Three phase motors

[artie]

Knowing zero about three phase motors except that machines with them appear cheaper on the second hand market.
It would appear that with modern electrics the 3 phase problem is easier to solve.
Now for the daft question I suppose all three phase motors are not the same, Is there a wide variety of power ratings for, say a table saw?

 

[Spectric]

Hi

The easiest option is to buy single phase machines, the next easiest option is to swap out the three phase motor for a single phase motor, then it gets more technical. In my opinion the best choice then is to get a sparky to install a digital convertor, this will provide 400 volt three phase and to more than a single machine depending on the power output of the convertor. The other option is an invertor and this will only provide 230 volt three phase so you need a dual voltage motor and to only a single load, so an invertor for each machine. The absolute ideal solution is to get a three phase supply to the workshop as you get plenty of power and once installed the job is done.

 

[guineafowl21]

To add to the answer above:

It would appear that with modern electrics the 3 phase problem is easier to solve.

Yes, with digital phase converters and variable frequency drives (VFDs or inverter drives). It’s generally cheaper and easier if your machine has a dual voltage motor (230 delta, 400Y or similar on the rating plate).

Is there a wide variety of power ratings for, say a table saw?

Yes, you can get pretty much any power rating you want in 3ph, although they usually are at the higher end.

But 3ph doesn’t necessarily mean high power - all motors should really be three phase; single phase ones are a compromise. 3ph motors are smaller, cheaper, smoother and more reliable.

 

[minilathe22]

It is easy to get confused with the various different voltage ratings on 3 phase motors. As has been said, some can be wired up to be connected to 230 or 440V, and some motors can only be used with one specific voltage. The ones I have seen are 230/440v, 440v only, and 670v. I am sure there are others.

The cost (especially secondhand) for single phase -> 3 phase inverters means that its not too difficult to get a 3 phase device running. Although not as cheap as for a single phase motor of course, hence the often reduced price.

Unless you live next to a power grid transformer, a quote for real 3 phase power is likely to be several thousand pounds, but would allow you to run a range of 3 phase devices, and you would not need to buy another inverter each time. The inverters usually also provide variable speed, which is very useful for some tools like a wood lathe, less useful for tablesaw/bandsaw I would think.

You can also make a fixed speed single phase converter with a big single phase motor with its spindle connected to a 3 phase motor, which makes it a generator of 3 phase.

I have noticed the brand new cost of motors in the 2 - 3HP range, single phase motors are a fair bit more.

 

[Duncan A]

Virtually all modern 3-ph motors are dual voltage so you can run them off 230V 1-ph mains with a suitable inverter.
Don't forget speed - they come in a number of pole configurations, usually 2 or 4 poles, the latter running at half the speed of the former.
Frame size, spindle diameter and length, and mounting arrangements, all need to be considered and should conform to the standard sizes; it is best not to buy the rubbish Chaiwanese motors that are often put on imported machines as they are frequently not standard sizes.

Most of the main motor suppliers have all the info you need on their website and quite a few of the inverter suppliers will sell you motor and inverter packages to make life easier.
Duncan