The B2P (single phase) and B3P (3-phase) series of controls are a proportional, infinitely variable power controller capable of delivering 0-97% of the applied line voltage to inductive loads. The B2P is specifically designed to drive transformers, but will drive resistive loads too. This is accomplished by phase angle firing a pair of inversely connected SCR's. Modular construction allows for simple and solderless field serviceability. There are four field replaceable items:
  • Printed circuit board
  • Fuse
  • Dual SCR package
  • MOV (Metal Oxide Varistors)
Unit of Measure


Voltage Designations

N/A 380 VAC 50/60 Hz


N/A 200 AMPS

Output Voltage

N/A 0 to 97% of input voltage

Control Signal

N/A 4 to 20 mA at 6 volts DC

Input Impedance

N/A 300 ohms


N/A < 5% deviation

Tracking (phase to phase)

N/A < 5% deviation (balanced loads)

Response Time

N/A <12 mS (std unit, non soft start)


N/A Convection: 30-80 amps
Fan (120 VAC): 100-500 amps


N/A 90 ºF (fan cooled units only)

Power Dissipation (Watts)

N/A 1.2 x maximum current

Minimum Wire Gauge (Copper Wire Only- 90 ºC Temp Wire)

N/A 3/0 AWG

Net Weight

N/A 45 Pound

Shipping Weight

N/A 55 Pound

Wire Lug Torque (90 ºC Temp Wire)

N/A 250 lb/in

Lug Size (90 ºC Temp Wire)

N/A 250MCM - 6


Soft Start

N/A S02-2 Seconds S05-5 Seconds S10-10 Seconds S20-20 Seconds

Current Limit

N/A CL- Current Limit CLP-Current Limit with Panel Mount Potentiometer

Voltage Limit

N/A VL-Standard 1 Turn PCB VL25-25 Turn PCB



  • Compact and light weight
  • 100 % solid state circuitry
  • Over-rated SCR power modules
  • Over-sized heat sink
  • Full power ratings up to 50 ºC (122 ºF) ambient temperature
  • Optically isolated 4-20 mA input standard
  • Thermostats standard on fan-cooled units
  • Electrically isolated chassis and heat sinks
  • Gold alodined chassis and heat sink
  • I2T fusing and MOV protection on all power SCR's
  • SanRex, SemiKron, International Rectifier and Fairchild semiconductors
  • Double sided FR4 VO-94 rated glass epoxy PCB's
  • Theory of Operation

    N/A PHASE ANGLE FIRED controls proportionally turn on a percentage of each power line half cycle. This gives smooth, infinitely variable application of power to the heaters. Imagine a light dimmer and how it provides power to a light bulb. This method will provide the most precise control of heaters. Phase angle fired SCR’s will respond the fastest to load change and provide maximum heater life. It is the most precise method of control. Phase angle firing can increase heater life up to seven times depending on heater type. Phase angle firing also allows options such as soft start, voltage limit and current limit. These options are not available with any other means of control. Graphs below shows phase angle fired voltage output on a 240 V power line.
    The standard input signal (4-20 mA) is applied to the blue input terminal block, and then fed to three ramp generators. The output of each ramp generator (one per phase) is logically ANDed with a common 20kHz oscillator providing a timed 20kHz "picket fence" output signal. Each "picket fence” output is fed thru an isolation pulse transformer, rectified and filtered. These DC signals are then used to fire the SCR's. Move’s provide voltage spike protection and RC networks provide DVDs suppression for smooth, reliable operation. I²T fuses connected in series with each phase input provide over current protection in the event of external wiring shorts, and or too large of a load. Additionally, a MOV (metal oxide arrestor) is connected in parallel with each SCR/ diode, providing voltage spike protection to the controller. Diodes are used in series with the SCR for sound engineering factors: Diodes are stronger than SCRs. Diodes can take higher temperatures than SCRs. Diodes will not misfire.