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Old 06-06-2009, 07:35 PM   #1
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Electrical Relay for Evaporative Cooler Power


I have a 20A circuit that uses too long of a run of #12 wire - probably almost 100 feet from the Circuit Breaker panel to the evaporative cooler. The cooler employs a 3/4 Horsepower motor (14.9A for fan on high and pump on). What I'd like to do to remedy this problem is to use electrical relays in order to provide power to the motor. This fix would allow me to keep my thermostat in the living room where it would be the most useful. One fact about evaporative coolers that those in non-desert part of the country may not know is that they use a line voltage thermostat, that is, the power for the unit runs through the thermostat housing. This is what made for the long wire run. So I'd like to employ the 120VAC (I measure 115V in my house) fan power wires that come from the thermostat to provide the on/off signal to the relay. I'd require two relays, for low and high fan operation. The relays would need to be placed in an outdoor rated housing. There's at least a couple of choices in types of 120VAC relays that I've seen on the internet: icecube style and rotary and probably there's many more. Of course, I'd supply an appropriately sized and wired circuit to power the evaporative cooler. I'd like to get feedback on this idea and advice on relays and outdoor housings.

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Old 06-06-2009, 07:46 PM   #2
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Electrical Relay for Evaporative Cooler Power


How is the low/high signal transmitted to the fan now? Is it a 3-wire cable? You could use general purpose contactors in a PVC junction box.

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Old 06-06-2009, 08:00 PM   #3
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Electrical Relay for Evaporative Cooler Power


Evaporative coolers typically have a blue hot wire for the water pump, a red hot wire for the low fan speed and a black hot wire for the high fan speed. These come out of the line voltage thermostat. The thermostat is supplied with a two wire cable, that is, black, white, and ground. I'm proposing to use the red and black outputs as the signal wires to the relays.

Could you explain in layman's terms this sentence: "You could use general purpose contactors in a PVC junction box." Thanks!
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Old 06-06-2009, 11:24 PM   #4
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Electrical Relay for Evaporative Cooler Power


Not many ice-cube relays are rated for 3/4 HP. The contactors InPhase is referring to are also known as definite-purpose contactors. One example is a Grainger # 5B132. It has a 120 volt coil, and can handle the motor. You'll need 2 of them. They need to be 2 pole, one pole for the motor, and the other for the pump.

Mounting them in a PVC junction box is a good plan. Both of them will fit comfortably in an 8"X8"X4'. A 6"X6"X4" will be a bit tight, but will likely work.

If you need help connecting these relays, post back, there's about a dozen or so of us around here that can guide you through it.

Rob
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Old 06-07-2009, 09:13 AM   #5
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Electrical Relay for Evaporative Cooler Power


It's good to read that this idea is feasible. One note, the electric water pump that is used to soak the pads is small so I'll probably just go ahead and leave it powered by the original blue wire. I'll check into the Grainger relay.
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Old 06-07-2009, 12:08 PM   #6
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Electrical Relay for Evaporative Cooler Power


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Originally Posted by highdesert View Post
It's good to read that this idea is feasible. One note, the electric water pump that is used to soak the pads is small so I'll probably just go ahead and leave it powered by the original blue wire. I'll check into the Grainger relay.
Right, but the pump needs to run whether the unit is on hi or low. Therefore, you need two double-pole contactors. One pole of each contactor will be for the speed, and the other pole will energize the pump. In other words, one pole of each contactor will be in parallel with a pole of the other, so that no matter the speed setting, the pump sill runs.

A diagram might look like this:
Attached Thumbnails
Electrical Relay for Evaporative Cooler Power-swampcooler.jpg  
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Old 06-07-2009, 12:29 PM   #7
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Electrical Relay for Evaporative Cooler Power


InPhase, What program are you using to draw and post your images? There are so many times a picture is what is needed. I have been told windows "Paint" works for this stuff?
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Old 06-07-2009, 12:35 PM   #8
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Electrical Relay for Evaporative Cooler Power


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InPhase, What program are you using to draw and post your images? There are so many times a picture is what is needed. I have been told windows "Paint" works for this stuff?
That's it. I keep it simple. Paint works good for stuff like that.
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Old 06-07-2009, 09:05 PM   #9
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Electrical Relay for Evaporative Cooler Power


InPhases drawing is exactly what I had in mind too.

Rob
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Old 06-07-2009, 10:00 PM   #10
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Electrical Relay for Evaporative Cooler Power


The water pump can be turned on/off independent of the fan. So, when it's nice outside, we just run the fan and not the water pump. Also, the water pump is something like 1/70 horsepower so it's OK to leave it on its blue hot wire that exits the thermostat. Even though it's a long run, #12 wire is more than big enough for this small load. I should have been more specific about that in order to paint the problem correctly. Thanks for the nice work on the schematic.
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Old 07-06-2010, 09:49 AM   #11
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Electrical Relay for Evaporative Cooler Power


I have a swamp cooler employing a Dial SelectaStat II 110v thermostat, and it really is a stinker. It works, but cannot seem to keep a steady temperature. We are constantly re-setting it and it is not programmable of course.

I want to hook the Swamp up to my programmable thermostat on the "cool" setting. I need to relay the thing, but can't seem to find the right relay. I am thinking I will not bother with "low" fan, and just run 24v to the relay and have the relay pass 110v to the high fan setting and the water pump.

Anyone have a recommendation on where and what for the relay?

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