Compressor from 3ph to 1ph

[Tengtooltom]

I have aquired a compressor with a 3ph motor.
The details on the plate of the motor reads:
5 HP, 2865 rpm, 7.8 amp mech, MO rating, LC184 Frame L5DTL971
Its a Crompton Parkinson with a 1 1/8 inch shaft which is 4 inches long. Its pulley has two "A" section belts and is 5 inch diameter.

My question is:
What type of 3hp single phase motor should I fit?
What size pulley should I fit to a 3hp single phase motor to drive it?
I know that I will not have the same output but I am just a "Hobby" operator compared to where this compressor was operating.

 

[Wendelspanswick]

I am pretty sure that a single phase 3hp motor will fail to power a compressor originally powered by a 3 phase 5hp motor. I imagine it will stall or burn out as the pressure increases.

 

[rtbcomp]

I'd fit a 2800 rpm 3HP single phase motor with a 3 inch double pullley (3/5 the diameter of the existing pulley). Keep the twin belts.

You'll need the smaller pulley to compensate for the lower torque in the 3 hp motor.

 

[Tengtooltom]

I'd fit a 2800 rpm 3HP single phase motor with a 3 inch double pullley (3/5 the diameter of the existing pulley). Keep the twin belts.

You'll need the smaller pulley to compensate for the lower torque in the 3 hp motor.

I understand re the smaller pulley etc but it was the ratio that I needed.
What about a slower speed motor and 5 inch pulley or would that be the wrong way to go?

 

[brightspark]

if u fit the smaller pulley on a 3hp motor u may get away with using it but would be best checking the full load amps on the motor when it is filling the tank with a clamp meter . that will tell u if u are overloading it and chance u may burn it out

 

[brightspark]

I understand re the smaller pulley etc but it was the ratio that I needed.
What about a slower speed motor and 5 inch pulley or would that be the wrong way to go?

that would double the torque but wouldnt give the motor output anymore hp increase

 

[Tengtooltom]

Can I fit a 4 hp 1 ph motor, or is this possible, or available?

What about fitting a 5hp engine? What changes would be necessary to pressure cut out valves etc?

 

[Bill Edwards]

Engine powered compressors are pretty basic. You have a valve to blow off when full pressure is reached. Your compressor will already have a relief valve to avoid over pressure in case the motor remains on for some reason. However, they aren't really designed for continuous operation and you should get one that is designed to be used all the time.

Some engine powered compressors have an air powered actuator which pushes the throttle closed when full pressure is reached to avoid having the engine flat out all the time. They also have some kind of unloader valve so the compressor isn't compressing air while the engine is idling which could stall it.
How far you would go with your setup would depend on how much/what sort of usage you would have for it vs cost. For the occasional use to fill a tyre a simple blow off valve may be fine, but if you don't want the thing running at full revs all the time then you have to improve things.

 

[Wendelspanswick]

You can get single phase motors in all sizes, they are not limited to 3 hp. The problem is the size, single phase motors are normally larger when compared to the same size 3 phase motor. Bigger size means more copper means bigger price.
The Master Blacksmith who taught me had a 12hp single phase motor from a Power Hammer he bought. The motor was massive, he scrapped it and replaced it with a 7hp 3 phase motor. The money he got from the old motor almost paid for the Power Hammer!

 

[CompoSimmonite]

I swopped "like for like" the 3 hp 3ph motor on a compressor for a 3hp 1ph. Didn't work I ended up having to alter pulleys and add an pressure unloader but even then it was never perfect.
Have you thought about a little Honda 3-5hp petrol motor instead of electric ?
Maybe the best option would be a 1ph to 3ph converter so you keep the original motor.

Paul h

 

[dannyp]

i swaped 3 hp 3ph brook for a 5hp 1ph chineese motor, kept the pully from the 3hp motor and both were 1450 ish rpm

the 5 hp motor used to play havoc with the lights, and didnt ast very long, problem is the chep ons use a starting cap to up there starting torque, a 3 ph motor has loads of torque and will happily accselorate a system with a lot of inertia up to speed quickly, cheep singel phase motors just die if the load has inertia.

now said compressor has a 6hp singel phase brook made in 1957 on it and its optimal

 

[rtbcomp]

I understand re the smaller pulley etc but it was the ratio that I needed.
What about a slower speed motor and 5 inch pulley or would that be the wrong way to go?

The smaller pulley will give the correct ratio, at least in theory!

It's worth mentioning that 3 phase motors are more efficient than 1 phase, so you may have to decrease the cut-off pressure to avoid an overload at high pressure as mentioned above.

 

[Tengtooltom]

I have looked at this 3.0 KW, single phase motor http://www.ebay.co.uk/itm/200670945376?
Would I need one of these? http://www.ebay.co.uk/itm/191031399180

Would it work?? As described above I would fit a 4 inch double pulley.

 

[ronan]

Would fitting a vfd work ? The chinese vfd's aren't bad and cheap enough compared to motor swaps.