[ARC5] ART-13 dynamotor woes

[Geoff]

A mains operated DC supply?

After listening to a DY-17 I quickly built a PS for my ATC and my ears have 
been thanking me.

Carl


----- Original Message ----- 
From: "Meir WF2U" <wf2u at ws19ops.com>
To: "ARC-5" <arc5 at mailman.qth.net>; "Milsurplus" 
<milsurplus at mailman.qth.net>; "ART-13_transmitters" 
<art-13_transmitters at yahoogroups.com>
Sent: Sunday, February 10, 2013 12:30 PM
Subject: [ARC5] ART-13 dynamotor woes


> 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
>
> Landrum, SC
>
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