SCR Analog Power Controllers

Zero Crossover Fired

Spang Power Electronics designs and manufactures a full line of single and three phase, zero crossover fired SCR power controllers.

In zero crossover control, the SCRs are gated at the moment the sine wave crosses zero and the anode is driven positive. Complete cycles of power are delivered at a time. Power control is not accomplished by gating the SCRs every cycle, but by having the SCRs ON some cycles and OFF others. The ratio of the number of cycles ON to the number of cycles OFF is varied to proportion the power to the load. Control is accomplished at a cycling rate which achieves the smoothest, most continuous required output power. For example, very low output is 1 cycle ON and 100 cycles OFF. Power output of 50% typically provides control of 1 cycle ON and 1 cycle OFF. Full output is continuous conduction. For this type of control, a variable time base is used instead of a constant fixed time base for the cycle ON-OFF switching.

Zero crossover control has the advantage of producing no radio frequency interference (RFI) since, turning on at zero, there are no abrupt changes in current or associated fields.

Product Line Overview

The "B" Series
The "B" series power controller offers the widest variety of ratings, features and options. This series is available in ratings from 15 to 3000 amps. Options include voltage, current or watt limiting, voltage, current or watt regulation, overcurrent shutdown and NEMA enclosures. The Spang "B" Series can also be equipped with special options such as pilot lights, meters, circuit breakers and water cooling.

The "C" Series
The "C’ series power controller is a lighter, more cost efficient unit which delivers peak performance under tough industrial conditions. This controller is available in three phase with ratings from 40 to 350 amps. Options include current limit and voltage regulation. NEMA 1 enclosures are also available.

The TC Series
The TC Series unit is a three phase controller specifically designed for transformer coupled loads. This controller is a two leg, 4 SCR design with two SCRs connected inverse parallel in two of the three lines connected to the load. Ratings are available in 40 to 350 amps.

The 650 Series
The 650 Series units are definite purpose controllers which offer economical power control in a compact package. Options include current limit and/or voltage regulation and are available in ratings from 15 to 110 amps.