 3 technitions. They hooked up every gismo they had. But in the end, they sent me home with no solution and a now broken 430. They inadvertentantly left a test pin in the tray and jammed up the pins when reinserting the unit.

A day later the chief technition called me and said. " Hey do you have a fuse on the comm circuit?"
"Ahh, yeah"
"Check it"
"Ahhh.. OK"

And low and behold, there is my 5 amp fuse blown. He said replace it with a 10 and I did and it now works.

So how much does it cost to replace a fuse?
1 RMA unit
$140 worth of "Troubleshooting time" for Stark
$.37 for the fuse

ARGH!!!!

hehe - been there done that

Bet, we know the *first* thing you'll check next time ...

Yell at me next time would ya. I've got about every piece of RF test gear known to man. Antenna checkers, spectrum analysers, SWR bridges, etc....Comes from being a Ham for over 20 years I guess

I'll be installing a 430 shortly. Does the manual call for a 5A fuse on that circuit? Just wondering if I need to watch for that.

Dave

430 indicators

Kahuna said:

...A day later the chief technition called me and said. " Hey do you have a fuse on the comm circuit?"
...
And low and behold, there is my 5 amp fuse blown. He said replace it with a 10 and I did and it now works. ...

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The 430 doesn't give an indication that it is not getting power on the comm circuit? That seems like it could use a design update.

A 5 amp was called out by stark when I Installed it.
I guess its 10 now.
5 amp made it 200 hours
Looking at the specs, page 1-3 rev L of the 400 series manual, it is 6amps at 13.75 volts when transmitting. So there you go.

And no there is no way of knowing. There are multiple power inputs for the nav and com on a 430 for redundancy. It looks and feels like it is working if the com fuse is out.

I've had an occasional problem with my starter circuit. I get in, flip the switch, and NADA. I then think it's a wiring problem, battery problem, etc. After tearing into the aft battery deck twice now, I've learned to check the starter fuse first because it was the problem both times.

I've learned my lesson so I can identify with you.

Bummer..

william weesner said:

makes me wonder what the rush in current is.

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In rush currents don't usually apply to solid state circuits, they are generally the product of incadecent lamps and motors start ups.

Now that's what I call a slow-burn fuse. 200 hours! I expect it uses just a tiny bit over 5 amps, and they round it up to 6.

Of Course.....

.....if you'd a circuit breaker instead of a fuse, you'd have seen it popped on the next preflight...right?

Paul rolls and ducks for cover....

fuse vs. CB

Ironflight said:

.....if you'd a circuit breaker instead of a fuse, you'd have seen it popped on the next preflight...right?

Paul rolls and ducks for cover....

Click to expand...

I think I'm going to rip out all my fuses and replace them with CBs - not!

Kahuna said:

A 5 amp was called out by stark when I Installed it.
I guess its 10 now.
5 amp made it 200 hours
Looking at the specs, page 1-3 rev L of the 400 series manual, it is 6amps at 13.75 volts when transmitting. So there you go.

And no there is no way of knowing. There are multiple power inputs for the nav and com on a 430 for redundancy. It looks and feels like it is working if the com fuse is out.

Click to expand...

Mike,
I admire your guts for even admitting this tale on list. I just want to remind you that the 10 amp fuse requires heavier gauge wire than the 20AWG required for a 5 amp load. You need 16AWG wire to ensure that a short in the radio will blow the fuse before the wire heats up to the point where it catches fire. Did you upgrade the power wire when you upgraded the fuse? Perhaps all you really need is a 7.5 amp fuse? (18AWG)
Charlie Kuss

FYI...we're going to start stocking some really neato blade fuses that have a little light built onto the top of them that illuminate only when the fuse is blown. We have some, but not all the amperages yet (hence them not being on the website yet), but when we do they'll be available on our website. If you're at OHS, stop by our booth and you can see what some of them look like (before and after they've been blown). They light up really nice and bright after the fuse blows to let you easily see when one is popped!

Cheers,
Stein.

RV6's, Minneapolis.

SteinAir said:

They light up really nice and bright after the fuse blows to let you easily see when one is popped!

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Sounds cool! How do they work? Does the heat of the fuse burning change the color of a dye or is it electric?

If electric, where do they get their path to ground? Does it rely on a small amount of trickle through the nominally disconnected circuit?

Just curious...

20 gage wire and a 10 amp fuse

chaskuss said:

10 amp fuse requires heavier gauge wire than the 20AWG required for a 5 amp load. You need 16AWG wire to ensure that a short in the radio will blow the fuse before the wire heats up to the point where it catches fire. Did you upgrade the power wire when you upgraded the fuse? Perhaps all you really need is a 7.5 amp fuse? (18AWG) Charlie Kuss

Click to expand...

I agree a 7.5 amp would be a nice choice.

I do agree 20 awg and 10 amp fues would not be my choice. The FAA best practice "AC" also agrees with what you are saying, calling for a max 7.5 amp circuit breaker or 5 amp fuse with a 20 awg wire. However......... it is "Best Practices" and there is some margin there.

A 20 awg wire is rated at ultimate or max chassis current rating is 11 amps (short length, not in large bundled) and fusing current is approx 58 amps! (By short length lets say about 6 feet, and large bundle is one where you can't see all the wires easily.)

A 20 awg wire can carry 11 amps without worry of fire. Lets say you ran a 9.9 amps continuous current, and the fuse does not open. The wire would get to 48F degrees above ambient (let's say 120F-140F). That's HOT but still not unsafe. The voltage drop is about 0.61 volts. That's beyond my design criteria for any one's comfort, but we are talking about an inadvertent short, not intentional power transmission.

I do agree 7.5 amps would be best, more comfortable. All my 20 awg wires are protected with 5 amps or less.

So I agree, but to say you must increase the gage is a design decision and not an absolute must. However I am with you, 18 awg is plenty for 10 amp fuse for under the panel wiring. You suggest 16 awg, but that's overkill in my opinion unless the run is real long. Cheers Big CK

Yes it was a 7.5 that I put in.
The wire is an 18ga for 8"