Electrical System Troubleshooting Guide

[Chip Sylverne]

Yeah that spark you got isn'the good kind...negative ground polarizes to the armature. You'll want to be taking that generator and regulator into the shop now...field windings are probably toast.

 

[Chip Sylverne]

Was this close...

 

[hamer]

Yea it was close. I guess that’s what I get for tinkering without fully knowing what I’m doing. I got the battery to field from a YouTube video on a similar voltage regulator but i guess the guy didn’t specify positive or negative ground. Definitely feel like an idiot.

 

[nrpetersen]

Opinion - It shouldn't have blown the field if it was only for a few seconds. You might have blown the regulator somehow.

 

[Chip Sylverne]

Opinion - It shouldn't have blown the field if it was only for a few seconds. You might have blown the regulator somehow.

Could always check that using the technique in post #76. Cowling's off anyway. In for a penny, in for a pound...If he gets juice, he knows it's the regulator now.

 

[flyingbrit]

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.

You may have reverse polarized the generator. Connecting battery to field only works for a "B" circuit where the field is internally grounded and the regulator connects the other end of the field to the armature via the vibrating contacts. Delco generally uses the "A" circuit where the field internal connection is to the armature and the regulator grounds the other end of the field via vibrating contacts. The standard way of polarizing an "A" circuit system is to momentarily connect the "batt" and "gen" terminals of the regulator. This makes a good spark because you are feeding the battery through the generator's armature as well as the field.

Here is a link to a Delco service bulletin:

http://www.ruiter.ca/mc/info/PDFs/1R-115.pdf

Polarizing instructions are at the bottom of page 4. Ignore the two unit material since they were used with a third brush type generator. The three unit material is actually for 6V systems, but your 12V/3-unit system is almost identical.

 

[hamer]

Thanks for the help guys. Forecast calls for rain the next couple days so I won't be able to test anything until it stops.

Thanks for that link flyingbrit, very helpful.

 

[Let'sgoflying!]

I have not read this entire (3-page) thread, but when it popped up again today I was wondering if anyone has used the info to come up with a troubleshooting flow chart for future use.

 

[hamer]

I have not read this entire (3-page) thread, but when it popped up again today I was wondering if anyone has used the info to come up with a troubleshooting flow chart for future use.

Not yet, but when I get to the bottom of this, I plan to put together a flow chart of everything I did to help others in the future.

 

[Let'sgoflying!]

That would be good. Seems like there is way too much flagellation going on when it should be a boring and quiet:
step A
step B
step C

 

[weirdjim]

I have not read this entire (3-page) thread, but when it popped up again today I was wondering if anyone has used the info to come up with a troubleshooting flow chart for future use.

Well, that's how Chip and I started this out ... just do this step by step. Then we got a lot of suggestions on how to "improve" the troubleshooting and how an alternator would make more sense and how this that and the other thing might be the problem ... sigh.

Jim

 

[Dan Thomas]

Well, that's how Chip and I started this out ... just do this step by step. Then we got a lot of suggestions on......how an alternator would make more sense..... sigh.

If a guy can afford it, the alternator is the best "fix" for generator problems. It's final, it's much easier to find parts, it has far more capacity at any RPM, and it weighs less. Not a dumb suggestion at all. There IS a time to toss ancient technology if it's possible and paractical. Nobody has tube-type NavComs anymore. I hope.

 

[hamer]

If a guy can afford it, the alternator is the best "fix" for generator problems. It's final, it's much easier to find parts, it has far more capacity at any RPM, and it weighs less. Not a dumb suggestion at all. There IS a time to toss ancient technology if it's possible and paractical. Nobody has tube-type NavComs anymore. I hope.

That was always my plan to begin with. However the gov. shutdown has put a huge delay on that as *I think* my only option to upgrade is via field approval, and the FSDO is closed. Going through the motions of testing the system has been a good learning experience for me since this is my first airplane.

Speaking of. One of the A&Ps I spoke to thought that I could install an alternator without a field approval. His reasoning was that the IPC for the O-290-D (PC-102-1_0) and the service instruction (SI1154U) lists a Lycoming alternator (LW-14371) as standard for my engine. At that point it would just be a filed 337 signed off by an IA? Any thoughts on that?

 

[Bell206]

Any thoughts on that?

Any OEM bulletin (e.g., service instruction) that alters an aircraft is not considered a major alteration. No 337 required. However, the bulletin must be specifically applicable to the model and in some cases serial number of the aircraft and you must follow the bulletin instructions. Most bulletins have the applicability info listed on the first page. Using strictly the IPC has it's issues and can cause more problems than not.

 

[hamer]

Any OEM bulletin (e.g., service instruction) that alters an aircraft is not considered a major alteration. No 337 required. However, the bulletin must be specifically applicable to the model and in some cases serial number of the aircraft and you must follow the bulletin instructions. Most bulletins have the applicability info listed on the first page. Using strictly the IPC has it's issues and can cause more problems than not.

Thanks Bell. That was my initial thought, regardless of the engine, it had to be tied to the airframe somehow. I'm attaching the two documents supplied. They seem to be specific to the motor but not the aircraft and even if it was there's about a zero percent chance there would be something tied to the C120 & O-290-D combo.

 

[Chip Sylverne]

Before you go tossing the genny overboard, there's something to be said for the old tech. First, it's pretty dead nuts simple and bulletproof in that the components are robust, there are no diodes or diode bridge to fail, and you can run it with a dead battery without worry of damage because it uses minimal armature voltage to excite the field. No, it doesn't create gobs of current, but you have no need for it in your application. You're not powering a glass panel, autopilot, strobes and a gazillion other toys. And it's reliable, and simple to troubleshoot once you figure out how it works. Once you get it sorted, you'll be happy with it in your little vfr airplane. Your radio doesn't care what made the electrons, and That grand or so you'll spend for alt and install buys a lot of avgas. Now if you were flying an IFR equipped airplane, I say go with the alt. But you're not.

 

[Bell206]

I'm attaching the two documents supplied.

The attached SI is only a part substitution document and does not install an alternator. Electrical systems usually fall under the airframe side of things and a quick check of the 120 TCDS shows only a generator. Since changes to the basic electrical system are major alterations, short of a Lycoming/Cessna SI on installing a alternator on a 120 you'll need to go the STC or field approval route. However, I'm with the generator group--fix and keep what you got.

 

[hamer]

We got a break in the rain so I ran to the airport and tried to repolarize the regulator, no spark and no change in the behavior with the engine on. So I may have permanently fried the voltage regulator. Does anyone think it’s worth taking to the auto electric shop to test?

 

[nrpetersen]

Fifty years ago (!) we had a small flying club at FCM with a '51 Tripacer w the Lycoming O-290 engine and an upfront oil cooler. It too, had the 20 A generator and we fought electrical problems etc. Being a bunch of engineers, we figured out a fix where we upgraded it with a junk 35A Rambler alternator and associated solid state regulator (they were new then), and using the old generator pulley. We made a drawing & got a one time approval from the local GADO office from back in the days when they did that sort of thing.

It absolutely made that airplane for winter and nite flying, and we kept it for about 4 more years. A hangar fell on it after we sold it so that was the end of it.

I still have the drawing - but its on vellum! But, does anyone still make a copy of that stuff? Can you bend 1/8 inch 4130 steel?

 

[JAWS]

I found the following training materials online. Nice to come directly from Delco themselves in the day.

http://www.delcoremyhistory.com/trainingmanuals.htm

Does anyone think it’s worth taking to the auto electric shop to test?

Yes.

PS Also found the following youtube link.

 

[weirdjim]

Where are we with this turkey?

Jim

 

[hamer]

It's been raining cats and dogs here in SoCal. Today is supposed to be the last day of it, so I can get back to the airport tomorrow. If I can't get it to repolarize then I'll pull it off and take it to the auto electric shop.

I've also been reviewing a few old delco remy manuals, trying to figure out how to adjust the voltage regulator. Hoping to have this figured out by the end of the weekend.

 

[flyingbrit]

If the generator was reverse polarized and ran for a while there is a good chance that the cut-out relay's points are burned up. In this case grounding the field and watching the ammeter may not work. However you can still ground the field and measure the output with a voltmeter connected to the generator's output terminal.

 

[hamer]

If the generator was reverse polarized and ran for a while there is a good chance that the cut-out relay's points are burned up. In this case grounding the field and watching the ammeter may not work. However you can still ground the field and measure the output with a voltmeter connected to the generator's output terminal.

Thanks I'll make sure to check that out. If that is the case, do you think I also need to pull the generator to get checked out? Or if I get the regulator worked out the generator "should" be unaffected?

 

[flyingbrit]

The reverse polarizing tends to damage the regulator, not the generator.

 

[hamer]

Photos attached, configuration is a little different than the delco remy bulletin. Gap seems pretty big on that second one.

 

[nrpetersen]

So primitive.....! Brings me back to my youth.

The gaps look about normal to me (compared to automotive ones about 65 years ago). But there is that little projection on the points of the cutout (the one closest to the camera), and it looks like a LOT of current has gone thru that point bracket.

Still suspicious that one or more of the three(?) resistors underneath is burned out causing excessive arcing at one or more of the points. Suspect bad regulator.

Good pictures.

 

[hamer]

Unfortunately the only auto electric shop I could find in town didn't have his bench tester anymore. I'll have to see if I can adjust it myself, I think at least filing that point down will help.

 

[Chip Sylverne]

The cutout points are what separates the battery from the system when the generator isn't generating, so It's going to get some higher current than the current and voltage points. That little peak doesn't look all that bad to me. Don't go manually closing that when connected to juice, you may not get it back open, or so I've been warned in the past.

Have you confirmed the generator produces voltage yet?

 

[flyingbrit]

Agree that that the small peak doesn't look too bad; I've seen a lot worse on ignition breaker points. OTOH a little gentle filing shouldn't hurt; just don't go crazy and file off the silver/tungsten contact material as the base steel/brass won't last long. BTDT.

You can do a crude test of the cut-out relay points by connecting an ohmmeter from BATT to GEN and then closing it with finger pressure. It should of course be very close to 0 ohms when closed.

Similarly, the voltage and current regulator points can be checked by connecting the ohmmeter from GROUND to FLD and looking for a zero reading. Open the voltage relay by hand and check that the the current relay is still providing a zero ohm reading and vice versa.

If you have access to a 0-16V power supply you could check the cut-in voltage and the voltage regulator set point. Connect the supply to the GEN terminal and ground. Adjust upward from zero. At around 12.6V the cutout points should close. At around 14V the voltage regulator points should open.

Bench testing the cut-out current and the current regulator set point is more involved, and probably easier to do on the plane unless you have a high current (30A) power supply and a carbon pile load.

 

[JAWS]

Interesting. The OP has another thread in the avionics section, discussing wanting to upgrade his 120 with some fairly gee wiz stuff (as far as an old Cessna 120 goes). If he really is looking into a few amu's for avionics, I would suggest starting with 1 amu to start and give his old bird a more capable and reliable electrical generation system.

If he was looking to just play day VFR once a month, I would say fix the existing 1940's tech. To do more, time to upgrade.

 

[hamer]

Agree that that the small peak doesn't look too bad; I've seen a lot worse on ignition breaker points. OTOH a little gentle filing shouldn't hurt; just don't go crazy and file off the silver/tungsten contact material as the base steel/brass won't last long. BTDT.

You can do a crude test of the cut-out relay points by connecting an ohmmeter from BATT to GEN and then closing it with finger pressure. It should of course be very close to 0 ohms when closed.

Similarly, the voltage and current regulator points can be checked by connecting the ohmmeter from GROUND to FLD and looking for a zero reading. Open the voltage relay by hand and check that the the current relay is still providing a zero ohm reading and vice versa.

If you have access to a 0-16V power supply you could check the cut-in voltage and the voltage regulator set point. Connect the supply to the GEN terminal and ground. Adjust upward from zero. At around 12.6V the cutout points should close. At around 14V the voltage regulator points should open.

Bench testing the cut-out current and the current regulator set point is more involved, and probably easier to do on the plane unless you have a high current (30A) power supply and a carbon pile load.

Thanks I have a PSU at work, might as well give it a whirl. Thanks for the help.

Interesting. The OP has another thread in the avionics section, discussing wanting to upgrade his 120 with some fairly gee wiz stuff (as far as an old Cessna 120 goes). If he really is looking into a few amu's for avionics, I would suggest starting with 1 amu to start and give his old bird a more capable and reliable electrical generation system.

If he was looking to just play day VFR once a month, I would say fix the existing 1940's tech. To do more, time to upgrade.

Yea, I know this thread has spiraled out of control a little, but I do plan to do an alternator conversion before I update any avionics (mentioned in that thread). I can't do that at the moment because the gov is shut down and the FSDO is closed. For my Airframe/Engine combo I need a field approval, unfortunately. I'm going through this exercise because I think it's a good exercise in troubleshooting. The guys here have really brought out a lot of knowledge that isn't easily googled.

 

[JAWS]

Thanks I have a PSU at work, might as well give it a whirl. Thanks for the help.



Yea, I know this thread has spiraled out of control a little, but I do plan to do an alternator conversion before I update any avionics (mentioned in that thread). I can't do that at the moment because the gov is shut down and the FSDO is closed. For my Airframe/Engine combo I need a field approval, unfortunately. I'm going through this exercise because I think it's a good exercise in troubleshooting. The guys here have really brought out a lot of knowledge that isn't easily googled.

Oh ok. Cool. I admit I read up on this subject a bit. Last time I dealt with this was "mumble " years ago!

 

[weirdjim]

If he was looking to just play day VFR once a month, I would say fix the existing 1940's tech. To do more, time to upgrade.

I have a working Narco Superhomer he can use if he needs it

Jim

 

[1RTK1]

I gotta fly up to weirdjim's some day and look at all his goodies.

 

[JAWS]

I have a working Narco Superhomer he can use if he needs it

Jim

LOL. I meant more the generator system!

 

[weirdjim]

I gotta fly up to weirdjim's some day and look at all his goodies.

I BEG your PARDON, sir??

Jim

 

[Chip Sylverne]

I BEG your PARDON, sir??

Jim

Hey, at least he said goodies, not junk!

 

[1RTK1]

I guess I set myself up for that. Electronics and what not. LOL

 

[RonP]

I am not a licensed mechanic for any vehicles nor do I play one on TV but would like to clear up some misconceptions with generator systems from my experience restoring cars, boats and motorcycles.

Electric starters will always turn in the same direction even if hooked up backwards. This is due to the field windings in series with the armature. To reverse the direction of a starter the field wires need to be reversed.

Generators are not made a positive or negative output. They take on that attribute when they are polarized. Old timers will remember when replacing a generator you shorted the field terminal on the regulator to the battery terminal. This magnetically polarized the field pole shoes to the correct magnetic polarity. Generators are "self exciting" which means they do not require an input to start generating. This is due to the small magnetic flux that remains on the pole shoes when the generators stops spinning. In operation when the armature starts spinning that small magnetic flux is enough to start creating a current in the armature. Each revolution increases that current until the voltage regulator starts controlling the generator output.

Other than Pipers my experience is an ammeter that swings + and - is measuring the current that goes in (charge) and out (discharge) of the battery, not the output of the generator. Initially the current into the battery will measure + and decrease to 0 when the battery is fully charged. Even though the ammeter is reading 0 indicating the battery is fully charged the generator output may be 10 amps (for example) providing current for the radio, lights, etc.

Solid state voltage regulators for generators have been around for easily 20+ years for 6 and 12 volt generators both positive and negative ground. Even more amazing is solid state voltage regulators are even made for old style 3 brush generators.

I have a 6 volt solid state voltage regulator on my 1943 Harley that uses the stock 6 volt 3 brush generator. My 1960 outboard motor has a 12V solid state voltage regulator on it.

One more ramble, mechanical voltage regulators are an amazing balance of electro-mechanical action. It is a careful balance of electro-magnetics, spring tension, air gaps, ballast resistors and temperature compensation both for ambient temperature affecting the battery and internal heat generated by the voltage regulator itself. I would not recommend adjusting it yourself unless you have the equipment and procedure the manufacturer recommends.

Ok, one more ramble (I lied before)......those of you with a knowledge of electronics know what a diode is; I.E. a one way path for current. If you study a mechanical voltage regulator one of the elements is the cutout relay. These really ingenious engineers of yore actually made a mechanical diode with an electro-magnet with 2 separate windings, contacts and uniquely wired. Yes, with no solid state components they created a mechanical diode. Amazing!

My second recommendation is to get a full understanding of how this mechanical diode works before venturing inside the mechanical voltage regulator. The knowledge will become paramount when making adjustments.