5.0 volts at the generator

[Larry E Trimmer]

I got generator troubles. The battery goes dead while driving but the generator light does not glow.
I am reading 356 electrics for my 356C and it says check the current with D+ off and you should get 7.1 - 7.5. I get about 5 volts at about 2500 to 3000 RPM. It says you can raise it 1/2 volt by pushing the contact but what about the other 2 volts.
I run the generator as a motor no problem. The B+ was touched to DF to energize.

So what to do if your generator is putting out 5 volts?
I do have a glow on the light at the signal indicater green that burns constantly which I have not yet figured out.

Any help?

Thanks

[Mike Zois]

Check the basics first....

Tight belt?
Fully charged battery via a trickle charger?

Test at battery terminals...
6.5 at rest
6.8+ at idle
7.2-7.5 at 2500 rpms.

[Larry E Trimmer]

To test at the battery terminals do you need to remove them from the battery, May sound like a dumb question but seems to me that the battery will always be 6.5 volts. no?

[Mike Zois]

6.5 volts IF it's fully charged and/or can hold a charge with the engine off ....

I use a Fluke and stick the probes in the terminals and prop the meter on the decklid. That's so I can see it while running the motor and working the gas pedal form the driver's seat.

[Larry E Trimmer]

I get 5.8 volts at the battery, at rest same and after the generator light goes out it is still 5.8.

I had the battery on charge all night but have run it for about 1/2 hr doing these tests.

Bad generator?

Larry

[Mike Zois]

If you don't have 6.5 volts at the battery after a full charge....the battery is likely toast. You COULD pull the battery and have that checked at a local parts store...IF they still have 6 volt testers....

However, until you have a good battery you can't really diagnose the charging system at home....the battery could be a casualty of a bad generator and/or voltage regulator.

In a perfect world, you would have a 6 volt load tester that tests everything.

[Larry E Trimmer]

The battery is an acid type that is only about 3 weeks old. It should be okay, maybe my volt meter is out a little.
Why would the generator light go out but the generator not be producing enough voltage?

Larry

[Mike Zois]

Does the light come on when you first turn the ignition on prior to starting? If not....burnt bulb. BTW, the light bulb is part of the charging system...bad bulb no charge.

Get a better tester....if you can afford a 356, you can afford a "Fluke"....%^B.

[Larry E Trimmer]

Generator light glows with key on and at idle, goes out at 2500 RPM or so. Thats my question is why would it seem to function at all if the generator is ot producing enough volts,
I would probably be better off to spend money on a mechanic rather than a better meter since I only know enough to get me into trouble.

Thanks for the help.

Larry

[Larry E Trimmer]

Can anybody tell me if the generator is toast or should I just replace it and hope for the best,
Can the generator be rebuilt?

Its not the voltage regulator if I get 5 volts at the generator?

Thanks

[Robert Kenton]

Does the light come on when you first turn the ignition on prior to starting? If not....burnt bulb. BTW, the light bulb is part of the charging system...bad bulb no charge.


Get a better tester....if you can afford a 356, you can afford a "Fluke"....%^B.

Mike- Which Fluke model to you have/recommend? Ideally it should work for both 6- and 12V cars. How about Mdl 87-5 as shown at action-electonics.com ?

[Mike Zois]

I have the Fluke 16 Multimeter. It measures AC/DC, temps, continuity, the size of my winky....more things than I need....but it's digital, can be used on both positive and negative sources and after 10 years still hangs in there. All I do is change the 9v transistor radio type battery occasionally.

It has auto shut off and USED to beep at me when it detected what I was looking for.....but that died sometime ago. Good deals can be had on evilBay.

[Chris Markham]

with D+ off and you should get 7.1 - 7.5. I get about 5 volts at about 2500 to 3000 RPM.

So what to do if your generator is putting out 5 volts?

Larry,
Since you're reading 356 Electrics, you're already in contact with the best source of information. The reason this thread has gone off-topic onto multimeters is that everyone is waiting for Joe Leoni or one of the other Certified Sparkies on the List to chime in with authoritative information.

But you can 1. get new brushes for your generator 2. have the generator rebuilt if you've an old-school automotive electrics shop in your area. Dropping it off at the Pep Boys probably ain't gonna do it for you. If you've got a hot rod shop in your area, drop in and ask them who they use.

But I'd try the brushes first. If you did the D+ off test at 2500 rpm, then the battery is a red-herring. You might have to solve that problem later. As for why the light doesn't come on...its threshold is ~4.5V if I recall correctly (and I probably don't). Errr....Joe?

Good luck!

[Larry E Trimmer]

Thanks Chris, I got 4 used generators from a friend today and I hope to find one that works. I guess I will take mine in to have it rebuilt.

I will post how I do after tonight.

Larry

[Larry E Trimmer]

I switched out the generator with the best of the 4 and I think I have success. The generator light went out at about 1500 RPM as the old one at 2500. The car ran after I disconnected the battery so it runs under its on power.
I have not tested the output yet since its 1:30 in the morning, doubt my neigbours would care for that. I'll keep my fingers crossed and do that in the morning.

The old generator appears to have a couple of wires that look burnt due to the plastic being a little stretched. The unit I took off had a stamping as "Bosch remanufactured" and looked very new.

Larry