1ph vs 3ph

[deema]

To answer your initial question, a 3 phase motor is usually more efficient and better balanced than a single phase motor. Will you notice the difference, the answer is highly unlikely. If you run the saw for long periods every day, them 3 phase is the way to go. If your not running it for long periods, then looking at secondhand prices I would always choose a single phase machine.

 

[sploo]

I can't remember the details but it cost me around £1,400 about 10 years ago it did the job ok but wasn't as powerful as mains 3 phase and the continuous humming noise did my head in. I only kept it around 10 months. Modern ones may be a lot better I wouldn't like to say but I will never regret getting 3 phase installed

Interesting. I know there are a variety of ways to produce three phase (e.g. rotary converters). The modern (£80-£120) HuanYang VFDs seem good; though I don't push them at trade levels of duty cycle. The fan in them is a bit noisy though.

I had a much older (and quite robust) unit (possibly British made) about 10 years ago (only 1/3hp if I recall correctly); which was silent. However it did cause some interference on the mains; such that my neighbour's lights went a bit funny when I used it!

 

[Spectric]

Don't confuse a true three phase supply with any method that creates three phase from a single phase supply. If you had a three phase domestic supply you would have 100 amps available per phase, you could run something like a 37Kw motor pulling about 60 amps.

The VSD approach requires the motor to be dual voltage as it can only output 230Vac three phase, this is not an engineering limation because they could be designed to output 400Vac but is down to EMC regulations imposed by the DNO's. They convert Ac to Dc then back to a simulated Ac output so are classed as a non linear load and can only supply a single load so you would need one for each machine. You do get a variable frequency output but do you really need it.

The digital phase convertor approach allows you to run 400Vac motors and as many machines as you want providing the convertor can meet the power requirements, but you do not get a variable frequency output. These devices use the existing single phase supply and just create the 3rd phase, and are classed as a linear load.

 

[sploo]

Don't confuse a true three phase supply with any method that creates three phase from a single phase supply. If you had a three phase domestic supply you would have 100 amps available per phase, you could run something like a 37Kw motor pulling about 60 amps.

The VSD approach requires the motor to be dual voltage as it can only output 230Vac three phase, this is not an engineering limation because they could be designed to output 400Vac but is down to EMC regulations imposed by the DNO's. They convert Ac to Dc then back to a simulated Ac output so are classed as a non linear load and can only supply a single load so you would need one for each machine. You do get a variable frequency output but do you really need it.

The digital phase convertor approach allows you to run 400Vac motors and as many machines as you want providing the convertor can meet the power requirements, but you do not get a variable frequency output. These devices use the existing single phase supply and just create the 3rd phase, and are classed as a linear load.

Agreed on all the above; but I would note that us home gamers don't have many 37Kw motors down the back of the sofa

I personally find the variable frequency output of the VFDs really useful; one is for a slow (1 to 3s) ramp up of machinery (to reduce the inrush current). The second is rather more fundamental: a spindle for a CNC machine (which obviously needs to be able to run at different rpms for different jobs).

The only limitation (without spending big money) is the lack of 400Vac; though maybe I've been lucky as I've yet to acquire a 3 phase machine that didn't have dual voltage capability. I would admit to once narrowly missing out on an old planer thicknesser that had separate motors for the cutter and feed - so obviously that would have been a problem (in that it wouldn't have run from a single VFD).