circuit to energize a relay for 30 seconds

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spindown
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circuit to energize a relay for 30 seconds

Post by spindown » Sat Dec 03, 2005 7:44 pm

I live on a farm and have to watch our water(well)use. I put a manually operated water circulator in our hot water line and it takes approximately 30 seconds to get hot water to the faucet. I would like to construct a circuit that I could activate that would turn the circulator pump on for 30 seconds and then turn it off. Any ideas? Thanks Paul

JPKNHTP
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Re: circuit to energize a relay for 30 seconds

Post by JPKNHTP » Sat Dec 03, 2005 8:00 pm

-JPKNHTP
-God Bless

Michael J
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Re: circuit to energize a relay for 30 seconds

Post by Michael J » Sun Dec 04, 2005 3:29 am

Even easier way,
See N&V April 2005 P:50 Universal Relay.

Just use the section after the OP Amp, with
a momentary swith to charge the input capacitor.

2 x Resistors.
1 x Capacitor change to 33µF or 47µF Electro.
1 x MOSFET 2N7000.
1 x 1N4004 Diode, MOSFET back EMF protection.
1 x 1N4148
1 x 12V relay.

josmith
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Re: circuit to energize a relay for 30 seconds

Post by josmith » Sun Dec 04, 2005 3:37 am

Do you intend to have the water circulate at intervals so it's always hot? You haven't mentioned what you want to trigger the circuit. A thremostat may be a better fix.

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philba
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Re: circuit to energize a relay for 30 seconds

Post by philba » Sun Dec 04, 2005 10:00 am

Like Jo, my first thought was "what's the goal here?". My second thought was "How does he expect to use it?"

I think ithe goal is to get hot water to the tap so you don't waste cold water by letting it run. In that case, a thermostat approach may be better - run the motor until there is hot water at the take off point for the faucet. A simple sensor (LM34, for example) and a comparator could be set up to give you a signal to turn on/off the pump. The advantage of this is you can use it anywhere with out having to adjust the time interval. By using a schmitt trigger configuration of the comparator, you can set it up to turn on with a push button, turn off when the temperature is reached and then not turn on until the button is pushed again.

How you use it is a much more interesting question. A button on wall by the faucet?

<small>[ December 04, 2005, 10:27 AM: Message edited by: philba ]</small>

spindown
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Re: circuit to energize a relay for 30 seconds

Post by spindown » Sun Dec 04, 2005 6:55 pm

Thanks to all of those who responded. My idea was to turn the circulator pump on just before using the hot water in order to conserve the pump, electricity, and the water heater. The temperature controlled circuit is a good idea that I had not considered.
Presently I turn on the pump and try the water until it is hot. I found from experience that it takes approximately 30 seconds to get hot water. I thought it might be smarter to make a timer circuit as you have suggested above. I will look up the back issue of NV and contact JPKNHTP for a copy of his schematic. Paul

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