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 120 VAC 50/60 Hz



Output Voltage

N/A 0 to 97% of input voltage

Control Signal

N/A 4 to 20 mA at 6 volts DC, 300 Ohms


N/A < 5% deviation

Response Time

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


N/A Convection: 30-100 amps
Fan (120 VAC): 150-1200 amps


N/A 190 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)


Net Weight

N/A 6 Pound

Shipping Weight

N/A 8 Pound

Wire Lug Torque (90 ºC Temp Wire)

N/A 45 lb/in

Lug Size (90 ºC Temp Wire)

N/A 1/0 - 14


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
  • I2T sub cycle fusing standard
  • 100 % solid state circuitry
  • Over-rated dual SCR power modules
  • Thermostat std on fan cooled units
  • Over-sized heat sink
  • Full power ratings up to 50 ºC (122 ºF) ambient temperature
  • Optically isolated 4-20 mA input standard
  • Electrically isolated chassis and heat sinks
  • 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

    These 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.
    The standard input signal (4-20 mA) is applied to the large blue input terminal block, processed and fed to an optical coupler. The output of the optocoupler controls the pulse generator which drives a pair of optocouplers. Each optocoupler is in series with its own isolated SCR drive power supply providing drive to a pair of inversely connected SCR's. To obtain superior linearity, the line voltage is monitored and optically fed back to the input stage of the controller. An I2T fuse connected in series with the SCR's provides over current protection in the event of external wiring shorts, and or too large of a heater load. Additionally, a MOV (metal oxide varistor) is connected in parallel with the SCR's, providing voltage spike protection to the controller.