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Master contactor failure (maybe?)

S

Sumo

Member
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
 
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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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
 
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.
 
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.
 
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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Sumo said:
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
Click to expand...

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.
 
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
 
Sumo said:
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.
Click to expand...

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
 
Don't forget the ground side

Don't forget to check the ground side also. Any poor connection or contact in the start circuit will cause cranking problems. Check that the engine ground is secure. A voltmeter can help track down bad connections. Good connections will not have a voltage drop while cranking (indicated by a significant voltage reading).

For example to check the ground side, connect the negative lead of the voltmeter to the negative battery terminal and the positive lead to the starter case while attempting to crank the engine. THIS MUST be done in a manner that will be SAFE for engine start because the next step is to observe the voltage while cranking the engine. A significant voltage indication (perhaps 0.5 volt or more) indicates a bad connection somewhere in the ground circuit. If possible leave the master switch off but still assume it is ON.

The positive or feed side can also be checked by connecting the positive voltmeter lead on the positive battery terminal and the negative lead on the starter contactor. There may be a higher voltage indication because of contactors but I think it should still be less than a volt.

If a significant voltmeter indication is found in either leg then it can be tracked down by measuring across smaller portions of the circuit.

Hope this helps but please do it safely.
 
My RV-9 presented with the same symptoms over a period of several months. After replacing solenoids, starter, and battery, I found intermittant master switch internal failure and the engine to firewall ground wire terminal improperly swaged; when I removed the shrink wrap to check swaging the terminal slipped off.
 
Sumo,

There seems to be quite a bit of confusion in this thread about the configuration of the high amperage side of your electrical system (battery, solenoids, starter, master switch and associated wiring.)

In my experience it is futile to guess at what is going wrong unless you understand the design of the system. My suggestion is that you take the time to trace out the wiring and draw a simple schematic that you can then use to help you isolate the cause of the problems. This should not be a really big task, since you only need to know how the system works at the "front end". If you don't have the skills to do this yourself I suggest you find someone to help you that is knowledgeable about electrical components and wiring.

Working on experimentals that someone else built can be frustrating, especially if the documentation is thin or non-existent. Ask me how I know!

Figure out the electrical system in your airplane, and then take a step by step approach to diagnosing the problem. Good luck!

John
 
BigJohn said:
Working on experimentals that someone else built can be frustrating, especially if the documentation is thin or non-existent. Ask me how I know!

Figure out the electrical system in your airplane, and then take a step by step approach to diagnosing the problem. Good luck!

John
Click to expand...

Rarely does anyone here talk about this in terms of a prebuy for new owners. Documentation of the various systems, especially electrical, should be high on the list. This is even more important for those less skilled in aircraft systems.

As John and others suggest, take the time now to get your electrical system drawn out. even if you don't know what's what, others can more easily help with troubleshooting.
 
It's going on 15 years old now...

bhester said:
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.
Click to expand...
 
BigJohn and JonJay,

Done - I got the master switch wiring all drawn out by hand now (I can follow it at least). After tracing everything, I do indeed have two contactors in parallel. And two master switches as it turns out. The only unique utility of this setup, as far as I can figure, is if I lose just one switch or just one contactor, it all still works. Neither "master" is working reliably, so I think the root of the problem is a 2nd master contactor failure (assuming one failed long ago and was never needed or noticed).

But, now that I've figured out how the wiring really is wired, on my next trip out I'm going to need to check each part of the line, from the master switch(es) on to ensure connections are solid. Maybe I'll need to R&R the master switch and one of the contactors, but we'll find out next weekend at this point.

Thanks all for the thoughts!
-sumo

BigJohn said:
Sumo,

There seems to be quite a bit of confusion in this thread about the configuration of the high amperage side of your electrical system (battery, solenoids, starter, master switch and associated wiring.)

In my experience it is futile to guess at what is going wrong unless you understand the design of the system. My suggestion is that you take the time to trace out the wiring and draw a simple schematic that you can then use to help you isolate the cause of the problems. This should not be a really big task, since you only need to know how the system works at the "front end". If you don't have the skills to do this yourself I suggest you find someone to help you that is knowledgeable about electrical components and wiring.

Working on experimentals that someone else built can be frustrating, especially if the documentation is thin or non-existent. Ask me how I know!

Figure out the electrical system in your airplane, and then take a step by step approach to diagnosing the problem. Good luck!

John
Click to expand...
 
So you have three contactors then ... two in parallel for the Master (12v power bus) and a third for the starter motor? Do you have an electrical diagram you can post? Something doesn't sound right.

You mentioned when cycling the Master Switch, you got various outcomes. Therefore it makes sense you might have a faulty master switch. The solenoids & contactors can all be easily checked with a multimeter for proper operation.
 
If wired as described, easy to check. Just turn on one master switch, check operation. Turn it off, repeat with the other master switch on.

Parallel means that either master contactor will power the plane and the start contactor.

My bet is on flaky ground circuit from the master switches.

Charlie
 
Possible failure path...

If indeed you do have two master solenoids wired in parallel & two master switches - do you also have two diodes, one for each master solenoid coil? If two solenoid coils are wired in parallel - the kick back current (on shut off) can be much higher than a single solenoid & if the diode installed (single diode) is not capable of the current then it would fail at some point - allowing the kickback current & resultant arc to kill your master switch(s) contacts over time.
Just something to ponder.
 
Just to back up Ralphs comment. Always look at the earth side early on in your diagnosis. I had a totally flat battery I thought. No volts readable with a multimeter. I removed the battery and it showed 12+ on a meter, so I was dubious about it being flat. Took it home and it was charged in no time.
Put it back in the plane and could read volts, so all good. Buttoned everything up and wheeled the plane out. Nothing. No volts.
I removed the front top of fuselage above the panel and what do I see, but all earths go to a forest of lugs and the one lug with a heavy wire, going back to battery has come adrift, only just adrift so that it can make contact if pushed slightly. Replacing the radio after replacing the battery moved it just enough to make contact but rolling the plane out broke it again.
I had a similar problem some time ago. I have LEDs across the fuses, the theory being that the LED will light if the fuse fails. I had a fuse fail, but it looked OK. I put a multimeter across the fuse contacts and it showed 12V, but it was only reading the flow through the LED.
 
0nB2ZpG5TsIK8--lnwKLwx6VA
.

https://share.icloud.com/photos/0nB2ZpG5TsIK8--lnwKLwx6VA#Manassas,_VA
Here’s the electrical drawing of the area of interest - freezing hands and slow flowing ink in the hangar today.

Spending the morning tracing and troubleshooting. As per standard “could it duplicate” today. Or rather, the problem is manifesting differently.

Resting battery, nothing on today is 12.4 V. Oddessy PC680. Lower than it should be, especially right off the battery tender. Clue 1. Checked voltages all along the path in the picture. Nothing unexpected.

I can turn on the master (via either switch now that I see how it’s meched - interesting redundancy and a lesson me (non-builder) to better understand the systems!). I can turn on all the electrical systems. Voltages readings aroud 11.8 now.

On to normal start up sequence, engage the starter and the entire electrical system shuts down.
I connect it to a good battery external and now everything works.

Sometimes it is the simplest solution - I sure went down an odd path because I was biting off on the voltage immediately after removing the battery tender then didn’t check again later.

Thanks for the suggestions and encouragement to better learn my system.
 
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Sumo said:
0nB2ZpG5TsIK8--lnwKLwx6VA
.

https://share.icloud.com/photos/0nB2ZpG5TsIK8--lnwKLwx6VA#Manassas,_VA
Here?s the electrical drawing of the area of interest - freezing hands and slow flowing ink in the hangar today.

Spending the morning tracing and troubleshooting. As per standard ?could it duplicate? today. Or rather, the problem is manifesting differently.

Resting battery, nothing on today is 12.4 V. Oddessy PC680. Lower than it should be, especially right off the battery tender. Clue 1. Checked voltages all along the path in the picture. Nothing unexpected.



I can turn on the master (via either switch now that I see how it?s meched - interesting redundancy and a lesson me (non-builder) to better understand the systems!). I can turn on all the electrical systems. Voltages readings aroud 11.8 now.

On to normal start up sequence, engage the starter and the entire electrical system shuts down.
I connect it to a good battery external and now everything works.

Sometimes it is the simplest solution - I sure went down an odd path because I was biting off on the voltage immediately after removing the battery tender then didn?t check again later.

Thanks for the suggestions and encouragement to better learn my system.
Click to expand...

Glad you found the problem. For future, you should know that battery tenders and odyssey batteries don't make good partners.

Larry
 
lr172 said:
Glad you found the problem. For future, you should know that battery tenders and odyssey batteries don't make good partners.

Larry
Click to expand...

+1. A few guys say they've had good luck leaving SLA batteries on 'smart' chargers, but many more have had early battery death while using them. SLA batteries just don't 'self-discharge' like flooded cell batteries, so maintainers are fixing something that 'ain't broke'.

I've used SLA batteries (cheap, no-name versions; not Odysseys) for a couple of decades, and I typically get 4-5 years out of them. And my plane sometimes sits for a month or more without flying. Only time I'll hit it with a charger is if it won't crank the plane, which is rare.

Charlie
 
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