Generator motors but won't charge

[krisbeetle]

Hi, I tested a generator I thought was good by making it motor and it functioned well.
I installed it on my engine and it does not produce a voltage, I then grounded df terminal (disconnected) while reving engine and tried to measure voltage from the D+ terminal and there was little to no voltage.

This is the testing procedure as per vw resource btw.

So it motors really strong but produces no voltage and by opening field to try to achieve 35 volts I got not much to nothing.

What does this mean is happening?

I want to know because I have a parts generator I could swap parts from.


So instead of saying generator is hooped I am trying to diagnose what is actually going on as it is highly suspect that it will motor but not charge.


Thanks for your help!

Kris

[Luft kühl]

You should measure about 35 volts at 3000 rpm. If not , the generator is probably shot.

[Dale M.]

Might try this test...

Generator/Regulator Test!

Disconnect all wires from Generator. (tag them so you get them back right)

Connect a test light ( 6 or 12 volt what ever is appropriate) on generator to the "D+" terminal ... Ground other side of light.

Ground "DF" or "Field" on generator.

Start engine... If light comes on and brightness increases as engine rpm comes up your REGULATOR is bad ( generator works ) Caution over revving engine to fast will cause light to burn out.

IF light stays dark ( does not light ) , check test setup again to be sure its right... If you rev engine up and light still does not light GENERATOR is bad.

People with experience using a VOLT-OHM meter could use the meter instead of light... look for VOLTAGE increase..

Dale
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“Fear The Government That Wants To Take Your Guns"
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
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All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

[krisbeetle]

I appreciate the info but I have already tested above mentioned.

Does anyone here know how generators work on a deeper level?

As in this indicates field windings or commutator windings are compromised?

As I mentioned above I have a spare parts generator.

I cannot find good information on generator diagnosing.

Why bother and not just replace? I like to get a deeper understanding of how things work in an increasing replace over repair society. It makes you a better mechanic when you brake down on the road.

Thanks for your help.

[Dale M.]

[modok]

If you did this and it "motors"

Then it should generate some kind of voltage when you spin it.

I think.....it's no different than a simple permanent magnet motor, with the exception the magnets are replaced with electro-magents (the field windings). Wired like type-A here

So when you "motor" it, your powering the armature and the field.

Being wired like this, when you spin it and ground the field it should ramp up in a viscous cycle, because the more voltage it makes the stronger the magnets are, powers itself, but how does it get started?

How does it work if it has no magnets? They say the weak residual magnetism in the cores is enough to get it started. Maybe you did something to de-magentize it so it won't self excite.....or maybe there is some short internally, I really don't know. To be honest my experience with these generators has been 75% of them just plain work, and half the guys want to replace them with alternators, so perfectly good ones are actually piling up unused.

[krisbeetle]

Thanks for chiming in! Appreciate it.

I just came down to the shop and thought I had it fixed. I got 14 .1 regulated volts out of it by pushing on the brushes (rather just the top one)

I let it run a minute saw idiot light was off .... Great!



Not for long, went and started it a couple more times pushed on brushes ..... Nothing.....

Polarized it again... Still spins....

Disconnected VR and Grounded DF terminal and measured with voltmeter from D+ terminal trying to get the 35volts out of it increasing rpms..... Could barely get 4-5 volts out of it....

Wtf???!!

So it is capable of 14 regulated volts for a minute but pushing on brushes isn't working anymore....

has anyone experienced this? Want to figure out what's going on even more now.

[modok]

Could just be a bad connection.....but where?
And one you can fix or one you can't?

One could test the ohms of the field if you pulled the brushes. But I don't know what it's supposed to read.

[busdaddy]

Mr. Bentley knows what the ohms should be.

Have a close look inside where the commutator meets the windings of the armature, if it's been overworked by a bad regulator or over revving during the full load test the solder could have melted, it'll be spattered all over the field coils where it spun out if it did.
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[Dale M.]

Or just plain worn brushes and springs are hitting brush holder and not allowing direct pressure on brushes/armature....

How long are the brushes.... How high up in holder is the top of brushes.....

Also look at commutator is the insulations between the commutator bars even with of above surface of commutator and causing brushes to bounce on commutator.... One of the procedures in generator rebuilding is to undercut insulator between copper bars of commutator...

Most reasons why people go to alternators is they put out about 55 amps where generators put out only about 30 amps, and alternators put out higher voltage and higher current at lower RPM's...

Dale
_________________
“Fear The Government That Wants To Take Your Guns"
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

[krisbeetle]

The old generator had a lot of "brush bounce" so to speak....

This generator I have in there currently (one I had kicking around) has a very minimal amount of brush bounce....


I charged the battery up and started bus, generator was working putting out 13.6-14.1 volts .... Great... Shut it down .... Started again.... Still working great....
Then all of a sudden stops putting out voltage....


Battery voltage after charged was retaining a little extra at. 13v ... Possibly provided a little extra? To excite??? I don't know....


I looked for melted solder as suggested and saw no traces.....

Will next try testing resistances of windings... Maybe find a growler for armature ......

[Q-Dog]

When the top of the brush reaches the top of the holder it is worn out and the spring can't maintain pressure on the brush. How worn are your brushes?
worn out.

New.

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