wiring a compressor

[tadworth]

I have a Matsu****a scroll compressor salvaged from an aircon unit, i want to build an air tool compressor with it, is it capacitor run ? what kind of switches do i need, all i know is it's single phase, and i have all the caps from the unit if i need them, and it will be running from a 6 kva generator.

 

[Strima]

You might want to check the output of the compressor, I pretty much guarantee it won't have enough displacement to run any thing more than a fish tank filter.

 

[Engineer54]

Can't see why you would even want to arse around, You can get cheap DIY sized air compressors for around 100 quid these day's, with about a 20 litre storage tank. Oh, and another slight problem for you, an AC compressor isn't an air compressor, it's a gas compressor...

 

[Marvo]

I also would advise against it. Refrigeration compressors aren't designed to run with non-condensible gasses like air. You're also going to have oil problems, a refrigeration system is designed that the oil from the compressor travels around the system and eventually returns to the compressor. To use it as an air compressor you're going to need an oil separator and return system. Even then some of the oil will still end up in the receiver tank which will play havoc with the air tools and even more so if you ever use it for spray painting. Add this to the fact it will be running outside of its rated design suction and discharge pressures, it will have a short life span.

If you still want to go ahead it will wire as a CSCR motor so you'll need the start relay, the run cap, the start cap, a pressure switch, a safety switch and an on/off/isolator switch. I would also include the thermal Klixon plus any internal thermistors in the circuit wiring as token LRA protection.

If you can give the exact model number I'll give you a diagram.

 

[Engineer54]

I also would advise against it. Refrigeration compressors aren't designed to run with non-condensible gasses like air. You're also going to have oil problems, a refrigeration system is designed that the oil from the compressor travels around the system and eventually returns to the compressor. To use it as an air compressor you're going to need an oil separator and return system. Even then some of the oil will still end up in the receiver tank which will play havoc with the air tools and even more so if you ever use it for spray painting. Add this to the fact it will be running outside of its rated design suction and discharge pressures, it will have a short life span.

If you still want to go ahead it will wire as a CSCR motor so you'll need the start relay, the run cap, the start cap, a pressure switch, a safety switch and an on/off/isolator switch. I would also include the thermal Klixon plus any internal thermistors in the circuit wiring as token LRA protection.

If you can give the exact model number I'll give you a diagram.

I could well be wrong here Marvo, i'll ask our Mechanical Engineer tomorrow. But i've always been given to believe, that with these combo type compressors used in fridges and AC units etc, the refrigerant gas is separated by heat and only the gas is circulated around. The oil remaining in the hermetically sealed compressor to cool and lubricate the motor and compressor pump. Many of the larger units have an integral low wattage heater that needs to be energised at least 8 hours to get the refrigerant into a gaseous state, before energising the unit. As refrigerant in it's liquid form it can mix with the oil.

 

[Marvo]

It can depend on the technologies employed in the manufacture. Some compressors have an internal oil separator but even then there will be an amount of oil carry through. The suction pipework in an AC or refrigeration system is sized at the design stage to provide sufficient gas velocity to return oil around the system. On the liquid side oil is easily carried because liquid refrigerant is a solvent.

The suction gas is drawn into the hermetic dome of the compressor where it is directed past the oil in the sump and the motor windings to cool them. As the pic shows there's no physical barrier, the suction gas flows freely through the entire dome. During compressor operation oil is splashed and pumped around inside the dome so some of it naturally gets picked up and carried by the gas.




With refrigerant the system superheat is set up to allow a semi-saturated vapour at the suction side of the compressor which allows for more efficient cooling of the compressor oil and motor, obviously with air it will just be gas with a much lower cooling capacity so high running temperatures are very likely. The case heater is there to prevent liquid slugging of the compressor especially on start-up. Scroll compressors aren't particularly prone to liquid slugging damage so they sometimes don't have a heater whereas recip compressors will not tolerate liquid and will nearly always have one, any liquid on the suction side of a recip compressor will result in valve failure or worse.

 

[Engineer54]

Our guy has basically told me the same as you have stated above. But insists that the oil separator(s) will allow only the finest of mist to travel with the refrigerant around the system in reciprocating compressor systems.

At least i've leant a little more on the subject...lol!!!

 

[tadworth]

It's a Matsu-i'm not allowed to say- a model 5KS205DAFO1

 

[Marvo]

It's a Matsu-i'm not allowed to say- a model 5KS205DAFO1

:rofl: Yeah the automatic swear-word filter isn't as clever as it makes itself out to be, it thinks you're trying to sneak in some bad language. I could think of several manufacturers (mostly German ones) that would also set it off.

I'll see if I've got a wiring diagram somewhere in my archives. What I can tell you off the bat is matsa-you-know-what is basically a panasonic compressor and it's single phase.

You say you've got the capacitors, what size are they in microfarads, have you got the relay and the klixon as well?
What Refrigerant does it say on the compressor name plate? Is it R22 for example?

 

[Strima]

:rofl: Yeah the automatic swear-word filter isn't as clever as it makes itself out to be, it thinks you're trying to sneak in some bad language.

Can't even say S****horpe...

 

[Marvo]

Okay, I don't have any literature on your particular comp model so here's my best guess at the wiring scheme. Please note the word 'guess'...... test the resistance of the windings to make sure the common, start and run terminals are in the position I've drawn them. The resistance of the start winding (C-S) will be around 30-40% higher than the run winding (C-R), obviously the resistance R-S will be the highest by far. I'm guessing the cap will be 30-40ish micro farads and 400ish volts discharge.