Field Winding Failure

[OilCan]

To begin with avoid any generator head built by Tawasi. I received one a couple years ago and did an
internal inspection. Poor crimps on lugs, worse of all was their lack of use of solder or maybe just pure lead at the pole connections, they were just twisted together, what solder was there just crumbled.  Anyway, I soldered the pole joints, repacked the bearings with a high grade grease before placing in service.

All this was to no avail, unit had been operated 3 months earlier but when I started it this week for a checkout no output. Pulled endbell, checked ohms on slipring to field got 58, seperated the joints to the field and found open.  Didn't get many hours from that brand. The stator is good, so is it worth keeping for a spare or will the tolerance be unusable with another rotor?

Pulled my spare from Rocky Mountain Power Systems to replace it with.

I have noticed some comments in regards to Georgia Generator ST heads, anyone care to comment on their quality control of the units you received?

[Tom Reed]

Did you try flashing it and check the diodes. They usually don't fail just sitting idle.

[OilCan]

Did you try flashing it and check the diodes. They usually don't fail just sitting idle.

Hi Tom,

Yes I did all that.  The actual field coils showed open. My guess the grade of copper
they used in the windings was very poor.  The coil wiring was brittle and not very flexible.
If they only twisted the 4-pole connections together without soldering I can't imagine
what they did to the things I can't see internally.  No heat damage.  The stator looks
decent. Bridge rectifier tested good.

[Ronmar]

Dam, I hate it when that happens.  It might be worth pulling the rotor for an inspection.  When I did the prep work on my ST-5(soldered lousy crimps and added sealed bearings), I made a little mistake in re-assembly that bit me about 2 hours later.  A wire run I improperly secured, got into the spinning rotor.  I got lucky in that it only broke the wire.  A close inspection of your rotor might show something that is repairable.  A motor shop could also possibly do a rewind...

[mobile_bob]

if it is the rotor that has failed, and you can't see where it is broken, i would much rather rewind it
as i would the stator.

just count the turns, and note the alternating directions (north and south), and rewind useing the same size wire
(or as close as you can get, go the size closest that is larger) then when you are done take it to a motor shop
to have dipped/baked and balanced.

save it for next winter, it will make a nice project when it is too cold to do anything else outside.

bob g

[OilCan]

Yep, I pulled the rotor, thats when I got a better look at their connections, you barely
touch them and the copper cracked and seperated.  I see where the field connections
enter the pole pieces but beyond that I can't see the "open" circuit in them.

I may do as a side project and pull down the pole pieces and see what happened internally and
see if it is user repairable.

There is a motor rewind shop in my area but the dopes claim they can't do generator rewinds.
I've taken a lot of large HVAC motors to them in the past.  Guess they don't need the money.

In the meantime I'll still be in the market for a spare gen head.  Hoping to see more opinions
on Georgia Generator's quality control on their product line.

[rcavictim]

I agree with Bob.  Rewinding a armature field coil set (4) would be a piece of cake compared to a stator.

I purchased a pair of big 24 kW (30 kVA) STC heads from Tom Osborne in Georgia and so far have no complaints above what was expected.  By that I mean the flimsy tin metal box that vibrates itself to death and needs to be changed as they ALL need to be changed.  I have a funny noise coming  from one head I'm now using in testing on my new Changfa 1115 powered genset.  I belkieve it is coming from one of the armature field coil forms is a bit loose on the armature and can knock around a bit from engine related speed variations.  I need to squirt some sort of glue in there soon.

BTW, Tom's company is NOT called Georgia Generator.  That is another firm entirely.  The confusion occured because Tom himself chose that as an ebay name.  Tom's firm is Millidgeville Aviation, Generator Division.

[OilCan]

I agree with Bob.  Rewinding a armature field coil set (4) would be a piece of cake compared to a stator.


BTW, Tom's company is NOT called Georgia Generator.  That is another firm entirely.  The confusion occured because Tom himself chose that as an ebay name.  Tom's firm is Millidgeville Aviation, Generator Division.

Thanks for correcting me on that.  I sometimes get him mixed up with Generator Store in Las Vegas because he used to ship out from Las Vegas, but his recent email indicates he will not be stocking in Vegas in the near future. I'm in Colorado.

I did manage to get my spare from RMPS up and running today, so I'm happy the system is back online.

[vdubnut62]

This is the generator part of Tom's outfit in Georgia.

http://www.centralgagenerator.com/index.php

I think his Son, or Son in law ran the other location in Nevada.

Tom cut me a deal over the phone on my 12kw unit, asked me what it went for on Epay then cut a bunch off it, then shipped it to me for another $90. I had it sent to a commercial freight dock though, where I work.
The unit looks great, very little vibration is very heavy and quiet. It has no funny growls buzzes or noise at all for that matter.
The bearings are very smooth, and do not heat up at all.
The doghouse is CHEAP!!!! I've seen thicker and heavier beer cans. It will be replaced eventually.
If I was in the market for another generator, I would not even think of going anywhere else. I like to deal with straight up people.
Anyway, that's my two cents.
Ron

[rcavictim]

Ron,

The sealed bearings run cool on mine as well.

You couldn't have put it better about the lack of thickness of the metal on the doghouse.  Ditto for the cover strap at the brush end and the outlet vents on the fan end.  Fans are cast aluminum.  Brush gear runs true and is solid.  My experience with Tom was as good as your's.  I wouldn't hesitate to send another his way or do repeat business with him myself.

[OilCan]

This is the generator part of Tom's outfit in Georgia.

http://www.centralgagenerator.com/index.php

I think his Son, or Son in law ran the other location in Nevada.

Tom cut me a deal over the phone on my 12kw unit, asked me what it went for on Epay then cut a bunch off it, then shipped it to me for another $90. I had it sent to a commercial freight dock though, where I work.
The unit looks great, very little vibration is very heavy and quiet. It has no funny growls buzzes or noise at all for that matter.
The bearings are very smooth, and do not heat up at all.
The doghouse is CHEAP!!!! I've seen thicker and heavier beer cans. It will be replaced eventually.
If I was in the market for another generator, I would not even think of going anywhere else. I like to deal with straight up people.
Anyway, that's my two cents.
Ron

Sounds great, I will keep that in mind.


Oilcan

[OilCan]

I pulled a couple of the pole pieces, boy those 10mm Allen bolts are in there!  Interestingly
when ohming the coil wiring I could not get a reading with both my probes on the same solder
joint.  Had to cut the wire tips off and read through fresh copper, after that each coil group
measured 7.4 ohms each.  Evidently they don't clean the insulating varnish off before twisting
and soldering the pairs.  Surprised this ran as long as it did.

Anyway, looks like it's worth rebuilding and glyptal the coils completely now that they're
accessible.  Will order a new bearing set and get rid of the plastic cooling fan as well.

Some of the coil wires might come up a little short, so what do you guys think about short wire
extensions soldered on the ends using tinned stranded wire at the pole joints instead of solid
wire?

These ends will be soldered together as well.  Let me know if you guys want photos with the
poles removed from shaft.

Thanks for the replies.


Oilcan

[rcavictim]

Oilcan,

If you are lucky enough that they used real copper magnet wire and not aluminum magnet wire then any soldering will be just fine. Use 60/40 rosin core radio solder.  Stranded wire will be fine with a good slobbering job.  

[mobile_bob]

Well that is certainly good news!

whatever you use for extension use the rosin core solder, and i would then use shrink tube over the joint
to add stiffness to the section, then secure the leads well with new cord binding and glyptal it well.

its going to be good for a long time now

while you are in there you might well go through all the stator connections and redo every one of them
no matter if they look good now or not. then rebind them and glyptal the stator as well.

or take both down to the motor rewinder and have them dipped and baked
afterwhich you probably will never have more problems with that head.

bob g

[OilCan]

Well I able to get my local rewinder to change their mind about ST heads.  They got out
of generator market years and ago only rewound motors and new sales.

Unfortunately this particular head (Tawasi) used aluminum wire in their windings.  Ended
up getting the stator windings clear expoxied and baked.  They also polished their
stator laminations in the bore.  Picked up a can of Vanguard Red dielectric paint Class F,
looked like Glyptal to me.  Painted my rotor field coils with that.

Wasn't easy soldering the tinned stranded copper wire extensions to the aluminum pole wires.
Sanded the ends and rosin fluxed then covered the splice with heat shrink.  Waiting for my new
metal fan from Tom Osborn to complete the reassembly.

If these windings ever go then will have then rewound with copper.  The motor tech said he could
do that and might possibly have to adjust the number of turns depending on the change from
metric wire  to awg.