Chromalox MaxPac, User Manual, Page: 6 / 44

4
2
†
This can be set to three cycles ‘On’ / three cycles ‘Off’ (see section on installation options).
Description
MaxPac I, II, and III
The Chromalox Model MaxPac IP, I, II and III Series are specifically designed for the OEM market. The Chro-
malox MaxPac I, II and III controllers are highly versatile SCR Power Paks. Firing modes includes On/Off
and DOT proportional zero voltage switching. Chromalox’s exclusive DOT (Demand Oriented Transfer) firing
switches the fewest number of cycles to provide the most precise zero crossover control. At 50% output the
units output alternates between one cycle “On” and one cycle “Off”. At 51% the output continues with one
cycle “On” one cycle “Off” and gradually integrates one extra “On” cycle for the additional one percent. This
DOT fired technique also minimizes temperature overshoot, temperature fluctuations and helps extend the
loads element life due to reduced thermal shock.
The power SCR assemblies consist of one, two or three SCR’s connected back to back with a semiconductor
fuse, RC Snubber and MOV protection. The firing circuit is based on common integrated circuit. Diagnostic
indicators are included as well as plug-in terminal blocks for easy customer interface.
MaxPac IP
The Chromalox MaxPac IP utilizes Single Phase, Phase Angle firing to modulate power to an inductive or
resistive load. Phase Angle control has the advantage of proportioning every cycle thereby providing very
fine resolution of power. Fast responding loads in which the resistance changes as a function of temperature
require Phase Angle control. The MaxPac IP offers a Soft Start feature that assures that the load power is
gradually increased from zero to the value set by the command signal in the event of a power interruption.
In addition, optional Current Limit is used to protect the load, SCR controller and the total system from large
surge currents that could occur at start-up.