Date: Fri, 12 Aug 2016 15:00:00 -0400
From: Ron Youvan <ka4inm@gmail.com>
To: amps <amps@contesting.com>
Subject: Re: [Amps] SCR to adjust 240v to 200v
On 08/12/2016 01:07 PM, Jim Durham wrote:
/* snip */
> Talked to Henry. They asked me the plate transformer number, which they
> looked up and said "Oh, that's the 200v European transformer". So, I put
> a hefty variac on the 240v AC incoming and all is fine, except I'd like
> to ditch the variac and was wondering about if anyone on here had any
> wise words about using an SCR instead to back the AC voltage off.
I would measure the incoming line Voltage RMS then I would locate a
used 240 Volt to (normal Voltage - 200) Volt transformer and buck the:
240 - 200 = 40 Volts at enough Amps with it.
SCRs are headaches just waiting for you.
> My experience with big SCRs (TV studio lighting) was that they tend to
> put out a lot of RF hash. I also wonder about how the choke and filter
> cap in the power supply would like non-sinusoidal AC waveform?
--
Ron KA4INM - Youvan's corollary:
## I concur. Use a 40 volt buck xfmr, but make sure u wire it up correctly,
so you buck 40 volts..and not add 40 volts ! SCRs are a pita, dont even go
there.
If you ever replace the plate xfmr, get a real one, but you would also have to
replace
the low voltage stuff, like the fil xfmr, and any control xfmrs, plus blower,
etc, etc, etc.
## any 240-40 vac buck xfmr will have to be able to handle the full normal
current.
IE: the 40 vac sec side, that gets wired in series with the 240 vac, will have
to handle
probably 15-20 amps. So a 600-800 va xfmr will be required. Buy it with
lotsa taps
on either the 240 side...and / or the sec side. Then u can precisely control
the voltage.
IE: pri taps at 235-240-245....and sec taps at 38-40-42 volts.
Jim VE7RF
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