A Spark of Hope

Posted February-March 1998

(Note: These two postings wrapped up an eighteen-month saga having to do with getting my Fly Baby's electrical system to work properly).

Part 1

The story thus far:

Back when I bought Moonraker, my C-85-powered Fly Baby, the previous owner pointed out a red switch on the electrical sub-panel. The purpose of this switch, supposedly, was to bypass the regulator and charge the battery at maximum rate.

After I blew out my new radio (probably due to overuse of the red switch), I safety-wired it to the off position and swore to never use it again. But then I noticed the battery just didn't seem to be charging during flights. I pulled the cowling, traced the wiring, and discovered all the red switch did was connect the regulator/generator to the battery. In other words, the normal mode of operation should be with the red switch ON!

I then figured the regulator was bad, and bought a new one at the auto-parts store. It seemed to do the trick for one flight. The following day, the overcharge condition was back.

That's where things stayed for about eight months. Moonraker has a plug-in battery-charger port in the belly, so I'd just hook up a charger during preflight. On long trips, I'd blip the red switch on occasion to add a bit of charge to the battery.

Moonraker also has a switch that disconnects the generator field from the regulator. While the switch checked out with an ohmmeter, it didn't seem to affect the charge rate. As of several months ago, I decided the problem was in the generator and resolved to pull it off and get it fixed over the winter.

I was stymied at first, though. For one thing, there isn't much room between the back of the engine and the firewall. I didn't have much room to take the generator off. Also, there were a lot of other accessories on the case. Access to one of the nuts looked a bit chancy.

I figured I'd solve the "limited room to remove it" problem once the generator was unbolted from the engine, and decided to start the removal with that nut with poor access.

I couldn't get a wrench on it. The left mag and the tachometer drive was in the way. I used distributor wrenches. I bought special wrenches. I bent wrenches. I ground wrenches. Still, I couldn't get a wrench into a position where it could turn it more than 1/13th of a rev.

The only way to remove it was to pull the left mag. Darn it, I didn't want to DO that. I knew the engine would need retiming, and that's something I've never done. But the last two times I flew, the generator wouldn't charge at ALL. My A&P buddy offered to time the engine when I was done, so last weekend I decided to bite the bullet and pull the generator.

The mag itself was easy...two nuts and a pull, and it was loose. Getting it moved out of the way was tough, though. I quickly realized why the leads were so long for that mag. I clipped three or four ty-wraps holding the excess lead to the engine mount, and was able to pooch the mag out of the way.

With the mag out, removal of the problem nut became easy. Except the case of the generator was open, and the nuts and washers had a tendency to drop down into the generator itself. I'd have to watch that on reinstallation.

Finally, the generator was loose. Back as far as it'll go...and it hits the tach drive cable and the cabin heat box. Loosen the heat box and try to shove the tach cable out of the way. Pitch up the back end of the generator, slide it out a bit, pitch it up some more, slide it out some more... and finally, out it comes, straight up, back end first.

I reach onto the flange to remove the old gasket. Hmmm...comes out in two pieces, with a little gap between them. Why? No matter, have to buy a new one anyway.

I slip the mag back into place temporarily, stuff a rag into the open generator hole, and haul away my parts. I had suspected that the field-coil was grounded to the case. On one of my previous investigations, I'd measured about 5 ohms from the field terminal to ground. That seemed a bit low, but it sure wasn't a dead short.

Monday, I drop off the generator and regulator at a local auto-electric shop. I don't tell them it's off an airplane...sometimes they get huffy. I tell them of the symptoms and about the overcharge even when the field coil They tell me to come back at closing time the following day, and they'll tell me what they found.

I went to the aviation-supply store to get a new gasket, and discover WHY the old one came off in two pieces: The gasket not only goes under the generator, but it seals the tach-drive takeoff too! It tore because I didn't unbolt the tach drive. Oh, well, had to replace it anyway, and with the tach drive off, it'll be easier to reinstall.

Back at the auto-electric place. "Your generator's fine," they tell me. "It was the regulator."

I felt like crap. I hadn't needed to take off the magneto and tear up the gasket. I could have just replaced the regulator again, a simple ten-minute job.

But waitaminute. "But the generator still ran at full charge, even with the field disconnected!"

The man shrugged. "Check out OK."

"Did it regulate OK on the test stand?"


I bought a new regulator and went home, feeling glum. Doggone it, if was just the regulator, there was no reason to have dug into the engine so far. I could be flying this weekend, instead of reinstalling parts.

But geeze, why did it still full-charge with the field disconnected?

I slap my DVM on the generator. Now the field resistance to ground is a tad over 1.1 ohms.

I call my mechanic buddy, and he recommends another auto-electric shop. I drove over during lunch today.

It's a pretty big place. One of the salesmen leads me back through the bookkeeping section and parts counters to the far back corner of the building.

"What can I do for you," asks the technician. He's big and bearded, like Grizzly Adams in a greasy blue shop coat. His workbenches are surrounded by starter motors the size of my thigh; the kind Boom-Boom uses on Badwater's pacemaker every morning.

I pull the generator out of the box. It looks like a slot-car motor compared to the behemoths stacked nearby.

The tech looks at it. "Do NOT tell me what it came out of," he said.

Ummm...OK. "It's all right, it's from an Off Road Vehicle."

"Great. Looks to me like it came from an airboat powered by a flat-four Lycoming."

"Ah...Continental, actually." I explain the problem, and the fact that another shop had already given it a clean bill of health.

"Let's give 'er a test." He fits a coupling to the drive gear. "It's funny, I'm not supposed to work on some kinds of parts, but the guys who rebuild them bring 'em over here for me to test 'em out."

"It's weird, all right," I told him. "The other outfit said it was fine. But at the time I pulled it out of the airplane...."

The man erupts in a coughing fit, coupled with severe mumbling.

I realize: "I mean, when I pulled it out of the AIRBOAT, it wasn't working at all."

He clamps it to a holder, engages the gear, clips on some wires, and spins it up. "Nah, look at that." He clips and unclips the wire to the field. The output stays fixed. "Your field is shorted to the case."

Whew. At least I now know that there is actually something wrong. I didn't pull it off for nothing.

The tech pokes at the generator. "Bearings are good. Sometimes the brush holder wears and short out the field, but this looks good. It's in pretty good shape, really, 'cept for the field. But I don't know if I can get the part. Have you looked into getting a replacement unit?"

I tell him of the rebuilt units I'd found for ~$300, and the alternator replacement I could get for about $350. He felt that was a bit steep.

He looks it up in his parts book. "I'll be durned, there it is." He makes a call. "Geeze, they got it in stock, just down the road. Costs $28. What do you want to do?"

I gave him the go-ahead, of course. Should have the generator back by Friday.

Maybe, just MAYBE, I'll get this electrical problem licked at last.

Part 2

(A summary of the last posting: I finally pulled my generator off the Fly Baby a couple of weeks back. The generator never has operated properly since I bought the airplane; it overcharged badly. I took the generator and the regulator into a local auto-electronics place. They said the generator was OK, but the regulator was bad. I was suspicious of the diagnosis, and took the generator to another shop. There, the technician quickly determined that the field was shorted to ground.)

You would hope that the rest of this story would be simple. Gosh knows, *I* thought there wouldn't be too much more of it. Goes to show you.

I picked up the generator from the rebuilder on Friday about two weeks ago. He'd replaced the coil. Parts cost was $38, plus another $30 labor.

One curse when I was trying to troubleshoot the original problem was the lack of data on the resistances of a GOOD generator. Prior to reinstallation, I took an ohmmeter to it. Resistance from the Armature to the Ground was one ohm, and from the Field to Ground was 8.2.

Reinstallation the next day was fairly straightforward. I'd had to pull the left magneto to get to the nuts holding the generator on, so I had good access.

I had anticipated one problem and managed to forestall it. You see, the generator case is wide open around each mounting-nut location. When I unscrewed the mounting nuts to take it off, the washers dropped into the generator. I *certainly* didn't want that to happen during installation! So I closed the gaps with duct tape.

Reinsertion of the generator was pretty easy. The gear drive didn't want to mesh at first, so I rocked the prop back and forth. That did the trick.

The first electrical shop had announced that the regulator was bad (I took in the regulator that had been on the airplane when I bought it, rather than removing the one I'd replaced it with, about 18 months ago). They sold me a new one, and I decided I might as well use it. Three 3/16" studs on the engine side of the firewall provide the mounting. By this time it was dark. I dropped one of the nuts, and rather than dig around on my hands and knees, I dug out an AN-3 nut from the cabinet.

The trouble was, the end of the stud was apparently damaged. I could get the nut started, but when I tried to tighten it the whole stud rotated, screwing itself back into the firewall.

I gave up for the night and came back on Sunday. I brought my hacksaw and a file, planning on cutting off the end of the stud and cleaning it up. Off came the regulator (again). I peered at the end of the stud in the light of day. Odd...the end didn't *look* damaged. I grabbed one of the nuts. It rotated a little rough, but threaded normally.

What the heck?

I took a close DAYLIGHT look at the stud. Sure enough. It was threaded 10-24 instead of the 10-32 of the AN nut I'd been trying to use.

One trip to the hardware store later, I had the regulator installed. I polarized it per instructions (touching a wire between the regulator +12 terminal and the Armature terminal), and was ready to try it out.

Couldn't, though. I'd had to pull the left mag off to get the generator out, but don't have the expertise to reinstall it. I called up my long-suffering mechanic friend Ed. He came out Monday. He'd never worked with an Eisemann mag before, so it took him a while to find the index marks, etc. But by the following Monday evening, Moonraker was ready to try out the new generator.

It's staying light later in the evenings, now, so I took my flying togs to work on Wednesday, and hit the airport after work. Crank it up and taxi out. Voltmeter stays at about 12.5 volts the whole way. Run up. No rise in voltage, no charge on the ammeter. Takeoff and climb out. No change. Turn on lights and strobe. Voltmeter drops, ammeter shows a discharge.

It wasn't working.

The wiring was good. The generator had probably been tested after the field was replaced. The regulator was brand new.

What *now*?

Last weekend, I did what trouble-shooting I could. The wiring re-checked OK. A buddy with an Ercoupe came by, and I prevailed on him to let me measure the resistances of his generator.

Both the armature and the field terminals were about 20 ohms to ground. MUCH higher than mine. His generator was connected to his regulator, but that should have made the resistances LOWER, not higher.

HAD my generator been tested after the repair?

The prospect of having the redo the entire process was looming before me. I called the tech, and explained the problem. He was confident that the generator was OK. "How can I wire it up to test it without the regulator?" I asked.

"All right. First thing, make sure EVERY electronic device is offline. Then connect the field terminal directly to ground, and connect the Armature terminal to the battery. Start the engine, but DON'T run it any faster than idle. You should see the battery voltage rise."

[Update and reminder:  When you hook up the generator like this, you're not only connecting it without a regulator, you're connecting the generator *as if it were a motor*.  The battery is trying to spin the motor, and it will draw a lot of current just standing still.   You should NOT connect it in this fashion for any longer than you have to.   Best bet would be to hook up a remote switch for the battery connection to the Armature terminal or have someone else apply power after the engine starts.  I did it myself, with just a clip lead, connecting it to the battery and then climbing into the cockpit and starting the engine.  I had no problems.  But I did hear from a man (15 years after I originally wrote this piece) who burned out his generator from leaving it connected too long.  So be cautious!]

I gave it a shot this afternoon. A clip lead from the field to the ground, and I connected the Armature and the +12V lines together at the regulator. The 12V supply at the regulator is controlled by a separate switch on the panel.

Crank up the engine. Flip the switch.

The bus voltage DROPPED. Bad sign.

I ran the throttle forward a bit. No change. A bit more.

The needle rose slightly.

I ran the throttle up to 2000 RPM, and the voltage increased smoothly with the throttle position. The generator was OK, after all.

Every regulator I owned was at the airport. I had the one originally on the airplane (that the first electrical shop had declared bad), I had the one I'd bought at the car-parts store to replace it, I had the one I'd just installed last weekend, and I had a $5 used one bought at the Arlington Fly-In Flea Market last summer.

Time to measure some resistances. Touch the meter to the regulator from the car-parts store, and note the readings.

Grab the original regulator....

Hey, wait a minute.

The regulators were NOT the same. Both had three terminals in the same order, but while the middle terminal was equidistant from the other two on the auto regulator, the original regulator had the middle terminal off-center.

Light dawned. I grabbed the regulator I bought at the aviation Flea Market. Its middle terminal was off-center, too. The one currently on the airplane had the equi-distant terminal.

The meters definitely showed a difference. While the auto regulators had a ~15 ohm Field Terminal to Ground resistance, the aircraft one had 2.2 ohms. And, of course, the generator wanted the field-terminal resistance low when it was to produce power.

Did the first electrical shop decide my original regulator was bad because they didn't realize it was an aircraft model? The second shop had recognized the generator's aviation origins...but maybe the first shop hadn't encountered them before.

Obviously, the next step was to put one of the offset-terminal regulators in. I played a hunch, and reinstalled the original regulator, the one that was in the airplane when I bought it.

Voltage was low during startup and taxi...but rose to the lower part of the green arc during runup. I flicked my glance downward during the takeoff run. Up to the middle of the green and stable. Once safely on climbout, on came the lights and strobe. The needle flickered but kept the same reading.

Then I noticed it. Whenever the radio broke squelch, there was a faint buzz in the background.

Generator whine. Sweetest sound I've heard in a long time.

For the first time since buying the airplane eighteen months ago, the electrical system was working properly. The whole problem all along had been the shorted field windings on the generator. That cost me about $70 to fix, plus a total of about $60 on two models of the wrong kind of regulator.

I've since been told that there are different types of auto regulators, and wonder if I got the wrong type. The original one was stamped "DELCO-REMY," so I wonder if the old GM-standard generator worked differently from my aircraft one. Maybe a Ford or other type of regulator would have worked. But let that be a lesson...just because it looks like the aircraft model doesn't mean it operates like it.

This is, I think, about my fifth major posting about the problems with Moonraker's electrical systems. I'm dearly hoping that it's the last. Then again, so are most of you, but for other reasons.... :-)

Update February 2009

Sadly, it wasn't my last bit of charging-system problems...but I went ten years until the next batch.  Check out that story, which also includes in-depth technical information and trouble-shooting tips.

Comments? Contact Ron Wanttaja.

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