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Starter disengage wire

Ron B.

Well Known Member
Van's has us remove a jumper wire on the starter and install a wire from the starter relay (on the "I" terminal) and run it to on the small terminal on the starter where you removed the jumper from.
Can someone explain the reasoning to me, enquiring mines need to know? They call this wire a disengage wire rather than an engaging wire.
 
Van's has us remove a jumper wire on the starter and install a wire from the starter relay (on the "I" terminal) and run it to on the small terminal on the starter where you removed the jumper from.
Can someone explain the reasoning to me, enquiring mines need to know? They call this wire a disengage wire rather than an engaging wire.

Since I don't want enquiring mines to possibly explode while thinking hard ;)....

It is an optional method of controlling the starter activation.

If the jumper is left in and used to activate the solenoid, the starter functions fine, but is slower to disengage when the key is released. In some instances there is a noise that is unsettling to some passengers (but Skytech says it is not detrimental to the starter).
If the I terminal is used to control the solenoid, the starter drive disengages more cleanly.
 
With all due respect to Van's you may want to review the following advice/diagrams from Skytec prior to wiring the starter.
I'm not a big fan of the LS starter for multiple reasons, do yourself a favor and upgrade to an NL or the B&C.

http://www.skytecair.com/Wiring_diag.htm
 
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Ok, it looks like a little DC electrical lesson is in order.....

I only have a basic 2 year electronics degree (from many many many years ago so I have forgotten the majority of it) so I don't claim to be anywhere near someone that can speak with any authority on the subject, so I fully expect others to chime in and correct me where needed.

When the jumper is left in place on a Skytech starter to avoid using a second activation wire routed to the solenoid, the power input side of the solenoid is connected directly to the power input of the starter motor.

When the start circuit is activated, the starter motor and the solenoid are both fed power via that one wire, the motor turns and the solenoid pushes the drive gear fwd to engage the ring gear of the engine making the engine turn.

When the start circuit is deactivated, power is removed from the starter motor and the solenoid, but the solenoid is still electrically connected to the +V input side of the motor.

Why does this matter? Because at this point the starter motor has now converted to being a DC generator. It is still spinning (driven by the now started engine) and with its power input connected to the solenoid, the Counter EMF produced by the spinning motor works against the collapsing field of the solenoid coil. This keeps the solenoid/starter drive engaged for longer than it would be if the power was interrupted instantly as happens when a separate activation wire is used.

This delay can be quite noticeable in some instances, and as I mentioned previously can cause an annoying noise that has the sound of an unhappy mechanical device. Particularly in instances where the engine goes to a rather high RPM immediately after starting (higher the RPM, the stronger the EMF that is produced).

As I said in my first post, Skytech has always said this was not detrimental to the life of the starter (do we know that for sure?), and that doing it the Van's way was optional.

I find it interesting that they now have this diagram on their web site and they say they don't know why Van's does it this way.... Well as far as I am aware, no one at Skytech has ever called to ask!

BTW, this wiring scheme was not my idea. It was conceived by the late Bill Bennedict... former general manager of Van's Aircraft (and Electrical Engineer)

BTW X2, I recommend caution in arbitrarily changing to the NL starter. If you are using the Van's supplied fwd facing induction system (affectionately referred to as the snorkel), an NL starter motor wont fit.

Bottom line? It is experimental... you can do what you want. We have been doing it this way for 18+ years and we get very good life out of our starter motors (and our normal mode of operation results in probably way more engine starts per hour than the average user).
 
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BTW X2, I recommend caution in arbitrarily changing to the NL starter. If you are using the Van's supplied fwd facing induction system (affectionately referred to as the snorkel), an NL starter motor wont fit.

It fit okay in my airplane, Scott, once I ground off the superfluous mounting lugs in accordance with Skytec's installation instructions. I had to do a bunch of fiberglass work to get the snorkel to fit around the alternator, but the starter required no fiberglass modifications.

20110814_wiring14.jpg
20110814_wiring17.jpg


(note: the above photos were taken during the fit-up process, all fasteners are temporary)

mcb
 
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It fit okay in my airplane, Scott, once I ground off the superfluous mounting lugs in accordance with Skytec's installation instructions. I had to do a bunch of fiberglass work to get the snorkel to fit around the alternator, but the starter required no fiberglass modifications.

20110814_wiring14.jpg
20110814_wiring17.jpg


mcb

Good to know.
I am still not sure it would work for all installations.
For example, the RV-14 comes with a molded fiberglass filter frame frame for the top. This limits the amount of positioning latitude available while doing the installation.
 
Thanks for th explanation

Ok, it looks like a little DC electrical lesson is in order.....

Thanks Scott, I was thinking back EMF was the issue, but probably combined with the fact that experimental uses some lightweight props with lower inertia and the engine winds up pretty fast on the first firings.

This is my reasoning why a certificated application may not need or use this wiring method.
 
Temporary?

Is it just temporarily fitted? There is a missing stud/nut on the forward left mounting hole of the starter to the engine.

Vic
 
Is it just temporarily fitted? There is a missing stud/nut on the forward left mounting hole of the starter to the engine.

Vic

It is missing, but on my O-360 that is listed as a bolt, not a stud/nut.... much easier to add later... :)
 
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Ok, it looks like a little DC electrical lesson is in order.....

I only have a basic 2 year electronics degree (from many many many years ago so I have forgotten the majority of it) so I don't claim to be anywhere near someone that can speak with any authority on the subject, so I fully expect others to chime in and correct me where needed.

When the jumper is left in place on a Skytech starter to avoid using a second activation wire routed to the solenoid, the power input side of the solenoid is connected directly to the power input of the starter motor.

When the start circuit is activated, the starter motor and the solenoid are both fed power via that one wire, the motor turns and the solenoid pushes the drive gear fwd to engage the ring gear of the engine making the engine turn.

When the start circuit is deactivated, power is removed from the starter motor and the solenoid, but the solenoid is still electrically connected to the +V input side of the motor.

Why does this matter? Because at this point the starter motor has now converted to being a DC generator. It is still spinning (driven by the now started engine) and with its power input connected to the solenoid, the Reverse EMF produced by the spinning motor works against the collapsing field of the solenoid coil. This keeps the solenoid/starter drive engaged for longer than it would be if the power was interrupted instantly as happens when a separate activation wire is used.

This delay can be quite noticeable in some instances, and as I mentioned previously can cause an annoying noise that has the sound of an unhappy mechanical device. Particularly in instances where the engine goes to a rather high RPM immediately after starting (higher the RPM, the stronger the EMF that is produced).

As I said in my first post, Skytech has always said this was not detrimental to the life of the starter (do we know that for sure?), and that doing it the Van's way was optional.

I find it interesting that they now have this diagram on their web site and they say they don't know why Van's does it this way.... Well as far as I am aware, no one at Skytech has ever called to ask!

BTW, this wiring scheme was not my idea. It was conceived by the late Bill Bennedict... former general manager of Van's Aircraft (and Electrical Engineer)

BTW X2, I recommend caution in arbitrarily changing to the NL starter. If you are using the Van's supplied fwd facing induction system (affectionately referred to as the snorkel), an NL starter motor wont fit.

Bottom line? It is experimental... you can do what you want. We have been doing it this way for 18+ years and we get very good life out of our starter motors (and our normal mode of operation results in probably way more engine starts per hour than the average user).

I guess I need some more educatin then.... I'm familiar with PFM (I gotta feeling that's what this must be) or this is just over my head :confused:

The original purpose of the 'I' terminal was a convenient place to pick off 12v during starter operation to bypass the coil resistor for better spark back in the day when cars had real distributors and one big coil.

You can see from the diagram below that the 'I' terminal is connected to the starter terminal inside the solenoid, this is just a bit "upstream" of the starter itself so unless there is some PFM happening somewhere in the wiring I'm not sure I understand what difference it would make connecting the solenoid using the 'I' terminal rather than the connecting it to the starter terminal.

Maybe that's why Skytec, who have some pretty smart folks working for them, can't seem to figure out why Van's does it this way.

ford-starter-solenoid-wiring-diagram-high-beam-light-lead-on-one-headlamp-by-using-a-circuit-tester-Use-the-following-procedure-For-lights-images.jpg
 
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Ok Walt. I concede.

You have proven that you are way smarter than me (I already new that) and everyone else at Vans.



For everyone else.....
The only down side to wiring it this way is one extra wire that maybe weighs 10 grams with connector. Other than that it hurts nothing (except that it is wrong :rolleyes:)

I have explained why Van's recommends doing it this way.... because of prior experience with start motor performance. With Van's business history, does anyone think anything would be added to the design if there wasn't some reason discovered at some point?
Regardless, it is a very simple thing to just delete the extra wire if you choose.

BTW Walt, The electrical lesson comment wasn't for you.... (I knew you would probably come back with an explanation of why it wasn't needed, regardless what I said)
It was for anyone (such as the OP) that was interested in hearing what the reasoning was (whether you agree with it or not).
 
Scott,
I agree with you 99.99% of the time and always appreciate your posts, so please don't take my questioning the theory on this one personally. Maybe it works, I don't know, if it does my simple brain just fails to understand why it would. That's why electronics is so much fun, sometimes it just doesn't make sense. Then again perhaps its time to re-evaluate, just "because we've always done it that way" doesn't necessarily make it right.
 
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Walt, I think your schematic symbol for the contactor is making it more confusing than it is. Bob Nuckolls posted a better schematic symbol a while back that makes it more obvious what's going on.

facdd36_721.jpg


The "I" terminal isn't connected to the exact same node as the output of the solenoid. It's a third connection, independent of the input and the output.
When the contactor opens, the "I" terminal disconnects from the output of the solenoid, which is not obvious from your diagram given the schematic symbol used in it.

Does that make sense?
 
RE: Starter Disengage Wire

If you dig further into the SkytecAir.com website, and read the "Jumper Wire 101" discussion, Skytec recommends that when using the "Experimental Aircraft" wiring diagram, the starter push button switch should be sized to carry at or above 30 amps for the Lycoming PM/LS starters and at or above 20 amps for the Lycoming HT starters.

Reference Note 2 in the Experimental Aircraft Wiring diagrams.
http://www.skytecair.com/Jumper101.htm

Bob Nuckolls wrote an article detailing why when not using an external starter solenoid the starter switch needs to be able to handle large currents and why it is also hard on the starter push button switch.
http://www.aeroelectric.com/articles/strtctr.pdf

If you use the Vans Aircraft wiring implementation and as Skytec points out the wiring implementation used by almost all certified aircraft, the starter push button switch only needs to be rated to carry 3-4 amps. The upside of using the Vans recommended wiring for the starter is that a lower DC current rated switch can be used and the switch will see less wear and tear and should last longer. So in a round about way, I think SkyTec actually answers the question on why Vans does it they way they do.
 
Walt, I think your schematic symbol for the contactor is making it more confusing than it is. Bob Nuckolls posted a better schematic symbol a while back that makes it more obvious what's going on.

facdd36_721.jpg


The "I" terminal isn't connected to the exact same node as the output of the solenoid. It's a third connection, independent of the input and the output.
When the contactor opens, the "I" terminal disconnects from the output of the solenoid, which is not obvious from your diagram given the schematic symbol used in it.

Does that make sense?

Thanks Gerald.
Your diagram shows the mode of operation that I understood occurred, but at this point I will take nothing for granted.
As soon as I get a chance I will be taking a close look at how the start solenoid operates.
I will report here what I find.

Edit: After doing a quick search I found this text written by Bob Nuckolls in the discussion thread where the above diag was originally posted...

"At some later time, there was a rise in popularity
of PM motors on light weight starters. If wired
per the B&C philosophy, counter emf voltages
generated in the starter motor during spin-down
would keep the jumpered, built-in contactor
energize for seconds after the starter button
was released."


And....

"There is another option for adding the external
contactor on a PM starter and dealing with the
run-on problem.

You can use the contactor's "I" terminal
to energize the solenoid-contactor yet
release it the same time that the starter
switch opens. "


PM starter means Permanent Magnet starter..... one that will turn into a generator while being driven by the engine.
I will do some testing to confirm that the start solenoid currently sold by Van's actually functions as detailed in the diagram.
 
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It's fiberglass - it'll fit - sometimes before, sometimes after we work on it. Some field adaptations require more effort than others, that doesn't make them wrong.

As for the rest - Scott, we appreciate that you know a bunch of stuff, and that you are trying to "educate the masses", but there are occasionally folks out here that know stuff too. It would be nice if you quit trying to be the smartest guy in the room.

Just my 2 cents, but I've only got 3 degrees, what do I know?

And this brings what valuable input to the discussion?
 
Thanks Scott
If the contactor was designed as in Walt's diagram I see no advantage to making a change from Skytec's method, but as shown in Gerald's diagram I see the difference.
I will wire mine as per Van's instructions.
 
Walt, I think your schematic symbol for the contactor is making it more confusing than it is. Bob Nuckolls posted a better schematic symbol a while back that makes it more obvious what's going on.

The "I" terminal isn't connected to the exact same node as the output of the solenoid. It's a third connection, independent of the input and the output.
When the contactor opens, the "I" terminal disconnects from the output of the solenoid, which is not obvious from your diagram given the schematic symbol used in it.

Does that make sense?

Great find on the diagram (I grabbed one off google), like Scott I think I have a couple of solenoids at the hanger that I can actually check operation of to see how they work, if they are wired the way you've shown in this diagram than that would explain how the Van's wiring would work (maybe all solenoids aren't the same?) Just goes to show you can't always trust what you see on the internet!

Update.. I found where Paul Dye dissected a starter solenoid and the 'I' terminal is connected to the center disc which disconnects when the relay drops out so the Nuckols diagram is accurate and the one I posted from google is not.
So if you have a PM starter I agree that Van's method looks like an alternative method to wiring the starter that may improve starter operation. Be sure to use a heavy gauge wire in the circuit as the starter solenoid draws a pretty good current.
I officially apologize to Van's and Mr. Daniels for ever doubting them! (and don't always trust the stuff you find with google!)

P1010787.JPG
 
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ok, you guys got me curious here, had to go check myself, main contactor, .5 amp, starter contactor 2.6 amp. so I think my fancy dancy red lit when activated 20 amp start button on the dash should work.....wiring still........in progress..............
 
As for the rest - Scott, we appreciate that you know a bunch of stuff, and that you are trying to "educate the masses", but there are occasionally folks out here that know stuff too. It would be nice if you quit trying to be the smartest guy in the room.
Just my 2 cents, but I've only got 3 degrees, what do I know?

You owe Scott an apology.
 
You owe Scott an apology.

+1 Absolutely.

Having spent a few years as a mechanic and getting a couple of ME degrees and 40 yrs of experience, here is a statement that I found profound:

"In theory there is no difference between theory and practice, but in practice there is."
 
Good subject

The only reason I joined this website was to be educated. I very much appreciate the individuals (Scott) that are willing to take the time to share knowledge.
 
Does anyone run a wire from the starter motor back to a light labeled starter engaged?

It is nice to know that power has been removed from the starter when the start relay is unpowered, they have been known to not open after the start switch is released.

(no degrees at all, just barely made it through HS :))
 
You owe Scott an apology.

I'll second that. Scott's patiently explained and shown me the real-world, experienced facts surrounding a few common (and one or two not-so-common) idiosyncrasies in airplane building (and manufacturing). And the most valuable of that information was gained through his experience. You pretty much always know what Scott's thinking on a given topic, because he's willing to share, and in my experience that's a good thing. :)
 
The last thing Scott would expect or need would be an apology. He puts himself out there on this forum and knows what he is getting himself into. We are lucky to have such a resource to keep all of us amateurs on track. People say things all the time on forums that woukdnt be said face to face. Let's give the guy a break and move on.
 
Calling people out isn't very civil either. No worries though. This is a fun place to hang and we all seem to have each other's backs as VAF'rs.
 
Great Forum to learn from

Scott takes his time to try and help us amateurs out and does a nice job. We don?t have to take everything as gospel, that?s our call. I wish I could add 10% of the help he provides (and others). Taking all of one minute to take a shot at him seems irresponsible. Getting input from people who actually do something and not take tests for a living is priceless.
 
Starter engaged and "I" contactor terminal

I was planning to use the "I" terminal to supply a "starter engaged" lamp. It seems that using "I" to engage the starter motor solenoid would preclude that lamp usage.

Does that seem correct? Or perhaps it would work with a big resistor in series with the lamp and ground?
 
So, can anyone update the information in this thread? All of the links go nowhere at this point (probably since Hartzell bought Sky-tec). I would like to know whether one can install the LS starters using the internal solenoid only, i.e., without a separate starter solenoid.

Thanks,
Greg
 
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