Single phase and 3phase???

[r896neo]

I am looking for a few woodworking tools and am considering trying to get 2nd hand cast iron stuff but much of it is commecial rated.

what do i need to be aware of when looking? Will any single phase machine work on a domestic supply? I am typically looking at stuff powered by induction motors up to 3HP.

Also I realize some sort of invertor/ convertor would transform a 3phase industrial machine to domestic use but what sort of money are these? Or is that a bad idea?

cheers

 

[Paul Barker]

You have to be careful what type of 3 phase motor it is if it is a PAM type
winding, one set of three windings,six tails and two speeds, you are in trouble. Many people fail to drive these motors with an "inverter".

Apart from that Inverters cost £700 upwards.

Or buy a transformer for £150 plus vat ish add a start switch a start cap and a run cap and maybe a slave motor or use your biggest machine as a slave.

 

[r896neo]

thanks for the reply paul would any single phase motor run on domestic supply?

 

[electronicsuk]

thanks for the reply paul would any single phase motor run on domestic supply?

If the supply is large enough then yes.

 

[Paul Barker]

Yes exactly, there aisn't much machinery you could fit into a dopmestic enbvironment that requires more than a domestic shower supply. Just don't use the shower at the same time.

3 phase motors run better than single phase as the pulses of motion are 120 degrees apart rather than 180 degrees.

As long as the motor you wish to drive is single speed (and not one of the tricky ones I mentioned first) you would get a more smooth running tool able to take a bigger cut than if you changed to a single phase motor.

You can get quite sofisticated these days using relays you can sense voltage drop on the capacitance formed phase and drop in some extra capacitance. Say when you take a sudden deep cut, voltage sags. You sense voltage with a voltage devider, if it drops below a certain voltage the primary coil in a relay drops out, causeing the relay to switch in a cap. When voltage is restored the relay coil is activated once more and switches the extra cap back out.

 

[r896neo]

thanks paul as you may imagine after the level of my question im not quite ready to get into the physics of it, i'm just getting a brief understanding in order to maybe buy some stuff at auction etc.

Cheers

 

[Hysteresis]

Yes exactly, there aisn't much
3 phase motors run better than single phase as the pulses of motion are 120 degrees apart rather than 180 degrees.

Puses of Motion??????
Have you not studied Rotating Field Theory.
Pulses of motion is a new one on me.

 

[Paul Barker]

Sorry if my understanding is wrong are you interested in explaining the physics?

 

[Hysteresis]

Hi Paul,
I could explain the theory of Rotating Fields as applicable to 3 Phase Electrical Machines and the extension to the specific case of single phase machines as I studied, and later lectured, Electrical Machine Theory at degree level. The theory is not difficult to understand but in order to describe it, it would take a few diagrams which develop the theory. To do it in words alone becomes rather cumbersome and tedious and I feel this is not the place to do it as it is a forum rather than a teaching medium.
I have described the theory to Electricians and indeed Chartered Electrical Engineers and they all were wiser and more comfortable with Induction Motors afterwards. If I had your e-address I could do it external to this forum as I feel the contributors to this forum would not be particularly interested.
You will note my DIY identification is Hysteresis, this is derived from the Magnetic theory relating to the magnetisation properties of the Iron Core.

 

[ricicle]

You will note my DIY identification is Hysteresis, this is derived from the Magnetic theory relating to the magnetisation properties of the Iron Core.

Are you 'loopy' then?......

 

[Paul Barker]

Hi Hysterisis, really it comes down to the question is the three phase motor superior to the single phase motor?

My email address is in my profile.

Thanks.

 

[plugwash]

Yes way superior, three phase into a motor means that the power transfer is constant (or at least very nearly so, there will probablly be some marginal asymetry in the motors coils).

Also single phase motors need some tricks to start which either add cost (in the case of a start capacitor) or reduce efficiancy (in the case of shaded poles).

 

[ricicle]

And you need smaller conductors (albeit 3 instead of 2) for an identically rated 3 phase motor (less current)

 

[Stoday]

3 phase motors run better than single phase as the pulses of motion are 120 degrees apart rather than 180 degrees.

Don't you mean 60 degrees rather than 90 degrees? You get power out of each half cycle.

 

[securespark]

a more smooth running tool

Matron!