Starting Trouble...anyone seen this before?

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Charles K
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Re: Starting Trouble...anyone seen this before?

Post by Charles K »

Thank you for the info on the Ess Bus causing start issues - would have never thought!
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Re: Starting Trouble...anyone seen this before?

Post by Steve »

Steve:

Did you not notice that your COM/NAV 2 was INOP? On my (2001) COM/NAV 2, DME, Autopilot (including electric trim) are INOP with the ESS BUS switched ON.

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Rick
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Re: Starting Trouble...anyone seen this before?

Post by Rick »

Charles K wrote: Tue Jul 14, 2020 8:26 pmThank you for the info on the Ess Bus causing start issues - would have never thought!
With a G1000 DA40, you would probably never get to the point of discovering the starting issue, because the MFD will not power up and you would sit there trying to figure out why your MFD is dead! (Don't ask me how I know this) :oops:
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shoffert
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Re: Starting Trouble...anyone seen this before?

Post by shoffert »

I'm rocking dual Garmin 430s...both were powered up. That would make sense since they both could be essential, and both could be turned off on the unit. I'm going to dig a little deeper into the books to see what I can learn, but I'll say there was nothing in the plane that was obviously not powered...day or night. Perhaps the essential bus switch isn't especially helpful in my setup...
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Re: Starting Trouble...anyone seen this before?

Post by Davestation »

I have, the left mag was grounded in the start position - bad ignition switch IIRC.


BTW the left mag P-lead is NOT grounded by the slick start, that would disable it entirely. There is a second post on the left mag for the retard breaker which it is connected to. The right mag is grounded through the ignition switch so that it doesn’t kick back since the right mag doesn’t have this function.
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Re: Starting Trouble...anyone seen this before?

Post by Rich »

Davestation wrote: Mon Jul 20, 2020 12:55 am I have, the left mag was grounded in the start position - bad ignition switch IIRC.


BTW the left mag P-lead is NOT grounded by the slick start, that would disable it entirely. There is a second post on the left mag for the retard breaker which it is connected to. The right mag is grounded through the ignition switch so that it doesn’t kick back since the right mag doesn’t have this function.
Upon digging further you are correct. What appears to happen is that the grounding bypass (via the p-lead through the ignition switch to bypass the main breaker contacts) gets connected to the SS power circuit, which is connected on the ground side through the retard breaker. With the main breaker contacts bypassed, instead the opening of the retard breaker points causes the primary field collapse, producing the high-voltage induced in the secondary field coils.
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Davestation
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Re: Starting Trouble...anyone seen this before?

Post by Davestation »

I was wondering why it said the post didn't exist when I hit reply...


The retard and main contacts are connected to each other so if the retard breaker post is grounded (during start) both points have to be opened for it to fire. The main points are still operating as normal, but between 25 and 0 the main coil is grounded through the retard breaker. When the retard breaker opens at 0 it will then fire. In other words: both points have to be open, and only both are open at 0 - when the main points open first at 25 but the retard points are closed and grounded, nothing happens.

If the P-lead is grounded, it will never fire - which is what could very well be happening in this case, through a defective ignition switch or chafed wiring etc. That is why it is up to the ignition switch to ground the right mag and the right mag only during start.
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