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Are you suggesting that the ability of the solenoid to pass hundreds of amps through the massive contact points are determined by the resistance in the small solenoid plunger coil circuit? How is this possible? The two circuits are electrically isolated.
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My Key-Switch Theory
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This may be a bit premature, but I now believe that my key switch is breaking the 12V circuit to the starter contactor, when it is turned to the extreme right. During the transition to this position, my prop starts moving, because the starter contactor is energized. Then, it's de-energized due to the faulty switch. I never heard starter contactor chatter during my starting attempts. Previous to last night, it would take 3-4 attempts at turning the key to get the prop past the compression stroke. My theory is, once past the compression stroke, the prop finally had enough spin momentum to start the engine, despite the key eventually breaking the starter contactor circuit. BTW, My key-switch is ACS P/N 11-03170 (A-510-2 FAA-PMA Approved). The key assembly was installed by the builder 12 years ago. Dale |
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IOW, what Dale said above ought to make sense if you consider that the switch worked correctly for a while, but then started "acting up". This kinda stuff happens all the time with sliding contacts - they get burned and oxidized at the edges. And I suspect youre in an edge condition. Eitherway, if you can make it function as Dale describes, that ought to clue you that its the switch internals themselves, and again, take apart your switch and you'll discover exactly whats going on. Noone else can say for sure with your particular switch, just speculate. |
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None of us can see/hear what you do. But low starter voltage will present somewhat different symptoms from a bad switch. If it's the switch causing the problem, the start contactor will either be engaged, or not engaged, or chattering. It *won't* cause a low voltage condition at the starter. So there will either be full start voltage, no start voltage, or pulsed voltage. Pulsed voltage caused by a chattering switch isn't likely to effectively move the prop.
If the switch is making and then breaking, the engine will likely still come up against a compression stroke; once moving, 'flywheel' effect will try to keep it moving. But you'd likely see the prop recoil slightly after hitting the 'spring' of compression. You can see the same effect if the battery is actually too low to push a blade past compression; the prop recoils when you release the start switch. Low voltage at the starter would likely drive the prop against the compression, and hold it there (until the switch is released; see above). |
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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). |
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Keep in mind the voltage sag when the starter engages. That same voltage sag will be present on the starter solenoid. If your start switch has bad contacts, the voltage getting to the starter solenoid my be adequate to hold it shut with no voltage sag, but once the starter drops buss voltage, the starter solenoid drops out from under voltage. I hate Cessna style legacy key igntion switches. I alway use toggle switches for the ignitions and a push button for the stater solenoid. Carl |
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Larry |
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If it tried to climb the compression stroke and gave up (solenoid dropped out), that's completely different than really slow to climb the compression stroke (low amperage at the starter), and you drop the key to try again. That's the trouble with diagnosis by internet - Words have very specific meanings to different people. |
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