Garmin GSA 28 blows fuse for Ray Allen Trim Servos

[Rough surface]

With the G3X auto pilot off my Ray Allen trim servos operate normally with the 4 way hat on the pilot stick. I have a single toggle switch to power the Garmin GSA 28 servos and as soon as power comes on for the servos it pops the fuse for the trim servos. My system calls for a 1 amp fuse for both pitch and roll trim servos (same circuit). I have put a 4 amp fuse in place and it still immediately trips the fuse when the servos are powered up. I have a G3X with GFC 507 controller, new system not yet flown.

I have pinned out all connections and the wiring is good. With the GSA 28’s off (no power) the Ray Allen trim systems operates normally. This confirms the wiring, in my mind. Is there a spike when the GSA 28’s see power that trios the fuse? Autopilot also works and checks fine but won’t auto trim because the trim motors are disabled with the blown fuse.

The relays are not required because I do not have the trims wired to the co-pilot stick. Just one stick is in control. RA stick grip is the G307, wiring attached below

RV-8A

[mulde35d]

The Ray Allen Trim servo's have an average amperage pull of 0.2 with a max amperage pull of 0.2.
The GMC 507 has an average amp pull of 0.1 with a max of 0.1.
The GSA 28's each have an average amp pull of 0.4 with a max of 2.8 each.

I had 3 GSA 28 autopilot servo's feeding off the same 7.5 Amp breaker with 20 AWG wire running to each of them (and back to ground).

Remember, the breaker is to protect the wire not the component. It sounds like you may have a short somewhere and the breaker is protecting your wiring. But difficult to diagnose without a multimeter and your electrical drawing diagrams.

[DennisRhodes]

Is this a new power up panel or one thats been in service for a while operational? May help in troubleshooting. Sounds like gound and power between the two devises may have got rolled somehow. Maybe confirm with VOM that 12 vdc is on correct terminals and polarity correct. Without diagram, hard to diganose, but best of luck in the process.

[BobTurner]

+1. Need wiring diagram. You cannot simply parallel existing trim wiring (including hat switch) and autopilot trim commands, without asking for trouble.

[DennisRhodes]

Keep in mind the RayAllen servo system by design swaps ground and power to reverse the direction of the DC servo motor. To tie that AP system in to that may require some isolation relays to keep the systems electrically separated.

[Rough surface]

Originally Posted by DennisRhodes

Is this a new power up panel or one thats been in service for a while operational? May help in troubleshooting. Sounds like gound and power between the two devises may have got rolled somehow. Maybe confirm with VOM that 12 vdc is on correct terminals and polarity correct. Without diagram, hard to diganose, but best of luck in the process.

It is new system, has not been flown yet, just finishing the build

[Rough surface]

Originally Posted by BobTurner

+1. Need wiring diagram. You cannot simply parallel existing trim wiring (including hat switch) and autopilot trim commands, without asking for trouble.

Schematics attached above for your reference
Thanks

[Longez]

Rough surface,

You will want to review page 27-12 of the Rev. AP G3X Touch Installation Manual.



The trim logic of the G3X Touch system requires that the input pins (11,12) on the GSA 28 servos see +12V on one pin and GND on the other pin for one trim direction, and the reverse of this logic for trim in the other direction. This is done for safety reasons to prevent a simple failure of the trim switching from causing a trim run-away.

According to your wiring diagrams, your installation is simply applying +12V to pin 11 in one direction and applying +12V to pin 12 in the other direction.

If you don't have a GAD 27, you will need to add a simple relay deck (which provides separate pitch/roll control) that is actuated by your stick grip switches to create the required drive logic with your existing stick grip.

Update: Looking at the Ray Allen wiring diagram for the G207 stick grip, it seems possible to use that stick grip without a relay deck. You should probably re-check your wiring against the RA diagram.

If properly wired, there is no reason that applying servo power would cause the fuse providing power to the stick grip to blow. The stick grip shouldn't even be outputting a power signal until one of the trim switches is pressed. When servo power is applied, the bypass relay inside the servo opens, and the trim inputs on pins 11,12 are no longer directly connected to the trim motor outputs on pins 13,14.

I wouldn't increase the size of the stick grip fuse above what the manufacturer recommends. This could damage the stick grip and perhaps other system components.

I would do some basic trouble shooting with a meter and the power off to find the wiring path that is shorted to ground. You can also unplug both servos, and plug them back in one at a time to further isolate the wiring problem. According to your wiring diagrams, you have an unusually large number of connectors in your system, which adds to the complexity.

Steve

[Rough surface]

Originally Posted by Longez

Rough surface,

You will want to review page 27-12 of the Rev. AP G3X Touch Installation Manual.

Attachment 19891

The trim logic of the G3X Touch system requires that the input pins (11,12) on the GSA 28 servos see +12V on one pin and GND on the other pin for one trim direction, and the reverse of this logic for trim in the other direction. This is done for safety reasons to prevent a simple failure of the trim switching from causing a trim run-away.

According to your wiring diagrams, your installation is simply applying +12V to pin 11 in one direction and applying +12V to pin 12 in the other direction.

If you don't have a GAD 27, you will need to add a simple relay deck (which provides separate pitch/roll control) that is actuated by your stick grip switches to create the required drive logic with your existing stick grip.

Update: Looking at the Ray Allen wiring diagram for the G207 stick grip, it seems possible to use that stick grip without a relay deck. You should probably re-check your wiring against the RA diagram.

If properly wired, there is no reason that applying servo power would cause the fuse providing power to the stick grip to blow. The stick grip shouldn't even be outputting a power signal until one of the trim switches is pressed. When servo power is applied, the bypass relay inside the servo opens, and the trim inputs on pins 11,12 are no longer directly connected to the trim motor outputs on pins 13,14.

I wouldn't increase the size of the stick grip fuse above what the manufacturer recommends. This could damage the stick grip and perhaps other system components.

I would do some basic trouble shooting with a meter and the power off to find the wiring path that is shorted to ground. You can also unplug both servos, and plug them back in one at a time to further isolate the wiring problem. According to your wiring diagrams, you have an unusually large number of connectors in your system, which adds to the complexity.

Steve

Thanks Steve, I have NOT checked the stick yet but that's because the trim works with no problems without the A/P powered. I am going to the hangar right now to check the stick just to be sure. I have a CPC connector at the base of the stick and if that is disconnected the fuse does not blow but I have no trim power either. I have already isolated each trim motor from the system in separate tests and that did NOT solve the issue. Even when both trims are out of the system the fuse blows so the stick needs to be check for sure.

[Laird]

I'm just curious but why put the servos on a separate switch?