[ARC5] ART-13 dynamotor woes

[Leslie Smith]

Hello Robert.
Exactly.  I saw a problem like this with a "toy" air compressor.
Chinese origin.  For air-brush work. 
The motor should have been "dipped" in transformer varnish and laced,
but there wasn't enough varnish or lacing to prevent movement in the
windings.

Result?  After about 5 hours or use the enamel between windings had
abraided and voila - a short between turns.  
Bad news for the earth-leakage device in the switch-board.  Poof - dead.

73
 
  Leslie Smith
  vk2bcu at operamail.com


On Mon, Feb 11, 2013, at 6:32, WA5CAB at cs.com wrote:
> Meir,
> 
> The DY-17A is a 4-pole motor/generator.  Looking at the exploded view (or 
> the dynamotor stator itself - I've looked at several hundred of them),
> you 
> will see that there are four field coil units.  The schematic (ref T.O. 
> 12R2-5DY17A-501) shows that electrically there are 4 shunt and 2 series
> windings.  
> However, being a schematic and not a wiring diagram, and considering 
> manufacturing procedures one could argue it's more likely there are 4 of
> each.  In 
> any case, strip the stator.  With a milli-ohmmeter determine which coil
> has 
> the short.  Remove the pole piece and examine the spots where the coil 
> touches the pole piece (more likely) or case (less likely).  I'd bet you
> will 
> find a small gap in the tape with bare copper visible in the gap where
> the 
> wire has been rubbing against the pole.  The wire itself is enamel
> insulated.  
> When starting, the wire is going to try to move.  Plus although the
> DY-17A 
> runs quite smoothly, there is some high frequency vibration.  It wouldn't 
> take a lot of scuffing against a corner to wear through through the
> enamel.
> 
> Robert D.
> 
> In a message dated 02/10/2013 11:30:34 AM Central Standard Time, 
> wf2u at ws19ops.com writes: 
> > Folks,
> > 
> > 
> > 
> > I have an interesting but aggravating problem with a DY-17A/ART-13 Eicor
> > manufactured dynamotor. The dyno, by the way is a late WW2 production, it 
> > is
> > in pristine cosmetic condition inside and out and it was never used before 
> > I
> > got it recently. After 3 weeks of running my ART-13 with it for a couple 
> > of
> > hours a week, in the middle of a  CW net it started to smell like hot
> > insulation. I shut it down and troubleshooting indicated that there is a
> > short to ground somewhere in the field coils. The remaining coil portion 
> > is
> > still able to spin the dyno at a much slower than normal speed, and the
> > increased current is heating it up fast. I isolated both HV and LV rotor
> > windings, they're OK. No other shorts to ground found anywhere in the 
> > unit.
> > 
> > I'm scratching my head, because the field coils are fed from the primary 
> > 28
> > VDC, so the insulation is not breaking down from high voltage. If there 
> > was
> > a manufacturing fault in the field coil installation, the short would have
> > existed from the get-go. How does a fixed field coil insulation break down
> > in a few hours of operation? Nothing is grinding, nothing is loose inside
> > the dynamotor. It spins completely freely as it should (by the way, there 
> > is
> > a label inside the end bells which says: "Do not lubricate!"). 
> > 
> > Should I venture and attempt to take the whole dynamotor apart and remove
> > the field coils to see if I can find the short?
> > 
> > 
> > 
> > Incidentally, my other dynamotor, the older DY-17/ART-13, after replacing
> > the HV brush caps (the newer Eicor has no brush caps in the dynamotor
> > itself) is working fine. It looks beat-up on the outside, and the 
> > dynamotor
> > itself looks like it was used a lot, but at least so far, so good.
> > 
> > 
> > 
> > Any thoughts?
> > 
> > 
> > 
> > 73, Meir WF2U
> > 
> 
> Robert Downs - Houston
> wa5cab dot com (Web Store)
> MVPA 9480
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