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How connect wires to my fridge compressor

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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How connect wires to my fridge compressor

Unread postAuthor: Tobin » Wed Sep 22, 2010 12:37 pm

I recieved a fridge compressor today. It have 3 inlet connectors but i dont know how to connect the cables. I just took a chance and blowed a fuse :roll:
How do i connect the wires the right way?
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Unread postAuthor: Technician1002 » Wed Sep 22, 2010 12:54 pm

If it has the three terminals that are just round pins set in a glass seal, you are missing the start relay. Power connect to the start relay and the relay sequences the contacts to the R and S terminals. The Common is tied to hot most of the time and the run and start go to neutral. This is opposite from the video as he states the common goes to neutral and hot connects to the run/start connections. The wire diagram shown in the video at 6:03 shows the power N going to the run/start side of the relay and the hot goes to a block to feed the light, thermostat (bottom item on the left) and then from the thermostat it connects to the C terminal at the bottom of the relay.

Here is a video covering the subject.
[youtube]http://www.youtube.com/watch?v=cuMHBUFXxFc[/youtube]
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Unread postAuthor: Tobin » Sun Sep 26, 2010 11:15 am

Ok interesting, but then can i connect the "neutral "to common, live wire to "run" and "start" and manually disconnect "start" when the compressor is running?
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Unread postAuthor: Technician1002 » Sun Sep 26, 2010 11:26 am

You can use a high current pushbutton to manually engage the start winding. The run winding remains powered even during the start. The sequence would be push the button, apply power, release the button. The time to start is very short. This can be done to test compressors.

DO NOT LEAVE POWER ON THE RUN WINDING WITHOUT IT RUNNING. IT WILL FRY IT IN VERY LITTLE TIME.

You might have been saved by blowing a fuse first.

Edit, I was looking for a simple wiring diagram. Found one. This shows power (The hot) connecting to an overload (a self resetting circuit breaker) and to the Common on the compressor. The Run and Start terminals go through the start relay to Neutral. The current is monitored on the run terminal. When high (compressor not running) the start is connected. When the run current lowers (compressor started) the start winding is disconnected. In the case of the diagram below, a variable resistor is shown in place of the start contact. For very small compressors a thermister is sometimes used. It heats up during start and goes to a very high resistance cutting off the start current.
Image

Here is another diagram showing a conventional relay. Follow power from the Line to the thermostat to the overload to the start relay to the start and run windings. Some compressors are wired with Common connected to N and some are wired with it to hot. It doesn't seem to make a difference.
Image
This configuration seems less common. Most I have seen have hot going to the common though the overload and thermostat with start and run going through the start relay to common.
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Last edited by Technician1002 on Sun Sep 26, 2010 1:01 pm, edited 1 time in total.
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Unread postAuthor: POLAND_SPUD » Sun Sep 26, 2010 12:56 pm

What you need functions like a car ignition switch. You can get switches with a knob that work exactly in the same way
First you turn it all the way clockwise and once the motor starts you release the switch and it returns back to the middle position
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Unread postAuthor: Technician1002 » Sun Sep 26, 2010 1:05 pm

POLAND_SPUD wrote:What you need functions like a car ignition switch. You can get switches with a knob that work exactly in the same way
First you turn it all the way clockwise and once the motor starts you release the switch and it returns back to the middle position


Almost. You want power applied to run and start at the same time, not going through run only to bump start. A switch that went from off to start then run would work better.
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Unread postAuthor: POLAND_SPUD » Sun Sep 26, 2010 1:16 pm

yeah, that's the thing I am talking about... once the motor starts the knob returns to 'run' position

I've got a switch like that on an old electric lawnmower so I am pretty sure it exactly the thing he needs.

Well, of course it would be the best idea to buy one of those PTC relays that you attach directly to the 3pin connector. I know that they are a bit overpriced in the USA but here they cost only about 4$
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Unread postAuthor: Technician1002 » Sun Sep 26, 2010 1:30 pm

You can take one for free from a dead refrigerator.. They unplug. Pick one up from a fridge about the same size compressor. They should be in the same HP range, but the exact fit is not required. These starters work for a range of sizes. Most domestic fridge compressors are about 1/4 to 1/3 HP.

Smaller fridges or AC units will require a properly sized relay to match the expected start and run current.
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