>
>
>-----Original Message-----
>From: Rich Measures <measures@vc.net>
>To: Steve Thompson <amps@txrx.demon.co.uk>;
>amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
>Date: 18 June 1999 09:22
>Subject: Re: [AMPS] hipot testing
>
>
>
>>>Is it an open transformer, Steve?
>>
>>
>>It's probably what you mean by open. It's not encased in a
>>sealed box of any sort but it has a very generous dip
>>coating of varnish. It's from a good maker (Parmeko) so I
>>expect it was vacuum impregnated too.
>
>? If the slightly-leaky transformer were mine, to drive
>out moisture,
>I would bake it in a 180 deg. F oven for a few days, and
>re-measure the
>leakage. If the leakage decreased, I would hot-pot the
>transformer with
>fiberglass laminating resin. (info on my Web site)
>>
>- good luck, Steve
>Rich...
>
>
>I doubt if that's the sort of leakage problem it has,
>although I'll give it a try. It was used in PSU which
>another member of the contest group built and a flashover
>happened and the mains fuse blew. Inside I found that there
>was no ht current limiting and one leg of the bridge had
>gone short.
? Not using a capable glitch R. in the pos. lead of an anode supply is a
standing invitation to grief. Putting a suitable MOV across the primary
winding (to absorb potentially destructive spikes) is probably not a bad
idea.
> In the course of trying to get things working
>again I found that there is a leakage path from the
>secondary to the core which goes conductive at about 600V.
? Center-tapped secondary transformers are not known for over-insulation
of the center-tap since it is typically grounded.
>I tried it with the ground connection lifted off the core and
>it worked ok. I spoke to a transformer winder who said there
>would be a carbon tracking path which would never go away.
? Polyester-resin has pretty good insulating qualities, provided one
drives off the moisture in the paper before potting.
>Yesterday I got hipot working and measured the primary
>insulation to core, which prompted my question about leakage
>levels. I'd love to get it going again as the secondary
>resistance is only 18 ohms and the power just keeps coming.
>
? 18 ohms is rather good for the V and A involved. .
- cheers, Steve
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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