3phase motor on single phase supply

[Coupster]

Looking at machinery costs and there are more options for quality 3 phase machines, but I only have single phase.
I have done some googling but want real opinions from you all on here. I would like for example to run a 5.5 hp 3 phase motor in my workshop. What are my options and what are the approximate costs involved in doing so?
Thanks for any responses.

 

[gaz1]

unless your lucky and 3 phase has already been supplied into the workshop

 

[Coupster]

Workshop is new build in garden about 30m from house so supply will be taken from the house....
Hmmm wonder if it's worth the saving on buying a 3 phase machine in the first place??

 

[Coupster]

And thanks for replies so far.

 

[WorkshopChris]

I would like for example to run a 5.5 hp 3 phase motor in my workshop.

Hmmm wonder if it's worth the saving on buying a 3 phase machine in the first place??

All depends on exactly what it is you want to run, you quoted 5.5hp for example. A vfd for that is going to be very expensive, as will a phase converter.
But drop down to below 3hp and the price and incoming supply requirements drop considerably.
Is your 5.5hp for a hydraulic pump or compressor? thats a big motor for most home sized kit.

 

[Coupster]

Ok a bit more info, it's actually for a table saw (wood stuff/day job). There's is more choice as far i can tell for quality second-hand industrial type saws, and for what they are the prices are affordable, single phase seems a lot rarer and more expensive for obvious reasons.

....What about changing the motors?

Budget is a definite factor here so am trying to kill two birds with one stone..get an affordable but very high quality older machine.

 

[chris y]

I have a few 3 phase machines and the supply to my garage is from the house.
The garage is about 30m from the house and its supplied from 10mm SWA buried.

I have a rotary converter, although not quite as pdg explained. Its a box of capacitors and a big transformer with a 3 phase motor permanently connected, its shaft is chopped off and it just spins and apparently smooths the crude 3 phase supply. The converter capacitors have to be tuned to match the motor until you achieve proper phase balance.
I bought this second hand, maybe worth a try. The previous owner had bought it as a static converter and basically added the motor and tuned the caps.

Mine has a 5.5hp motor spinning, and I run up to 3hp machines with it.
Its wired to a blue 240v plug from a 32A breaker in the garage. I tried is with a 16A and it couldn't start.

I wouldn't be tempted to use it on any fancy electronic machinery as apparently 3 phase from converters is a bit crude, not properly phased at 120 degrees and not always balanced. The frequency should be fine though.

If you hit lucky you might get a converter like mine for a few hundred quid, although its not often they come up for sale.

Its a good solution for me because it lets me use lots of different machinery without rewiring or modifying.

 

[thinfourth]

Have a hunt around for the thread i posted last year about converting an AJAX milling machine from 3 phase to single phase by using a VFD.

 

[Coupster]

Looks like a new rotary converter will be upwards of £700 (only did a quick ebay search), second-hand would be good but probably be lucky to find one as Chris y says.
Thinfourth - thanks il have a search.

Is changing the motor to single phase one a sensible/viable option?

 

[graffian]

The simplest solution is to get a large three phase mnotor and get it rotating with a pull cord and put 240V to
it and get three phases off it. If you do a search you will find yanks running workshops with cnc machines running converters like this!
I tried it and ran a Pratt&Whitney grinder like that, it worked.

Static converters, basically a box of capacitors. plenty online about them and how well they run stuff.

rotary converters. plenty online, I built one and it runs a 5.5hp ingersol rand compressor, total cost was around 200 quid and it's been running faultlessly for years. I woudln't worry about something with electronics running on one, don't connect any coils or electronics to the wild phase.

 

[Coupster]

There are some real clever clogs on here, I won't be making anything myself as it would end in disaster.
Vfd's are affordable though so that is an option. What do I need to consideri when using it in conjunction with a large table saw.

 

[Burdekin]

Do you need one that big? Would a 3hp one be big enough for you?
http://s237712126.websitehome.co.uk/woodworking/

Quoted from BoostEnergy

"
Summary of VSD/VFD advantages and disadvantages
Advantages:

• Single to three phases, a true 3-phase output but at 220V 3-phase. So motor must be connected into Δ.
• Full and smooth variable speed control across entire speed range.
• Quiet operation.
• High torque down to lowest speed, with automatic compensation with load - to maintain shaft speed.
• Complete electronic and thermal overload protection.
• Forward / Reverse direction control functionality.
• Generally very competitively priced vs. a phase converter.
• Very compact frame size by comparison.
• Excellent starting torque characteristics.

Disadvantages

• Motor must be wired into Δ otherwise will have reduced torque. If an existing motor cannot be wired into Δ this is a problem, and the easiest solution (providing you don't want speed control) is a phase converter.
• Capacity range 0.2 to 2.2-kW. Commercial single to 3-phase inverters only tend to go up 2.2-kW / 3-hp. Therefore for particularly large machine tools (such as bigger Colchester lathes etc) the phase converter is the solution.
• Inverters are best suited to run one dedicated motor only. Therefore for applications where one or more motors need to be run, of mixed size, and/or at the same time a phase-converter is required."

 

[Coupster]

Do you need one that big? Would a 3hp one be big enough for you?
http://s237712126.websitehome.co.uk/woodworking/

Quoted from BoostEnergy

"
Summary of VSD/VFD advantages and disadvantages
Advantages:

• Single to three phases, a true 3-phase output but at 220V 3-phase. So motor must be connected into Δ.
• Full and smooth variable speed control across entire speed range.
• Quiet operation.
• High torque down to lowest speed, with automatic compensation with load - to maintain shaft speed.
• Complete electronic and thermal overload protection.
• Forward / Reverse direction control functionality.
• Generally very competitively priced vs. a phase converter.
• Very compact frame size by comparison.
• Excellent starting torque characteristics.

Disadvantages

• Motor must be wired into Δ otherwise will have reduced torque. If an existing motor cannot be wired into Δ this is a problem, and the easiest solution (providing you don't want speed control) is a phase converter.
• Capacity range 0.2 to 2.2-kW. Commercial single to 3-phase inverters only tend to go up 2.2-kW / 3-hp. Therefore for particularly large machine tools (such as bigger Colchester lathes etc) the phase converter is the solution.
• Inverters are best suited to run one dedicated motor only. Therefore for applications where one or more motors need to be run, of mixed size, and/or at the same time a phase-converter is required."

To be honest, no it doesn't have to be that big, 3hp would be fine. I just happened to find a particular saw with a huge motor.
What does the triangle symbol mean?

 

[Burdekin]

To be honest, no it doesn't have to be that big, 3hp would be fine. I just happened to find a particular saw with a huge motor.

Could you run it with a 3hp 3phase motor? I assume it depends on how thick timber you will be cutting so maybe okay.

Or find a 3hp saw and then you can get a cheapo VFD.

 

[Coupster]

• Could you run it with a 3hp 3phase motor? I assume it depends on how thick timber you will be cutting so maybe okay.
  
  Or find a 3hp saw and then you can get a cheapo VFD.

  
  
• yes, both options, but I'm thinking probably easiest to find a 3hp 3phase and buy a vfd

At least i have options now if using a vfd is do able at the cost I've seen them

 

[Burdekin]

• 
  
  
• yes, both options, but I'm thinking probably easiest to find a 3hp 3phase and buy a vfd

At least i have options now if using a vfd is do able at the cost I've seen them

Yep.

But if you are intending on getting multiple 3phase machines I'd definitely consider a converter. I have a Boost Energy one http://www.boost-energy.com/phase-converters and run three phase around my workshop to run my lathe, milling machine and drill. Speak to the guys before ordering if you do decide to go that route, they will help you with the correct sizing. I was going to get a larger one but they advised me it wasn't necessary.

 

[Burdekin]

Seeing the price of those just confirms how glad I am to have chosen the VFD route

It's possible to get 10 or more cheapy direct from China 3+kW VFDs for the same money as one of their 1.5kW units...

But, I'm happy to rewire and reconfigure to suit instead of just plug in.

Yep and I'm happy to pay a bit more to keep the machines original, not having to mess about rewiring and not having a VFD for each motor. A converter is simple, plug in and everything works as it should and how it was designed.

 

[Coupster]

Seeing the price of those just confirms how glad I am to have chosen the VFD route

It's possible to get 10 or more cheapy direct from China 3+kW VFDs for the same money as one of their 1.5kW units...

But, I'm happy to rewire and reconfigure to suit instead of just plug in.

Yep and I'm happy to pay a bit more to keep the machines original, not having to mess about rewiring and not having a VFD for each motor. A converter is simple, plug in and everything works as it should and how it was designed.

Thanks chaps, gives me some food for thought.

 

[WorkshopChris]

Something important to consider you said woodworking machines, many bigger machines will have brakes fitted to conform with the requirements for woodworking machines, as blades and cutter blocks need decelerate and come to a stop in under 10 seconds.
Some will be mechanical occasionally built into the motor some will brake units incorporated in the control gear to inject dc back into the wingdings to slow the spindle.
Obviously this will have a effect on any conversions you need to make most vfd's have brake features but will normally need external resistors needed to cope with the demands of braking a shaft with plenty of momentum.
Phase converters normally cope with brakes OK providing you avoid the artificial phase.

 

[chris y]

From the type of rotary converter I described the 3~ is as good as from the elco, just lower powered. The frequency will (effectively) match what you put in. It'll also be perfectly balanced (unless you put an unbalanced load on).

The type you have I would best describe as a hybrid - it's a bit better than a static converter...

I hadnt heard of doing it the way you describe before but it makes sense that it would be better quality 3 phase as you explained.

Is it practical to get a single phase motor big enough to run a 3 phase motor as a generator to in turn run say a 3hp motor on a big lathe without clutch?
I have no idea at all of how much bigger the single phase motor would need to be to cover efficiency losses through the system and start a motor under load.