Wiring DH48S Timer to be self-latching

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Joined Jan 22, 2021
I am trying to wire a DH48-S timer to operate a three phase pump. I have a remote controller that operates a relay at the pump. The pump is located about 1 km from my house. The remote controller relay can be configured to close the relay either momentarily or to open and close the relay (in two separate clicks). It is represented by the momentary switch S1 in the attached circuit. The load of my circuit is the coil of a three phase contactor which activates the pump.

The timer, depicted below as a simple relay (RL1), does not act in a predictable fashion when connected as shown. The timer turns on and starts counting when I pulse SW1, but then turns off immediately I remove the contact. It is as though the switch in the timer does not operate when connected in this manner. If I leave SW1 closed until the time cycle finishes, the timer stays on and the load stays connected, ie it seems that the time switch activates at the end of the 'on' cycle. Note that with the power connected directly across Pin2 and Pin7, the timer relay functions perfectly.


The circuit connections for the DH48S timer is shown below
I have tried connecting Pin2 to the NC contact (Pin5) instead of the NO (Pin6) but this causes the timer to immediately activate and start counting to the set point, whereupon it resets itself and begins the count again.

I could connect the remote in the supply line and have power going straight to the coil of the timer. However this would mean that I would need to have the remote configured as an on/off switch and would need normally to press it twice to reset (first time to disconnect the timer, and the second time to reconnect it). By wiring it as shown, I only ever need to switch it once, and do not need to worry about an external power failure triggering the pump on power reconnection.

I could also connect the remote switch to the reset of the timer (Pin 1 to Pin 3). This works but if the power supply is interrupted and reconnected, the pump will operate, and I do not want this to happen.

I could wire the timer via a separate relay using the shown circuitry for the relay, and I know this would work. This is probably what I will end up doing.

However can anyone please explain this anomalous behaviour of the timer when connected in this manner. Why does it not behave like a simple relay? Is there any way around this without using a separate relay?