UnPossible

UnPossible

Well Known Member
Hey ? at the airport working on getting my RV-7A airworthy and ran across something a bit strange this evening. Earlier I pulled my plane out of the hanger away from the buildings to do some magnetometer calibration of the G3X system.

Once I finished with the calibration, I decided to try the starter motor for the first time, as I recently hooked up the wiring for the starter motor. One of the things that Aerosport power recommends before first engine run is to remove the lower plugs and hit the starter for several seconds to blow out any remaining preservative oil?. Well with the starter hooked up, and the lower plugs removed, I decided to try the starter motor?. All looked good, prop turned, no electrical smoke, etc. Not sure if this is anyway related to the problem below, but wanted to include it just in case.

Once I ran the starter motor a couple of times, for a few seconds each time, I shut off all the electronics and killed the master switch to tow the plane back to the hanger?. However, when I killed the master switch, nothing happened. My position lights and G3X screens (which are wired to the master) stayed on. No matter what I did, I could not get the master to switch the main power off.

I ran to the hanger for a 10mm socket and wrench and disconnected the battery, which did the trick. Once back in the hanger, I reconnected the ground and the lights and G3X screens came back up?. weird. I grabbed my multimeter and went to work playing Jr. Electronics detective.

My first step was to check the master switch? with the battery disconnected, the resistance to ground across the switch went from infinite, to a fraction of an ohm depending on the position- which is what I would expect to see.

Now with the battery reconnected, and my Nav lights on to see if I was getting system power, I removed the lead wire from the small terminal on the front of the master solenoid that goes to the master switch?nothing happened. The master stayed engaged. Please correct me if I am wrong, but unless this post is grounded, the master solenoid should be off. I am assuming that for whatever reason my master solenoid died an early death.

Please let me know if I am missing anything or if there are any other reasons for the system to not want to shut off. (BTW ? I have been using the master switch for a few months now and it has worked fine up until now? I haven?t made any recent changes to the electrical system that I can think of that might possibly be related to the master solenoid/switch).

Thanks,
Jason
 
It sounds like the solenoid is stuck closed. I could be wrong, of course. I know that whenever I engage mine you hear that solid "thunk" when the electromagnet closes the switch. Is it possible that it's getting powered from somewhere else? If it were mine, I'd probably put my voltmeter on the small solenoid leads to see if they have a voltage. I haven't looked at my wiring schematic in ages, but I think you should not be reading anything there...makes sense, no? If you are, then something is energizing it.

Thinking about this further, if you have no other power source and you remove your battery from the circuit, you should hear that "thunk" when the solenoid is de-energized. If not, then I'd guess it's stuck closed. It's mechanical internally, and I'm not sure if tapping on it gently will free anything up. May be worth a try.

I suppose you could also check for continuity through the solenoid with the battery disconnected. That'll tell you if it's closed or open.
 
Sounds like contact points fused together under amperage load from starter.

Possible A. Master sol not rated for amperage load

B. Low battery voltage from earlier battery use caused high amp draw from starter and master contact points weakest link.

Either way...replace unit even if releases.

Thanks
Jack
 
Do you have your master solenoid handling the current from your starter motor?

We had a plane down here not too long ago who hooked his amp meter in series with his starter...and wondered why it went off-scale high with lots of smoke when he cranked the donk.
 
Its stuck. Disconnect 2 big wires and little wire. Ohmeter across big posts and you will see continuity/low ohms. If so, replace it. Once points have welded they are undependable. Even if you whack it and they release, the points are degraded and will let you down.
 
It's easy to rotate the big terminals when tightening them. When you do so, the contactor won't work as it is supposed to. So replace the contactor and be careful not to rotate the big (or small) lugs.
 
Thanks for all the suggestions.... I'm going to run down to the hanger over lunch and test the resistance across the main terminals.... guessing I won't find much.

Fortunately, this the master solenoid is only $20 or so to replace.

Is there anything special about the master solenoid Vans sells? I need to order some additional stuff from ACS and just figured that I'd order the replacement from them.

Thanks,
Jason
 
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UnPossible said:
Is there anything special about the master solenoid Vans sells? I need to order some additional stuff from ACS and just figured that I'd order the replacement from them.
Click to expand...

They're pretty much the same parts as far as I could tell. The ACS one has plastic thingys over the mounting feet, I presume to dampen vibrations, but they work just the same.
 
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