Master Relay is Hot

[jiott]

I have finished all the wiring and started testing today. I have two issues so far:

1. After about 15 minutes of being turned on, the master relay housing becomes hot to the touch, especially on the bottom. It gets to the point where you can only hold your finger on it for about 3 seconds, but does not seem to continue getting any hotter. During this time nothing much was drawing current on the panel; the radio was powered up but not transmitting. Whether the Skyview EFIS was on or not did not seem to make much difference. Is this normal, or should I be worried?
2. The intercom has a "stuck mic" that I am working on, but haven't found the cause yet. Seems to maybe be in the PTT wiring.

Jim

[Dorsal]

Probably the coil in the relay which I believe needs to dissipate around 10 W, this is independent of load. I don't think you need to worry, might check my own while at the hangar this weekend.

[jiott]

Thanks Dorsal. I will be very interested in how hot yours feels. You are right in that the relay coil is continuously powered, independent of any other loads. I'm just surprised at how warm it gets.

Jim

[jdmcbean]

Jim
Check the ptt button... And a close look at the shields... If even a single strand of the shield is soldered or crimped to the wire it will cause the stuck mic.

The relays tend to stay very warm.

[jiott]

Found my stuck mic problem. The cause is a heads up to anyone using the Kitfox supplied control stick PTT buttons! When you wire up the little microswitches you will notice that there are two small solder terminal tabs for each side of the switch. You only use one each, so the other two are extras that you bend out of the way or cut them off. What I did was bend them down toward the ID of the control column. Unknown to me they just barely touched the top of the aluminum column when the switch cap was pushed down into place, effectively grounding out both my pilot & co-pilot PTT switches, causing the stuck mic fault. After much agonizing and head scratching, the fix was easy-just bend those little tabs the opposite way toward the center of the column (or just cut them off).

Hopefully this will save someone some mysterious trouble.

Jim