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@fsmail.net>
To: "Mark Beckwith" <r-emails@n5ot.com>; <amps@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@n5ot.com>
To: amps@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@n8zfm.com>
To: "Amps" <amps@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
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
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