Master Solenoid Replacement - Wiring Question

[Z W]

The master solenoid has failed on my 1982 M20K.  When the master switch is turned on, the panel stays dark and the solenoid just clicks repeatedly for a while, then stops.  I was able to get it to kick on while connected to external power at 14v, but as soon as external power was removed, the solenoid went back to a failed state and clicked repeatedly, then stopped.  This solenoid is bolted to the side of the battery box in the tail.

The parts manual says it is a 6041-H-105A, which matches the one that came out of the plane.  That item is no longer available anywhere I can find, except used salvage items.

I've obtained a SkyTec 12V-STS-M12 FAA/PMA replacement solenoid.  I thought this would be a simple swap.  However, the old solenoid had a strange jumper wire running between the switch poles of the solenoid.  It's marked with a "F" flag and has some kind of resistor in it (pic below).  I don't understand what it does and I can't find any wiring schematics for the old solenoid.  I also can't find any wiring diagrams or schematics in the parts manual or service manual for the plane.

If I understand how the new solenoid works, and I think I do, I wouldn't expect this jumper wire to be necessary, and expect it might even prevent it from working.  Can anybody tell me what it does, and whether it should be re-installed on the new solenoid?  I've found some poorly done wiring back there behind the battery that I am cleaning up and taking care of, so I'm questioning what I'm seeing before I put it all back like it was.

Thanks in advance.

 

[PT20J]

The "jumper" wire is a flyback diode to quench the EMF created when current is removed from the coil and the magnetic field collapses. It's polarity is important.

Your description of the symptoms sounds more like a weak battery than a solenoid. 

Skip

[Z W]

Thank you.  Had never heard of that, learned something today.  I'll put it back on just like it was.

The battery is 1.5 years old and was sitting on a maintenance charger, but I'll keep that in mind as well.  I guess it could be bad.

[LANCECASPER]

2 hours ago, Z W said:

The master solenoid has failed on my 1982 M20K.  When the master switch is turned on, the panel stays dark and the solenoid just clicks repeatedly for a while, then stops.  I was able to get it to kick on while connected to external power at 14v, but as soon as external power was removed, the solenoid went back to a failed state and clicked repeatedly, then stopped.  This solenoid is bolted to the side of the battery box in the tail.

The parts manual says it is a 6041-H-105A, which matches the one that came out of the plane.  That item is no longer available anywhere I can find, except used salvage items.

I've obtained a SkyTec 12V-STS-M12 FAA/PMA replacement solenoid.  I thought this would be a simple swap.  However, the old solenoid had a strange jumper wire running between the switch poles of the solenoid.  It's marked with a "F" flag and has some kind of resistor in it (pic below).  I don't understand what it does and I can't find any wiring schematics for the old solenoid.  I also can't find any wiring diagrams or schematics in the parts manual or service manual for the plane.

If I understand how the new solenoid works, and I think I do, I wouldn't expect this jumper wire to be necessary, and expect it might even prevent it from working.  Can anybody tell me what it does, and whether it should be re-installed on the new solenoid?  I've found some poorly done wiring back there behind the battery that I am cleaning up and taking care of, so I'm questioning what I'm seeing before I put it all back like it was.

Thanks in advance.

 

I had my Master Relay go out on an M20M in 2017 and was able to find a New (old stock) identical part number.

It looks like there's at least one new old stock one matching your part number on Ebay (at least there was when I did the search - that can change by the minute) : https://www.ebay.com/itm/175994963507?epid=17011544565&hash=item28fa1e0633:g:G5oAAOSwxIxlPZTw&amdata=enc%3AAQAIAAAAwKGyltPFYiAGxj5NWOZ%2BvDwqxhgPpPNyH%2Br1VNekeLgwAyEkQ6Ti75DZCUsvY6B%2BVDEWQ2%2Bu61i8y5qdJvmjmVYEYKsK7p4w51ho7R3y%2B2wMP2QXCz7p4mbFXb9iaG6HqhP%2BI%2Blwtp1Rr2DtEixUto%2BgvzhGn%2FSY%2FNF8M97IpZQSompQevzAruyCD%2BbpT2dydiCuiUuUI%2FtRPGGsJnSwRqv%2Bq380eqv%2B%2FJRRN8qE%2FecQqGGpFXpn2ubbWLaevbDBrw%3D%3D|tkp%3ABk9SR7C99_CNYw

 

[Z W]

1 hour ago, LANCECASPER said:

It looks like there's at least one new old stock one matching your part number on Ebay 

 

Close, but it looks like that's a 205A (400 amp), not a 105A (200 amp).  There is one 105A listed on Ebay that says "New" but the photos look a long way from new.

I'm comfortable with the SkyTec / Lamar replacement now that I know about the flyback diode.  I was just confused because it looked like a jumper wire between the switched poles.  I couldn't understand how it would even work like that.  In fact, the diode prevents power passing through which makes a little more sense, although I'm still not sure I 100% understand how it does.

I did however just hook the old solenoid up to my 12v truck battery using jumper cables and it seems to be working.  So investigation continues.  I think it's either the battery or a bad wire connection.  Given the state of the wires I found behind the battery, a bad connection seems possible.  I guess the old solenoid will stay on the shelf as a spare.  It's looking a little rough and corroded anyways.  

Thanks for your thoughts and help.

[201Mooniac]

This might be the right one, brand new https://skygeek.com/eaton-aerospace-6041h105-relay-12v-1-15-electromagnetic.html?utm_source=googlebase&utm_medium=shoppingengine&utm_content=eaton-aerospace-6041h105-relay-12v-1-15-electromagnetic&utm_campaign=froogle&msclkid=11a1a5a5024017fb9a5cc0d9d211ca4c

[LANCECASPER]

54 minutes ago, Z W said:

Close, but it looks like that's a 205A (400 amp), not a 105A (200 amp).  There is one 105A listed on Ebay that says "New" but the photos look a long way from new.

That's the one I meant to copy. Best of luck

[A64Pilot]

When the magnetic field collapses there is a spike in electrical energy that goes through the wires and this spike can be bad for electronics. The diode functioning as a one way electric valve prevents the spike, as it functions as a one way valve it’s orientation is important, the electrical gurus are cringing from me calling a diode a valve, but it’s how a mechanical, not electrical person like me can understand the function.

Google found this, it’s a Grumman channel but that part doesn’t matter.

If you bought a Lamar relay my bet is you will never buy another, they are very good relays. 

 

[Z W]

This is the replacement master solenoid I bought:

https://www.aircraftspruce.com/catalog/eppages/skytec07-03565.php

It looks and feels very high quality and has good reviews, both here on Mooneyspace and elsewhere, as far as I can tell.  I will put the diode back on it, in the proper direction, and see what happens.

Also ordered a new Concorde RG-35AXC battery to replace the Gill, proper milspec wires, AMP wire terminals, and a hydraulic hex crimper for the 2-gauge wires. Trying to make a scheduled trip happen on 12/28 so not taking any chances.

Recently had to replace the starter solenoid, found that a shop had previously installed a cheap version now available only at NAPA, although it has the same part number as the Mooney parts catalog (24059).  Learning more and more you have to watch what you let someone install on your plane.  It lasted about a year and a half.  When it failed, the prop started turning slowly as soon as the master was turned on, even with mags off and key out of the ignition.  Mooney has a SB to replace some old solenoids for that reason.  Got my attention for sure.  That may have been why I immediately blamed the master solenoid this time.

SB is below.  I would not install a new old stock Cole-Hersee solenoid.  I think the new Lamar FAA/PMA units seem like the way to go.

[Fly Boomer]

3 hours ago, Z W said:

I was just confused because it looked like a jumper wire between the switched poles.

Pretty sure the switched poles are the fat connectors.  The skinny connectors, when energized, complete the circuit between the fat boys.

[Z W]

Yeah, I just meant the poles connected by the switch.  What you said is probably more technically correct.

[A64Pilot]

The little terminals go to the coil that is the electromagnet. Magnetism and electricity are closely connected of course, I believe it’s the collapse of a magnetic field that causes the surge of electricity that fires our spark plugs for instance so it can be a significant amount of current.

https://www.denso-am.eu/news/deneur21_04_ignition-coil-basic-principles#:~:text=The magnetic field is initially,the magnetic field to collapse.

Note electricity to me is smoke and mirrors I’m no electronics expert, I dabbled in it as a kid but that was before transistors were even wide spread and it took transformers to change voltage and only AC or pulsating DC to run through a transformer, none of that is true today of course.

So occasionally I get things wrong because what used to be true no longer is, but most of our aircraft have systems that are very old school

[N201MKTurbo]

Just to geek out on this, the energy stored in an inductor, is stored as a magnetic flux. The voltage at the terminals equals the rate of change of the flux. The flux equals the current times the inductance of the inductor. This brings us to the voltage at the terminals equals the current divided by the rate of discharge (V=dI/dt). Which brings us back to the voltage at the terminals when the current source is removed. The energy has to go somewhere. In the movie above you saw the arc in the switch. This is because the current is controlled by the resistance across the terminals. Without anything else, it is the resistance of the air between the switch contacts. This resistance is extremely high, so the voltage goes extremely high to establish the discharge current. When the voltage gets high enough it will ionize the air between the switch contacts, which significantly lowers the resistance of the air and lets the discharge current flow until the magnetic flux goes to zero. If you give it a lower resistance discharge path, such as a resistor across the terminals, the voltage will be much lower to establish the discharge current. The problem with a resistor is it will be continuously dissipating energy (heat) whenever the coil is energized. The solution to this is to use a diode which has a high resistance in one direction and a low resistance in the other direction. This has very little energy dissipation under normal operation and high dissipation during the current removal event. 

[EricJ]

Just a little more geeking out in the context of an automotive relay (which is the same function as the solenoid, just smaller).

For anybody who's changed an automotive relay, there's usually a diagram on the relay that shows the pins, and whether or not it has the diode built-in (they nearly always do).   The coil is between pins 86 and 85 in the diagram below, and if a positive voltage is applied to 86 so that sufficient current flows through the coil to 85, it throws the switch from pin 87a to 87.    The diode is the little triangle thing between pins 86 and 85, and it only allows current to flow through it in the direction of the triangle, which is the opposite of the direction of the current through the coil when it is energized.    When the current through the coil is interrupted, it creates a large negative voltage, i.e., potential from 85 to 86 instead of the other way, so the diode provides a path for that current to go, essentially short-circuiting the coil.   This prevents the voltage spike from being able to damage anything around it, or radiate a pop noise into the radio, etc., etc. 

The diode is only there only to provide a path for the current spike that happens when the coil is shut off.   It's a normal enough thing that nearly all modular relays have them built-in.

[N201MKTurbo]

Just to clarify for those people with current flow dyslexia. 
 

 A diode will conduct when the cathode (the line) is more negative than the anode (the triangle).

Conventional electron flow is from negative to positive. So, the triangle points opposite to electron flow.

I think the symbol was originally meant to illustrate a cats whisker detector, an early solid state rectifier.

https://en.wikipedia.org/wiki/Crystal_detector

Tangent alert!

The article above says this is an obsolete technology, but when I used to work on voltage standard systems, the 75GHz frequency counter used a mixer that had a cats whisker in it.

[PT20J]

19 minutes ago, N201MKTurbo said:

Conventional electron flow is from negative to positive. So, the triangle points opposite to electron flow.

Now you’ve gone and confused it

“Conventional” current flow is positive to negative.

”Electron” current flow is negative to positive.

But we’re off in the weeds and probably not helping someone that just wants current to flow when the master switch is flipped on. 

[EricJ]

1 hour ago, PT20J said:

Now you’ve gone and confused it

“Conventional” current flow is positive to negative.

”Electron” current flow is negative to positive.

But we’re off in the weeds and probably not helping someone that just wants current to flow when the master switch is flipped on. 

The sources of the confusion are the US Navy and the FAA.   AFAIK they're the only ones that insist on using "electron flow" as a current description.    The rest of the world understands math and energy.