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  #31  
Old 06-26-2018, 11:51 AM
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airguy airguy is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
Unless the high current contacts in the start contractor have deteriorated.
This is one of the failure modes of poor starter performance and is why the starter troubleshooting guide walks you through measuring voltage drop across all connections and components while passing a lot of Amps (while cranking).
Bingo, we have a winner.
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Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #32  
Old 06-26-2018, 12:19 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by airguy View Post
Bingo, we have a winner.
Agreed, which if true means that the key switch replacement is not "the" fix.
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  #33  
Old 06-26-2018, 12:24 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by airguy View Post
Bingo, we have a winner.
However, OP indicated in the first post that he replaced the solenoid, without improvement, while troubleshooting. Pretty unlikely that the old and new solenoids are both bad.

Larry
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  #34  
Old 06-26-2018, 01:54 PM
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Dale D Dale D is offline
 
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Quote:
Originally Posted by lr172 View Post
However, OP indicated in the first post that he replaced the solenoid, without improvement, while troubleshooting. Pretty unlikely that the old and new solenoids are both bad.

Larry
Guys,
To clarify, my symptoms were such that with each twist of the key-switch, I would see the prop turn 20-30 degrees, then stop. At the peak of compression, it was like watching the prop move 20-30 degrees in slow-motion. Once past the compression stroke, the next turn of the key would spin the prop with momentum, just a blade or two, to start the engine.

As a side note, I disassembled the original starter contactor, after I replaced it a couple of weeks ago. It showed minimal signs of arcing between the copper disc and two power lugs. This is what lead me to believe I might have a faulty master contactor.

More testing is needed to definitively say that the key-switch is the culprit.
But, I do believe this is the weak link in the system. Once replaced, I will be very interested to see the condition of the key-switch internal contacts.
Dale
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Last edited by Dale D : 06-26-2018 at 03:54 PM.
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  #35  
Old 06-26-2018, 05:55 PM
rv7charlie rv7charlie is offline
 
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It really is difficult to troubleshoot over the internet, and after a bunch of back & forth, sometimes it's hard to remember the original symptoms. :-)

quote from the 1st post in the thread:
Measured Voltage at various locations, per Sky-Tec’s trouble-shooting guide: 13.0 Volts (No-Load) at battery, 11.0 Volts (When Prop is Cranking) at battery, 10.6-10.7 Volts at starter (When Prop is Cranking), No measurable resistance on major power and ground cables. Above Voltage tests were with newest Odyssey battery, alone.

Hooked old & new Odyssey batteries in parallel and retested.
Result: Same start-up symptoms.

unquote.

If the above quoted measurement is correct, and voltage at the starter terminal isn't dropping below ~10.5 volts *under load*, then I'm having a really hard time seeing how either of the contactors or the start switch is the culprit. If there was high resistance anywhere on the positive side of the circuit, then the voltage at the starter terminal would be much lower than what was measured; the starter windings would appear as a virtual short to a high source-resistance current source.

What we don't know is the voltage measurement between the starter case and the battery negative post while the starter is under load. (hint, hint)

It's worth remembering that a lot of stuff has been swapped out. Stuff can get moved, even if the problem is in the ground path. That could easily explain why things are working well at the moment. Remember those no-start situations with that old car, when wiggling the battery connections 'fixes' it?

Last edited by rv7charlie : 06-26-2018 at 06:08 PM.
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  #36  
Old 06-26-2018, 08:25 PM
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Dale D Dale D is offline
 
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Default Key Switch - The Culprit

Just an update...We now have a trend!

I went flying again this evening, and the starter never hesitated once in 4-5 turns of the key-switch - cold or hot-start - just by turning the key only far enough to engage the starter.

I'm sure I could duplicate the previous symptoms by turning the key all the way to the CW stop. However, I was busy enjoying watching the 149-NL spin the prop with gusto. That was a welcome sight for me.

I would go so far to say that I would have the same successful results with my previous LS starter, my old starter contactor, and old master contactor, knowing what I know now.
However, that train has left the station, and my ticket-to-ride cost 1/2 AMU.
Sigh...

Dale
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  #37  
Old 06-26-2018, 09:03 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Dale D View Post
Just an update...We now have a trend!

I went flying again this evening, and the starter never hesitated once in 4-5 turns of the key-switch - cold or hot-start - just by turning the key only far enough to engage the starter.

I'm sure I could duplicate the previous symptoms by turning the key all the way to the CW stop. However, I was busy enjoying watching the 149-NL spin the prop with gusto. That was a welcome sight for me.

I would go so far to say that I would have the same successful results with my previous LS starter, my old starter contactor, and old master contactor, knowing what I know now.
However, that train has left the station, and my ticket-to-ride cost 1/2 AMU.
Sigh...

Dale
With these symptoms, you're not looking for failing contacts on the swithc, but an ill placed stop that is letting the rotating assembly go too far and therefor severely limit the contact surface area between the two contact plates
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  #38  
Old 07-03-2018, 01:11 PM
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Interesting how things work out...

I have the same ACS key switch in my plane, and for 260 hours it has worked flawlessly. This past weekend I experienced the same symptoms that were laid out here in this thread while starting up for an IFR training flight. If the key was rotated hard against the stop, the contactor dropped out. Back off just a hair and the contactor picks up and the starter engages.

I guess I'll replace the rotary key switch with two toggles and a pushbutton as others have recommended.
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Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #39  
Old 07-03-2018, 01:52 PM
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Since you have confirmed good voltage to the starter, try a simple test, put a test light clip on the starter +, ground the test light up on the firewall to where you can observe it while cranking, start engine while watching test light, if the engine stops keep the key in the same position while looking at the test light, did the light come on while cranking? then did the light go out when the prop stopped? remove clip from starter and work your way back through the power path to narrow it down.
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  #40  
Old 07-03-2018, 02:19 PM
rv7charlie rv7charlie is offline
 
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Here's a data point that *might* come into play if the start switch itself is failing.

A lot of early starters had a mechanism that the spinning starter used to drive the bendix forward into the ring gear. In those old systems, the start switch contacts only had to handle a few amps to pull in the starter contactor. A lot of newer starters use a big solenoid (an actual solenoid) that pushes the bendix forward and at the same time, supplies the high current contactor switching at the starter. This solenoid takes a lot more current to activate than a simple contactor.

IF (again, IF) you have a later version starter with that solenoid on its side, and you use an old style ignition/start switch designed to drive a contactor, then you MAY see shorter than normal life in the start switch contacts. Of course, the same thing would apply if you use a low current push button to activate the same starter. IIRC, B&C sells a start PB rated at around 15-20 amps.

Worth what you paid, etc...

Charlie
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