What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Solenoid testing

If it's a master solenoid, one of the large terminals will be marked BAT
Using some wire and a 12 volt source, (assuming this is for a 12v system) such as a battery, apply 12v plus to this terminal
Touch the negative to the small terminal on the front of the solenoid.
If it clicks when the ground is applied, it is at least opening and closing the circuit.
To test voltage flow, use a volt ohm meter to measure from the other large terminal to the ground of the power source when the solenoid is closed.

On a solenoid with two small terminals on front, first verify the two small terminals are not wired to a main terminal, then apply the 12v plus to one of the small terminals and negative to the other small terminal and it should click closed same as above.
 
TShort said:
Is there a way to bench test a master solenoid?
Click to expand...

Yes.

I?ve found master solenoids with intermittent high resistance across the main contacts. Easy way to check is remove it to the bench, connect a good digital ohm meter across the big terminals, and repeatedly power the coil terminals with a battery. A good solenoid will be the same nil ohms every time. Any variation in ohms makes it a throwaway.
 
Above will tell you if the coil is good, and if the plunger moves when the coil is powered.

It won't tell you whether the contacts will pass the rated current of the contactor. To tell that, you'd need to apply the rated load, and either measure current, or measure voltage drop across the large terminals while the load is applied. (Should be down in the 'noise' range of the measurement circuit; a couple of tenths of a volt on a typical digital meter.)
 
DanH said:
Yes.

I?ve found master solenoids with intermittent high resistance across the main contacts. Easy way to check is remove it to the bench, connect a good digital ohm meter across the big terminals, and repeatedly power the coil terminals with a battery. A good solenoid will be the same nil ohms every time. Any variation in ohms makes it a throwaway.
Click to expand...

Thanks.

In the last 16 hours, I've had two separate total electrical failures. Volts drop off to nothing, and the power comes on and off.

The most recent event was over KS, enroute from KIDP -> KAEJ, and occurred right when I hit a pretty good thermal bump.

I replaced the master solenoid prior to the flight home, and it was uneventful.

As the issue is quite intermittent and unpredictable (first event was in clear smooth air), I'd like to test the old solenoid and get an idea if it is the issue. As it stands, leaving the home base area makes me a little nervous since the issue isn't 100% clear.
 
TShort said:
In the last 16 hours, I've had two separate total electrical failures. Volts drop off to nothing, and the power comes on and off.

The most recent event was over KS, enroute from KIDP -> KAEJ, and occurred right when I hit a pretty good thermal bump.

I replaced the master solenoid prior to the flight home, and it was uneventful.

As the issue is quite intermittent and unpredictable (first event was in clear smooth air), I'd like to test the old solenoid and get an idea if it is the issue. As it stands, leaving the home base area makes me a little nervous since the issue isn't 100% clear.
Click to expand...

Variable resistance across the main contacts creates an unpredictable cranking problem. You're describing an entirely different issue, one not likely to involve a main contact. Could be as simple as an intermittent open in the coil path to ground.

Good luck. Nobody likes an intermittent problem; it's hard to find if it won't stay broken.
 
Interesting, thanks Dan.

So what you are saying is that the resistance is intermittently high with repeated activation of the solenoid, not intermittently high while the solenoid is activated / power is flowing. Which I guess makes sense, unless the solenoid moved (which was my thought as the second episode occurred during turbulence).

The wire to the master switch and solenoid is good at both ends; finding an intermittent open between the ends (if that's the issue) is going to require some disassembly.

It definitely won't stay broken, which makes finding the issue difficult.
 
It's mounted on an airframe powered by a Lyc. It's *always* shaking if the motor's running. Same thing applies to the master switch, and every connection related to the control circuit, and the power circuit, on both the supply side, and ground return side.

Any contact point anywhere in the system that has corrosion, or isn't properly tightened, is subject to vibration-induced intermittent interruptions.
 
TShort said:
Thanks.

In the last 16 hours, I've had two separate total electrical failures. Volts drop off to nothing, and the power comes on and off.

The most recent event was over KS, enroute from KIDP -> KAEJ, and occurred right when I hit a pretty good thermal bump.

I replaced the master solenoid prior to the flight home, and it was uneventful.

As the issue is quite intermittent and unpredictable (first event was in clear smooth air), I'd like to test the old solenoid and get an idea if it is the issue. As it stands, leaving the home base area makes me a little nervous since the issue isn't 100% clear.
Click to expand...

Good example of a single component failure resulting in total loss of power. Components will always fail. Proper design assumes this and provides redancancy so total power loss will not be the outcome.

Carl
 
TShort said:
So what you are saying is that the resistance is intermittently high with repeated activation of the solenoid, not intermittently high while the solenoid is activated / power is flowing.
Click to expand...

Correct.

I've had two separate total electrical failures. Volts drop off to nothing, and the power comes on and off.
Click to expand...

Thomas, it is very difficult to correctly diagnose an electrical problem without a wiring diagram for that particular aircraft, as well as some knowledge of component choices. There are many wiring variations out there.

That said, the above description doesn't suggest a solenoid problem. In general, a master solenoid drop-out would disconnect the battery, but the alternator would have continued to supply power. If I am understanding the quote correctly, you should be looking at crimps and connections which can disconnect both battery and alternator.

Is the main bus supplied power via a large wire (a #8 perhaps) from the battery-side big terminal on the start solenoid?
 
Last edited:
You must log in or register to reply here.
Back
Top