Electrical System Troubleshooting Guide

[Chip Sylverne]

Come on, folks. We are SEWAGGING and RECTORANDOM troubleshooting here. Lets get some data before taking off on a wild goose chase.

Jim

We know the generator produces voltage, and we know the regulator maintains correct voltage, at least for a while, and without a load. What we don't know is the failure mode, whether the system slowly loses juice or quits abruptly. Having said that, tracing wires, checking crimps and cleaning grounds and contacts should be done anyway, because it's cheap and easy, before throwing any expensive parts. A new regulator won't do any good if the field wire is damaged. One thing I've learned over the years, Start with the basics. You never know, you might get lucky.

 

[weirdjim]

We know the generator produces voltage, and we know the regulator maintains correct voltage, at least for a while, and without a load. What we don't know is the failure mode, whether the system slowly loses juice or quits abruptly. Having said that, tracing wires, checking crimps and cleaning grounds and contacts should be done anyway, because it's cheap and easy, before throwing any expensive parts. A new regulator won't do any good if the field wire is damaged. One thing I've learned over the years, Start with the basics. You never know, you might get lucky.

Chip, we agree ... sort of. We can't trace wires because the system works just fine ... cold. How do you "check" a crimp and if I hear one more time about "bad grounds" I'm going to blame it on the coffee. Yes, I've had bad grounds. Mostly Maxwell House.

Nothing, NOTHING replaces taking readings when the system falls apart, making a good guess as to what has happened, proving that happening with more measurements, and finally pointing the accusing finger. No, not THAT finger.

My guess as to what we are going to find is that generator gets hot, the commutator gets a little larger, and the brushes are pushed out of the way. But I'll be dipped in cow $#1+ and rolled in cracker crumbs if I'm going to suggest pulling the generator and sending it off for "overhaul" before we nail it down to that particular piece of equipment.

Lucky? The harder I work the luckier I get.

Jim

 

[hamer]

I made it to the airport for a quick check this evening. I didn’t have a ton of time, but I went to the runup, turned everything on and ran it up to 2000-2200RPM. I held it there for a few minutes. It started out strong, in the mid-13s then started to slowly drop, within 5 min I was at 12.2V at 2200 RPM. With around a 10A load.

Sounds like the generator is shot?

 

[Chip Sylverne]

You check a crimp by visually examining it, giving it a good yank, then cutting it off and using a clean solder connection . Jim we're talking about a genny system here, they don't come any more bone simple. How long does it take to pull out the generator and install new brushes...an hour? While you're in there, clean up the commutator. If it's got a big channel worn in it, yeah, send it out to be cut. You 've probably found your problem. Heck, pull off the belt, disconnect it from the harness and "motor" it for a few minutes. If it continues to turn smoothly, it probably good. You can spend more time diagnosing this kind of simple stuff than just going ahead and doing.

Don't A&P's fix anything themselves anymore? Does everything get "sent out"?

 

[Chip Sylverne]

I made it to the airport for a quick check this evening. I didn’t have a ton of time, but I went to the runup, turned everything on and ran it up to 2000-2200RPM. I held it there for a few minutes. It started out strong, in the mid-13s then started to slowly drop, within 5 min I was at 12.2V at 2200 RPM. With around a 10A load.

Sounds like the generator is shot?

Here's what i would do were I you. I would get on the horn to my A&P and say "hey, I think I've narrowed it down to the generator, how 'bout supervising sn IRAN?". Then I would research and order a rebuild kit, or source brushes, a bearing and bushing kit. Probably less than $25. Then I would pull it out, disassemble, clean it and see whats what. If the armature looked good, I'd clean it up. Throw a VOM on the field coils and check they were in spec. Generators are ancient tech, a million rebuild how-to's online. ..hard to screw one up if you know one end of a screwdriver from the other. Then I'd take the money I saved and buy avgas.

But that's just me. Others would buy a rebuilt for $300, or do an alt conversion for $800.
You've got an old airplane, might as well get used to getying your hands dirty.

 

[Tom-D]

You check a crimp by visually examining it, giving it a good yank, then cutting it off and using a clean solder connection . Jim we're talking about a genny system here, they don't come any more bone simple. How long does it take to pull out the generator and install new brushes...an hour? While you're in there, clean up the commutator. If it's got a big channel worn in it, yeah, send it out to be cut. You 've probably found your problem. Heck, pull off the belt, disconnect it from the harness and "motor" it for a few minutes. If it continues to turn smoothly, it probably good. You can spend more time diagnosing this kind of simple stuff than just going ahead and doing.

Don't A&P's fix anything themselves anymore? Does everything get "sent out"?

There is nothing in this thread that show me that the generator is at fault. The generators don't work for a while, then quit and start again the next start.
OBTW, I want to watch you change out a starter plus replace the brushes In an hour.

 

[hamer]

Here's what i would do were I you. I would get on the horn to my A&P and say "hey, I think I've narrowed it down to the generator, how 'bout supervising sn IRAN?". Then I would research and order a rebuild kit, or source brushes, a bearing and bushing kit. Probably less than $25. Then I would pull it out, disassemble, clean it and see whats what. If the armature looked good, I'd clean it up. Throw a VOM on the field coils and check they were in spec. Generators are ancient tech, a million rebuild how-to's online. ..hard to screw one up if you know one end of a screwdriver from the other. Then I'd take the money I saved and buy avgas.

But that's just me. Others would buy a rebuilt for $300, or do an alt conversion for $800.
You've got an old airplane, might as well get used to getying your hands dirty.

I may give this a try, watched a few YouTube videos and it looks relatively easy.

Does anyone think my generator just needs to be repolaraized? I did unplug the battery when I did some work on the transponder, I didn’t know the generator would need to be repolarized. Seems like the problem has gotten worse since then. But if it lost its polarization would it ever be able to charge at all? Could that explain the weird reading from the amp meter? I did look at the amp meter today and the wiring looked correct, the grd/pwr were going to the right place.

 

[Tom-D]

I may give this a try, watched a few YouTube videos and it looks relatively easy.

Does anyone think my generator just needs to be repolaraized? I did unplug the battery when I did some work on the transponder, I didn’t know the generator would need to be repolarized. Seems like the problem has gotten worse since then. But if it lost its polarization would it ever be able to charge at all? Could that explain the weird reading from the amp meter? I did look at the amp meter today and the wiring looked correct, the grd/pwr were going to the right place.

no,, it produces voltage, of the correct polarity.

 

[Tom-D]

It does appear to be working, but again need to test over time. What worries me is that the battery starts to fail after 20-30min at cruise, where I should have full generator output. It does also happen when I'm going touch and goes, but I spend a lot of time at idle coming down to land.

I'll make sure I get the ammeter wiring fixed, it's been a little confusing with it backwards.

After I've re-read this,, this is perfectly normal for a generator system.
20-30 at cruise the amp needle will be/ should be at 0, battery fully charged.
start doing T&Gs the battery will discharge, because the generator is not turning fast enough to support the system.

I think. you should stop picking on this and go fly.
If you want this symptom to go away upgrade to an alternator system.

 

[hamer]

After I've re-read this,, this is perfectly normal for a generator system.
20-30 at cruise the amp needle will be/ should be at 0, battery fully charged.
start doing T&Gs the battery will discharge, because the generator is not turning fast enough to support the system.

I think. you should stop picking on this and go fly.
If you want this symptom to go away upgrade to an alternator system.

I agree that the touch and go behavior makes sense, but I don’t agree that the cruise behavior does. If the battery is fully charged, and full generator output is available, why would the battery start to fail? The first thing that happens is the encoder shuts off and I lose my alitude report on the transponder, then the radio starts to fail, when I try to transmit I have to hold the PTT down for a few seconds before it clicks the mic. The voltage also drops to ~10v with every transmission, (then returns after I release the PTT, it however returns to a lower value each time).

 

[Chip Sylverne]

There is nothing in this thread that show me that the generator is at fault. The generators don't work for a while, then quit and start again the next start.

I guess you've never maintained a Massey Ferguson with Lucas electrics then.

There's only three things here that can be at fault; the genny, the control box or the wiring between the two. Apparently the control box looks new-ish. Jim describes a pretty credible failure mode for the genny. Why not do an IRAN? At best, it fixes the problem for very little money, at worst, he has a freshened genny, gains a little confidence from his A&P and learns something in the process.

 

[Ravioli]

Ooooh, the high rent district.

Now you can bill him for the advice. If he's hangared there he can afford it!

 

[flyingbrit]

The classic way of determining whether generator or regulator is at fault is to "full field" the generator while it is running and watch the ammeter for a high charge indication. On a typical Delco-Remy system with a type "A" circuit this means grounding the field terminal of the generator. To do this while airborne, an extension wire like Jim suggested could be used. Connect one wire to the field terminal and the other to a ground. Inside the cockpit place a switch across the two wires. When the discharge symptom occurs, close the switch. If it starts charging, the regulator is likely the problem. If if still discharges, the generator is the culprit.

 

[Chip Sylverne]

Which brings to mind one last shot. There are two types of genny's; the field internally grounded, or externally grounded. Most aircraft genny's are of the externally grounded type. Those have regulators that have three internal controllers; A voltage regulator, a current regulator and a cutout. Internally grounded field types only have two controllers, a cutout and a voltage regulator, and uses a bucking coil to control current. The two types aren't interchangeable, and the external ground regulators have three lugs, but they aren't evenly spaced. The photo you posted, they are evenly spaced. How many controllers were inside when you opened it?
Maybe you have the wrong regulator installed?

 

[Dan Thomas]

For once, I am going to have do disagree with you Mr. Thomas.
The old 40's 50's vintage generators /regulators / starters would work just fine hooked up either way. My first car was a '59 Sunbeam Alpine that, like a lot of English junk, was built with a positive ground system. When I bought it, a previous owner had taken it to Sears and they had installed the battery with a negative ground configuration - like a "normal" car. Everything worked fine - and had been working that way for some time. Even the two speed (off and on) electric windshield wipers worked (there was no radio). I re-did things back to the original positive ground just because it seemed to be the right thing to do.
Now, a "modern" alternator, or electronic regulator, or radio, or... won't work and you will likely end up with an expensive repair bill. But in any case, that doesn't seem to be the problem with the O.P's aircraft.

I think you're right. The generator's field and armature would both be reversed so it would produce reverse current and keep the battery going. And the starter's field would also be reversed as well as its armature, so it would continue to operate normally. Basically, anything series-wound would still work. -1 x-1 = +1.

Modern stuff with its diodes and other semiconductors would get roasted instantly. Permanent-magnet starters would run backwards.

 

[Tom-D]

I agree that the touch and go behavior makes sense, but I don’t agree that the cruise behavior does. If the battery is fully charged, and full generator output is available, why would the battery start to fail?

Because the generator probably is a 12 AMP generator, and the load is more than that.
Plus we really don't know if the battery is ever fully charged.

@ spruce
1101876 O/H 1101876 GENERATOR 12V 12A Gear 07-00079 $342.00

this is most likely what's on his 0-290-

 

[hamer]

Which brings to mind one last shot. There are two types of genny's; the field internally grounded, or externally grounded. Most aircraft genny's are of the externally grounded type. Those have regulators that have three internal controllers; A voltage regulator, a current regulator and a cutout. Internally grounded field types only have two controllers, a cutout and a voltage regulator, and uses a bucking coil to control current. The two types aren't interchangeable, and the external ground regulators have three lugs, but they aren't evenly spaced. The photo you posted, they are evenly spaced. How many controllers were inside when you opened it?
Maybe you have the wrong regulator installed?

There are 3 controllers inside, photo attached.

Because the generator probably is a 12 AMP generator, and the load is more than that.
Plus we really don't know if the battery is ever fully charged.

@ spruce
1101876 O/H 1101876 GENERATOR 12V 12A Gear 07-00079 $342.00

this is most likely what's on his 0-290-

It’s a 20AMP. The data plate says 20AMP, as does the part number: Delco Remy 1101899. It’s also belt driven not gear.

This happens during daytime VFR, the only thing running is the transponder and radio ~4-5A total.

 

[hamer]

I found a local classic auto electric shop that can take a look at it. I may have him bench test it and possible overhaul, just for the learning experience.

 

[455 Bravo Uniform]

I found a local classic auto electric shop that can take a look at it. I may have him bench test it and possible overhaul, just for the learning experience.

I wouldn’t add another variable just yet, unless that’s the most likely culprit.

 

[Raymo]

Why in the name of the holy St. Potluck are you confusing the fellow by recommending troubleshooting for alternators when he has a generator?

Jim

Just trying to help the OP with some troubleshooting ideas. Looks like an alternator is in his future now, so they will certainly help then (and other folks that find this thread).

 

[Chip Sylverne]

There are 3 controllers inside, photo attached.




It’s a 20AMP. The data plate says 20AMP, as does the part number: Delco Remy 1101899. It’s also belt driven not gear.

This happens during daytime VFR, the only thing running is the transponder and radio ~4-5A total.

Well, that looks like it oughta be the right regulator, 1118300 series or equivalent. If you want the service manual for it, I have a .pdf

 

[flyingbrit]

Hmm, googling 1118300 finds a 6V, 45A unit....

https://www.robertsandson.com/product/1118300/

 

[weirdjim]

Lycoming says that Delco part number 1119226 is the correct regulator for that generator. Be interesting to see if the OP can read a part number on the regulator.

Jim

 

[Chip Sylverne]

I guess I copied the wrong p/n. In any event, here's a pic from one for sale on eBay using Jim's part #. Note the offset terminals.

 

[Chip Sylverne]

Another image of the correct regulator

 

[JAWS]

The link below seems somewhat applicable. There are links to manuals at the end of article.

http://www.bowersflybaby.com/tech/spark2.html

 

[hamer]

Found a part number, it was buried on the other side. Looks like it's an automotive one. A little confused as to whether it's the correct type or not?

 

[weirdjim]

And there is darned little online info on a 7121 voltage regulator except a little info that it was probably from a GM automobile in the 1950s. I'll throw out a suspicion that the previous owner found the problem you have and decided the cheapest shotgun he could fire was to replace the voltage regulator with one from ebay. That regulator is clean as a whistle. I doubt it is a year old.

That didn't work, so he limped it along until he sold the airplane. That is a SEWAG and has no basis in proof.

I'm with Chip. Run the field terminal into the airplane, fire the engine up, and see how much voltage you can get MOMENTARILY grounding the field terminal directly after the mechanisms have had a good long while to warm up. I'll still stick with my original hunch (again, without proof) that you've got brushes/commutator problems inside the genny. That's a cheap (as airplane fixes go) fix at the auto electricals shop.

Jim

 

[hamer]

Thanks for the help Jim. I'll see if I can get this tested over the weekend and report back.

 

[flyingbrit]

Found a part number, it was buried on the other side. Looks like it's an automotive one. A little confused as to whether it's the correct type or not?

Looks like an aftermarket replacement for a 55-62ish GM. There wasn't much difference among these (all 12V, negative ground, 3 unit) except for the current regulator setting, which was typically 25, 30 or 35 amps i.e. higher than your 20 amp generator. It will still work, but there will be some risk of overheating the generator if it is asked to put out >20 amps for more than a few minutes. Your auto electric shop should be able to test the current setting and possibly even adjust it down to 20 amps.

 

[hamer]

Looks like an aftermarket replacement for a 55-62ish GM. There wasn't much difference among these (all 12V, negative ground, 3 unit) except for the current regulator setting, which was typically 25, 30 or 35 amps i.e. higher than your 20 amp generator. It will still work, but there will be some risk of overheating the generator if it is asked to put out >20 amps for more than a few minutes. Your auto electric shop should be able to test the current setting and possibly even adjust it down to 20 amps.

Very interesting, I wonder if it wasn't setup correctly and that's what's causing the problems with the generator. So your suggestion would be to pull off the generator and regulator and have them properly set by the shop before re-installation?

 

[Chip Sylverne]

The other thing you can do is a "motor" test. Slip the belt off the pulley, disconnect the wires from the genny. Put a jumper from the armature to the field terminal and touch the armature post with a jumper cable from the battery. If the genny is good, there will be a small spark, and the genny will run smoothly like an electric motor. If it's jerky, or runs for a while and stops, the problem is the generator. That's my preferred method with my tractors, because it takes the regulator out of the equation completely. If it motors well, no question it's the regulator. Just an alternative method.

 

[nrpetersen]

In the mid 1950s I worked as a flunkie in a car repair garage where the boss would replace voltage regulator contacts rather than a whole regulator to save repair costs. Sometimes he would encounter one that absolutely wouldn't cooperate & he felt bad having to replace the whole regulator ($5!). In hindsight I suspect one of those wire wound resistors on the back side of the regulator assembly was open causing the points to burn or the generator to behave mysteriously. Diodes were not common then and those resistors probably served as flyback current arc suppressors.

 

[hamer]

The other thing you can do is a "motor" test. Slip the belt off the pulley, disconnect the wires from the genny. Put a jumper from the armature to the field terminal and touch the armature post with a jumper cable from the battery. If the genny is good, there will be a small spark, and the genny will run smoothly like an electric motor. If it's jerky, or runs for a while and stops, the problem is the generator. That's my preferred method with my tractors, because it takes the regulator out of the equation completely. If it motors well, no question it's the regulator. Just an alternative method.

I'll give both methods a try, because it can't hurt to have more data.

I've never messed with a belt system, any hints on getting the belt back on and tension correctly?

 

[flyingbrit]

Very interesting, I wonder if it wasn't setup correctly and that's what's causing the problems with the generator. So your suggestion would be to pull off the generator and regulator and have them properly set by the shop before re-installation?

No, I would still test the generator by grounding the field terminal when the failure condition is present. If it's good there is little point in removing it and taking it to the shop; there is nothing to adjust on the generator. In this case the regulator is bad so take it to the shop and have them repair it AND adjust down to 20V. If the generator is bad take it in for repair PLUS take the regulator in for adjustment.

 

[Chip Sylverne]

I'll give both methods a try, because it can't hurt to have more data.

I've never messed with a belt system, any hints on getting the belt back on and tension correctly?

Generally, about 1/4" to 1/2" deflection in the center of the longest belt section with firm pressure is what you want to protect the generator bearings. All due respect to Flying Brit, an old A&P I know always checks the genny isolated, either by motoring or the following method, to protect other systems from accidental overvolt or transient spike.

If you're uncomfortable removing the belt, another way to check the genny isolated on "A" circuit Delco's is to remove the arm and field wires, taping them up to prevent shorts. Put a jumper from field to airframe ground. Connect a voltmeter in series from the arm post to airframe ground. Start the engine and slowly bring rpm up from idle to 1500 or so, note voltage as you advance. The voltage showing should increase with rpm if the genny is good.

My bet is the regulator is somehow incompatible. As Jim said, that regulator looks brand new. OtOH, your previous testing showed the genny putting out good voltage. Airplanes generally have less dynamic current demand than auto's, (blowers, lights, turn signals etc.) maybe that enters into the design of each. bwthdik. Interested in what you find out.

 

[hamer]

Thanks for the help guys. Hopefully I'll have something to report by the end of the weekend.

 

[Dan Thomas]

I've never messed with a belt system, any hints on getting the belt back on and tension correctly?

Cessna specified belt tension for an alternator so that it would slip with anything more than 18 foot-pounds of torque (IIRC) applied to the alternator. Use a socket that fits the pulley nut. A 20-amp generator wouldn't need that much.

 

[hamer]

Okay, finally got around to this today. If I understand correctly, it appears like the voltage regulator is the culprit. At full load, and 2000RPM when I pushed the switch there was a tiny blip in the voltage and ammeter. However, when I took all the load off, at 2000RPM, the ammeter was only readying about 10-12A, like it normally does. When I hit the switch the amps jumped to almost exactly 20A. This tells me there’s something wrong with the regulator setup.

I also looked at the back of the ammeter wiring and it appeared to be wired correctly. Could anything else cause the reverse polarity on the reading?

I’m going to upload a few photos of my setup.

 

[hamer]

Well I just tried to short the battery to the field (engine off) to see if that would help, got the spark but now the entire charging system doesn’t work, no movement In volts or amps when I rev up. Might be time to take it to an expert.