compressor pinout

Discussion in 'General Electronics Chat' started by lokeycmos, Dec 26, 2012.

  1. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
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    hello, i have a compressor from an old fridge that was given to me. i want to make a vacuum pump out of it.there are 3 wires, red, black, and white. could someone please tell me which wires goto the capacitor and wich goto mains? thank you!
     
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  2. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
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    here is the fourth pic
     
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  3. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Here's my guess, based on wiring up totally different motors with the same wire colors:

    For CW:
    N to Black
    L to Red, and
    L to cap, then from cap to white.

    For CCW:
    N to Black
    L to White, and
    L to cap, then from cap to Red.

    No, I did not bother googling the model number and looking for manufacturers drawings to verify it's correct. That's your job.
     
  4. tinkerman

    Member

    Jul 22, 2012
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    This type of motor can not be reversed. The start and run windings are internally brought to a common. Are there three pins on the motor? If that is correct you should be able to measure resistances between the pins and find which is common. One winding will be low which is the run winding. Another pair will be higher which will be the start and last combination will be the reading of both windings. I believe the black wire should be the run winding, the white is common and the red is start to the capacitor.
     
    Last edited: Dec 26, 2012
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Another thing to consider is that refrigerator compressors use the oil that is put into the refrigerant to lubricate the compressor. No refrigerant - no oil - no oil -burned out compressor.

    Most of them also have a 'potential relay' instead of a centrifugal switch to kick out the start winding.
     
  6. #12

    Expert

    Nov 30, 2010
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    Another thing to consider is that some compressors have the outer case containing the high pressure and some have the case connected to the low pressure side of the pipes. If the case of that compressor becomes full of vacuum it starts acting like a vacuum tube. Electrons jump off the wires and head for ground, rapidly eating the insulation off the windings. Rule of thumb: Never let the low side go below one atmosphere.

    You can devise a way to seperate the oil from the discharge flow and let it back into the intake side of the compressor, but the accumulation of atmospheric water and leaking electrons will make for a very short lifetime. I've done this, but not to get a vacuum, and for me, rusty old compressors are easy enough to get. If you ever try to make it into a temporary compressor, be absolutely sure you have more than one over-pressure safety device. Those compressors will go past 450 PSI long before they pop an over-current protection device.

    They are so dangerous that I would consider banning this sort of discussion on AllAboutCircuits.
     
  7. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Mind = blown.

    What on earth are you talking about? I don't doubt you, I just don't understand you.

    Are you saying that, if the case comes under vacuum, the load on the motor goes away? sort of like a propeller cavitating or a tire spinning out? And this causes the motor to burn up?
     
  8. tinkerman

    Member

    Jul 22, 2012
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    Na, these compressors work for both vacuum and pressure. They will build to 500 lbs or more and can develop about 25 inches of vaccum. They will heat because they don't have the freon in them for cooling and as compressors they will pump oil somewhat since they don't use oil rings. But they do work fine for short periods before over heating. When they do get hot the overlaod device opens until it cools. Many frig compressors use a current actuated start relay not a voltage relay. Used a large air conditioner unit as compressor for years even to paint and air tools for short periods.
     
  9. #12

    Expert

    Nov 30, 2010
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    Pacifically for strantor: When the case around the motor gets its gas pressure sucked out, be it atmosphere or Freon, the windings actually act like a direct heated cathode in a vacuum tube. The windings emit electrons into the vacuum space at any point with a voltage that is negative with respect to the metal case of the compressor. Of course, that starts, stops, and modulates at the frequency of the power line voltage.

    Confirming tinkerman, refrigerant compressors "steal" their cooling from the gas stream, for whatever heat they can't radiate through the case or conduct away through the pipes that are connected to them, and almost all of the heat goes into the gas stream. This is confirmed by enthalpy calculations about the resulting pressure, mass flow, and temperature of the expelled gas. In fact, heat dissipated through anything except the gas stream is so small that it is neglected during calculations when designing a refrigerator, freezer, or air conditioner.

    The compressor/motor does become, "unloaded" when there is no gas left to pump, but that is different from the "emitting electrons into a vacuum" activity. Consider an equation for horsepower needed to compress a gas, then remove the gas. Presto! No horsepower required (besides friction losses) because there is no "head" pressure resisting the piston during the compression stroke. The motor is vaguely synchronistic with the power line frequency so it doesn't over speed, but when the compressor sucks on a vacuum, the amperage and the slippage of the motor become less.

    ps, I'm a bit surprised at the things I know about refrigeration, but that's because I've been doing it for over 40 years. I went to classes, I bought the books, I passed the state licensing test with a score of 96.75% after taking 80 minutes to complete an alleged 8 hour test. I am certified to design anything up to half a million B.T.U.s per hour and my word is valid in a court of law. These things rarely come up on this site because it's not a refrigeration site. Refrigeration is my day job. Electronics is my hobby. Electronics is also my "ace in the hole" when it comes to keeping up with the changes in the industry. A black box changer doesn't stand a chance against me when confronting new designs, and new designs happen, frequently. For instance, there was no legal minimum efficiency in 1970. Right now, the minimum legal efficiency (S.E.E.R.) in Florida is 13 B.T.U.s per watt hour. You'd be amazed at the tricks that have been used to delay fan starting, stopping, and running speed, just to squeeze an extra tenth of a B.T.U per hour out of an air conditioner.

    I believe there are other Freon jockeys on this site, but the subject is rarely discussed here.
     
    Last edited: Dec 28, 2012
  10. gerty

    AAC Fanatic!

    Aug 30, 2007
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    I worked for a Carrier air conditioniing manufacturing plant for 28 years as a electronics tech, don't know squat about air conditioning..:eek::eek:

    edit: I take that back...they were green for a long time and now they're grey.....
     
  11. debe

    Well-Known Member

    Sep 21, 2010
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    I can asure you using an old fridge compressor as a Vac pump is quite safe. The main problem is they dont go down to as low a vac as a proper vac pump. But they certainly can be used on small domestic fridges (used to use one untill i could aford a proper Vac pump)
     
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  12. debe

    Well-Known Member

    Sep 21, 2010
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    Just dug it out & it still works hasnt been used for years. Its an old 1/4HP Kirby fridge compressor, the little plasic container on the left was to collect any oil the compressor may pump out (never had to empty it, only ever colected a few drops) I used this for years on domestic fridges.
     
  13. strantor

    AAC Fanatic!

    Oct 3, 2010
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    ah, so you literally meant that it acts like a vacuum tube. I thought it was a simile. Thanks for the explanation!
     
  14. tinkerman

    Member

    Jul 22, 2012
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    Don't you think that pressure operation is a far greater concern than vacuum? If the motor fails due to insulation break down it's not a huge loss. Improperly dealing with it's use as a compressor can be very dangerous if one doesn't know what he's dealing with and how to manage it.
     
  15. tinkerman

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    Jul 22, 2012
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    debe: you were able to get 30 inches vacuum? Any unit that I used only went to about 25.
     
  16. #12

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    Nov 30, 2010
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    By definition, 30 inches of vacuum is "all of it", outer space empty. A common needle gauge will show 30 inches of vacuum, and that often fools the amateurs, but a needle gauge is a crude device compared to the good ones. There is no vacuum pump on Earth that can do a perfect vacuum, but 50 microns of mercury column is a well known standard for refrigerators. I have seen 35 microns achieved many times. It is measured with a thermistor. Apply current, the thermistor heats up, any gas that is present conducts heat away from the thermistor.

    One very important part of "pulling a vacuum" on a hermetic system is to remove water. At 70 F, water boils at .3631 PSIA or .7392 inches of mercury column. This is entirely achievable, but not at 25 inches of vacuum. You would need to heat the whole machine up to about 135 F to get the water to boil at 25 inches of vacuum. Still, this is achievable without exotic measures, just put the whole machine in your truck and park it in the sun (if you live in Florida).

    An interesting problem encountered when trying to suck the water out of a hermetic system is water drops that are hiding below the surface of the oil in the sump of the compressor. For this, you thump the compressor and watch the vacuum gauge. If it wiggles, you have hidden water droplets.

    So...using a refrigerator or air conditioning compressor to get a vacuum (of sorts) is a very good way to re-purpose an otherwise boat anchor to operate a solder sucker. You can get a foot pedal from Grainger to intermittently connect your tank of vacuum to the solder sucker. The high pressure side of the equation is where the real danger exists. Every treatise I write on air conditioning starts with, "If you can't name four ways to get maimed or killed working on this job, stop now."
     
  17. tinkerman

    Member

    Jul 22, 2012
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    I like you idea for a solder sucker. I've rewound old small vac pumps that are used in medical applicaitons. I was considering finding an old unit again for just that prupose. Don't draw down to anywhere near that. Much more compact and lighter. Familiar with vacuum. When reconditioning grid power transformers they always draw down to the region you mention with special pumps and hold it for hours to draw any moisture out of the windings before refilling with oil. Same for SF6 gas filled equipment.
     
    Last edited: Dec 28, 2012
  18. #12

    Expert

    Nov 30, 2010
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    Sucking solder doesn't require a very high quality vacuum. Probably 15 to 20 inches will do. Imagine blowing mercury (a liquid metal) through a small tube with 7 to 10 psi of air pressure. Anybody here worked with professional quality solder suckers? The difficulty I ran into is finding a regulator to turn the electricity to the pump off at a certain vacuum. Pressure switches everywhere but no vacuum switches.

    off topic, but I never heard of SF6 until I saw it on this site. I know just enough chemisty to recognize a very stable compound when I see it. The volts per inch must be amazing.
     
  19. debe

    Well-Known Member

    Sep 21, 2010
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    Heres a 12V DC Vac pump that has a built in Vac switch that cuts it out at 17inch made by Hella. It was salvaged from an old BMW car at the wreckers. It was to asist the cruise control & cut in if the Vac fell below 17 inch. Ideal for a solder sucker, knew it would be handy for something.
     
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  20. tinkerman

    Member

    Jul 22, 2012
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    Isn't that neat. I'll have to watch for one. I know a couple wreckers fairly well but they deal with domestic models mostly.
     
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