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Terrences Web Site
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Date: 1-15-2010
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Number of Hours: 24.00
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Manual Reference: None
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Brief Description: Add automatic electric outlet to compressor
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I use a Harbor Freight 90385 2.5 Hp, 8-gal air compressor. My garage has only a single 20-amp circuit. In the winter, I use a 1500 watt electric heater which draws ~13 amp. The 2.5 horse motor should draw about 16 amps. Plus I believe that the lights are on the same circuit. Clearly, I will have a problem trying to run the compressor and heater at the same time. This hasn't been much of a problem in the past because I only used the air compressor to power the rivet tool, which is not done very often. However, I got a new air drill which I plan instead of the electric drills I used in the past. So that I wouldn't have to turn off the heater whenever I used the compressor, I decided to add an automatically switched outlet box to the compressor.
I wired an Eaton D7PF2AA power relay into the compressor control circuit by cutting the power cord and cutting the "hot" lead to the overload protection switch, as shown in Fig. 1. An catalog photo of the relay and the mount is shown in Fig. 2. I put the relay into a standard 22.5 cu. in. electric outlet box. The final installation is shown in Fig. 3. It was a tight fit, so the the relay extendsed out through the side of the box. The box is held to the compressor moving handle with two tie wraps which pass through holes in the side of the box.
The relay and wiring were a tight fit in the box and I had to plan the routes of the wire very carefully so that everything would fit. During testing I noted very bright flashes whenever the compressor kicked on or off. The relay is rated at 20 amps, using both poles of the DPDT relay. However, a subsequent examination of the Eaton catalog revealed that, while the relay is rated at 20 A for resistive loads, it is only rated at 0.5 Hp. That suggests that the inductive load of the electric motor requires a much more robust relay. I do not expect this relay to last very long switching this two horse motor.
I was unable to get the relay to function reliably. Ultimately, I discovered that I have been wasting my time on this proje
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Sdhematic for relay wiring
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Eaton D7PF2AA Relay & Base
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Outlet box mounted on compressor
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