150 A at about 20 V implies a VA of about 3KVA, so you need a dimmer or autotransformer at the input AC of this rating at least.
The transformer you need is one with input AC requirement you select, may be 200V AC and output of about 15 to 20 V RMS having a current sourcing capacity of your interest (150A). As you are using high currents, the rectifiers may also work out expensive, decide you plan to use half wave, full wave centre tap or bridge configuration.
The rectifier in the PDF data sheet from above post will server your purpose.
I think with this info you can plan the unit.