For economical general usage, this is the preferred method of using a transformer with any thyristor power-control unit. The SCR control can usually accept virtually any ac voltage input--simply wire the SCR control transformer to the conventional voltage on the primary--So that whatever max load voltage is required can be easily provided by the transformer secondary in front of the SCR unit.

For example: Cutting or sealing plastic sheet or plastic foam is often done easily by heating nichrome wire and using a wire frame to cut plastic blocks out to any given size. The 1-5 foot lengths of wire, however, require low ac voltages to keep from burning up the wire. Also, worker safety considerations require low voltages on the unprotected wires.

A thyristor unit connected to a buck/boost type transformer's 12/24 or 16/32 vac secondaries can easily control several hundreds of amps to many wires in parallel. The maximum current and/or number of wires is determined solely by the transformer's secondary voltage.

Figure 5

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