Swapping from 3 Phase to Single Phase motor

[GingerNuttz]

Hi new member here

Just bought a 3 phase compressor a few weeks back and swapped it to a single phase motor, when the compressor hits 50 psi but motor is bogging down and tripping the little cut out switch on the motor. Both the 3 phase and single phase motor are the same 2.2kw and 2800 rpm, i ran the 240v motor on another compressor with no problems at all.

I've found a slight leak in the un loader valve when its building pressure, would this cause the motor to start bogging down? I don't know output of the pump but its no more than 18CFM. Are these 2 motors roughly the same? or is the 240v under powered?



I was going to order a 4hp motor and 4" pulley but i thought i would ask before forking out nearly £200.

Any help would be appreciated guys

 

[rtbcomp]

If there's air coming out of the unloader that means the non-return valve on the tank is leaking, although it shouldn't show up as a problem until you start the pump with pressure in the tank.

The first thing I would check is that the belt is tight, if it's slack the motor can bog down because the pump doesn't get going fast enough for the flywheel to carry it over the compression at top dead centre.

 

[GingerNuttz]

Just checked the belt and it seems fine about 1/4" of movement from the center when pushing down. The air leak is significantly worse than i thought, turned the other compressor off and its leaking from 0-50 psi and then the motor trips. I'll pull the pipes off later and see if i can clean the valve or find a replacement.

 

[rtbcomp]

It could be that the motor is struggling to start and gives up at 50psi. Does it seem to get up to speed?

You can check the NRV without removing it (on most compressors). Make sure the tank is empty and remove the large blanking plug from the valve, watch for the spring. A clean out is all it might need.

 

[GingerNuttz]

Thanks for the help RTB I'll get the NRV checked tonight, the compressor gets up to speed no problem but as the pressure starts building closer to 50 psi it just slows down to the point it trips.

The motor was on another compressor (ABAC) up until yesterday and would run to 150 psi without any problems

 

[GingerNuttz]

Took the NRV apart and there was nothing left of the plunger so i swapped it for the one from the ABAC and still the same problem, runs to 50 ish psi and the motor struggles like mad. I'll order up a new motor and NRV just to be on the safe side.

Thanks again rtbcomp

 

[p0689109]

Just a idea but when it trips the cb is the pump able to be turned by hand by pulling on the belt? I am suggesting that as its warmed up the pump might be seizing maybe?

 

[roofman]

Look out for a knacked hot or cold industrial power washer...they do come along at not silly money and have a very nice 3HP single phase in them often with a nice 4" pulley too

 

[dannyp]

have ou ever seen the compressor work correctly with the 3ph motor on it ?

 

[GingerNuttz]

Just a idea but when it trips the cb is the pump able to be turned by hand by pulling on the belt? I am suggesting that as its warmed up the pump might be seizing maybe?

The pump can be turned by hand when it trips, no pressure has built up on the cylinder.

 

[GingerNuttz]

have ou ever seen the compressor work correctly with the 3ph motor on it ?

Yes the compressor ran to pressure when I collected it. I've ordered a 4 hp motor plus a new nrv as I can't afford the downtime.

On the plus side I've got a spare ABAC compressor I can put back together and sell

 

[p0689109]

What amp rating is that 4 hp on 240v then. 13 or 16amp

 

[God mode restorations]

4hp would be 16 amp I would of thought .

 

[Turbo]

When you swap from a 3 phase to a single phase motor you usually have to go for a higher hp motor. Even though both your motors have the same hp the 3p will have more torque. See if you can find a single phase version of your compressor or one with the same output & see what motor size it uses.

Normally a 3hp motor is used on a 14cfm compressor so it would struggle on a 18cfm pump.

You will need a very good supply to to feed that 4hp motor, a 3hp needs a 16a supply so the next size up is 32a plug with 6mm cable and a 32a type c breaker.

 

[p0689109]

That's what I was getting at!

 

[GingerNuttz]

The 4hp is 16 amp, we use the blue 3 pin ends for our plasma and mig so will get our spark to do the same for the compressor. I'm not to clued up on the dark art of electricity lol

 

[GingerNuttz]

Well 4 hp motor solved the problem The motor was 18.6 amps not 16. Cheers for the help guys

Ginger