The Stovebolt Site Forums The Shop Area The Electrical Bay I've seen the light!

Had my truck out for a spin last night, right at dusk. Was poking around under the hood afterward, and after revving the engine a few times, I noticed that I had some pretty bright light (sparks) comin' out the back of my generator. It only happened when I revved it pretty good.

My truck has it's original 6 volt system. I recently replaced the brushes in the generator, and generally cleaned up a few thing inside while I had it apart. Other than that I really haven't done much with the electrical system. I get a pretty good deflection from the ammeter needle under normal operation. It will range from slightly discharging at idle, to halfway between middle (neither charging or discharging) and pegged on the charging side, when i rev it.

I know that there will be some sparks produced, but i think mine might be a bit excessive...What's going on?

You might have a shorted commutator bar, or one winding in the armature shorted to ground. Every time that one passes under the insulated brush, it will make a big arc. Eventually, the brushes will burn out from the short. If you disassemble the generator and the leading edge of one commutator bar is burned, you've found the problem. It takes an armature "growler" to diagnose a bad armature, something only an electrical service shop or a rebuilder will have now. They used to be standard equipment for virtually all shops, back when generator and starter rebuilding was a routine thing.
Jerry

Is ammeter always pegged to charge when above idle or just for a minute or two after starting?

When you had it out did you check to ensure mica was properly undercut?

What did you use to clean the starter? Trichs MEK laquer thinner can attack insulation. I try to use only soap water and a paintbrush rinse well with clean water then final rinse with isopropyl alcohol.


Is your ammeter telling you the truth? Get another ammeter and check to ensure it is reading proper.

danbentler

I don't think the meter should ever be pegged. I would guess that it is putting out more than maximum amps and in thast case you have a regulator issue.

Let me clear up some confusion:

My ammeter never pegs out. At idle it will show a slight discharge. When revved, it will swing to about HALFWAY up the charging side.

On a side note, I picked up a generator at a swap meet this weekend. I think it's out of a 54', so I should have some spare parts to mess with.

As I understand, you should be able to see small gaps between the bars of the commutator, otherwise it's worn down too far.. correct??

Thanks Guys

The gaps are where the insulation is between the segments. Sometimes they get filled with dirt. I clean the area with wood alchohol and a nylon scrub pad. For a quick test I ground the field and connect a battery to the ground and armature. If the generator is good, it will turn like a motor.

Just got done looking through the shop manual... Why is it bad to clean up the commutator w/ emery cloth? Does it make it too rough? shop manual suggests 00 Sandpaper... what is that in modern standards? What should it be cleaned with? I've seen soap and water, alcohol, and nylon scrub pad...any other ideas?

I believe emery cloth has particles that are conductive and that is a no no.

How is this done properly? Thin hacksaw blade??

Professional rebuilders had a small high speed saw that cut the mica between the commutator bars to a depth of about 1/16" or slightly less. It's a pretty difficult job without the proper tools. If you're very careful with a fine-toothed hacksaw blade with the kerf ground off the teeth, it's possible to undercut the mica that way, but it's a tedious job with a lot of room to make mistakes.
Jerry

Hmmm. Well, I guess i'll crack open the swap meet generator I got and see if the armature is the same (it didn't have a tag) If the armature has the same overall dimensions will it work? Or are there undetectable differences between armatures that look the same?

Supposedly it's out of a 54 truck, but that's what he said about the 216 carb he sold me!

Mix n match parts ??
Working with friend who is converting vehicle to electric drive. Burned up the armature - takes motor to the great guru of electric vehicle motors who does mix n match. Did not work.

The point here is do not do mix n match unless you know both units are identical
OR you got a bunch of junk and lots of free time so when it does not work it is not much wasted.

Dan bentler

Are there any Electrical Guru's out there who know if there's any differences between the old Generators? I believe there were some rated at different outputs, but nut much besides that.

Yes, there are different generator ratings, and to keep life simple, you need the voltage regulator to match. Most passenger car and light truck generators were rated for about 35 amps- if I remember correctly. You can use a voltage regulator rated for a higher generator output on a lower-output generator, but not the other way unless you can adjust the regulator to control the generator- which you can do, but you need to know what you are dealing with. There should be a tag on the generator which will identify the output, but you have to have either a cross-reference manual or the OEM parts manual in order to determine the rated output.

Armatures of the same overall dimentions should function, but you need to be careful with the voltage regulator settings. If you stick with about 35 amps at about 7 volts, you should be alright- as long as the generator functions. There is quite a bit to testing a generator properly, but with an ohmmeter or test light, you will be able to get useful information. Basically, one brush goes to ground, the other should be insulated. Both external terminals should be insulated, one goes to the field wire, the other goes to armature brush-the insulated brush. The field winding should have continuity from the field wire terminal through to the other end- probably around 3 ohms of resistance, plus or minus a little- I don't remember the number at the moment. The armature bars should be insulated from the core/shaft, but you can find continuity between bars. That won't tell you much, but any connection from a bar to the core/shaft is not a good thing- the armature is grounded and needs to be re-wound. Or replaced.

Hope this helps.

Harvester

Fortunately, there's still an old-school starter/generator shop in the town where I do a lot of business, run by an old geezer about my age who's a second-generation owner of the shop. He not only knows how to fix the oldtime stuff, he's got a warehouse full of parts his father used to use when he ran the business back in the 50's and 60's When a fellow stovebolter needed a special-design end frame for a Delco generator, Stan had one stashed away! Let me know what you need, and there's a pretty good possibility I can help find it!
Jerry

Thanks for all the help guys....

The swap meet generator looks exactly (and I do mean exactly)like the one in my truck...except it doesn't have a tag. not even holes where the tag rivets would have gone. I'm thinking it's a newer reproduction generator, not one of the original delco-remy's.

Since my genny is working fine, I think I'll leave it for now...I figure worst case scenario my brushes will get used up a little faster due to the excessive sparking. I'll hang onto the extra gen just in case. I definitely need to find a good electrical rebuild type shop here in KC. If any of you other Cowtown boys see this, let me know!

Thanks,

worst case is not brush consumption. It is arcing and sparking on the commutator and real world case is when you get a flashover which basically destroys the unit. If you are unable to turn it on a lathe which is highly likely to be needed take it to a rebuild outfit. Bring the regulator also.

Dan Bentler

Leitmotif-

I'm curious what you think the problem is? The only suggestion I've heard is from Hotrod Lincoln ("You might have a shorted commutator bar, or one winding in the armature shorted to ground.") Would turning on a lathe solve this problem??? I don't understand how it would. (but then again I'm still learning). If anyone else has any ideas as to what my problem is, I'd love to hear it.

Just so everyone understands - I had no idea that there was anything going on, until I saw the sparks. It charges the battery fine (as far as I can tell).

Thanks Everyone

Bryan,

Some sparking at the brushes is normal when the generator is under load, but flashing like an arc welder indicates a problem.

No, turning the armature/commutator will not solve either a ground or short in the armature. Measure with an ohmmeter set the the highest range, from the commutator to the core/shaft. There should be infinite resistance. Anything less indicates a ground between the commutator and the core. But keep your fingers off the meter connections when you do this or you will measure yourself instead of the armature.

If you don't have an ammeter, buy an inductive/clamp-on type from an auto supply and hold it over the armature wire after you start the engine. You should see about 35 amps with the engine running at 1800-2000 RPM. A little more or less is alright, but without knowing the rated output of the generator, you shouldn't be above about 40 amps. If you only see 25 amps or so at that speed, I would suspect the generator is operating as it should, but maybe the voltage regulator needs adjusting. More on that if you need it.

Harvester

Harvester-

I don't believe that it is arcing...although it's kinda difficult to get a good look at it. My generator is a Delco-Remy 1100028 4B25. I'm not sure what it's rated output is, because it isn't listed here:

http://chevy.oldcarmanualproject.com/shop/1954truck/54ctsm1217.html

I will try to see how many amps it is producing.

To get an idea of maximum output you'll need to create a big load on the battery. I'd suggest turning on high beam headlights, electric wipers (if equipped), cigarette lighter, brake lights, and any other demand you can think of, then rev the engine to a steady 1500 RPM or more. Measure the current flow at the armature wire, and you'll get a pretty good idea what the generator is capable of producing. Be aware that there's a "current regulator" which is part of the 3-unit regulator, (along with the cutout relay and the voltage regulator) and that's supposed to set the generator's maximum output. A generator can destroy itself trying to meet the current load unless that regulator is operating properly. Alternators are self-regulating due to stator winding resistance, so a current regulator isn't required with an alternator.
Jerry