• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Master Solenoid Sticking?

NunavutPA-12

FRIEND
67.8N,115.1W CYCO Canada
Intermittently, my master solenoid seems to "stick".

Turn on the Master switch - can hear the solenoid activate.
Turn the key - engine turns over to a compression stroke and stops.
No further power to the starter when the key is turned. No power to the avionics or anything else.
It appears that the solenoid is de-activated.
Master switch left ON and in about ten seconds, I can hear the solenoid activate again.
Engine will usually start normally at this point.

I have a feeling that the starter pulls enough current that the voltage to the solenoid drops to the point where it "opens". Then, as the voltage rises after a few seconds the solenoid "closes" again.

It looks to me as if the solenoid is defective and needs to be replaced. I have another on order - should get it in about three or four weeks ( !!! ).

Thoughts?
 
You have a bad cable connection. Check all battery and starter connectors and ring terminals starting at the battery ground cable, to the positive cable, then through the master relay to the start relay.

Web
 
Intermittently, my master solenoid seems to "stick".

At what point in the described test sequence do you think the solenoid is "stuck" and in what state do you think it is stuck? Sounds to me like it pulls in when it has enough voltage and drops out when it doesn't. A few simple test with a voltmeter should show where the problem is. I'd start with the voltage at the battery terminals then voltages at master solenoid input, output, and control terminals.

My money is on a bad battery. If it was a terminal the voltage would rise as soon as the start solenoid was released not be delayed by several seconds.
 
Last edited:
At what point in the described test sequence do you think the solenoid is "stuck" and in what state do you think it is stuck? Sounds to me like it pulls in when it has enough voltage and drops out when it doesn't. A few simple test with a voltmeter should show where the problem is. I'd start with the voltage at the battery terminals then voltages at master solenoid input, output, and control terminals.

My money is on a bad battery. If it was a terminal the voltage would rise as soon as the start solenoid was released not be delayed by several seconds.

It's a good idea to replace the switch when you replace the solenoid as well. Inexpensive part.
 
Or...install a dirt simple, no electrical drain if left on, mechanical master switch. Especially applicable if using a EarthX or similar near the firewall, with a short push for under the panel is how I have mine. Saved weight also. Exp only of course. Summit Racing has a good selection.
 
As for master switches, I usually just check out toggle switches. They seem to have a very long life, especially the mil-spec ones. Now the Cessna style rocker switches are a completely different story. Typical $1.50 switch sold for $35. Poor quality and not even remotely sealed. I've found bunches of them over the years that have caused intermittent operation or charging system issues. They seem to fail by developing resistance at the switch contacts instead of failing open or closed. So if you do much Cessna work, always check that switch for high resistance, on both poles of the switch. You'll be surprised how many you find with issues.

The mechanical master is not a bad idea. Not sure I'd use it on an aircraft with a charging system, but it's great for battery only systems, as Courierguy points out, due to not adding an extra current draw to the battery load. Any battery cutoff from an RV or race car will work well. The same rules apply for mechanical switches as master relays. Mount it as close to the positive battery terminal as possible, Keep the hot cable as short as possible, and keep the hot terminals covered.

And I'd sign a mechanical switch off as complying to CAR3 specs. No functional difference between a mechanical switch and the original Piper master switch wired directly to the battery.

Web
 
FWIW, my Commonwealth has a mechanical master as designed. Switch is right above the battery and is turned on by pulling a knob.

I chuckled a little when my mechanic said he thought the master was defective because he didn’t hear the solenoid click. But the Cutler-Hammer enclosed knife switch was working just fine.


Sent from my iPhone using SuperCub.Org
 
As luck would have it, when I got in the plane this morning, I noticed I had left the master on for about 40 hours. No problem! I have it about 8" from the EarthX, with a light pushrod going under the panel with a T handle. By swapping out my earlier old school Odyssey located in the tail, AND the old solenoid, it was amazing the amount of wiring, switches, large gauge cabling and terminal ends I tore out, best of all, now it's idiot proof.
 
Web,

I think you are spot-on about my master SWITCH being faulty. I had ordered a replacement (Cessna type) before reading your post about toggle switches.

I'd like to order a couple of toggle switches and replace the rocker switch at some point. I see that Aircraft Spruce has toggle switches - they vary widely in price and (I assume) in quality. Can you recommend a particular brand?
 
Back
Top