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Wiring a ST3PF Delay Off Relay

Wiring ST3PF Delay Off RelayPosted on Friday, 25-Oct-2013
The Fjui ST3PF is a time delay relay switch that comes in numerous voltages and time delay ranges. When you apply power, a coil is energized which flips an internal switch. When you remove power the switch stays flipped for the set amount of time. Unlike most relays, the ST3PF is available in 110 volt AC - there's no need for a separate low voltage power source to trigger the relay. The limitation is that the load being run by the relay cannot draw more than three amps.

I use the ST3PF (bigger than I expected) for a mini sump pump that draws less than an amp. The pump is triggered by a simple float switch. Without the ST3PF to keep the pump running after the float switch turns off, the pump would be turning on and off constantly.

The drawing is presented as an alternative to the "8-pin timer wiring" one that I didn't find very helpful. The drawing shows a basic switch circuit (left) with the addition of an ST3PF (right). Only four of the eight pin connections are needed/used.

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Re: Wiring a ST3PF Delay Off Relay
Posted by Lester on Thursday, 22-Jan-2015

Re: Wiring a ST3PF Delay Off RelayHaving the same power supply voltage to the coil of the relay, pin 7, and also the thing you want to stay on for more seconds, pin 8, will not work. When you kill the power to the relay the other thing will go off right away as well and a few seconds later, you will hear the relay switch. I made a diagram to show how it works to have a solenoid valve close 30 seconds after the water pumps stops. This is to let the water slow down before the valve closes to prevent water hammering.

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Re: Wiring a ST3PF Delay Off Relay
Re: Wiring a ST3PF Delay Off RelayPosted by Dave on Wednesday, 02-Feb-2015

Thanks for writing. As we both discovered, pins 7 and 8 need power. There is no reason your pin 8 couldn't get power from the same source as your controller/pump. Adding lines from the right side of your Controller to Power Supply would make your circuit pretty much the same as mine.

This drawing is more correct (SW location) and may make more sense/be more useful. In this drawing your controller would be SW1, your pump between pins 7 and 2, and your solenoid coil would be "load".

Folks needing the ST3PF to delay turning off a load greater than 3 amps would need "load" to be a relay coil (C2) controlling the relay switch (SW3) and the primary load (L2)... Two power sources might be easier/cheaper here, e.g. line voltage for SW3/L2 and low voltage for everything else.

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