Motor ON-OFF Control

For this situation, I would Google "programmable relays". In principle, an octal "repeat cycle timer" could do this, but I don't think they have such a large ratio between on and off times. (I could be mistaken about that, so don't abandon that possibility.)

Something like this,is the easiest, cheapest way I can think of:

http://www.grainger.com/Grainger/TORK-Timer-6WPA0?Pid=search

Look for a dual repeat or flip-flop timer.

http://www.danaherspecialtyproducts.com/uploadedFiles/Siteroot/Eagle_Signal/Products_and_Solutions/Timers/SX160%20Dual%20Setpoint%20Repeat%20Cycle%20Timers.pdf

The most likely existing circuit comprises start & stop buttons in series with an overload relay and a hold contact in parallel with the start button. Ideally the stop button should be the latching type that you have to twist or pull out manually to reset it after operation. Remove one connection as shown and add a change-over switch, which will allow hand operation as now, or automatic operation from the new timer. Use a SPDT (single pole double throw) assymetric timer that has adjustable on and off times (Google RS Components Stock No 385-6935 or similar).

Leaving the stop button operable is important for safety reasons (Post 2 does not include it). Having the ability to run the pump manually for longer than the pre-set 5 minutes is a feature that you will come to appreciate in future.

Ok, we had this problem and found a relay that works great for this. I signed up just to pass on the info. Using a "Relay, Time Delay, Multi Function" works great. It is a simple time delay using an I/O setup on the top or side of the relay. The one relay from Grainger below can go between .1 second and 1024 hours. The only catch is that you must set the switches as 1/10th of a second, 1 second, 10 second, 1 mintue... etc, and then they all act the same. We used the common 1 minute setting.

For example, we had to have an hour on and 3 minutes off. We set the relay to minutes, and used switch 1 and 2 (values 1+2) to get the 3 minutes off. For the 60 minutes on, we used switch 3, 4, 5, and 6 (values 4+8+16+32) to get the 60. The system is easy to modify and pretty intuitive. The values go up to 512 minutes for switch 10, so 3 hours is doable in most cases. I would call the company to verify, but this may solve your problem.

http://www.grainger.com/Grainger/MACROMATIC-Time-Delay-Relay-6MPP3