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  #1  
Old 01-06-2019, 04:13 PM
Sumo Sumo is offline
 
Join Date: Apr 2014
Location: Las Vegas, NV
Posts: 22
Default Master contactor failure (maybe?)

Hi friends,

Looking for some advice. I've got an RV-6A with a Lycoming IO-360 and Skytec starter, 750hr TT. I bought it flying about 350 hours ago.

Went flying a week ago, and after a fuel stop, I tried starting back up, head a "clunk", then nothing. Tried again and it worked... gremlins I thought...

Then I went to go flying today, and after turning the master power on: "clunk clunk". Then nothing. My engine display, which is always on if the master power is on, was "off". I toggled the master switch a few more times for troubleshooting and got a wide variety of results. In some cases, I'd get the prop spinning like normal. Other times, I'd turn the starter switch on and absolutely nothing would turn on - not even any "clunks" of the master contactor/solenoid.

I confirmed the battery is healthy (I keep it on a tender and then checked the voltage independently - good). The weather was mild.

I replaced the starter solenoid about 2 years ago after a similar problem. This one is different because sometimes I'm not getting any power at all... but when I get power I can engage the starter.

So, I "think" my master contactor has failed. I only have 1 battery and 1 alternator, but the plane has 2 master contactors in line. When I heard the "clunk"s, they were coming from just one of them. No noise from the other at all.

There is no marking on my contactors, but they look kind of like Aircraft Spruce's LAMAR SOLENOID 12 VOLT CONTINUOUS (X61-0028) - just without the sticker.

Do master contactors fail like this? Thoughts?

Thanks for your help!
-sumo
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  #2  
Old 01-06-2019, 05:23 PM
Pat Hatch's Avatar
Pat Hatch Pat Hatch is offline
 
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Location: Vero Beach, FL
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Sumo, sure sounds like the master contactor. Shop around for one, I would check with B&C Specialties as well. I've always had good success with the B&Cs in my airplane, $35 with the diode already installed for you. Make sure you have the spike suppressing diode in any case, which will make it last a long time.

EDIT: Correction, the spike suppressing diode increases the life of the master switch, not the life of the master contactor!

I'm assuming the second contactor is your starter contactor, the master will be continuous duty, the starter will be intermittent duty. You can disconnect the cable to the starter and you should hear the start contactor "clunk" when you push the start button if the battery master is on.
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Last edited by Pat Hatch : 01-07-2019 at 09:26 AM. Reason: The diode does not increase the life of the contactor.
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  #3  
Old 01-06-2019, 05:59 PM
rv7charlie rv7charlie is offline
 
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Location: Pocahontas MS
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Pretty sure that the diode is there to protect the switch. It's across the coil; not the relay contacts.

I agree it's probably the master, but it should be easy to verify. What does the volt meter say when the master is switched on? Does it drop at all when the start button is pushed, and if yes, how much? A healthy battery and good hot side (*and ground side*) connections should show 12+V until the start button is pushed, and it should drop to around 9-10V if the start contactor 'makes', and the starter is in the circuit. If V doesn't drop at all, there's a problem; if V drops a lot, there's a problem. But bad connections can be at the relay contacts, or anywhere else between Bat + & Bat - .

The symptom descriptions are a bit hard to follow; some seem to indicate that there's starter movement when the master is switched (!?), and others seem to indicate that the start button is controlling the efis. Also hard to follow which actions cause which 'clunks', and whether there are multiple 'clunks' from one action, or sequential actions.

Charlie
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Old 01-06-2019, 06:12 PM
Sumo Sumo is offline
 
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Pat - thanks for the thoughts and advice. I'll check with B&Cs. It's an odd set-up. I have two master contactors in parallel which then feed into the single starter contactor. (All connected to a single battery).

Charlie - you're right. At least as installed in my plane, the diodes across the master contactors are to protect the master switch from a surge backwards as the magnetic field collapses.

So, no I see my description is hard to follow. I'll try to clarify.

Today, master switch on:
- sometimes: success in my normal sequence of events through starting the prop
- sometimes: "clunk clunk" nothing
- sometimes: absolutely nothing, not even reading voltage on my engine instruments.

It was unpredictable as to which outcome I would get. I did to good old jiggle test and everything seemed solidly connected, leading me to think there's some intermittent failure in the master contactor.
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  #5  
Old 01-06-2019, 06:22 PM
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Sam Buchanan Sam Buchanan is offline
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The two contactors in parallel is an odd architecture, maybe someone was trying to add another layer of reliability????

You might consider eliminating one of the master contactors to align your wiring more along a traditional scheme...and remove a source of confusion during troubleshooting.
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  #6  
Old 01-06-2019, 07:18 PM
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bhester bhester is offline
 
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Thumbs up Mine has two

Mine has two the first one is part of the Over voltage protection per Bob Nuckolls - AeroElectric plan. Along with my original Van's internal regulated 60A alternator 12 yrs. old (with no cooling tube) and still going, finger crossed.

How old are your? I replaced my Battery contactor my starter contactor and my battery at 8 yrs. old, just because I thought it might be a good thing to do. I haven't replaced the OV contactor.
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Last edited by bhester : 01-06-2019 at 07:34 PM.
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  #7  
Old 01-06-2019, 07:49 PM
gasman gasman is offline
 
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Quote:
Originally Posted by Sumo View Post
Hi friends,

Looking for some advice. I've got an RV-6A with a Lycoming IO-360 and Skytec starter, 750hr TT. I bought it flying about 350 hours ago.

I confirmed the battery is healthy (I keep it on a tender and then checked the voltage independently - good). The weather was mild.

I replaced the starter solenoid about 2 years ago after a similar problem. This one is different because sometimes I'm not getting any power at all... but when I get power I can engage the starter.

So, I "think" my master contactor has failed. I only have 1 battery and 1 alternator, but the plane has 2 master contactors in line. When I heard the "clunk"s, they were coming from just one of them. No noise from the other at all.

Do master contactors fail like this? Thoughts?

Thanks for your help!
-sumo
You should have one continuous duty master and one intermittent duty starter solenoid...... in series (in line).

When installing a solenoid make sure you don't rotate the lug as you tighten the nut. It will cause a poor contact inside the solenoid, if this is not the case, then.....my guess is you have a failing master SWITCH.or a bad connection in the master switch line.
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  #8  
Old 01-06-2019, 08:09 PM
MJarreau MJarreau is offline
 
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Default Transients

I think gasman is right. Can you put the contactors on a bench? If so, you might find them to be rock solid. It sounds to me like an open somewhere in your circuit.

Good luck!
Mike
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  #9  
Old 01-06-2019, 08:10 PM
rv7charlie rv7charlie is offline
 
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Quote:
Originally Posted by Sumo View Post
Pat - thanks for the thoughts and advice. I'll check with B&Cs. It's an odd set-up. I have two master contactors in parallel which then feed into the single starter contactor. (All connected to a single battery).

Charlie - you're right. At least as installed in my plane, the diodes across the master contactors are to protect the master switch from a surge backwards as the magnetic field collapses.

So, no I see my description is hard to follow. I'll try to clarify.

Today, master switch on:
- sometimes: success in my normal sequence of events through starting the prop
- sometimes: "clunk clunk" nothing
- sometimes: absolutely nothing, not even reading voltage on my engine instruments.

It was unpredictable as to which outcome I would get. I did to good old jiggle test and everything seemed solidly connected, leading me to think there's some intermittent failure in the master contactor.
OK, need actual
1. your action: effect,
2. your action: effect, etc
New set of actions: start over with sequence of action/effect.

We have no way to know if 'clunk clunk' means master, then start, or master, master, or a master dropping in and out on its own.

If flipping the master switch sometimes lights up the system and sometimes doesn't, it could be the master contactor (almost certainly not *both*, though), or the switch itself, or DC from the downstream end of the master contactor coil to the switch, or bad wiring between the switch and ground.

Wiggling the terminals and not getting movement really doesn't prove you've got solid electrical connection. Especially on the battery terminals, they can be rock solid but the mating surface can be corroded. A no-load voltage check will show normal voltage, but a load will cause a big voltage drop. If the corroded mating surface is on the ground terminal, and you don't know where to probe, a voltage check with a meter might appear normal.

If you truly have two master contactors *in parallel* (really unusual), the odds of *both* contactors failing at the same time would be one in something with a bunch of zeros after it. It would take a failure of both at the same time to take down your system.

Charlie
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  #10  
Old 01-06-2019, 08:29 PM
Sam Buchanan's Avatar
Sam Buchanan Sam Buchanan is offline
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Quote:
Originally Posted by bhester View Post
Mine has two the first one is part of the Over voltage protection per Bob Nuckolls - AeroElectric plan.
Really doubt your contactors are wired in parallel......
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