Hot Master Switch

Nav8tor

Nav8tor

Line Up and Wait
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Nav8tor
I had an experience last weekend which will lead me to be much more cautious in the future when turning on the master switch. I had heard of hot mags, where the mags can fire even with the mag switch in the off position, but I wasn't aware, until last weekend, that its possible to have a "hot master" condition that will cause the starter to spin the engine as soon as the master is turned on.

After about an hour of flying a C-182, I landed and shut the engine down for about 20 minutes. I got back in the airplane and restarted the engine but right after it started I heard a loud grinding sound what obviously wasn't normal. I immediately thought it was a hung starter but the ammeter looked normal. I pulled the mixture to idle cut off and the engine tried to shut down, but it kept turning over at very low RPM. I turned the the mag switch to off but the engine kept turning. I turned off the master, and the engine finally stopped.

After a minute of so I decided to try starting the engine again to see if the noise occured again, but as soon as I flipped on the master switch the prop started to turn (the mag switch was still in the off position).

I found out the next day that the starter contactor had gone bad, essentially bypassing the starter switch.

In the past I haven't paid very much attention to the prop when turning on the master during preflight because it never dawned on me the the prop could turn, but from now on I'll make sure no one is near the prop any time I flip on the master.

Lee
 
I would say your problem is a hot starter, not a hot master. Your master switch works exactly as intended. Don't blame the master because a contactor behind it is shorted. :D
 
Regardless where the short actually occurred, if it happens when the Master Switch is turned on, it is still a dangerous situation.

I make it a habit to announce "Master On!" (almost as loudly as "clear prop") everytime I switch one on, regardless of the aircraft I'm in. By making it a point to know where all persons are in relationship to your aircraft when activating ANY system, chances of some sort of incident/accident are greatly reduced.

You have given us all a great reminder that sometimes electro-mechanical equipment does fail!
 
Nav8tor said:
I found out the next day that the starter contactor had gone bad, essentially bypassing the starter switch.
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The 201 has an annunciator light that will come on if the starter becomes energized in flight.
 
what are you supposed to do about it bill? is there a breaker for it?
 
there probably is. i do know that the cessna 150 does not have a fuse for the starter, but your electrical system is light years ahead of the 150.
 
tonycondon said:
what are you supposed to do about it bill? is there a breaker for it?
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You are supposed to shut off the master. Since the master contactor and the starter contactor are in series that will kill the starter. Assuming you were asking about a breaker that would stop the starter, there is no such thing as it would have to pass the several hundred amps of starting current.
 
that sounds reasonable is reasonable lance. i thought maybe there was some other way to prevent losing all the other electric stuff just because of a starter malfunction.
 
tonycondon said:
that sounds reasonable is reasonable lance. i thought maybe there was some other way to prevent losing all the other electric stuff just because of a starter malfunction.
Click to expand...

Nope although my electrical system has a redundant connection to power the GPS/NavCom, MFD, and XM Wx that would still allow those units to work with the master off. But it's unlikely you'd ever encounter a starter contactor failure in flight since you have to engage the starter for it to happen. Having an in-cockpit indication of this problem should preclude taking off in that condition. You can detect a hung starter by the indications on your ammeter (big charge that doesn't taper off quickly) but warning light is more obvious and less likely to be missed. (note to self: get busy and install the starter engaged warning lights in the Baron).

BTW, anyone who finds that their starter turns over as soon as they turn on the master has very likely flown their entire last flight that way which means the starter is probably also toasted to the point of being about to fail.
 
cant you make the 480 annunciate it in a pretty female voice? :)
 
lancefisher said:
You are supposed to shut off the master. Since the master contactor and the starter contactor are in series that will kill the starter. Assuming you were asking about a breaker that would stop the starter, there is no such thing as it would have to pass the several hundred amps of starting current.
Click to expand...

Besides, if there was breaker, it wouldn't blow in this case. The starter would draw exactly what it draws when you start the engine. This is not a short in the circuit.
 
yes but if there was a breaker, you could manually pull it so that only the starter would be removed from the electrical system, not all electrical equipment.
 
lancefisher said:
You are supposed to shut off the master. Since the master contactor and the starter contactor are in series that will kill the starter. Assuming you were asking about a breaker that would stop the starter, there is no such thing as it would have to pass the several hundred amps of starting current.
Click to expand...

Go easy on him...He's from Iowa. There is a reason that Tony likes gliders.
 
Assuming you were asking about a breaker that would stop the starter, there is no such thing as it would have to pass the several hundred amps of starting current.
Click to expand...

If only they all had one of these:
:D
 

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colomtnflyer said:
You have given us all a great reminder that sometimes electro-mechanical equipment does fail!
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I'll go further than that...

I say..If it has tits, tires or transistors...at some point its gonna give you trouble.:yes:

Kelvinism 363
 
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