J

jet

Member
The second 2 amp trim fuse blew today during flight. Aircraft has 30 hrs total time. Wondering if others have experience this. Trim works fine and travel times okay when working. Could voltage spikes on each actuation slowly deteriorate the fuse to the breaking point? Would it be feasible and acceptable to install a larger fuse such as a 3 amp? Have done a search on the subject and unable to fine anything.

John s/n 317
 
Wire shorting to ground?

Does the fuse blow only when you are pushing the trim switch or does it blow even if you are not pushing the switch? If it blows when you are not pushing the switch, then I would expect an electronic problem with the control board. If the fuse blows only when you push the trim switch, then I would suspect the wiring going to the servo. Try to figure out exactly when the fuse blows, like trimming down or trimming up. The cable passes over a sharp edge way back in the tail. A wire could be shorting to ground. This could be checked out with an ohmmeter at the trim servo power wires: white wire and white/red wire. If this is an intermittent problem, then it will be hard to troubleshoot.
Ray Allen says the servo uses 0.15 amps at no load. They have no way of knowing what the current will be under load because that depends on the installation and mechanics and lubrication and etc. Since nobody else has posted about this problem, it makes me think that a 2 amp fuse should carry the load. Usually it is not recommended to replace a fuse with a larger size. I would only do that as a last resort, even though the wires should be able to easily carry 3 amps without over heating.
It is extremely unlikely that a voltage spike is causing the fuse to blow. If there were an over-voltage condition, the Dynon would alarm.
Joe
 
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Our tests show the servo draws about 0.5 amps max under load.

Sounds like there is something intermittent that is shorting. Don't forget the motor wires can also short to each other - one is ground and one is power depending on the motor travel.
 
Blown Fuse

If it makes you feel any better I had a Trim fuse blow also. That was about 35hours ago. Have no idea why.:confused: I do remember monkeying with the trim quite a bit that day while in auto pilot cruise. Noticed it blown when trying to trim for landing.

Gary
 
Gary,

That was my condition as well. I was pulsing the trim while in autopilot cruise - hdg and alt hold - to see when the out of trim alert would show up on the Dynon when the fuse went. On the ground I noted that my trim acuator times stop to stop had increase to 31 and 33 seconds - probably set wrong originally - so I reset it to the lower end at 25 seconds but hesitate to think this had anything to do with it.

John s/n 120317
 
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