C-85-12 Generator failure

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dlsmith

Pre-takeoff checklist
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Dylan Smith
Hey all, I had an interesting experience tonight. I was flying along in the luscombe and noticed my ammeter was showing a fair amount of discharge. The battery began to die fairly quickly, and was soon gone. Of course this was at night, so I got to make a landing with no light inside or out :yikes:

It still has the stock generator. It has always struggled to keep up a bit, and I wonder if this is the cause of my radio transmit problems. I'm running a Valcom 760, Garmin GMA340 audio panel, landing light, nav lights, panel lights, and a Garmin GTX320.

Should I even try to troubleshoot the generator, or is this load enough that it's time to ditch it for a B&C system? By the way, all of the fancy gadgets in the cabin were on it when I bought it, so don't blame me :lol:
 
It could be that the generator has given up the ghost but it could also be a shorted cell in your battery or a bad VR. A bit of troubleshooting is in order to determine exactly what is going on before blindly throwing money at it. The original generator, in working form, would be capable of handling the load.
 
Okay, I'll see if I can do some troubleshooting. I just wasn't going to waste my time fixing it if it would be inadequate to begin with


Also, could the battery cause a total failure? I know mine is getting rather weak
 
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dlsmith said:
...Also, could the battery cause a total failure? I know mine is getting rather weak
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They can and I can't explain to you exactly how but it has to do with material flaking off the plates as they age and eventually it can build up to the point where it can short out a cell or two and then your generator is trying to pump a 9 volt battery up to 12 volts and it ain't never gonna happen.

A few simple checks with a voltmeter will give you some clues, a shorted cell will be obvious. Is your GEN light on?
 
Silvaire said:
They can and I can't explain to you exactly how but it has to do with material flaking off the plates as they age and eventually it can build up to the point where it can short out a cell or two and then your generator is trying to pump a 9 volt battery up to 12 volts and it ain't never gonna happen.

A few simple checks with a voltmeter will give you some clues, a shorted cell will be obvious. Is your GEN light on?
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There is no gen light, only thing I have is the ammeter. Pulling the battery and testing it in the morning
 
You might want to check the generator capacity and load you are putting on it.
I have a "large" 25 amp generator and when I added strobes I needed to go to LED Nav lights.
I like the generator system in planes, they work well. I do run a electronic VR, I hate points in any electrical system.
 
You may have a bad battery, you may just need a set of brushes for your generator, may be a regulator fault, may be an excuse to lose some weight and get an alternator.;)
 
Troubleshoot before arbitrarily replacing components. No sense throwing money at it indiscriminately.
 
Norman said:
Troubleshoot before arbitrarily replacing components. No sense throwing money at it indiscriminately.
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There is the factor of cost of diagnosis. There are situations where diagnosis becomes a painstaking process that costs time $. If one is looking at an option of full system replacement/upgrade, finding out exactly what the problem is once a few common issues have been eliminated, it becomes a waste of money. When I was buying my 310, the old owner was having trouble diagnosing why the left generator wasn't coming on line, I made him a deal, I would buy the alternators, he covers the install, problem solved and I had the alternators I wanted for the panel I was going to put in plus I got rid of 50lbs in the 50 year old charging system.
 
Jimmy cooper said:
I would get an alternator. Price is ok and much better than old generator.
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$900 for the BC433 30A PMG
$1200 for the Plane Power ER-14 kit 50A

see Classic Aero and talk to Doug Combs for specs

Both are STC'd The B&C is a pretty slick little unit that only weighs five and a half pounds but honestly the old Prestolite will work fine, you can get bearings and brushes for next to nothing. Nine hundred bucks is nine hundred bucks, you might just need a battery or voltage regulator or it might just be a broken wire somewhere.
 
I bet it's brushes. Cheap to fix, but maybe now days expensive to get properly diagnosed.
 
Generators have one advantage over alternators: you can hand-prop the airplane when its battery is totally dead and the generator will pick up and recharge it. The field pole shoes in that thing carry residual magnetism that allow that to happen. The alternator's rotor also carries a bit of residual, but the diodes in it have a one- or two-volt breakover that prevents bootstrapping.

And that advantage is the only one. Generators are heavy, easily double the weight of an alternator. Generators are longer, too. They're typically 25 or 35 amps, while an alternator will be 60 or 70. The generator will often not put out anything until the engine is at 1200 RPM, making a long taxi at night a pain, while the alternator is working right from idle. The generator's brushes don't last long, maybe tow or three hundred hours, and less if you work it hard, because the brushes are carrying the entire output current. The alternator's brushes are tiny and last a long time because they're only carrying the max 4 amp field current. The alternator's regulator is simpler and lighter.

You'd have to upgrade the output wiring for the larger current and install a larger output breaker.

On the subject of regulators: I've had many more failures with the electronic regulators than with the mechanical ones, some of them lasting only a few weeks. The electronics in them are sensitive to burnout by voltage spikes, and some of them are also sensitive to stray RF from poor com antenna coax connections and will trip when you transmit. That problem can take a mechanic a long time to track down if he's not aware of the potential.

Dan
 
Dan Thomas said:
Generators have one advantage over alternators: you can hand-prop the airplane when its battery is totally dead and the generator will pick up and recharge it. The field pole shoes in that thing carry residual magnetism that allow that to happen. The alternator's rotor also carries a bit of residual, but the diodes in it have a one- or two-volt breakover that prevents bootstrapping.

And that advantage is the only one. Generators are heavy, easily double the weight of an alternator. Generators are longer, too. They're typically 25 or 35 amps, while an alternator will be 60 or 70. The generator will often not put out anything until the engine is at 1200 RPM, making a long taxi at night a pain, while the alternator is working right from idle. The generator's brushes don't last long, maybe tow or three hundred hours, and less if you work it hard, because the brushes are carrying the entire output current. The alternator's brushes are tiny and last a long time because they're only carrying the max 4 amp field current. The alternator's regulator is simpler and lighter.

You'd have to upgrade the output wiring for the larger current and install a larger output breaker.

On the subject of regulators: I've had many more failures with the electronic regulators than with the mechanical ones, some of them lasting only a few weeks. The electronics in them are sensitive to burnout by voltage spikes, and some of them are also sensitive to stray RF from poor com antenna coax connections and will trip when you transmit. That problem can take a mechanic a long time to track down if he's not aware of the potential.

Dan
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There are self exciting alternators as well.
 
Dan Thomas said:
...And that advantage is the only one....
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Well I think the other advantage is that it's already there and, for all we know, still works (it hasn't been proven that the generator is at fault here)

So personally I don't see a compelling reason to tear it out and put a thousand dollar hole in my wallet. My Luscombe still has the original Prestolite generator and the lights and radio work just fine.

I'd also have to disagree that generator brushes need to be replaced every 200 hours. Checked maybe but not replaced.
 
Silvaire said:
Well I think the other advantage is that it's already there and, for all we know, still works (it hasn't been proven that the generator is at fault here)

So personally I don't see a compelling reason to tear it out and put a thousand dollar hole in my wallet. My Luscombe still has the original Prestolite generator and the lights and radio work just fine.

I'd also have to disagree that generator brushes need to be replaced every 200 hours. Checked maybe but not replaced.
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Yeah, no, brushes last way longer than 200 hrs. You shouldn't go through 2 sets in the life of your engine.
 
Okay, well I've determined that the battery and connections are not the problem after putting a hot battery on it, cleaning and tightening everything. I'm still not showing a charge. I'll try the regulator next
 
dlsmith said:
Okay, well I've determined that the battery and connections are not the problem after putting a hot battery on it, cleaning and tightening everything. I'm still not showing a charge. I'll try the regulator next
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I would inspect the brushes and commutator first.
 
The VR on this thing says something about a "trouble-shooting light". Any clue what that is and how to use it? Thanks.
 
A 'trouble shooting light' is usually a small screwdriver looking pointy probe with a light bulb in it and a ground wire coming out of the handle. You can find where the power is and isn't quickly and easily. You just touch it to different contact points and find where in the system the electricity isn't.
 
Oh okay, a test light then. From the way it was worded I couldn't tell if it meant that or something integrated into the regulator
 
Silvaire said:
$900 for the BC433 30A PMG
$1200 for the Plane Power ER-14 kit 50A

see Classic Aero and talk to Doug Combs for specs

Both are STC'd The B&C is a pretty slick little unit that only weighs five and a half pounds but honestly the old Prestolite will work fine, you can get bearings and brushes for next to nothing. Nine hundred bucks is nine hundred bucks, you might just need a battery or voltage regulator or it might just be a broken wire somewhere.
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I just paid $818 out the door for my Plane Power unit incl wiring and regulator. The only thing I had to add was a 7.5 amp CB. Weight was 7Lbs and puts out 50 amps no problem from 1300revs. This included a drive gear for the E225 engine, and I think the drive gear for the C85 is about the same.
 
I have really enjoyed my Plane Power alternator in my 8E. It was a joy to replace the old generator. There were always issues.

I bought mine straight from Plane Power for $750. They were offering a special, and I got a $200 rebate. A sweet deal! However, that was several years ago.

I have had zero issues with the new lightweight system.

Deb
 
Good to see you weigh in Deb. I read a lot of your posts and comments when looking at this plane, and they were extremely helpful and a primary reason I bought it!

I haven't had any more time to dig into this problem yet, and probably won't this week due to classes and trying to finish my cfi. I'm not sure I can justify an alternator conversion at the moment if rebuilding the generator will do the job, but I will update as I dig deeper.
 
I owned a Luscombe F model a few years back. It had been all redone by a real pro. Who had also been a superintendent for a manufacturer. He put in a 60 amp alternator to power wingtip strobes a landing light and a transceiver and transponder. ( Concorde battery) It was a real beauty. The alternator was much lighter than the old generator as was the lightweight starter. On my Stearman was a distributor which was constantly screwing up and I wasted a lot of time taking it off, having it repaired, etc. same on the cessna 195.
 
dlsmith said:
Good to see you weigh in Deb. I read a lot of your posts and comments when looking at this plane, and they were extremely helpful and a primary reason I bought it!



I haven't had any more time to dig into this problem yet, and probably won't this week due to classes and trying to finish my cfi. I'm not sure I can justify an alternator conversion at the moment if rebuilding the generator will do the job, but I will update as I dig deeper.
Click to expand...


Hope you enjoy your Luscombe!

Good luck chasing down the charging issue. Hopefully, it's a simple fix.

Deb
 
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