Electrical System Troubleshooting Guide

[bluerooster]

Maintenance poker. Each is hoping his opinion is right and will win the hand. It's the best most here can do without actually being there and troubleshooting it ourselves.

But Jim is leading him through a methodlical test procedure that will ultimately have the problem sussed.

 

[flyingbrit]

Old timers will remember when replacing a generator you shorted the field terminal on the regulator to the battery terminal.

Good post generally but you are absolutely incorrect about the polarizing technique for an "A" type circuit like the OP's and most Delco/GMs. In this circuit the regulator grounds the field via the regulator points. At rest, the points are closed. So if you connect the battery to the field terminal all you are doing is short circuiting the battery to ground via the closed regulator points.

The usual polarizing method for an "A" circuit is to connect BATT and GEN terminal together. Since one end of the field is connected to the GEN and the other end is grounded via the regulator, this makes current flow thru the field in the correct direction and polarizes the generator. A high current will also flow backwards through the generator since you have bypassed the cut-out, hence the usual recommendation to just "flash" it momentarily.

Your polarizing method works OK for the "B" circuit. This was used by Ford, Lucas, Bosch and possibly others. However there is a less stressful way of polarizing a "B" circuit: disconnect the FLD terminal from the regulator and connect it to the BATT terminal. This causes the battery current to flow through the field only, not the armature. 2 amps instead of 50+ amps.

 

[RonP]

Flyingbrit is correct with regards knowing what type of generator field type, A or B, and proper procedure when polarizing a generator. My example was to jog memories regarding the procedure in the days when generators lit the roadways.

His message is clear to not go about shorting things unless you know exactly what you have. This also includes when a solid state regulator is substituted for a mechanical regulator. It may be painful for us males but we do have to read the directions before proceeding. I have a scrap box with electric devices that will attest to the latter.

An interesting side note that is common with old cars and motorcycles is a 3 brush generator. They are sometimes described in old manuals as "self polarizing" which is a misnomer. All generators have to be polarized to get the pole shoes magnetized with the correct magnetic polarity.

What made 3 brush generators "self polarizing" is they typically have a boost field that is connected to the light switch. When the lights are turned on this boost field in the generator is energized to boost the generator output. Even without the generator spinning when the lights are turned on current flows through the boost field which in turn magnetically polarizes the pole shoes.

I have many lessons learned and less dollars in my wallet not taking time to read, understand and proceed!

 

[nrpetersen]

Our o-290D powered Tripacer of 50 years ago had the same 20A Delco Remy generator and similar voltage regulator to that the OP is trying to resurrect. It was a conventional General Motors negative ground system with the field internally connected to the +12V output so that the alternator F terminal had to be grounded to achieve max output. There was no third brush (which was a poorman's voltage regulator used on some prewar tractors etc.)

 

[hamer]

Unfortunately I think it's time to give up on this. I pulled the voltage regulator and the only auto electric shop I found had no interest in working on it. He said he gave away his machine to test it years ago.

I cleaned all the contacts and re-gapped them per the Delco Remy bulletins. I even bench tested it per the directions in this thread, every thing appeared to be working on the bench.

Once it got back into the airplane there was still zero response from the system. No more charging the battery with higher RPMs. Not sure if I permanently damaged the VR or generator, but I guess I could have.

At this point I'm held hostage by this shutdown, will have to wait for the FSDO to reopen and hope they aren't so backlogged I'm grounded for months by the time I get this alternator conversion approved.

 

[RyanShort1]

I guess I am not understanding why you can’t buy an alternator set up with an STC and go ahead and fly the airplane? I did just that with my Cessna 120 that I owned three years ago and I don’t recall ever having to get the FSDO to sign off on the STC? I think my A&P / IA had me running in a day or so and the alternator was soooo much better.
I wish I still had her. A friend sent me this pic of her last month.

 

[hamer]

I guess I am not understanding why you can’t buy an alternator set up with an STC and go ahead and fly the airplane? I did just that with my Cessna 120 that I owned three years ago and I don’t recall ever having to get the FSDO to sign off on the STC?

The only alternator conversion STC I've been able to find is one that specifically calls out the C85, C90 & O200 engines. My C120 has an O-290, so *I think* my only option is a field approval.

 

[hamer]

Great photo, love the polished ones!

 

[flyingbrit]

Perhaps you have de-polarized the generator? Here is how you can test the generator with an ohmmeter:

1. disconnect both leads of generator
2. generator field terminal to generator output should read about 6 ohms
3. generator output terminal to case ground should read very near zero ohms, and should not change much when generator is rotated.

Since you have a power supply, an easy and fool proof way of polarizing generator is to connect a 12V supply, positive to generator output, negative to field terminal. Field should draw about 2 amps and you can leave it connected for several seconds without concern. Be careful not to touch field terminal when connecting/disconnecting the power supply, as the field's inductance can generate a big voltage spike a la ignition coil.

If the generator passes the ohmmeter tests and you have polarized it, it is ready for testing while running per instructions in previous posts.

 

[hamer]

Thanks Brit, I'll give it a try. Unfortunately I don't have access to AC power at the airport, but I think I should be able to go through the same process with a fully charged battery.

 

[Dan Thomas]

I guess I am not understanding why you can’t buy an alternator set up with an STC and go ahead and fly the airplane? I did just that with my Cessna 120 that I owned three years ago and I don’t recall ever having to get the FSDO to sign off on the STC?

Most STC's have AML's as part of their approval. An Approved Model List, and your airplane needs to be on it. Your mechanic probably found your airplane on it and didn't need to interact with the FAA on it.

Here's an example https://www.google.ca/url?sa=t&rct=...A04075CH.pdf&usg=AOvVaw3EWoSjfsq2FTmXk0eHiCHQ

 

[Bell206]

The only alternator conversion STC I've been able to find is one that specifically calls out the C85, C90 & O200 engines. My C120 has an O-290, so *I think* my only option is a field approval.

Have your mechanic contact the alternator STC holder directly and inquire about adding the O-290. If it is an AML-STC the holder can add additional models to the list. However, if the 290 conversion requires additional modification outside the "base data" of the STC then it may not be possible. But it's worth a call.

 

[hamer]

Have your mechanic contact the alternator STC holder directly and inquire about adding the O-290. If it is an AML-STC the holder can add additional models to the list. However, if the 290 conversion requires additional modification outside the "base data" of the STC then it may not be possible. But it's worth a call.

I'll look into it, thanks for the suggestion. I believe the C85/90 & O200 use a gear driven alternator while mine uses a belt driven, and I think that may be enough of a deviation to prevent being able to add it.

 

[JAWS]

From the sounds of it, you want to modify a modification (add an alternator to an stc'ed engine installation). What does the original stc and drawings for the engine change show? The documentation might be useful in this endeavor. I would think it would be needed should a field approval be the final route.

 

[hamer]

Well after all this I wasn't able to get my current system working. And after the government shutdown I finally got verbal approval from the FSDO for the field approval of the B&C Alternator kit. Fingers crossed it'll be installed on Friday and I'll be airborne again.

I have to say I'm very impressed with B&Cs attention to detail, documentation and customer service. I'll keep you guys posted on the progress, and I'm happy to share my signed 337 if it helps anyone else in my situation.

 

[455 Bravo Uniform]

Nice!