A

A5555

Well Known Member
What is an acceptable method to add a small diode (IN4007 or similar) to a wire. Is it acceptable to simply solder the diode to the wire in-line and cover with shrink wrap or is this a failure point? thanks, Steve
 
It depends. Diodes can get hot is the danger.

I've put diodes on a terminal block and on a prototype circuit board in a electrical box.
 
One important item is to make the heat-shrunk component a part of a wire bundle for support.

Don't have it in a single floating wire...
 
Heat

Recently I tested some similar diodes (15amp i think versus your 10amp). With an 8amp load at 12V DC it got to 120-140 deg F.

Also, I note that Bob's recommendation that Joe linked (thanks Joe!) indicates 1-3amp diodes. I like his approach of using a dsub connector and hood. Pretty slick.
 
thanks

thanks for the instructions

the diodes I plan to use are 1 amp for duplicate trim switch, infinity grip switch and panel switch; and 3 amp for duplicate flap switch, infinity grip switch and panel switch

Steve
 
Steve,

It sounds like you are planning to make a "diode OR" logic function. While this may make sense it may not be required. You only need a diode or if the switched lines will take on the multiple voltages. For example +12V and ground. If on the other hand you have open and switched to ground as the two conditions then you can connect the switches in parallel without the need for the isolation diode. I would need to see a sketch of what you plan to do to confirm the need for the diodes.

Personally if you do indeed need the diodes I would probably use a terminal strip and crimp/solder one lead of the diode to a crimp lug and then solder a wire to the other end. Use the terminal strip jumpers to tie the outputs together. Then if you need to break the connection to test each input it will be very easy to do.
 
here's the Ray Allen instruction for 2 trim switches

I admit I am stumbling along on this one. For elevator trim I have one infinity grip with Pat Hatch relay board and a separate trim relay switch on the panel. My thought was if I need to disable the infinity stick I can use the trim switch on the panel or the co-pilot can use it. Wiring diagram from Ray Allen is linked. He calls for diodes. Is this a reasonable approach?

http://www.rayallencompany.com/RACmedia/instructions2rs2.pdf

After looking at this more I see I may have a basic flaw. If I need to disable the infinity grip by pulling the breaker for the relay board I will loose both the trim control on the stick and the panel. I could use two relay boards, one for the stick and the other for the panel switches, but is it acceptable to have one servo controlled by two separate relays. What if both are pressed at the same time.... now this is getting complicated.
 
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First off, I don't see the need for diodes. Take a look at this aeroelectric circuit:

http://www.aeroelectric.com/articles/flaps.pdf

Yes, I know it says flaps, but the same thing works for trim (just eliminate the limit switches).

Second, if you really want redundancy, you could use a DP3T switch like this:
http://www.mouser.com/ProductDetail/NKK-Switches/M2046SS1W01-RO/?qs=sGAEpiMZZMvudeGI7i40XL4zZIJnfTMJO5CdeMklpQ8%3d

Wire it as depicted below:


1etoba.jpg


To be honest I've only seen one other plane where the owner was concerned with this. He wired in a reversing switch, with the thought that if one relay was stuck, he could reverse his trim to get it back into limits before cutting it out. You couldn't pay me enough to put a reversing switch in a trim system.

I have two trim relays, an easily accessible circuit breaker, and two trim switches wired in parallel without diodes (ok, reverse connected "catch" diodes across the relay coils, but they're just there to keep the switch contacts from arcing).

Paige
 
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Steve,

I haven't gotten to the trim servos yet so I'm trying to look at all of the details. I would need to see how the relay deck is configured.

I think I understand what is going on though in a general sense from looking at the Ray Allen schematic. Someone can pipe in to help us out.

Each of the trim switches is an ON-OFF-ON switch so normally each of the inputs into the relay deck is open. When the trim switch is pressed one on the relay deck inputs will be pulled low. One of the relays is then energized. The relays control the direction of the applied voltage to the servo motor. One, two or more switches can be connected in parallel. While diodes are shown in the Rayallen schematic I'm not sure of their purpose.

As far as I can tell without the relay deck schematic there is nothing to prevent both inputs from being activated by two switches being pushed in different directions. This may just be handled by Pilot in Command procedure not sure without more relay deck info.
 
The whole point of the relay logic is to prevent the "two switches simultaneously pushed in opposite directions" problem, which would otherwise result in blown fuses or CBs. One of the switches will have priority over the other.
 
BobTurner said:
The whole point of the relay logic is to prevent the "two switches simultaneously pushed in opposite directions" problem, which would otherwise result in blown fuses or CBs. One of the switches will have priority over the other.
Click to expand...

Bob,

If you look at the aeroelectric circuit that I posted the link for, you'll see that it is taken care of by the relays themselves. You have an up relay, and a down relay. If both are actuated at the same time, you connect +12V to both sides of the motor...result no voltage difference, and it doesn't move.

Edit: I found the answer to the RAC switch diode mystery here: http://www.rayallencompany.com/RACmedia/instructionsRS2withmods.pdf

So apparently when the RAC switch is centered, the two white wires are connected together-- hence the need for the diodes. The other option is to modify the switch as depicted above.

If you're not using their switch, no need for diodes.

Paige

BTW, I love how they have you connect the red switch wire to ground.
 
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The VP-X should solve these problems because:
- no relays, all solid state (trim and flaps)
- pilot and co-pilot switches are wired directly into the VP-X
- pressing both up/down (conflicting) switches stops the trim motor right away
- holding both down disables the switches
- you can then run the trim from the EFIS screen as a backup

The install manual is up on our web site http://verticalpower.com/documents/ if you want to see if that works for you.
 
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