# Relay Coil Energy Saver Schematic Circuit Diagram

Some relays will become warm if they remain energized for some time. The circuit shown here will actuate the relay as before but then reduce the ‘hold’ current through the relay coil current by about 50%, thus considerably reducing the amount of heat dissipation and wasted power. The circuit is only suitable for relays that remain on for long periods. The following equations will enable the circuit to be dimensioned for the relay on hand:

R3 = 0.7 / I
Charge time = 0.5 × R2 × C1

Where is the relay coil current? After the relay has been switched off, a short delay should be allowed for the relay current to return to the maximum so the relay can be energized again at full power. To make the delay as short as possible, keep C1 as small as possible.

In practice, a minimum delay of about 5 seconds should be allowed but this is open to experimentation. The action of C2 causes the full supply voltage to appear briefly across the relay coil, which helps to activate the relay as fast as possible. Via T2, a delay network consisting of C1 and R2 controls the relay coil current flowing through T1 and R3, effectively reducing it to half the ‘pull in’ current. Diode D2 discharges C1 when the control voltage is Low. Around one second will be needed to completely discharge C1. T2 shunts the bias current of T1 when the delay has elapsed. Diode D1 helps to discharge C1 as quickly as possible. The relay shown in the circuit was specified at 12 V / 400 ohms. All component values are for guidance only.

The ohm is the unit of electrical resistance in the International System of Units. It is named after German physicist Georg Ohm.
The ohm is defined as an electrical resistance between two points of a conductor when a constant potential difference of one volt, applied to these points, produces in the conductor a current of one ampere, the conductor not being the seat of any electromotive force.
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