I will now introduce you to other tools I often use in
conjonction with the isolation transformer.
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On the picture on the left, you can see a Variac. A Variac
is in fact an autotransformer with a variable output.
Here is the shematic of a variac:
COM -----) || The output voltage rages from 0 to IN.
( ||
) ||
OUT -->) ||
) ||
( ||
IN -----) ||
This is very useful to obtain any ac voltage instantly, instead of looking
for a specific transformer. It can also be used to test power supplies,
when you want to see how they react to voltage variations.
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Sometimes, a voltage higher than the mains voltage is needed.
I use a auxilary transformer designed to step 347volts down
to 115 volts. I just use the secondary as if it was
the primary, and I obtain a 347 volts output. In combination
with my variac, It can output any voltage between 0 and 347 volts.
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For safety in case of a short circuit, you can limit the
current by powering the circuit in series with a bigger load. I
use light bulbs, ranging from 10W to 150W, depending on the
expected load. In some situation, I have used a 1500W toaster oven.
I learned this trick by reading the sci.electronic.repair faq.
Here is the exact page.
On the picture, you can see what I use to power a devices
in series with a load. The switch on the left is the master switch,
the switch on the right selects between a series output or direct
output. The left part of the plug is the output, and the right
part is for using another device as load. The light bulb is in
parallel with the left part of the plug.
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