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question for you experts (master relay)

C

Christopher Murphy

Well Known Member
When I built my airplane a long time ago I installed the master relay such that the coil has to pull the plunger up. ( upside down I guess... it made the wire routing easier.

Over time I notice that when I flip the switch on, it takes a few seconds or longer. for the plunger to snap up and make the contacts close.

Any thoughts on this?

cm
 
Sounds like it needs to be replaced. I would not trust it. The electrically induced magnetic field pulls against a spring that is substantially stronger than gravity. If it is struggling to pull against the spring, it is due to fail completely soon.

Larry
 
question

lr172 said:
Sounds like it needs to be replaced. I would not trust it. The electrically induced magnetic field pulls against a spring that is substantially stronger than gravity. If it is struggling to pull against the spring, it is due to fail completely soon.

Larry
Click to expand...

Since its upside down the coil is holding the spring tension and gravity. If its right side up the coil only has to over come the spring force... so Im thinking having it upside down is causing it to start failing sooner.

I replaced the original master relay after about 16 years of service. Now the new one is slowly failing after only two 2 year of service. Im wondering if I should go through the effort of turning it right side up.?

cm
 
Christopher Murphy said:
Since its upside down the coil is holding the spring tension and gravity. If its right side up the coil only has to over come the spring force... so Im thinking having it upside down is causing it to start failing sooner.

I replaced the original master relay after about 16 years of service. Now the new one is slowly failing after only two 2 year of service. Im wondering if I should go through the effort of turning it right side up.?

cm
Click to expand...

It's highly doubtfull gravity has any impact. If you listen to a good one operate, you'll hear how much force they impart. Gravitational force on a 3-5 ounce part is quite minimal.

Larry
 
Data sheet

A quick look at the White-Rodgers Datasheet on a typical master contactor says:

"Mounting Position
? Recommended mounting with cap down"

In this mounting position, The plunger is indeed pulled UP against the spring (and gravity).

This is the manufacturer's recommended "correct" mounting position and should be fine. Other contactors may be different.

That being said, if it is not performing correctly, replace it...not worth worrying about it for $35...
 
But first....un-do the connections, check for any tarnishing/corrosion, clean, re-install. Unlikely to fix it, but it costs nothing to check.
 
And don't ignore the possibility that it's something other than the contactor causing the problem. There's a bunch of wire terminations, a switch, and a bunch more wire terminations, and that ever present but rarely checked, Ground.

Quick troubleshooting hint:
Use a jumper wire to tie the low side control terminal (the one *not* tied to the battery post) of the contactor directly to a good ground. (Don't let the arc startle you.) If you get a normal 'snap' of the contactor the instant you make the connection, you likely have other issues.

Charlie
 
rocketman1988 said:
A quick look at the White-Rodgers Datasheet on a typical master contactor says:

"Mounting Position
? Recommended mounting with cap down"

In this mounting position, The plunger is indeed pulled UP against the spring (and gravity).

This is the manufacturer's recommended "correct" mounting position and should be fine. Other contactors may be different.

That being said, if it is not performing correctly, replace it...not worth worrying about it for $35...
Click to expand...

Thanks for all the good info. Mine is mounted with the cap down. I already ordered a new one but I did test on the old one and it worked fine. I found a loose ground wire so maybe that was the issue.

cm
 
My guess would be low voltage at the control wiring side of things.
I would check to make sure you have 12v + at the control side.
If the ground problem you mention is for the control side then that would/could have been the issue.
 
A non-electrical issue that could cause this is any oil/grease that may have gotten inside the unit and is now drying up and getting thick. As this thickens with age it will become more viscous and the magnetic field developed by the coil will take longer and longer to pull the contactor slug up into the solenoid. In that case the coil would be just fine - it just needs a good internal cleaning - which raises the question of CAN it be opened up and cleaned.
 
As vital parts go, they are cheap and easy to swap. My advise is to replace it and then keep the old one that you know still works in your flyaway kit. That way you have a spare of the correct model that may be tired but you know still works. Unfortunately, on occasion, new parts suffer from infant mortality, especially electo-mechanical ones.
 
Christopher Murphy said:
Thanks for all the good info. Mine is mounted with the cap down. I already ordered a new one but I did test on the old one and it worked fine. I found a loose ground wire so maybe that was the issue.

cm
Click to expand...

The STANDARD Master Relay is HOT from the battery all the time. The switch completes the ground path. IF you had a loose ground, that would have created high resistance and lowered the voltage the relay saw for activation thus creating the issue you had.
 
Nail on the head

Greg

That relay was covered with sticky dried up brake fluid that seeps out from doing alot of acro. But it seemed to work ok when I tested it with a battery I had on my bench. In any case for 23 bucks its getting replaced because its one of those items than can leave you stranded. My main question was how it should be mounted

Cm
 
Christopher Murphy said:
Greg

That relay was covered with sticky dried up brake fluid that seeps out from doing alot of acro. But it seemed to work ok when I tested it with a battery I had on my bench. In any case for 23 bucks its getting replaced because its one of those items than can leave you stranded. My main question was how it should be mounted

Cm
Click to expand...

Oh yeah, for $23 it's not even worth trying to take apart and clean. R&R and move one.
 
Chris, if you still have issues with the new master relay, check your master battery switch. I had a problem similar to yours and still had issues with a new master relay. Turned out to be my $4.75 battery switch.
 
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