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Air Conditioner compressor wiring

A place to ask general spud cannon related questions.
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What would be true in my specific case?

Unread postAuthor: Shingoshi » Wed Aug 12, 2009 8:08 pm

roughboy wrote:the highest is 200psi but it can go much more than that. i checked the compressor, the capacitor and could not find any word saying 15uf or 25uf. how would i know if it's a 15uf or a 25uf?
Since I'm not limited by the factors (chamber pressures) any of you have to work with, just how high of a pressure do you think I would be able to achieve with this compressor? Some of the things I'd like to be able to power with this compressor are Vortex Tubes and Venturi Injectors.

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Re: Ok, here's a really N00b question!

Unread postAuthor: Technician1002 » Wed Aug 12, 2009 8:26 pm

Shingoshi wrote:
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


The capacitor can't be shared. The compressors need their individual starter. Sorta like trying to share one starter motor for 4 cars.. LOL... not going to work.

The caps are most often used on motors that need a larger starting torque such as an A/C that hasn't bled off the head pressure before restarting. Fridges often have plenty of off time to bleed off the head pressure before restarting.
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Re: Ok, here's a really N00b question!

Unread postAuthor: Shingoshi » Wed Aug 12, 2009 8:56 pm

Technician1002 wrote:
Shingoshi wrote:
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


The capacitor can't be shared. The compressors need their individual starter. Sorta like trying to share one starter motor for 4 cars.. LOL... not going to work.

The caps are most often used on motors that need a larger starting torque such as an A/C that hasn't bled off the head pressure before restarting. Fridges often have plenty of off time to bleed off the head pressure before restarting.

Starter motors for cars must be physically connected to the driveshaft of each engine. The only physical connection of the capacitor is electrical. So this wasn't that crazy of a question. The idea was simply if the capacitor was powerful enough, could it start more than one unit. Think of it as having one very large capacity battery being shared between multiple engines. That would work, because our connection is electrical. So being that your analogy isn't precise, I'll wait to hear what someone else has to say about this.

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Unread postAuthor: Shingoshi » Wed Aug 12, 2009 9:00 pm

Maybe I didn't understand you. I thought the capacitor was only responsible for starting the motor. If that's correct, then I think my statement is also correct.

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Unread postAuthor: c11man » Wed Aug 12, 2009 9:08 pm

Shingoshi wrote:Maybe I didn't understand you. I thought the capacitor was only responsible for starting the motor. If that's correct, then I think my statement is also correct.

Shingoshi


first of all tech is a proffesinal electrition so i think he knows what hes talking about. and second what advantage would you get from one cap instead of 4?
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Wasn't trying to be argumentative...

Unread postAuthor: Shingoshi » Wed Aug 12, 2009 10:06 pm

c11man wrote:
Shingoshi wrote:Maybe I didn't understand you. I thought the capacitor was only responsible for starting the motor. If that's correct, then I think my statement is also correct.

Shingoshi


first of all tech is a proffesinal electrition so i think he knows what hes talking about. and second what advantage would you get from one cap instead of 4?
I just wanted to make sure. From the discussion here, it seemed that the capacitor was being compared to a car battery, and not the starter motor. And as far as the advantage goes, having one very large capacitor would likely be cheaper than buying and wiring four of them. Overall, the system would be less complex to manage over time. That's why I was asking.

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Unread postAuthor: Technician1002 » Wed Aug 12, 2009 10:19 pm

The inductance of the motor is matched to the capacitance of the starting cap to provide a phase shift. This is used to provide a rotational field to start the motor turning. Too big of a cap is bad and will result in too much current and an incorrect phase shift to properly start the motor. It may result in burning out the motor.

Always match the size of the starting cap to the size of the motor. Like a cannon Chamber Barrel ratio, there is an optimum range. Efficiency and power drops when run far outside the range.
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Thank you for a more precise answer...

Unread postAuthor: Shingoshi » Wed Aug 12, 2009 10:46 pm

Technician1002 wrote:The inductance of the motor is matched to the capacitance of the starting cap to provide a phase shift. This is used to provide a rotational field to start the motor turning. Too big of a cap is bad and will result in too much current and an incorrect phase shift to properly start the motor. It may result in burning out the motor.

Always match the size of the starting cap to the size of the motor. Like a cannon Chamber Barrel ratio, there is an optimum range. Efficiency and power drops when run far outside the range.
Sorry about my first response. But I really was thinking in terms of electrical current as being able to be shared. So at least now I know that I need four capacitors. One for each compressor. It was your analogy that through me off here.

This really has to be hilarious. A computer cooling tech asking for help from potato gun shooters. How many of you actually use compressors of this type for your application? I'm just now getting ready to calculate the total CFM of these four compressors.

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Re: Thank you for a more precise answer...

Unread postAuthor: Technician1002 » Thu Aug 13, 2009 12:37 am

Shingoshi wrote:
Technician1002 wrote:The inductance of the motor is matched to the capacitance of the starting cap to provide a phase shift. This is used to provide a rotational field to start the motor turning. Too big of a cap is bad and will result in too much current and an incorrect phase shift to properly start the motor. It may result in burning out the motor.

Always match the size of the starting cap to the size of the motor. Like a cannon Chamber Barrel ratio, there is an optimum range. Efficiency and power drops when run far outside the range.
Sorry about my first response. But I really was thinking in terms of electrical current as being able to be shared. So at least now I know that I need four capacitors. One for each compressor. It was your analogy that through me off here.

This really has to be hilarious. A computer cooling tech asking for help from potato gun shooters. How many of you actually use compressors of this type for your application? I'm just now getting ready to calculate the total CFM of these four compressors.

Shingoshi


When I worked in a classified data center, the techs learned refrigeration so the operation didn't need to be shut down very often for outside contractors. I learned on several 100 ton chilled water systems.

When you calculate the CFM, remember for use in air the inlet pressure is much lower than the compressor inlet design pressure. If you are using an R22 compressor that is for A/C use, it is referred to as a high temp compressor. It has a lower displacement than a freezer compressor of the same power. The freezer compressor using a lower boiling temperature has a lower vapor pressure so the compressor is designed with a larger displacement for the lower volume of inlet gas due to the lower pressure. In general AC compressors are higher power due to the higher BTU load unless you are talking about icemakers which use a low temp compressor at high BTU's.

If you are going for high efficiency at high pressure, taking the 4 compressors you speak of and stacking them so 3 feed one, you can get high volume at high pressure. The first 3 would be in parallel as a first stage to take one atm (0bar) and boost it to 3 atm (2 bar). The volume of air then feeding the single second stage at 2 bar will have 3 times the CFM than it being fed an inlet of atmospheric pressure. The second stage will be in normal operating range with an inlet of about 45 PSI and an outlet of about 200 PSI.

To prevent disaster in case the second stage fails, use a 150 PSI pop off between the stages. Never feed more than 200 PSI into the inlet of a fridge compressor. The shell is not designed for it.

As a computer cooling tech, you probably knew most of the compressor limitations and normal operation pressure range for an R22 or R134a system. I posted this for the general spudder population.

Be safe. Condensation will damage the compressors over time.

To clear up the function of the starting capacitor, if you look at a motor like a steam engine with a flywheel and piston and connecting rod, it is easier to visualize mechanically what is going on electrically.

If a steam engine is parked with the piston fully extended or retracted, applying power won't make it start rotating. A single phase electrical motor is electrically the same. A magnetic field is alternating back and forth. The rotor in the middle can't go back and forth.

Once started a flywheel on a steam engine takes care of getting the rod off center for the next stroke. An AC electrical motor is the same. Once rotating the back and forth magnetic field applies power to the rotating part.

To get either started, an off center force needs applied. In a steam engine a second cylinder or more is used. Steam trains have the two cylinders on each side 90 degrees out from each other so a train can start. If one is at top or bottom stoke, the one on the other side is mid stroke and can apply motion.

A 3 phase electric motor is much like the steam train and has 3 coils, 120 degrees apart. A 3 phase electric motor does not need a starting capacitor.

Homes don't have 3 phase electric power, so this in a refrigerator is like a single cylinder steam engine always parked at top or bottom dead center. It needs an off center cylinder to push it off center.

The capacitor provides an electrical phase shift. This in conjunction with the main run winding provides the off center rotation needed to start the motor. After the motor is started, this coil is shut off for efficiency. To get the proper phase shift and proper start current, the capacitor is matched to the motor size. This is why only one cap can't be shared between the motors. I hope this helps.
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Unread postAuthor: Shingoshi » Thu Aug 13, 2009 3:16 am

Man! I'm nowhere near the tech you are! I'm going to copy this to a file that I can refer as often as I need to. I really appreciate this response. I think maybe I ought to be building spudguns instead of computers.

Really, Thanks a lot!
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Unread postAuthor: Shingoshi » Thu Aug 13, 2009 3:23 am

May I please have your permission to post this in the thread for the project I'm building. I think every chance more people have to get good information, is good for everyone. So I really hope you approve.

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Unread postAuthor: Shingoshi » Thu Aug 13, 2009 3:51 am

Ok. So I need more clarification here.
1.) So I have a high-temperature A/C compressor. How does that affect my selection of available refrigerants? Like CO2 or Propane? Which refrigerant will give me the lowest temperatures possible while being usable in this compressor's oil?

2.) What I was going to attempt to determine, is how this compressor would compare to an air-compressor. I want to try to power a vortex tube with these four compressors. Running the first three in parallel into the final stage, would that give me the pressures needed for the vortex tube?

3.) I plan on using a liquid-cooled 60-plate heat-exchanger in place of a condenser. I was thinking I would need to in order to handle the load in a small space. I'm building my system inside of a Pelican 1780 Transport case. I'll still have an external radiator for the liquid-cooling loop.

4.) Do I need three pop-off valves? One between each of the four compressors?

I think for the sake of respecting this thread, I should ask you to respond at this link instead (http://www.hardforum.com/showthread.php?t=1428264). I'm going to repeat these questions there as well. However, if you feel any of your answers would be helpful here, and not off-topic, then go ahead and answer here instead. At least my thread will let you see just how insane I am!

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Last edited by Shingoshi on Fri Aug 14, 2009 5:49 pm, edited 1 time in total.
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Unread postAuthor: smiley_666 » Thu Aug 13, 2009 6:18 am

im sorry that im not contributing anything, but STOP double and tripple posting, its what the edit button is for
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Unread postAuthor: Technician1002 » Thu Aug 13, 2009 11:07 am

Shingoshi wrote:Ok. So I need more clarification here.
1.) So I have a high-temperature A/C compressor. How does that affect my selection of available refrigerants? Like CO2 or Propane? Which refrigerant will give me the lowest temperatures possible while being usable in this compressor's oil?


Are you building a spudgun or making an icebox??? If you need refrigeration, that will be another topic. If you are looking for cryogenic temperatures for extreme overclocking, that should be covered elsewhere. This thread is for an air supply for spudding.
In you are interested in cryogenic multistage refrigeration, pm me.

2.) What I was going to attempt to determine, is how this compressor would compare to an air-compressor. I want to try to power a vortex tube with these four compressors. Running the first three in parallel into the final stage, would that give me the pressures needed for the vortex tube?


The 4 compressors will provide plenty of pressure at moderate volume in a 2 stage setup. Refrigerator compressors are much lower power than a typical shop compressor so the volume will be much less. Most refrigerators are fractional horsepower in the 1/8 to 1/2 hp range.

3.) I plan on using a liquid-cooled 60-plate heat-exchanger in place of a condenser. I was thinking I would need to in order to handle the load in a small space. I'm building my system inside of a Pelican 1780 Transport case. I'll still have an external radiator for the liquid-cooling loop.


For air, you are not releasing the heat of a phase change. Only the heat of compression needs taken care of between stages. Look at the cooling between stages on scuba and paintball compressors to get an idea of the size requirements.

4.) Do I need three pop-off valves? One between each of the four compressors?


You need 2 pop off valves. One simply mounts on the manifold of the junction of the output of the first stage. A normal shop compressor pop off is of sufficient capacity to handle the 3 compressors in parallel as they are lower volume than a typical 1.5-3.5 hp shop compressor.

The second high pressure pop off is for the outlet so if your pressure switch fails, the plumbing doesn't explode.

I think for the sake of respecting this thread, I should ask you to respond at this link instead (http://www.hardforum.com/showthread.php?t=1428264). I'm going to repeat these questions there as well. However, if you feel any of your answers would be helpful here, and not off-topic, then go ahead and answer here instead. At least my thread will let you see just how insane I am!

Shingoshi


Instead of bracketing the URL, use the URL tag so the link works like below;
http://www.hardforum.com/showthread.php?t=1428264

When copy and pasting to another thread, please leave a link to the original post for those wishing to read the original thread. I am not a member of the other thread and am unlikely to create an account to post this there. Go ahead and post, but give credit to the original source with a link to this thread.

On the electrical side, consideration should be given for starting all four compressors. The start current may be quite high. It would be recommended to start them in pairs. Starting the second stage with one first stage will start 1/2 the compressors while not building any pressure between stages. Then the second pair of the first stage can be started with no head pressure. This increased volume will raise the first stage output pressure to normal 2 stage operation.
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For the sake of being respectful of this thread...

Unread postAuthor: Shingoshi » Thu Aug 13, 2009 12:57 pm

Technician1002,
I've decided to pm you instead of continuing this here. My topic doesn't belong here.

Shingoshi

EDIT: Is there anywhere in this forum where a topic such as mine can be discussed? I'm sure there would be others to find it, just as I found this one (using Google). This way, I wouldn't be the only one benefiting from our private discussion.

EDIT: I just got my compressors today. I'm really surprised by just how small they are. These things are really tiny. I've got all four of the sitting tightly grouped together inside of my Pelican 1780 Transport case. I haven't mounted them yet. I've only positioned them for the sake of orientation to see how much space I have to work with. I think easily I have room for one more compressor. Which would allow me to run a 4:1 first and second stage setup.

I've taken a picture of them in their present arrangement with the reservoirs above them. But I won't be able to post any pics until I have a mini-USB cord.

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