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Air Conditioner compressor wiring

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Unread postAuthor: roughboy » Sat Mar 28, 2009 2:22 pm

mine says 4/35 uf

On mine I didn't use the capacitor. i took it off
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Unread postAuthor: ralphd » Sat Mar 28, 2009 2:31 pm

The manufacturer determines the MFD and voltage. There is a formula to use that I'm sure can be found somewhere but usually the average joe doesn't know anything about the motor that drives the compressor, which is needed. The manufacturer has already optimized this by application...ex. fridge, freezer or air conditioning. As long as it starts the rest is efficiency of the operation and I don't think any one of us care about that with the short time these things run and what we use them for. You can get a capacitor rated for higher voltage but don't go lower.
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Unread postAuthor: daberno123 » Sat Mar 28, 2009 2:48 pm

So is the capacitor even necessary?

@roughboy
Have you had any trouble starting it without the capacitor?
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Unread postAuthor: TurboSuper » Sat Mar 28, 2009 3:15 pm

Theoretically speaking you do need the capacitor, otherwise you'd need to start the motor by manually rotating the shaft.

I say "theoretically" cos I've never gone and tried this myself...
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Unread postAuthor: daberno123 » Sat Mar 28, 2009 3:26 pm

I don't want to damage this, so I think I'll go ahead and order a 25uf/370 VAC capacitor.

On another note, my 900 psi rated nylon hose came from Mcmaster, along with the appropriate compression fittings. However, due to my inability to count 1/16"s on a ruler, I accidentally ordered a 3/8" compression fitting for the outlet tube instead of the 5/16" one it needs. :cry:

I guess its time for another order from Mcmaster. :wink:
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Unread postAuthor: c11man » Sat Mar 28, 2009 3:47 pm

i think that once i get enought money i will buy one of those compressors for my next project
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Unread postAuthor: daberno123 » Sat Mar 28, 2009 3:50 pm

Once I get everything all figured out I'll probably write a how-to for setting these up like the one Poland_Spud did for fridge compressors.
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Unread postAuthor: ralphd » Sat Mar 28, 2009 4:10 pm

Pick it up at a local hardware store. They are no different, just measure first. The capacitor is almost always needed. It depends on the application. For air conditioning, the capacitors are used to keep the start winding slightly out of phase of the run winding. Just picture a circle with two dots. When electricity is applied, the capacitor is essentially powered with the run winding then discharged in the start winding. That causes the dot to move and the other dot(the run winding) follows it. In refrigeration and bigger systems that use thermal expansion valves, you may need more torque to get the compressor to start. This is where relays are used and sometimes each winding has its own capacitor. Look at the last wiring diagram that you provided.
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Unread postAuthor: daberno123 » Sat Mar 28, 2009 4:12 pm

Thanks, I'll check Lowes next time I go. Hopefully that will be tonight.
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Unread postAuthor: POLAND_SPUD » Thu Apr 16, 2009 1:28 pm

every fridge compressors I've seen had something like this --> http://chlodnictwo.istore.pl/pl,product ... n0011.html

I don't think that there is any capacitor there... am I right? it's just a relay (it makes a buzzing sound when starting up)?
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Unread postAuthor: Technician1002 » Thu Apr 16, 2009 2:23 pm

daberno123 wrote:So is the capacitor even necessary?

@roughboy
Have you had any trouble starting it without the capacitor?


If you think of an electric motor like a steam engine with only 1 cylinder, they park at top dead center every time. There is no torque to toss it off center either way so they can't start until pushed off center.

A second coil (cylinder) can provide this push from another angle. Using a starting relay and cap, a rotational force can be provided for starting, and after it is spinning, the push pull of a single phase power can be used to keep it running much like a single cylinder steam engine.

For low starting torque applications a low starting current circuit can be used, and this is often referred to as the Run Cap on fan motors. It does not disconnect after it starts. The high current required for the starting torque of compressors, they disconnect after starting to prevent overheating and burn out. Starting current is typically between 5-10 times run current.

With the start circuit disconnected, most single phase AC motors can be spun in either direction and then power applied to run either way. I have rope started one this way for fun that had a dead start circuit.

every fridge compressors I've seen had something like this --> http://chlodnictwo.istore.pl/pl,product ... zruchowy,d anfoss,103n0011.html


Most that have one of those has an external cap mounted elsewhere, but some compressors have a "Shaded Pole" and don't need a cap. The item is a starting relay. The run current "main winding" feeds the coil of the relay which has few heavy turns. The stalled compressor draws lots of current and closes the relay which feeds power to the start winding to provide starting torque. After it is spinning the run current drops to normal and the start relay drops power to the start winding. It's simple and takes care of how to time how long to leave start current applied.

Some of these are calibrated by weight instead of a spring. Don't run them on the side or upside down.

***Edit*** added google search to a refrigeration book explaining this;
http://books.google.com/books?id=cjt2KdeeEaoC&pg=RA1-PA359&lpg=RA1-PA359&dq=how+motor+starting+relay+works&source=bl&ots=tM2Foq7jvh&sig=wfwgtKCmwB43IMF7O5w_wlWbF_M&hl=en&ei=g4jnSbj4J4Wjtgef69HEBQ&sa=X&oi=book_result&ct=result&resnum=9
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Unread postAuthor: POLAND_SPUD » Thu Apr 16, 2009 4:21 pm

ohhh that's exactly what I meant... I've never seen a cap on a fridge compressor so I suppose that they are more common on AC compressors
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Unread postAuthor: rp181 » Thu Apr 16, 2009 5:02 pm

They are actually present on lots of motors, from compressors to lathes to paper shredders. Sometimes they are built in, sometimes they are external. It usually depends on the capability of the company.
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Let me introduce myself by first saying Thank You!

Unread postAuthor: Shingoshi » Wed Aug 12, 2009 7:11 pm

daberno123 wrote:Can I just use any capacitor for this, or does it need to be a special run capacitor?

I've been browsing some HVAC parts sites but can't find any 270 volt capcitors, only 370 and 440.
I have just purchased FOUR of these for a special project I'm engaged in. Reading the specs given by Ralphd, I now know that I'll have 2480 Watts of cooling. This is what I was hoping for, since I'm building a fully self-contained computer cluster inside of a Pelican 1780 Transport case.

Now while this site is not dedicated to computers, the information contained in this thread will help me understand exactly what I need to do. So I'm really glad someone had need to start this.

Thank You!
Shingoshi

EDIT: Upon reading this link (http://www.rechi.com/en/web_en_products ... tegoryId=3), I see that some information was incorrectly forwarded.

R22 39R131F 115V / 60 Hz / 1φ 6kg 7.75cc 1320Kcal/Hr 5238 Btu/Hr 1535Watts 620W power consumption 2.13 EER (Kcal/HW) 8.45 EER (Btu/HW) 2.48 COP (W/W)

So the actual cooling capacity of this unit is 1535 Watts. For most of you this doesn't matter. But for others who build computers and find this link (as I did), this will help clarify things.
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Last edited by Shingoshi on Wed Aug 12, 2009 8:50 pm, edited 1 time in total.
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Ok, here's a really N00b question!

Unread postAuthor: Shingoshi » Wed Aug 12, 2009 7:22 pm

TurboSuper wrote:That's fine, the only disadvantage to using an over-rated cap is the size, really. Usually AC motors have big metal oval-shaped caps (they're unpolarized electrolytics, I believe). You'd probably want one of those.
Being that I have four compressors, is it possible to use a single larger rated capacitor for all of them? How many components can I have shared among all of my compressors?

Shingoshi
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