Special Effects w/o the Six Pack

by Terry Cobb (University of Maryland, Balt. Co.)

Last time, I detailed how to convert a portable dimmer pack into a high capacity chaser. The same control circuit can also be used without having a dimmer pack. All that needs to be done is to replace the controller/resister/dimmer pack with a DC power supply and a relay with a DC coil (6, 9, or 12 volt DC is typical). Referring to the diagram, the relay coil is connected between the positive terminal of the power supply (whose voltage is proper for the relay) and the terminal of the transistor that was formerly connected to the control lines (the collector).

Notice that the relay has a diode placed in reverse across the coil. This is very important as it protects the transistor from emf of the relay coil. Without this diode the emf would destroy the transistor. This diode can be any available small signal diode such as 1N914, 1N4148, or equivalent. The transistor must be of a voltage and amperage rating to handle the coil requirements of the relay used. The amount of wattage that can be controlled is limited by the rating of the contacts, note that is two contacts can be wired in series that capacity is doubled, i.e., a double pole relay.

This method is, of course, more noisy than the dimmers and you have to do the 120 volt AC power wiring instead of merely plugging in the lights. Be sure to follow safe practice and not leave exposed wires. All 120 volt sections must be completely enclosed in an electrical box (metal or plastic).