RE: [CAD_CAM_EDM_DRO] Variable Transformer

Others have noted that an autotransformer does not provide isolation -- and
that isolation is CRITICAL for safety. They are correct.

An autotransformer, such as a Variac, is a fine way to adjust the output of
the power supply. If it has sufficient capacity to handle the current, I
can easily see using it to cause a few percent adjustment, up or down, in
the output voltage of a usual transformer-rectifier-capacitor unregulated
power supply.

If you need a few percent increase or decrease, you can also use a
vacuum-tube filament transformer as an autotransformer to add or subtract
from the line voltage. The current limit of the filament transformer as
autotransformer is the secondary winding current rating. If you have a 20
amp, 12.6v center-tapped filament transformer, it can be used to increase
or decrease the line voltage wither 6.3 or 12.6 volts. It would be able to
supply 20 amps of AC to your power supply.

Just watch the power levels. When running a transformer at other than it's
rated voltage, it is important to watch both the current limits of the
windings (which I think is limited by the wires), and the VA limit of the
transformer (which I think is limited by the magnetic capacity of the core).

-- Carl



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