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SHUT PLANE DOWN EVERYTHING STAYED ON


Danb

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I shut down my Bravo this morning and was getting out of the plane and noticed everything was lit up. I proceeded to turn off the master a few times to no avail. Looked for a breaker for the master none found, I finally pulled the battery breaker to turn stuff off and not run down the batteries.

WHAT UP.?

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@Danb ,

Sounds like the master relay is stuck in the on position...

Find relay by the battery, tap on it... See if it releases?

Or wait for a mechanic to give better advice.

Relays have a tendency to fail with age and hours... it might be time to swap in some new master and avionics relays(?)

PP thoughts only...

Best regards,

-a-

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Solenoids can weld themselves via the contacts in the on position.   The Mooney one looks to be take apartable.   You could take apart and clean.   At one point I think I found the Mooney Master Solenoid at McMaster Carr.   Sometime a good wack will unweld them. But replacement is the best option.

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7 hours ago, Yetti said:

Solenoids can weld themselves via the contacts in the on position.   The Mooney one looks to be take apartable.   You could take apart and clean.   At one point I think I found the Mooney Master Solenoid at McMaster Carr.   Sometime a good wack will unweld them. But replacement is the best option.

Yes, replacement is the correct action.

What many may not know is that relay contacts are typically plated with a thin layer of specialty metal depending upon application requirements (many silver alloys, sometimes tungsten, or gold).  As you can imagine, after they weld themselves together, this plating is long gone!  Cleaning/filing is a temporary fix, at best.

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On 6/30/2019 at 2:59 PM, MikeOH said:

Yes, replacement is the correct action.

What many may not know is that relay contacts are typically plated with a thin layer of specialty metal depending upon application requirements (many silver alloys, sometimes tungsten, or gold).  As you can imagine, after they weld themselves together, this plating is long gone!  Cleaning/filing is a temporary fix, at best.

The high amp constant duty industrial ones I have taken apart   (We used to throw the black plastic ones on the floor so they would never get used again.)  did not seem to have anything more than what a new bolt would have on it.  The failure generally is usually the electromagnetic coil and the windings not the conductor plate.

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5 hours ago, Yetti said:

The high amp constant duty industrial ones I have taken apart   (We used to throw the black plastic ones on the floor so they would never get used again.)  did not seem to have anything more than what a new bolt would have on it.  The failure generally is usually the electromagnetic coil and the windings not the conductor plate.

I'm not sure how you could tell, visually, as common high-current contact platings are microinches of various silver alloys; silver-cadmium-oxide (becoming less common thanks to European RoHS requirements), and silver-tin-oxide are common and would appear no different than zinc plated bolts (which used to be cad plated).

I was only responding to your comment about welded contacts which are typically caused by excessive switched current due to undersizing/improper application of the relay, or a failure in the circuit being switched....or, they just plain wear out! (Loss of plating with wear eventually results in excessive resistance which causes excessive heating leading to failure of the contacts).

I am not aware of how coil winding failures would induce contact welding, nor do I have failure mode/rate data to offer a factual basis to establish whether coil or contacts are the most prevalent relay failure mode.  My seasoned opinion based on my personal experience as an EE is that moving mechanical parts, such as contacts, are much less reliable that coils of wire in transformers, inductors, and relay coils which have no moving parts.

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14 minutes ago, MikeOH said:

I am not aware of how coil winding failures would induce contact welding, nor do I have failure mode/rate data to offer a factual basis to establish whether coil or contacts are the most prevalent relay failure mode.  My seasoned opinion based on my personal experience as an EE is that moving mechanical parts, such as contacts, are much less reliable that coils of wire in transformers, inductors, and relay coils which have no moving parts.

Agree about the plating.

While this does not apply in the OP case.   As I think it was welded closed.   From a practical standpoint it's the relay coils that fails.  Practical experience being the 240 volt one in the air conditioner that failed last summer.  No worries I had a spare.    And maintaining a fleet of 200 trucks with Motorola radios with solenoids used to prevent voltage spikes from starting. Probably 1 in 10 that had a mechanical issue.

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1 minute ago, Yetti said:

Agree about the plating.

While this does not apply in the OP case.   As I think it was welded closed.   From a practical standpoint it's the relay coils that fails.  Practical experience being the 240 volt one in the air conditioner that failed last summer.  No worries I had a spare.    And maintaining a fleet of 200 trucks with Motorola radios with solenoids used to prevent voltage spikes from starting. Probably 1 in 10 that had a mechanical issue.

Very interesting.  Did you FA the coils to determine if was insulation failing (shorted winding) or wire breakage?  The relays I've dissected have all been contact failures.  I wonder if you are experiencing lower quality from aftermarket relays?  Maybe crap insulation, or undersize copper windings?

I had that happen once with a fuel pump relay that I stupidly replaced with an aftermarket one.  It quickly failed but was due to undersize/inferior contacts...but outside it looked identical to the OEM one.

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More than likely it was not really the coil. but more the coil connection to the terminals.   And yes bad installation is a contributor.  If the installer gets crazy tightening the terminals.   This was in the 1980s.   I put myself through college installing two way radios.   We never could keep a metal can solenoid in service for very long.

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Some PP notes for @Danb...

Hmmmm.... Dan, can you describe with additional detail what is and isn’t working?

0) switches and circuit breakers

Some Mooney switches are also circuit breakers... In this case we probably have some pretty large Circuit Breakers on the panel related to the main busses that we are turning on and off... right at the top of the panel... expect the master and radio switches to not be circuit breaker type... they just use just enough power to flip the relays... the power that runs through the relays is circuit breaker protected...

 

The main Relays...

1) Battery relay

One relay selects Battery one or two... to be active. You can hear the relay click while selecting the battery... (while on the ground) I get a solid thunk, as if it is nearby... use a digital voltage indicator (JPI works) to check the voltage change between the two batteries... if the voltage doesn’t change some the relay may not be doing its job...

 

2) Master relay

Another relay operates master power... on or off. This is the one we think has welded itself closed...  this one clunks when it comes on... If it is welded closed... i’m Not sure if it can clunk or not...

 

3) Radio relay

The third one of interest... The radio master... it is a safety mechanism, so that it is normally closed... it opens when the master relay closes... and closes again when you throw the switch for radios to be on...

So... when the radio relay fails to get power, it typically fails closed and delivers power to the radios anyway...

If the radio master fails closed... the radios will be left powered up when the radio master switch is turned off...

Turning off the Master switch, stops sending power to the radio bus... so, I expect the radios to run out of power quickly after that...

I think it may have been Skip that described failing the radio relay to demonstrate how the safety mechanism works... I have no idea how to fail that relay from inside the cockpit...

 

4) Starter relay...

If we got this far and haven’t figured out which relay isn’t working... we have gone too far using a PP for guidance...  :)

 

 

Get out the voltage meter... get ready to check volts around the relays back by the batteries...

Probably need a friend to throw the switches while you are reading the voltages... and listening for the thunks...

Plan C,  start reading the Maintenance Manual To See where all these things are mounted...  :)

How far away is KUKT (Quakertown, PA) there is a really cool Mooney mechanic there... with a fine grill. Probably take him about 10 minutes to identify what’s not working properly....

PP thoughts only, not a mechanic at all...

Best regards,

-a-

 

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Bat#1 and Bat#2 have separate relays, the common point is the ground connection from the master switch.. so it is probably shorted to ground somewhere in the left hand panel. 

pulling the battery breaker does remove the batteries from the power bus. 

In the schematic the common line from the switch goes to wire PB09A18 and there directly to a ground buss plug.. so look for a short between the battery select switch and and master switch.   Or that the master switch failed. 

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Anthony Paul explains it better than this accountant could do. Unless there is a short related to the Master I’m assuming it’s the master switch, I ordered one today, pricy from Mooney about $170. 

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Thinking about it.. it could still be a welded #1 or #2 relay.... or a short on the wire from the relay to the switch. .. open the back battery compartment and assume that all relays are "hot".  then you can test them there. 

I wouldn't buy new hardware until testing.. should only be a few checks.  

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19 minutes ago, Danb said:

Anthony Paul explains it better than this accountant could do. Unless there is a short related to the Master I’m assuming it’s the master switch, I ordered one today, pricy from Mooney about $170. 

$170?  Goodness, that's a bargain! :lol:

All joking aside, fixing a short could potentially cost more than that with the time to rewire and test everything...

Edited by jaylw314
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