Looking for information on compressor electrical items

[Marsden Foulkes]

Hello All,
I'm currently trying to revamp a 3ph 200l compressor that has most of the electrical equipment missing. I found this site by researching 3ph to 1ph motors. Some excellent info on here so I thought I'd join.
I'm a mechanical fitter by trade although I have worked on electrical devices throughout my working career.
Always better to get information from more qualified and knowledgeable people.
Cheers!

 

[Pete999]

So what is missing exactly?

 

[westward10]

Yes welcome.

 

[LankyWill]

Usually on a DOL starter, is the compressor 3 Phases and the Supply Single?

 

[Pete999]

Hello All,
I'm currently trying to revamp a 3ph 200l compressor that has most of the electrical equipment missing. I found this site by researching 3ph to 1ph motors. Some excellent info on here so I thought I'd join.
I'm a mechanical fitter by trade although I have worked on electrical devices throughout my working career.
Always better to get information from more qualified and knowledgeable people.
Cheers!

Got a picture of the data plate on the motor?

 

[Marsden Foulkes]

When I had it it was missing:
Pressure switch
D.O.L starter
Bleed line
Relief valve
It did have a 5.5hp 3ph motor but the lead was cut off at the motor. I've checked the motor and if seems fine. I'm thinking of fitting a 5hp 1ph motor and doing research on that was how I came across you guys.

 

[Marsden Foulkes]

By the way, how do I post a pic on here?

 

[Marsden Foulkes]

My concern is that the 1ph 5hp motor takes 25 amps and that may be too big to run from a normal domestic supply. I believe running it through a 25 amp D.O.L starter with overload should give me some protection but it's this sort of thing that I need advice on and hopefully I can get that here

 

[Marsden Foulkes]

Here is the plate from the original 3ph motor. Compressor is a Clarke SE25C200

 

[Marvo]

I don't think you'll get away with fitting a 5HP single phase motor for several reasons;

It will be lower HP than the original so it will probably be overloaded unless you reduce the pulley ratios to reduce mechanical load. This will obviously negatively effect the air output of the unit.

It will have approx start current of 120A and run current of 25A compared to the 3-phase figures of 14.5A and 8.4A of the original. This means all the electrical switchgear, supply wiring and internal wiring and cabling will need replacing with much larger items to prevent volt-drop becoming an issue.

Single phase motors have far less starting torque compared to their 3-phase counterparts so you may need a more elaborate air off-loader to allow a larger time window of off-load starting torque.

I'm not saying that fitting a single phase motor is impossible but you're probably going to have to be prepared to reduce the performance of the unit and spend far more money on the supply and control gear than you would if you stuck with a 3-phase motor the same as the original spec.

 

[westward10]

You will need something in the region as you say of 5hp for single phase and would be cap start, cap run however, the run current will be in the region of 17 to 20A but the start current could be up to 80A. Yes it is possible with a 5hp cap start/run motor.

 

[Marsden Foulkes]

Thanks for the input and taking the time to reply. I appreciate your help.

 

[Marsden Foulkes]

Ran up the compressor with a 3hp single phase motor and it ran OK cutting out at 8 bar and restarting at 6 bar without any issues. Think I may go for 4hp motor as this will obviously draw less current, (and cost less!) and output shaft is still correct diameter

 

[westward10]

I would stick with the 5hp, is it cap start and run.

 

[Marsden Foulkes]

Yes it is cap start / cap run. I havent bought it yet but the cost difference between 4hp and 5hp is only £1! i'm just concerned that the 5hp motor may be too much for my house supply.