[ilfixit]

Hi everyone and thanks for the site, I'm new to this site and hope I can offer and find some helpful information.

I have a project ahead of me wiring new 110/220 motors to a dual pump air compressor. I have exhausted the search for a phase converter as I have no luck interacting with individuals selling there products on the local and national trading lists, and was prescribed heart medication when I learned the price of a new one to run my application. And I'm not building one.
My question is, how can I run the wires to two single phase 2 hp 60 hz 1725 rpm motors and use one plug. Also should I connect them using 220 or 110 the motors are rated for both. and the last thing, can I use the pressure switches that were used for the 3 phase original operation???

I'd really like to know the advantages and disadvantages between using 220 vs. 110 and somewhat understand better why there is 3 phase, I learned its like flowing water with less interruptions.

I have a 220-230 outlet installed running off of a double 20 amp breaker that I'm using to operate my current 1947 66 gal compressor if this helps, but I don't remember what gauge wire I have run from the box to it. I could figure it out though.

If you have any suggestions please help me out, Thanks

 

[carmusic]

run them at 240v, you must check if they are temperature ptotected, if they are, you can connect them together but you need at least a 40 amp breaker
you will also need a contactor to run them on/off since the pressure switch wont be able to control a 4 hp load

 

[DexterII]

Welcome. There are enough electricians here, so I am going to sidestep the wire sizing, etc., but try to fill in some of the blanks. So guessing that you bought a used duplex unit, and are going to install single phase motors on it. First off, just because it had two pumps and motors doesn't mean that you need to run both of them, unless you like watching the wheel in the meter go around. Duplex units typically run either lead-lag, meaning that the pressure switches are staggered and the second one only kicks in when the first one needs help, or alternating, meaning that one unit runs one time and the other unit the next time. Seldom are they set up to both kick in each time. Either of these require a control panel, which are not inexpensive. So the first thing I would do is look at the spec's for the pumps that you have, and see if they are compatible with the tank, such that one unit would suffice with the second setting offline in reserve. 2 horsepower duplex sounds like it may be a climate control unit, for which it is not uncommon for the pulley sizes to be different than shop units, causing them to run slower. It is also likely that they are single stage units. Both of these, pulley size and single stage point to lower pressure, so you may want to determine exactly what you have before putting a lot of money into it.

 

[joed]

240 or 220, it's the same thing, will be lower current. You can use smaller wires and lower breaker.
The old pressure switches should work fine. Not knowing exactly how they were connected I would estimate you will be using two of the three sets of contacts, since you are only switching two hots instead of three.

 

[mpoulton]

3 phase motors are more efficient than single phase, smaller for the same power ratings, and have much better starting torque. You are certainly right that it's a waste of money to get a phase converter just to run a pair of 2HP motors on an air compressor though. Wire your single phase motors for 240V. They run slightly more efficiently at the higher voltage, and you can use smaller wire and lower current. There is no advantage to running them at 120V if you have 240V power available.

As far as wiring goes, you'll need about 24A total for both motors at 240V. Your 20A breaker is definitely not big enough. A 30A breaker and #10 wire is the minimum. If you are starting both motors at the same time (one pressure switch, for example) then you may need to use a 40A breaker to handle the starting current. You can still use #10 wire though (motor circuits have special rules that allow larger breakers with smaller wire). If the motors will not be starting at the same time, then a 30A breaker will most likely work just fine.

Your 3ph pressure switches will work for single phase motors as long as the ratings are adequate. If the switches have a single-phase rating on them of 2HP or more, that's fine. If they do not have a 1ph rating on them but are rated for 3HP or more 3ph, that's fine too. If they only have amp ratings not horsepower, then you'll need them to be rated for 12A minimum.

To hook up the motors and switches for single-phase, you'll just wire the incoming power to two of the terminals on each pressure switch. Wire one motor to the other side of each pressure switch. Leave the third pole (pair of terminals) empty on each switch.

It will be important to adjust the pressure switches so the compressors both start regularly. If you have one of them starting at a higher pressure than the other, the other compressor may not run very often at all, which will cause much greater wear on the first compressor.

 

[ilfixit]

WOW !!!! Thanks so much for the info, all of you have been a great help so far. DexterII you nailed it, it is a climate control unit, I guess I should have mentioned that. I hope I'm not wasting my money and time on this unit!! Joed, Thanks and mpoulton, you answered all my questions. I will now look at the ratings with a bit more knowedge of what I'm looking at and try to figure out how to set this up, as long as I'm not wasting my time with the unit in the first place??? All I plan to do is use the compressor for sand blasting as my 7 cfm doesn't quite keep up with me and I'm nervous around it because of its age. I know this isn't the best setup but until a 125 cfm give or take trailer compressor falls in my budget, it might have to work. I'm using a 20 gallon pressure pot from TS and what a pain in the back side, but I'm getting it to work by trial and error! mostly error right now. Am I wasting my time?

 

[hueco]

this one brought to my mind another question regarding the way three-phase motors start versus how split-phase motors start. Will three-phase motors start when running off split phase power? I had an experience with a car wash which lost one phase and none of the motors would run.

 

[bernie963]

hi,

Not sure what you mean " I'm using a 20 gallon pressure pot from TS".

any pictures of the compressor unit? A lot of dental office compressors are dual pump configurations. You may get some ideas for a set up from Ritter or Pelton Crane web sites.

good luck and keep us posted.

also "Garage Journal" website has a compressor forum which is great.

Bernie

 

[bernie963]

http://www.garagejournal.com/forum/showthread.php?t=27378

this is the thread

Bernie

 

[ilfixit]

hi,

Not sure what you mean " I'm using a 20 gallon pressure pot from TS".

Sorry, Tractor Supply

also "Garage Journal" website has a compressor forum which is great.

Bernie

Thanks for the link Bernie, looks like a lot of show and tell but maybe they can help me with as to why the pressure pot manufacturers put a ball valve on the bottom of there tanks and assume abrasives will flow out !!??

 

[Bondo]

why the pressure pot manufacturers put a ball valve on the bottom of there tanks and assume abrasives will flow out !!??

Ayuh,.... On my cheapy pressure pot, I use that valve to regulate the amount of abrasive allowed into the air stream,....

If yer gettin' alota cloggin', it's usually because of too much moisture,...
Does yer pot have an air dryer mounted at the inlet,..??
Do ya leave the drain cracked abit when yer usin' it,..??

Shakin' the pot usually helps,...
Vibratin' it oughta help alot more, I bought an air powered bolt on vibrator, but haven't gotten to mountin', 'n tryin' it,...
An ole power sander wasn't violent enough,....

 

[ilfixit]

This is a pic of one of the pressure switch labels, there both exactly the same but on the tank there are labels warning not to change the pressure range. One says 70-90 and the other 60-80 ???

This is the unit I'm working on;

 

[ilfixit]

hi,

Not sure what you mean " I'm using a 20 gallon pressure pot from TS".

any pictures of the compressor unit? A lot of dental office compressors are dual pump configurations. You may get some ideas for a set up from Ritter or Pelton Crane web sites.

good luck and keep us posted.

also "Garage Journal" website has a compressor forum which is great.

Bernie

Ayuh,.... On my cheapy pressure pot, I use that valve to regulate the amount of abrasive allowed into the air stream,....

If yer gettin' alota cloggin', it's usually because of too much moisture,...
Does yer pot have an air dryer mounted at the inlet,..??
Do ya leave the drain cracked abit when yer usin' it,..??

Shakin' the pot usually helps,...
Vibratin' it oughta help alot more, I bought an air powered bolt on vibrator, but haven't gotten to mountin', 'n tryin' it,...
An ole power sander wasn't violent enough,....

Yeah Bondo, I do have the moisture trap on the tank and on the compressor , though I read is nearly useless at the compressor as the air has no time to loose its heat there. I just bought this pot and it was returned. The last victim added sand to his black beauty and it was getting moisture clog. I'm working on resolving that. I started to drain the pot and watched bugs and rubber pieces of sorts fall into my bucket, maybe I'll have better luck with dry BB and less bugs and such!!!! Holy $##&$&!!!

 

[carmusic]

View attachment 230138

This is a pic of one of the pressure switch labels, there both exactly the same but on the tank there are labels warning not to change the pressure range. One says 70-90 and the other 60-80 ???

This is the unit I'm working on;
View attachment 230146

if the switch control one motor each you are ok with them

 

[Bondo]

maybe I'll have better luck with dry BB and less bugs and such!!!! Holy $##&$&!!!

Ayuh,.... Dependin' on the tip size yer gonna use, black beauty is my least favorite media,....
Too many clogs,....

You can sieve yer used media, but ya need a screen smaller than yer tip size,....

Yer thread has reminded me, I wanta figure out what's different with blastin' bakin' soda, inteada sand,...
I'd use my blaster more with soda, I think,...
I see conversion kits, but don't see what they do for the money spent, vs just dumpin' soda into the pot,...

 

[ilfixit]

yep, both motors are controlled by separate switches Carmusic. The wiring is hard for me to follow probably since it was three phase hook up, at least I think. the wires go directly to the motors then are split back to the pressure switches.

 

[ilfixit]

Ayuh,.... Dependin' on the tip size yer gonna use, black beauty is my least favorite media,....
Too many clogs,....

You can sieve yer used media, but ya need a screen smaller than yer tip size,....

Yer thread has reminded me, I wanta figure out what's different with blastin' bakin' soda, inteada sand,...
I'd use my blaster more with soda, I think,...
I see conversion kits, but don't see what they do for the money spent, vs just dumpin' soda into the pot,...

I'll never attempt to use soda again, I used it to blast my last projects frame in a garage and nearly ran out of air and had to crawl to the door gasping for oxygen. The stuff got all over the place and what I didn't find lurking in crevice and seams in my aluminum garage doors rotted out the metal. It hardly made any impact on removing the paint much less the rust and was a seriously messy job. I bought the complete setup and returned it all the next day. If you attempt to use this please get a vary good breathing device with oxygen !!!

 

[DexterII]

In regard to the pressure adjustment warning, does it look like a factory label or something that the facility it came from added? If the latter, maybe the previous user added it because they had pressure sensitive equipment in the system that they did not want their people to damage by jacking the pressure up. If it looks factory, I would look at the label welded to the tank, to see what its' working pressure is. It's more likely than not 200, but should be verified. After that, there probably isn't any difference in the pistons, valves, etc. that would be hurt by running harder, but don't know if it might affect the oil pumping or slinging system. And the check valves are most likely standard, but I would imagine that you'll need to install a higher rated safety valve if you do decide to increase the pressure. Sand blasting requires a pretty good supply of air, and, as I alluded earlier, it's possible that the motor pulley is sized different than a standard shop unit, so the cfm it puts out could be a little less than a comparable non-climate control unit.

 

[ilfixit]

Just to add, I like to see the sparkly bare metal when I'm done blasting with not a lot of mess and I'm really close. I was a absolute disbeliever in the black beauty but am now convinced its the only way to go as far as it staying mostly dry, etches the metal, has much less dust and contains, they say, a lot less silica that kills you in the long run. I was using a smaller pressure pot and courser BB is why things didn't work in the past. I'm almost there!!

 

[mpoulton]

That pressure switch is only two-pole not three, so all the stuff we said about leaving a connection off the switch does not apply. It is big enough for one 2HP motor at 240V.