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C-180 Intermittent weird master switch power problem

sj

sj

Staff member
Northwest Arkansas
Ok, we have been chasing this one for a while and did some more chasing today.

Sometimes when you turn the master switch on, you get the clunk from the master solenoid, but no power. Yesterday, it was acting up. With the master OFF I pulled out the next door alternator field breaker and stuck it back in (this is a 55 C-180). Then turned on the master and it worked. I think it was a coincidence because the two are really not related and the engine was not running. We pulled the panel out today, did a bunch of continuity and other tests on the switch and the system and check a lot of connections, but could not get it back into the "fail" mode.

I have not been able to find a wiring diagram for a 55 c-180, but I assumed it works like most where the master DPST grounds the master solenoid lead to activate it, and then the other side connected the power to the main bus. However, the "bus" side did not seem to make any difference as when operated independently, the solenoid grounding side also sent power to the bus - so I am not sure what the other side does, unless it activates the alternator connection or something.

We once - a year or so ago - had things "flicker" in flight where the whole panel went off an on - which really sounds like bad ground or a loose connection. This is the third solenoid in a year, so I think we can rule that out.

Any thoughts appreciated!

sj
 
Old fashioned DPST toggle switch like you would get at the National Aviation Parts Association.

27300015_primary_225px.jpg

sj
 

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C 180 master solenoid diagram

Here's a screen shot. I hope.

Web
 

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See that is the way I thought it was supposed to be, but it seems to turn the bus on even with the bus side disconnected.
 
Wow! I made the pic come up!

Okay. It works exactly the same (electrically) as the stock switches do. It sounds like you have a bad crimp terminal or crusty connection. Locate the D-19 and D-27 wires in the diagram above. With the switch 'off', D-19 should read battery voltage and D-27 should read 0 ohms to ground. When the switch is turned 'on', both wires should read 0 volts. To bypass the switch, Pull D-19 off the switch and ground it directly to the airframe. If it turns on the master relay, the problem is probably in the switch. If not the problem is most likely in the relay itself.

Web
 
SJ said:
... but it seems to turn the bus on even with the bus side disconnected.
Click to expand...

Explain? When wired as per the diagram, battery voltage will be on the relay control coil as long as the battery is connected. Regardless of the state of the bus.

Web
 
Does it have an alternator instead of the original generator? Would that make a difference in the wiring diagram? jrh
 
Thanks Web! Will check out the switch and solenoid again as well.

sj
 
Are you getting voltage through the solenoid, 12v on both big terminals with master on? Contacts burn and corrode, the only fix is to replace the solenoid with the correct one for continuous on duty. The master should only control the solenoid and gen/alt, buss connection is through the master solenoid.
 
burning through solenoids is usually due to bad connection (loose crimp, ground or such) causing intermittent power surges, or using a intermittent solenoid where there should be a continuious.
 
Update! After noodling around with it all the other day and checking connections, things worked great for a quick trip to Boulder yesterday which involved starting the plane eight times. On the second to the last start at our fuel stop on the way home, this time the STARTER solenoid buzzed on the first attempt, then reluctantly started on the second. When we got back to the hangar, I (of course) tried it again and just a big click with all the lights dimming when the starter button was depressed. It was late after a long day of flying, going back to check it this morning.

Oh boy.

sj
 
SJ said:
Update! After noodling around with it all the other day and checking connections, things worked great for a quick trip to Boulder yesterday which involved starting the plane eight times. On the second to the last start at our fuel stop on the way home, this time the STARTER solenoid buzzed on the first attempt, then reluctantly started on the second. When we got back to the hangar, I (of course) tried it again and just a big click with all the lights dimming when the starter button was depressed. It was late after a long day of flying, going back to check it this morning.

Oh boy.

sj
Click to expand...

watch the voltage as that happens, maybe you got a broken plate in battery???

dimming lights mean not enough power, or too much load.... you may have a starter that is "binding"(field winding core is out of round, and is rubbing on itself/outside internally, can't think of right words...)
 
mike mcs repair said:
watch the voltage as that happens, maybe you got a broken plate in battery???

dimming lights mean not enough power, or too much load.... you may have a starter that is "binding"(field winding core is out of round, and is rubbing on itself/outside internally, can't think of right words...)
Click to expand...

Thanks folks! I have turned it over to the mechanic to sort out while I am out of town - unfortunately I was going out of town in this plane but too much going on to trust it in IMC which there will be PLENTY of on this trip due to Matthew closing in the East coast.

sj
 
My money is on a bad crimp or poor connection some where between the battery, master relay, and the starter relay. A poor connection here will allow enough power to run the usual stuff on the bus bar, but not enough to wing over the starter. The same issues on a battery ground cable will cause the same problems.

Web
 
Web, same thing the mech said. Prolly a crimp. He is going to go through the whole megillah.

I greatly appreciate your help!

sj
 
Also I have found starter cable under floor with area 1 or 2 long with insulation worn through and arcing to belly skin :)
 
mike mcs repair said:
Also I have found starter cable under floor with area 1 or 2 long with insulation worn through and arcing to belly skin :)
Click to expand...

Mike, actually told the mech to look at that. An ancient mouse nest had eaten through the hefty under floor cable years ago - it was patched up real nice, but worth a second look.

sj
 
SJ said:
Mike, actually told the mech to look at that. An ancient mouse nest had eaten through the hefty under floor cable years ago - it was patched up real nice, but worth a second look.

sj
Click to expand...
A mouse, say it isn't so, couldn't be possible not in your tightly sealed hanger!
 
SJ said:
... I (of course) tried it again and just a big click with all the lights dimming when the starter button was depressed. sj
Click to expand...
I had a similar problem with my 185. The solenoid was sticking. I had to take off the cowl and rap the solenoid with a pair of pliers to shake it loose. After having to do this while drifting across a pond once too many times I replaced the solenoid with a Cole-Hersee solenoid. A much better quality than the one Cessna uses. No more troubles.
 
OLDCROWE said:
A mouse, say it isn't so, couldn't be possible not in your tightly sealed hanger!
Click to expand...

Actually those particular mice were from the previous owner's tightly sealed hangar, which uses the same kind of insulation as mine :)

sj
 
N86250 said:
Does it have an alternator instead of the original generator? Would that make a difference in the wiring diagram? jrh
Click to expand...

Not really. When you change over to an alternator, the field power will use the same set of contacts as the generator field did. In this case the D-28 and D-30 wires would be replaced by a wire coming from the field breaker and one going out to power the regulator.

Web
 
wireweinie said:
Not really. When you change over to an alternator, the field power will use the same set of contacts as the generator field did. In this case the D-28 and D-30 wires would be replaced by a wire coming from the field breaker and one going out to power the regulator.

Web
Click to expand...

OK. Guess I was thinking about some I'd seen with alternators replacing generators and extra old wires taped up with no place to go. Makes a guy wonder why is it still there, where did it used to go, why is it still hot, and what is on the other end? All these electrons require too many brain cells to figure out what took a crap sometimes. jrh
 
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