Simple Circuit Reduces Relay Coil Power

摘要

FELLOW ENGINEER sanjay R. Chendvankar of Mumbai, India, recently offered a novel way of reducing current through a relay coil (see "Driver Saves Power In Energized Relay," April 7, p. 85). His idea utilized an unused normally closed pair of contacts of that relay to reduce the driving voltage to the relay once it was energized. The design works very well, but what do you do when an unused pair of contacts is not available? It is well known that an energized relay coil will maintain contact closure even after the driving voltage is reduced somewhat. For many years, we have been employing a very simple approach to reduce the relay's driving voltage without relying on unused contacts or sophisticated circuitry. All we do is add two common parts: a resistor and capacitor in parallel.