[Amps] Large Variac controlling HV power supply

[David Jordan]

Once you bring up the power supply you could engage a shunt-relay to by-pass 
the variac.  I never did on my amp.  I determined the voltage drop was on 
the line, not the variac and I was using a 30amp rated variac.  Also, if you 
built a hefty enough HV supply a few volts drop on the input won't be felt. 
I was using 300Mfd for the 6KV, 30,000mfd for the 1KV screen supply with 
choke on the center tap.  The supply was rock solid.

Good Luck,
dave
wa3gin
----- Original Message ----- 
From: "peter chadwick" <g8on at fsmail.net>
To: "Mark Beckwith" <r-emails at n5ot.com>; <amps at contesting.com>
Sent: Thursday, October 31, 2013 9:12 AM
Subject: Re: [Amps] Large Variac controlling HV power supply


>I have seen it said that it isn't a good idea because the variac regulation 
>isn't that good. Having said that, in my youth, I worked on a tx where we 
>had a fairly large 3 phase variac feeding a 25kV transformer, and the 
>output was wound down a bit to give us 18kV at 4.5 amps.
>
> Admittedly, a choke input filter, so it wasn't wound down too far. So it 
> should be OK.
>
> 73
>
> Peter G3RZP
> ========================================
> Message Received: Oct 31 2013, 12:28 PM
> From: "Mark Beckwith" <r-emails at n5ot.com>
> To: amps at contesting.com
> Cc:
> Subject: Re: [Amps] Large Variac controlling HV power supply
>
> I think guys have been doing this since time began.  I have two different
> boat anchors out in the barn built exactly as you describe, both built by
> other people (one is a bona-fide Henry industrial something-or-other).  I
> assumed it was "best practice."
>
> 73,
> Mark - N5OT
>
>
> ----- Original Message ----- 
> From: "Dave Trainor" <dave at n8zfm.com>
> To: "Amps" <amps at contesting.com>
> Sent: Wednesday, October 30, 2013 2:52 PM
> Subject: [Amps] Large Variac controlling HV power supply
>
>
> > Is there any disadvantage (other than size) in utilizing a large 30 amp
> > variac to supply the line voltage to the HV transformer in a power 
> > supply?
> > I have a 5000V 3A transformer that came from an industrial induction
> > heater, and the variac from the same to control the voltage. Now both of
> > these are large, but considering a floor roll around unit for the power
> > supply and building the variac into the top with its steering wheel
> > control.  Since I have both the cost is small but is there a 
> > disadvantage
> > to doing this power wise? I expect at the current draw for legal limit I
> > should see no voltage sag at all at 3000v since the cycle dyne induction
> > heater the transformer came from was a 10kW unit CCS of course.
> >
> > Thanks,
> > David Trainor - N8ZFM
> >
> >
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> > Amps at contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
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