My Maule eats solenoids!

Ben Jaensch · Post by **Ben Jaensch** » Tue Jun 10, 2008 10:07 pm

G'day

If anyone can suggest what's behind this I'd be grateful.

Newly acquired M5-235C, based just outside Melbourne, Australia.

No response to main batt switch, all wires connected ok, battery charge good and healthy. Replaced solenoid from the tail, mounted on frame close to battery. All good, a great day's flying.

Six days later zero response to the batt master switch again! Seems unlikely that the new solenoid died of natural causes in that time, and once again the battery is well charged. Is there a fault that could be killing solenoids? My understanding is that they are very simple components.

Cheers

Ben

a64pilot · Post by **a64pilot** » Wed Jun 11, 2008 3:06 pm

They are simple components. Check to make sure it has a good low resistance ground. If the grounds good, I bet you just got a bad one.

belandd · Post by **belandd** » Sat Jun 14, 2008 9:28 pm

I had solenoid fail also. Make sure you are buying a "continuous duty " solenoid for your replacement. Not a "intermitent duty (starter)" solenoid.

they look the same but only the continuous duty unit will last.

Ben Jaensch · Post by **Ben Jaensch** » Tue Jun 17, 2008 8:54 am

G'day again

Thanks guys.

a64pilot, I'm not sure of the meaning of a "good low resistance ground" or how I would check that.

It has been suggested that there is a leakage to ground/earth through the master switch but I guess that would drain the battery, which is not happening.

belandd, I'm guessing that by using a replacement solenoid with the same part number I missed the trap of using an intermittent use device in a continuous use application. So it's probably not that simple a problem, unfortunately.

belandd · Post by **belandd** » Tue Jun 17, 2008 10:01 am

check the p/n to be sure it is correct installation

Trust but Verify!

a64pilot · Post by **a64pilot** » Wed Jun 18, 2008 3:30 pm

You check the path to ground with a multi-meter set to Ohms. High Ohm reading = high resistance and high resistance = heat.
Two kinds of wire in an electric heater, the low resistance wire carries the power to the high resistance heating element, but does not get hot because it does not resist current flow, the heating element does because it resists current flow.
If you don't have a "good" ground then the solenoid will get hot due to high resistance.
Beland is absolutely correct about intermittant duty solenoids, they have a duty cycle of so many minutes on followed by so many minutes off. Exceed that cycle and the coil will overheat and burn up resulting in an open circuit. "continous" duty solenoids have no duty cycle, but can't carry as much current as say a starter solenoid which has a duty cycle.

silvaire · Post by **silvaire** » Thu Jul 10, 2008 12:45 am

a64pilot wrote: Beland is absolutely correct about intermittant duty solenoids, they have a duty cycle of so many minutes on followed by so many minutes off. Exceed that cycle and the coil will overheat and burn up resulting in an open circuit. "continous" duty solenoids have no duty cycle, but can't carry as much current as say a starter solenoid which has a duty cycle.

Not exactly true because the current for the starter motor has to pass through the master relay as well as the starter relay (both relays are in series). In fact The starter relay needs only to carry the current required for the starter motor whereas the master relay must carry the starter motor current plus the current to run everything else on the aircraft at the same time (everything goes through the master)

The difference is in the action of the relays. The master relay (or continuous use relay) has a hard pull in/easy hold and the action is slower so it is not suitable as a starter relay because the slow action will allow arching across the contacts as it is closing. An intermittent duty solenoid has a fast action with easy pull in and a fast release to minimize arching across the contacts. It requires more power to actuate and hold in the closed position because the opposing spring forces are greater in order to minimize the action time when it is released.

As for checking the wiring. Check the ground under the panel on the other side of the master switch. Also check the master switch itself. You can bypass it by grounding the wire from the relay. You can also test the relay by grounding the switch side terminal right at the relay. Don't ground the battery side terminal or you will be arch welding with your jumper wire!

210TC · Post by **210TC** » Thu Jul 10, 2008 12:49 pm

I learned something today. Now for the other 364 days?

a64pilot · Post by **a64pilot** » Thu Jul 10, 2008 5:38 pm

Silvaire,
Your right of course, the starter solenoid has to pull it's current through the master.

a64pilot · Post by **a64pilot** » Mon Jul 21, 2008 9:45 am

OK,
Had me going for a little while. Any electrical "user" on an aircraft electrical buss will have to pull it's power through the master solenoid. So of course the master solenoid has to have the capacity to handle all of the loads that can be placed on it.
That's got nothing to do with continous or intermittant duty though. It's the electromagnet or "coil" in the solenoid that will over heat in an intermittant use solenoid if it is tried to be used continously. It's got nothing to do with the amount of current that does or does not pass through it.
Belandd is correct. If you try to use a starter solenoid as a master, you'll be replacing them regularly.

My Maule eats solenoids!

My Maule eats solenoids!

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