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Topic Options
#406629 - 09/20/20 11:15 AM Generator, Regulator, or amperes gauges?
Peanut92 Offline
Safety Pilot

Registered: 04/27/20
Posts: 26
Loc: Tennessee
I was 30 minutes from my home airport and noticed the generator light was very dim, but on at 2,000 rpms. My light comes on at 1,100 or so. I shut everything down but the radio. Upon landing and parking, it wouldn’t quite start backup. It had obviously drained the battery in flight. AP buddy of mine diagnosed some today. Regulator is a made in USA Delco. Looks absolutely new. Cleaned contacts. Cleaned and inspected brushes which also looked incredibly clean and full of material. The armature looked very clean. I charged the battery last night. After all of the connections were cleaned and checked, she fired right up. No charge. No discharge. Fuse looks good. The generator light comes and goes with the 1,100 rpms I’m familiar with. Is the ampers meter broken? What’s this a symptom of?

#406630 - 09/20/20 11:34 AM Re: Generator, Regulator, or amperes gauges? [Re: Peanut92]
4313 Offline
Pilot in Command

Registered: 11/05/13
Posts: 256
Loc: Iowa
I'd check voltage at the buss and then at the armature while running to see if you are in the 13.8-14.2 range for both. If the buss is low then the fuse may be the issue. Get the wiring diagram out of the mx manual to figure out where to check for charging voltages.


#406633 - 09/20/20 12:33 PM Re: Generator, Regulator, or amperes gauges? [Re: 4313]
skyhawk3 Offline
Bronze Pilot

Registered: 05/06/11
Posts: 592
Loc: Vancouver BC
I have usually found that the contacts in the voltage regulator are the problem. The contacts actually arc a very small amount when opening and closing, like any relay. Over time they get dirty and pitted. If you cleaned them and it is now working - that was most likely the problem.

Edited by skyhawk3 (09/20/20 12:34 PM)

#406639 - 09/20/20 08:55 PM Re: Generator, Regulator, or amperes gauges? [Re: skyhawk3]
Henry M. Offline
Gold Pilot

Registered: 08/23/11
Posts: 2064
Loc: Leander, TX
I got a cigarette lighter voltmeter for my 172. It saved me a short time later when I started on a sightseeing trip and noticed the low voltage, but barely a movement on the ammeter. I had LED lights and a modern radio, and there was just not that much current draw. I turned around before there were any issues. Look for cigarette lighter volt on Amazon. Many have ISB ports to boot. Less than $20. Some less than $10.

In my case, the regulator was old and I needed a new one. I had a generator too.

It is very bad to fully discharge a battery. It may come back, but it won't have as much cranking capacity as before.

I find a voltmeter a much better indicator of the charging system health than an ammeter.
1965 C182H


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