Re: Homebrew Variacs? (fwd)

---------- Forwarded message ----------
Date: Thu, 16 Jul 1998 09:41:27 GMT
From: Mike Harrison <wwl-at-netcomuk.co.uk>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Homebrew Variacs? (fwd)

>> Date: Tue, 14 Jul 1998 18:53:56 -0700
>> From: Stefan Bishay <stefan00-at-gte-dot-net>
>> To: tesla-at-pupman-dot-com
>> Subject: Homebrew Variacs?
>> Is it possible? I was thinking take a piece of 12" thickwall PVC pipe,
>> about 6" long, wrap #10 enamel coated wire around it in the standard variac
>> fashion, and  machine up some kind of rotor/brush assembly. Would this
>> work? Any special considerations? What kind of current will 10 AWG wire
>> handle at 240v in that application?
Forget trying to make it look like a normal variac and apply some
lateral thinking...
Large mains stepdown transformers can often be bought cheaply from
hamfests/surplus etc. Use several of these with primaries in parallel,
and secondaries in series to provide a number of different voltage
taps.  With suitable switching, you could get a large number of
different output voltages. You could build a cam switch to switch the
secondaries around to provide a progressive output increase in steps
of a few volts, or use relays and a diode matrix on a rotary switch to
select the required relay coils.

Alternatively, find a nice big transformer and wind a new secondary
with taps to select the output voltage. 
Make the first tap half the voltage of the others - this will double
the number of voltages you can get from the other taps. 

Or wind several secondaries, each twice the voltage of the previous,
to allow selection of voltage by combining windings in a binary
fashion. 4 windings (10,20,40,80V) could give you 0-150V in 10V steps.
You could use a binary rotary switch and 4 relays to select the output

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