Blew a 3A Fuse duing engine testing

[Jeff_R]

I have been running a dual SV1000 for a while on the ground in prep for a first flight. We were adjusting the idle and mixture settings, and during an enginer start, the pilot-side SV died. At first I thought the backbattery had died, but later confirmed it wasn't - if blue a fuse. That EFIS is powered alone from a 3 amp automotive fuse, which seemed to have exhibited a fast, high energy failue. I have started this engine dozens of time and never had a problem.

The backup battery for the copilot's EFIS has always been defective and we just recieved a replacement, but it was not installed, so that EFIS dies every time we do an engine start.

We used the Dynon cables for the wiring. I replaced the fuse and it powered up again, but we did no more engine testing. We run a PMAG for starting and there was no engine kickbacks or signs of anything that could have generated a voltage or current spike. I don't know how to download the Dynon data to see if that might reveal an issue in the making.

I presume the SV has internal TransZorbs for protection, but wonder that it might have been to cause the overload. Well, transzorbs will fail with a short, so I guess they would be ok. There was burning around the vaporized portion of the fuse wire, so I have to believe there was significant current event.

Any ideas? And how do you down load the data log???

Thanks!

 

[dynonsupport]

Page 2-1 of the install manual lists the consumption of a screen at 3.5A and page 4-7 says to use a 5A fuse. So blowing a 3A fuse is totally expected.

It will blow when you start the engine because the voltage drops, and thus the current goes up. Devices like SkyView have complex power supplies in them that draw constant wattage. Watts are volts x amps, so when you drop one the other must go up.

SkyView's power supplies are designed to DO-160, and for 28V airplanes, which requires 60V tolerance during engine start. The power supply is much more complex than a transorb trying to absorb the overvoltage, and as mentioned above, the current actually goes down as the voltage goes up. So I'm 99% sure the only issue was that your voltage dropped during engine start and blew the undersized fuse.

There currently is no user accessible datalog inside SkyView. We're working on it and it will be in a software update in the near future.

 

[airguy]

Page 2-1 of the install manual lists the consumption of a screen at 3.5A and page 4-7 says to use a 5A fuse. So blowing a 3A fuse is totally expected.

D'oh! RTFM strikes again...

 

[Jeff_R]

Boy, do I feel stupid. Old age setting in.

Other than embarassing myself, I am glad the solution is so simple, and glad that it was discovered before the plane took to the air!

D'oh for sure!

 

[DennisW]

I am personally opposed to the use of fuses in aircraft and intend to change mine all to breakers. What does Dynon Support think about this?

 

[dynonsupport]

We have no opinion on the use of fuses versus breakers. Either works fine with our products as long as they are appropriately sized.

 

[mmarien]

In my understanding fuses, breakers and solid state devices like VP-X all do the same thing. They protect the wire from over current. If the current is to much for the wire the protection device will open the circuit. The myth is that you can reset it once. However, if you think the problem is going to fix itself between the time it blows and when you reset it then you have a lot more faith in the self healing properties of inanimate objects than I do.

IMHO the best thing to do is fly it back to where you can get it fixed before you reset it and start a fire. With that in mind fuses appear to be a superior protection device in that they can't be reset.