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Starter contactor wiring question

9

9erDriver

Well Known Member
Due to interference with engine mount (self induced - should have measured better when fabricating custom battery box), I would like to mount my starter contactor upside down and swap the big in and out terminals. Unlike the master, the starter contactor power terminals are not labeled, leading me to believe it is not 'polarized' like the master contactor. Thoughts?

startercontactor.jpg
 
The starter contractor is mounted the other direction because it was found to activate under g loading and engage the starter while flying. It is written up in the RVator. The article did not say at what G loading, so it might still be in the range of your 9, but it was not during aerobatics.

Now you know the risks.

On a building note. One mistake left uncorrected can precipitate up to 5 other required changes downstream. It is best to go back to the plans if at all possible or it will continue to haunt you with additional changes like this one.

I have learned this from experience.
 
You've convinced me

Thanks for the info and RVator reference, Bill. I definitely don't want to risk starter engagement in flight. I'll modify my battery mount and get the contactor oriented correctly.
BillL said:
The starter contractor is mounted the other direction because it was found to activate under g loading and engage the starter while flying. It is written up in the RVator. The article did not say at what G loading, so it might still be in the range of your 9, but it was not during aerobatics.

Now you know the risks.

On a building note. One mistake left uncorrected can precipitate up to 5 other required changes downstream. It is best to go back to the plans if at all possible or it will continue to haunt you with additional changes like this one.

I have learned this from experience.
Click to expand...
 
9erDriver said:
... I would like to mount my starter contactor upside down and swap the big in and out terminals...
Click to expand...

You'll be fine, Steve. Bob Nuckolls of Aeroelectric Connection fame has debunked this OWT for ages and one of his explanations is here.

What it says, basically, is that the spring force in the solenoid is so strong that no amount of G-force the aircraft can survive will operate the contact.

I too received "the warning" when I asked about a starter solenoid location for my RV-8A. Mounting it inverted provided better routing for the "fat wires" so that's what I did. That was about 200 landings ago and not all of them were "grease jobs" <g> but I'm well-satisfied with the installation.

--
Joe
 
I believe Bob Nuckolls thoughts on contactor mounting. But there is another reason not to mount the master contactor upside down. It will NOT work! Your master contactor only has one small terminal that is connected to the coil. The other end of the coil is connected internally to the battery input. So the big fat cables would have to be longer so that they will reach the transposed terminals and still be electrically correct. Like BillL said, "One mistake left uncorrected can precipitate up to 5 other required changes downstream."
An RV-12 builder inadvertently mounted his master contactor upside down and nothing worked. You can read about it HERE
Joe Gores
 
Just to clarify my post above, the master contactor will work in any mounting position as long as it is wired correctly, which might require longer cables if the plans are not followed.
Joe Gores
 
Mich48041 said:
I believe Bob Nuckolls thoughts on contactor mounting. But there is another reason not to mount the master contactor upside down. It will NOT work! Your master contactor only has one small terminal that is connected to the coil. The other end of the coil is connected internally to the battery input. So the big fat cables would have to be longer so that they will reach the transposed terminals and still be electrically correct. Like BillL said, "One mistake left uncorrected can precipitate up to 5 other required changes downstream."
An RV-12 builder inadvertently mounted his master contactor upside down and nothing worked. You can read about it HERE
Joe Gores
Click to expand...

True statements for the master contactor, but not the same as the starter contactor which require a power input on the coil terminal (the other side of the coil is grounded thru the mounting plate).
 
FWIW

Many years ago, in order to debunk this myth, I cut apart my old starter contactor, weighed the plunger, and then measured the force required to cause G-force induced engagement. I can't remember exactly what the number was, but I do remember it was above 7G's. Since heavy duty aero is not on my list, I never worried about how my units are mounted.

YMMV - My results only reflect the unit(s), Cole-Hersee, that I am using.

David Howe
 
True statements for the master contactor, but not the same as the starter contactor which require a power input on the coil terminal (the other side of the coil is grounded thru the mounting plate).
Click to expand...
My mistake, I should have read the original post better. The starter contactor in the picture has two small terminals for the coil. Mounting in any position should not be a problem. An arc suppression diode should be installed on each contactor coil with the arrow pointing towards positive. A diode will prolong the life of the switch that energizes the coil.
Joe Gores
 
HFS said:
Many years ago, in order to debunk this myth, I cut apart my old starter contactor, weighed the plunger, and then measured the force required to cause G-force induced engagement. I can't remember exactly what the number was, but I do remember it was above 7G's. Since heavy duty aero is not on my list, I never worried about how my units are mounted.

YMMV - My results only reflect the unit(s), Cole-Hersee, that I am using.

David Howe
Click to expand...

Thanks for the factual information on this David. I had no first hand knowledge and believed the RVator, having no other information. I suppose that an overheated spring could have weakened and damaged a couple of planes, but your finding indicates that it is not a fundamental design problem. Mine is already installed, so i will just leave it.

Thanks for sharing, I certainly learned something.
 
so back to my original question...

OK so sounds like the consensus is that mounting position is not critical to starter contactor performance.

Can anyone tell me then is there a problem with reversing the ins/outs on the starter contactor power terminals? Isn't this contactor basically a remotely controlled, polarity agnostic, high amperage switch? All of the above assumes that I will use the 's' coil terminal to actuate the contactor per the plans.

Inverting the contactor and reversing power terminal polarity will allow me to keep the master-starter bus bar short.

thanks guys for all the replies.
 
You can invert the contactor and use the "S" terminal to activate the contactor and it will close to allow current to flow between the 2 large studs just fine. If however you want to use the "I" terminal functionality, it may not work properly if the power feed isn't "normal".

Contrary to a prior post, only one of the two small terminals is connected to the internal coil and it's labeled "S", the other side of the coil is connected to the mounting base and is grounded all the time. Applying power from your start switch or button to the "S" terminal engages the contactor. The other small terminal is labeled as "I" and can be used to show when the contactor is closed (it will have power to it when the contactor is engaged). Some ignore this terminal and some connect it to a light on the panel to show "starter engaged".

Bob
 
One time I posted on the aeroelectric list suggesting to use a bus bar between the contactors. Others, including Bob Nuckolls, said that bus bars are prone to cracking from vibration. They recommended using welding cable.
Joe Gores
 
Contrary to a prior post, only one of the two small terminals is connected to the internal coil and it's labeled "S", the other side of the coil is connected to the mounting base and is grounded all the time. Applying power from your start switch or button to the "S" terminal engages the contactor. The other small terminal is labeled as "I" and can be used to show when the contactor is closed (it will have power to it when the contactor is engaged). Some ignore this terminal and some connect it to a light on the panel to show "starter engaged".
Click to expand...
I stand corrected. Bob is right.
Joe Gores
 
Not all starter contactors are constructed the same. Those with terminals marked "S" and "I" have one end of the coil internally grounded to the case. Other brands like the X61-0030 LAMAR SOLENOID sold by Aircraft Spruce have two small terminals for the coil. One terminal is for negative and the other for positive. The X61-0030 does not have an indicator terminal. See the Standard Installation Diagram (PDF)
Joe Gores
 
NOT a myth

HFS said:
Many years ago, in order to debunk this myth, I cut apart my old starter contactor, weighed the plunger, and then measured the force required to cause G-force induced engagement. I can't remember exactly what the number was, but I do remember it was above 7G's. Since heavy duty aero is not on my list, I never worried about how my units are mounted.

YMMV - My results only reflect the unit(s), Cole-Hersee, that I am using.

David Howe
Click to expand...

Dave,
I do not doubt the results of your single test, but it is just that …a single data point. I can give you TWO data points where a start solenoid was pulled closed during a 5 G maneuver. Two starters were destroyed to the tune of $700 + dollars and the airplane was almost lost to an electrical fire…… the wiring was so hot it was smoking. Hans “Cobra” Miesler does a maneuver in our show… “rolls around the smoke”. He goes from .5 to +5 to make it work. Two times during the 2013 Airshow season his starter solenoid was pulled shut and it destroyed his starter. He then mounted his solenoid upside down and problem solved. Not a Myth.

If you want to see the maneuver that killed the starters due to the solenoid go to 3:22 in this video

http://www.youtube.com/watch?feature=player_embedded&v=nJbyP-4ZjoQ

As an aside, our show maneuvers are carefully picked and limited by the density altitude here in Denver. During our Alamosa show this year the DA was 10,500 sitting on the runway! I’m not sure we would know how to fly in thick air!!!!!
 
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Off Topic Tony Spicer comment above: Tony would you tell me where you got the brake resevoire that mounts on the cylinders??? Thanks Gary
 
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