3k st alternator just stopped mid work

[vdubnut62]

You might want to check the connections to the rotor from the slip rings. Just sayin.
Ron.

[BruceM]

Those ohm readings are way too high.  About 0.2 ohms over what your test leads measure when touched together is where it should be. Bad brushes, inadequate holder, dirty slip ring?  Oil is a nasty contaminate for graphite brushes/slip rings, will create this kind of issue, also.

[tyssniffen]

ok, so, crazy.

about the high numbers. perhaps my meter is just moving the decimal? 

but, I did a complete test, with alligator clip to the wire end of the brush, other probe at the bottom - opposite - side of the ring.  here's my crazy results:

   slot A (west)   slot A after spinning      Slot B (east)   Slot B after spinning
brush#               
1      2.1         2.3                     3.5         3
2      3.5         3.4                     5.6         2.1
3      2         2.4                       2.3         4.7
4      1.5         2.1                     2         2.7
5      3.7         2.1                     11.2      3.8
6      2.8         1.7                     2.6         2.6

W.T.H.?

[tyssniffen]

You might want to check the connections to the rotor from the slip rings. Just sayin.
Ron.

inside the case? is that a complete disassemble?

[Combustor]

            Looking back at your great pics of brushes and holders, it seems to me there is a helluva lotmof unsupported brush hanging out there. Perhaps someone here can tell me that's normal for an ST unit, but seems to me most other machines have the holders within 2 or 3 mm of the slipring, so that the brush is fully supported and guided. Could be there is very little spring tension and the brush is out of line and jamming when the ring rotates.
          Is it possible to slot out the holes in the insulated bracket or otherwise modify to support the brushes closer to the slipring as other makers do? It could solve several problems and it seems you have little to lose. A whole new piece of insulating panel drilled to correct dimensions could be an easy fix. Sure those brushes need more support than they have at present.
Regards,
Combustor.

[BruceM]

What are your ohms reading with probes touching each other? (This is the test lead resistance.) What are your readings if you measure with each probe on opposite sides of the slip ring? 

The ST heads do have a larger amount of unsupported brush than most other designs, this is normal, and is not likely to be your problem, as long as there is adequate pressure of brush against slip ring.

[tyssniffen]

ok, so, because I did the test with the extra alligator clip attached to the probe, I'm answering this question both ways:

west ring - with clip on one probe - .9
east ring - with clip on one probe - .9

west ring - just probes - .6
east ring - just probes - .7

probe to clipped probe (just meter to test lowest resistance): .6
probe to probe: .6

?

[BruceM]

The brushes may not be your problem; the intermittent problem just happened to change with changing of the brushes... or a loose wire or failing connection.

The slip rings seem fine, though the tip vs clip reading indicates a bit of glazing, so some polishing of the ring ( 400 grit on a stick held against the spinning ring- clean very well after) is a good idea.  The brush connector to slip ring readings seem high to me even once you subtract the 0.6 ohms for the meter leads but I'll check my ST-3 to confirm this. 

Check your rotor ohms (measured at the slip rings), also the harmonic, and stator windings ohms, now that it seems to be more reliably failed.  Intermittent problems can be hell to fix.

[tyssniffen]

Also, just to make sure I've updated the situation completely:

as this thing runs, I'm getting a solid voltage out - it's just oddly low, and isn't even consistent with what I've reported earlier.  Right now, it puts out 62.3 volts. if I speed it up or slow it down, it jumps around, but never jumps past say, 65v.

I certainly don't SEE any bad connections, but haven't closely examined rotors to rings yet (?)

[tiger]

Once again, the rotor windings  have to align with the stator windings where the harmonic windings are. The brushes have to align  with the rotor slip rings to transfer the harmonic  voltage to the rotor. The ST Gen Series have a history of faulty bearings full of Yak fat.  You need to align the above with a dial gage and bearing shims to achieve the above first!
good luck!

[tyssniffen]

Once again, the rotor windings  have to align with the stator windings where the harmonic windings are. The brushes have to align  with the rotor slip rings to transfer the harmonic  voltage to the rotor. The ST Gen Series have a history of faulty bearings full of Yak fat.  You need to align the above with a dial gage and bearing shims to achieve the above first!
good luck!

everything seems to be in the same position as it always has been.  It's been fine for years... do those things tend to move around?

could any of this have to do with a loss of 'residual magnetism'?  of being turned off with a load on it?

[dieselgman]

Please forgive if you have already mentioned this, but have you flashed the field to check excitation voltage buildup? I think your symptoms appear to preclude a problem with field magnetism to start up generation. Your field voltage may be off to cause the low output though.

dieselgman

[tyssniffen]

Please forgive if you have already mentioned this, but have you flashed the field to check excitation voltage buildup? I think your symptoms appear to preclude a problem with field magnetism to start up generation. Your field voltage may be off to cause the low output though.

dieselgman

I *have not* done that.  where can I learn about how to do that? starting to google now.  how's this grab, with my further questions added?

To restore the small amount of residual magnetism necessary to begin voltage buildup, connect a 12 volt battery to the exciter field while the generator is at rest, as follows:

Remove exciter field leads F+ and F- from the voltage regulator.  [where/what is this on the ST3K?]
CAUTION: Failure to remove the field leads from the regulator during flashing procedures may destroy the regulator.
Measure the exciter field resistance from the F+ to the F- lead. You should be able to read some resistance as you are measuring a continuous winding. An infinite resistance reading would indicate an open in the exciter field. Also check to be sure there is no path to ground.
Connect F+ to the positive pole of the battery.
Hold the F- lead by the insulated portion of the lead wire, touch F- to the negative pole of the battery for about 5 to 10 seconds, then remove.
Reconnect F+ and F- to the regulator. Repeat the procedure if the generator fails to build voltage.

[dieselgman]

That is a good description and instruction for field flashing. That is generally only indicated or required when you have zero output voltage due to no residual magnetism left in the rotor. In many sets, the output voltage is regulated by a small variable dc voltage fed back into the excitation windings.

dieselgman

[tyssniffen]

well, here's some more input.

while I was sitting there staring at it, I decided to wire it for 220, just to see what it would do.

it put out 110 or so, and went crazy when I put a bit of a load on it.

when I set it back to 110v (60hz), it no longer put out the 60ish it was putting out, and instead only did about 15v

is there something going on with the sine wave??