ST head prep

[okiezeke]

Me too, ordered 2 10,000 uf  caps to try to level out some input DC noise.  Then I'm going to put the 20-2 back together if I can remember how.

Zeke

[okiezeke]

Doug,
I finished rebuilding my second ST15.  Some pics.









What a garage is for

[rcavictim]

Zeke,

I like the exhaust pipe header you put on the ST head. Nice large radius bend so you don`t lose any power.   

[Stan]

Don't laugh...a friend of mine designes circuit boards for FM repeaters and that's exactly what he has told me on occasion.  I copied a "universal test board" from the ARRL handbook and he took it and modified it so there were no "corners" in the etching.  Mind you, that's for rf stuff.
Stan

[okiezeke]

ontology recpitulates phylogeny.

The ST is still in a larval stage and hasnt lost its tail yet.
Zeke

[rcavictim]

Don't laugh...a friend of mine designes circuit boards for FM repeaters and that's exactly what he has told me on occasion.  I copied a "universal test board" from the ARRL handbook and he took it and modified it so there were no "corners" in the etching.  Mind you, that's for rf stuff.
Stan

Stan

I`m certainly not laughing and your RF buddy is correct.  It is a bad idea to make sharp bends in any ground wire connecting to a lightning rod.  The use of large radius gentle bends is absolutlely necerssary.  When lightning current races down the wire during a hit it will literally leap off the wire into the air again at any sharp bend in the wire!

In RF circuit board trace design it is perfectly acceptable to have a sharp 90 degree bend IF a 45 degree angle is cut to truncate the OD of the corner.  This provides a discontinuity in the line properly placed which will act as a `mirror` that will reflect the wave around the sharp corner. This technique is the standard practise in microwave work.  I used to work with this stuff.

[okiezeke]

Oh,  Still worth the effort, though.
Zeke

[Doug]

Looks like you you have been buisy .......

I like the fact they added a Guset on the foot for this head.
Some don't, not sure how much strength this adds but I know I prefer it....

Looks good Zeke, keep us posted.

And to answere your question about the empty slot.

If you dived the stator in 4 sections 90 mechanical deg from each other you will find that each coil group is less than 90 mechanical degrees. This is called a cord factor ( Americans call this span, the English throw ) and its done on purpose so the machine will produce less harmonics. Depending on the number of poles and slots the CF changes from machine to machine.

[okiezeke]

Doug,
We finally had a genuine power failure.  I rolled the 1115-ST15 out of the garage and fired it up.  Ran beautifully.  Carried the whole house including hot water heater for about 2 hrs, then, no power out.  A peek at the brushes showed all four wires in the area ripped apart.  Looks like one field feed wire came loose and tore out the other three.  Will pull the back plate off tomarrow and repair the carnage.  Will try to have everything tied/epoxied down tight to keep this from repeating.

The gen power did produce a noticable flicker in traditional tube type fluorescents, but none in the compact fluorescents.  Go figure??  Everything else ran fine.

Zeke

[Doug]

Modern CFLs use an electronic ballast with a chopping speed of 1000 hz.
Old florecents ( you probably have magnetic ballasted F40 s right? ) will flicker and flash with all the noise and there's little that can be done. You can replace the older magnetic ballast with a newer electronic one and the flicker will be gone.

Not sure what let go from your description:
Did the brush assembly come a part on its own or did something from the rotor come loose and tare up the brushes?

Post a picture please

If its a brush holder failure you might want to consider an upgrade using some parts from a Baldor DC motor. The brush holders could be fairly easily adapted by a savy fellow like you.....

[okiezeke]

Doug,
Brushes and holders are fine.  The field feed wires to the brushes, and the wires from the rings to the rotor were all ripped in two.  Its hard to tell which wire went first, as all are broken.  Could get a pic but wouldnt show much as I already removed the debris.  There are a couple of spots where a wire touched a commutator ring, but just surface burns, no deep damage.

I can see the ends of the rotor windings where the wires broke off, and looks like there is enough left to get a crimp connector on them.  I'll wire or epoxy the connector to the rotor insulator to protect the fragile aluminum wire from flexing.  All the rest is multi strand copper and should be OK if I route them carefully and support anyplace that looks like it might want to break.

Zeke

[Doug]

OK:

I wonder what happened....
Sounds like the binding let go from centrifugal force but I'm just guessing

You might want to try some fiber glass epoxy resin and glass roven. Thasts plenty strong to hold and non conductive but you'll never get it a part if anthing ever comes apart.

If your crimping copper to Aluminum get some copper never sieze ( or better the right kind of anti oxide compound for alum copper splices, since it makes realy good never sieze any way ) and just give the alum a light coat before your crimp. I doubt you would ever have a problem if you do it dry but a little insurance is cheap. 

[okiezeke]

Doug,
I'll get some in the morning.  There is only about an inch of wire left before it disappears into the rotor winding, so I need to do it right on the first try.  Will probably never know exactly why it failed, but I'll sure try to rebuild it solidly'
Zeke

[Doug]

Carefuly, with your very best.... smallest..... sharpest pen knife scrape the varnish off the wire.

If this was copper you'd just burn it with a torch and soldier but since its aluminum your going to have to scrap and that enamel is on their good!

[okiezeke]

Doug,
I hear you!  Damn aluminum wire is delicate stuff and I dont have any to waste.  Have an x-acto type knife set with razor sharp blades that should do the job.  I looked at wire today, and the local stuff was just lamp cord.  Ordered some industrial quality super flexible multi strand  from McMaster today, figured I needed the quality.
Zeke