DIY full size air compressor - am I mad?
Discussion
I've done a bit of googling for 3 phase inverter and I see several that can apparently convert from single phase 220V 50Hz to 3 phase variable frequency. The ones marked 3hp seem to be 2.2kW. Could I use this with a 3hp motor or would I need a larger capacity inverter to allow some margin for losses? 2.2kW on 240V mains supply would seem to draw 10A, so within the maximum 13A allowable on a standard mains plug. Do I really need to get a 16A supply considering that it's going to be for home/DIY use and therefore the duty cycle is going to be fairly low? As well as automotive tools, I use a compressor to drive a nailer and other shoe-making equipment.
paralla said:
I'd think a large capacity air cooled motorbike engine would be a more suitable starting point for an engine/compressor conversion. I think a compressor and no conversion is a better end point though.
Not sure we're still talking about a conversion. The OP dates back a few years!GreenV8S said:
Duty cycle isn't the problem - it's the startup current draw that I think will be the limiting factor. A rotary phase converter helps with that.due to the mechanical inertia.
As long as it as an unloader(would be unusual if it doesn't) a 3hp inverter will drive it; soft start and ramping will take care of the rest and avoid blacking out the neighbours. 
s p a c e m a n said:
I've got a vague recollection of a friend wiring up a 3 phase car lift to work on single phase, is that possible or was I not paying enough attention at the time?
You can drive a 3 phase motor from single phase, it requires capacitors, a relay, etc; it does reduce the power and starting torque of the motor though.hidetheelephants said:
s p a c e m a n said:
I've got a vague recollection of a friend wiring up a 3 phase car lift to work on single phase, is that possible or was I not paying enough attention at the time?
You can drive a 3 phase motor from single phase, it requires capacitors, a relay, etc; it does reduce the power and starting torque of the motor though.LunarOne said:
I've done a bit of googling for 3 phase inverter and I see several that can apparently convert from single phase 220V 50Hz to 3 phase variable frequency. The ones marked 3hp seem to be 2.2kW. Could I use this with a 3hp motor or would I need a larger capacity inverter to allow some margin for losses? 2.2kW on 240V mains supply would seem to draw 10A, so within the maximum 13A allowable on a standard mains plug. Do I really need to get a 16A supply considering that it's going to be for home/DIY use and therefore the duty cycle is going to be fairly low? As well as automotive tools, I use a compressor to drive a nailer and other shoe-making equipment.
Inverters are speced on peak current drawn, so you are limited to 13A full load current at 240V that is 3.1kW max motor size.The trick with air compressors for mix duties is to put a large storage vessel on it. That way you can pull more air flow than the compressor can deliver, but only until you drop the pressure in the vessel so far that the kit won't work. It will also take longer to get back up to pressure because of the vessel volume. Avoid using piston compressors for this if you can as they do not long hard use.
LunarOne said:
OP did you ever get anywhere with this? This evening at my local Sainsbury's petrol station I saw a Clarke Industrial air compressor standing in a Hippo bag, clearly awaiting collection. I checked at the petrol station to see if there was any chance I could have it, and they said they couldn't see why not but to ask the manager in the main store. So I went and asked and they said I was welcome to it. So I came home and got my A4 Avant which it turns out is only just big enough for the compressor. Apparently it works fine, but was removed when they renewed the air machine and the car wash a couple of weeks ago. I haven't been able to test it as it's got a 3-phase motor and I don't have a 3-phase supply, but I did hear of ways to convert the motor to use a single phase supply, or to change the motor for a single phase one. I'm not sure of the exact specs as it was dark, but here are some photos of the unit, now standing in my garage. My current compressor is a 25l Wolf Air and when using it with air tools the compressor fires up after just a few seconds and I've been hankering after a bigger vertical compressor for ages. From what I can see online, it's 14CFM and has a 150 litre receiver. A great freebie if I can get it going and maybe worth something to someone even if I can't!
At 3HP belt driven you may be able to swap the motor for a single phase motor.Other option is just use the 150 tank as a storage vessel to sop the wolf coming in so often.
I will take a while to charge it the first time though.
Its going to be ~£100 for a 1 to 3 phase inverter or £150-£200 for a replacement motor with the pain of getting the right shaft size, mounting etc
I would have thought something like this https://uk.banggood.com/4KW-220V-20A-Single-Phase-... would do it.
A 4kw unit will do a 3hp motor.
Mind you Clarke seem to do a direct replacement unit https://www.clarketooling.co.uk/product/clarke-3hp... but it is £250
I would have thought something like this https://uk.banggood.com/4KW-220V-20A-Single-Phase-... would do it.
A 4kw unit will do a 3hp motor.
Mind you Clarke seem to do a direct replacement unit https://www.clarketooling.co.uk/product/clarke-3hp... but it is £250
Edited by Gary C on Saturday 7th August 13:51
Super Sonic said:
"full size"? I once worked on a building site putting diesel in stuff and the compressors were up to portakabin size.
Well, if you want to play that game 
Our air systems at work use 4 3m x 3m receivers then into two 20m long by 4m diameter receivers from 6 oil free screw compressors, and thats just the instrument air.
Each of the eight diesel engine start systems use 3 reciprocating compressors and 4 1m x 3m receivers then the general service air system uses four more big (2 are portakabin size) screw compressors and 3m x 3m receivers.
Thats 34 compressors in all with a huge reservoir of air to keep essential systems running if we loose site supplies.
Then the 50 or so fire systems each have their own compressors to run the air detection for dry deluge valves.
And then we have the Forced Air Compressor system. This compressor runs off a 3.3kV motor and has a four stage centrifugal compressor with wheels the size of big dinner plates. Only runs up to about 14 bar but the CFM is huge and is used to purge the reactor of CO2 and fast cool the turbine if we want to work on it as soon as possible after a trip.
Then there are the various hydrovane and test compressors around the site.
Edited by Gary C on Saturday 7th August 14:06
Gary C said:
Well, if you want to play that game
Our air systems at work use 4 3m x 3m receivers then into two 20m long by 4m diameter receivers from 6 oil free screw compressors, and thats just the instrument air.
Each of the eight diesel engine start systems use 3 reciprocating compressors and 4 1m x 3m receivers then the general service air system uses four more big (2 are portakabin size) screw compressors and 3m x 3m receivers.
Thats 34 compressors in all with a huge reservoir of air to keep essential systems running if we loose site supplies.
Then the 50 or so fire systems each have their own compressors to run the air detection for dry deluge valves.
And then we have the Forced Air Compressor system. This compressor runs off a 3.3kV motor and has a four stage centrifugal compressor with wheels the size of big dinner plates. Only runs up to about 14 bar but the CFM is huge and is used to purge the reactor of CO2 and fast cool the turbine if we want to work on it as soon as possible after a trip.
Then there are the various hydrovane and test compressors around the site.
Nice size system!Our air systems at work use 4 3m x 3m receivers then into two 20m long by 4m diameter receivers from 6 oil free screw compressors, and thats just the instrument air.
Each of the eight diesel engine start systems use 3 reciprocating compressors and 4 1m x 3m receivers then the general service air system uses four more big (2 are portakabin size) screw compressors and 3m x 3m receivers.
Thats 34 compressors in all with a huge reservoir of air to keep essential systems running if we loose site supplies.
Then the 50 or so fire systems each have their own compressors to run the air detection for dry deluge valves.
And then we have the Forced Air Compressor system. This compressor runs off a 3.3kV motor and has a four stage centrifugal compressor with wheels the size of big dinner plates. Only runs up to about 14 bar but the CFM is huge and is used to purge the reactor of CO2 and fast cool the turbine if we want to work on it as soon as possible after a trip.
Then there are the various hydrovane and test compressors around the site.
The largest we look after has 3400kW of compressors to make air bags.
I'm guessing yours is on a power station?
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