The Stovebolt Site Forums The Shop Area The Electrical Bay How to check generator output

I'm not sure my generator is putting out enough juice, and would like to check it. I have a brand new shiny multi meter I got for christmas, but I'm embarassed to admit I'm like the little boy who finally coaxed the little girl into his red wagon. I don't know what to do next.

I think I should set the dial to the DC side, but where? I have number that read: 1000; 200; 20; 2000m; and 200m. I also would assume I put the two probes on the generator with the motor running, but which is the positive and which is the negative, or to put it another way, which is the red one and which is the black one, and what should the reading be.

I don't understand anything about anything electrical and hate messing with it. Any help would be appreciated. Thanks, Allen

Allen,

Didn't one of the elves suggest this item several months ago..good show. I'll be the parent here!!READ THE DIRECTIONS! If its an analog meter..the kind with the needle or pointer and the dial face with millions of tiny numbers you should put on your specs.

The RED lead would be positive and the BLACK would be negative. These would only apply when using a function that was polarity sensitive, such as reading DC voltage. If you touch them to the wrong poles, it's OK, the meter just deflects bass-ackwards and you change.

Your right about setting it to DC. I think the numbers you mentioned are resistance values (ohms). Look at the dial face and you should see some notation indicating DC voltage. Start out with your tests AT THE BATTERY, not in the engine compartment.

Put the meter on DC and stick the red lead to the positive post and black to the negative post. The battery should be about 12.6 volts, so knowing that, look at the scale where the needle points and "reverse" figure it out. The needle should pass through one of the scales with a 12 on it or near it.

That is the scale you will use. Now you can see how it works. This was done with the rig off. Now have a friend start the rig and rev it up. Do the same thing again, but you should see much higher voltage now..maybe high 13's. If this is the case, the generator is working.

The meter will help with all kinds of things. Read the pamphlet that came with it, and every chance you get, use the meter. It is probably fused so you can't really hurt it.

When you start dinking around in the engine compartment, and the truck is running, it's too easy to get something tangled up in a fan, or stick a finger where it doesn't belong. Get comfortable with the meter first.

If your meter is not analog, but is digital, delete this post-post haste! Have fun with your new toy..go get those amps and volts!
Stuart

Hi Allen!

Before we get too far into the finer points of using a VOM, what does your dashboard Ammeter say?

If the needle is over to the right with the throttle open, then you've got a good generator. If it's at 0, very low positive, or any negative setting, then your generator (or the voltage regulator) has a problem.

Stuart:

Wasn't a 53 Chevy a 6v system?

Allen:

Are we talking about the Buick, or the 6400?

Brendan,

Quit showing your brains....DOH! I plead guilty on 2 counts of stupidity. :rolleyes:


Stuart

Allen:

If we're looking at the truck, and you follow Stuart's procedure, you will read anywhere from 6-8 volts on the battery when the engine is running. (provided it's stock, that is.) You will want to have someone on the throttle or have the engine idling fast to check the generator. Generators don't put out a consistent amount of juice. It's directly related to the RPMs that the engine is turning out. (Faster = more juice)

I may not know beans about alternators, but darn it if I don't know generators and old vehicles/farm equipment!



Don't feel too bad. The Ammeter is a "Little Known, Seldom Used" (at least these days) trick that lets me cheat. I'm all for not diging out tools that I don't have to.

The 6400 was a 6 volt when new, but before I bought it someone had "converted" it to 12 volts. By converted I mean I think they stuck in a 12 volt battery and changed all the light bulbs. I can't get the gas gauge to work, and I have a new sending unit, so l think the gauge is fried.

I'm not sure about the Ammeter. I don't know if it is working. I get a little movement out of it, but only very little. It never moves much to the right, and I only get a very small movement to the left when I turn on the lights. (I still don't have the headlights working. Don't know what that's all about)

I thought that if the generator is working, then I probably have a bad gauge. Does that make sense?

I think if the generator is working, then the only other place I could have a problem would be with the voltgage regulator. Does that seem correct? How do I check that with my new toy?

The Buick was 12 volt when new. I just did a rough redo on it, and am still messing with the original wiring. That has been a lot of fun. The horn has recently quit working, and I keep putting off looking for the problem because I really hate working with wiring and electrical problems.

The meter is digital {thank God}, but I still think I get the general idea from Stuarts messsage. Thanks Guys. Allen

PS: I did try reading the directions, but they seem to assume that I already know how to use the meter. I guess it's not really that hard, but having never tried using one before, it looks confusing.

With the meter set to read 12v DC, what reading did you get with the engine running? was is 13- 13.5 volts? If not, let us know.

Okay, that's bad. There's more to a 12 volt conversion than just changing lightbulbs and the battery. The stock generator and voltage regulator WILL NOT charge up a 12v battery properly.

Which could explain why it's not working.

Yes, if there isn't a voltage reducer on that gas gauge, then it's fried. You may want to look at the coil, as well. There should be a ballast resistor in there ahead of it to reduce the voltage after the truck starts to extend the life of the coil. 6v coils are available from the various vendors that support this website.

The ammeter doesn't care about voltage. It just cares about amperage. If the ammeter was bad, you'd not be able to start the truck (or you'd have a fried wiring harness). the fact that it moves means that it works.

As for the headlights... are they 6v? Check the fuse on the switch. There may be a short in the old wiring and it may have blown.

The first order of business is to figure out what that generator is. If it's 6v generator, then you probably will want to replace it and the VR with 12v equivalents or go back to a 6v battery. (Personally, I'd go back to 6v... less of a pain in the butt.)

Yeah. I know how that goes. I was checking my horn out the other day. It works, it was just wired bass ackwards by someone somewhere along the line. That, and I think that there's a blown fuse somewhere along the line, cause nothing on circuit works.

The meter is Digital. That is good. If it has several settings for each measurment (DC, AC, Resistence, et cetera), then be sure to start out at the biggest setting and work your way down. This will prevent meter fryage. (Granted, on a car, the voltages involved will only be like 18v max, but still...)

If you have just one setting for each, then you're golden. It's autosensing and a piece of cake to use.

In closing, We need to figure out what that generator is. Get the numbers off of it, and we may be able to look that up for you.

Then we can give you advice from there.

Thanks everyone: I haven't been able to work on the truck for a few days. Hope to get back to it soon.

I do have a question though:

If I use the meter on the battery with the truck not running and get a reading of about 12, does that mean the battery is fully charged, or is it just telling me I have a 12 volt battery? Dumb question I know, but I don't know the answer. Allen

Allen,

No such thing as a dumb question. This is what I think I know!

Voltage reading vs percent charged.
12.6v 100%
12.4v 75%
12.2v 50%
12.0v 25%

If your meter reads around 12.5v your golden, as Brendan would say..With the truck running, you might see as high as 14.3. This is true with an alternator, but I don't know if the GEN will do the same thing.

Your meter is telling you the "pressure", or voltage in the entire system. Did you read the manual? Bad boy!

Stuart

I did read the manual, but it is very small, doesn't have much information, and what there is seems to be based on the assumption that I already know how to use the meter. So far, it has all been trial and error, and the information I have gotten from this site. I suppose that what I should do is to look around and try to find a book that explains how to use the meter.

I think I'm just a little lazy. I like working on the mechanical side of the project, but I have never understood electricty. To me it's like a foreign language: Volts, Amps, Ohms, Watts, and who knows what else. I can't see what it is doing, and I don't like fooling with it.

Thanks for the info about the readilng vs percent charged. I will check it when I work on the truck again. I have a bad of habit of finding trouble where none really exists, and it may very well be that everything is working ok, and I'm making something out of nothing. If the battery is charged, and stays that way, then I will assume everything is ok, and move on to something else that really need working on. Thanks Allen

Allen, I've had the same problem at times, and I tapped lightly on the regulator cover and unstuck the points in it. If your truck sits for a long time, this might be part of the problem...Be sure not to tap to hard or ya can damage the regulator.

Just a little trick an Ole Timer once showed me on these turkey,s
For I.D,ing a GM GENERATOR or STARTER,Brendan,
If the Delco-Remy tag is Black and Silver---6Volt
If it,s Red And Silver---12 Volt
Good luck