Common Application of Timer Relays
Timer relays are work like regular relays, except that they have a time delay feature built into them. Their delay feature allows for control of circuits based on time events. A standard relay will close or open a circuit upon application of voltages across its terminals. However, timer relays have a delayed action, delaying either closing or opening of the circuit upon application of voltage to its terminals. Timer relays come with a built-in control feature like a knob, which makes it possible to adjust their delay times. Here are some of the applications of timer relays that will help guide you.
Auto-power off circuits
Off-delay timer relays delay remain in either closed or open position for a given period even after the trigger voltage is removed. The relay remains energized until the end of the delay cycle after which it is de-energized. Any application of trigger voltage immediately resets the timer. Off-delay timers are a major part of auto shut-off headlights in modern cars. The timer delay leaves your car's headlights on even after you switch off the vehicle. The delayed shut off gives you time to see where you are going for a few seconds after stepping out of your vehicle.
Defrost timers
Most Refrigeration systems have built in relay timers that turn on heaters built into evaporators in refrigeration systems. The heater's purpose is to melt any ice build up within evaporator vents; remain on for a given period of time. Usually long enough to melt any ice build up in the evaporators. Such relay timers are called "interval on" timers. Upon application of the trigger voltage, the relay is energized and begins its cycle. At the end of the cycle, the relay will go back to the state it was before any triggering voltage was applied. It does this even with the triggering voltage is still applied across its terminals. Therefore, if the relay's default position is an open circuit, application of an input voltage causes it to change to the 'closed' position for a given period after which it resorts back to its open position, and vice-versa.
Protection circuits
Timer relays can help provide circuit protection of electronic circuits and equipment against surge voltages. Upon application of a voltage across its terminals, an 'on-delay' timer relay will wait for an entire cycle at anytime before switching to its energized state. Removal of the triggering voltage resets the timer. This delay often can protect sensitive circuits against initial surge voltages when a circuit is powered on.
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