HOME and how to join Forum Open Area General Scott topics New Year present Re: Re: New Year present


If you only have a single phase 230v domestic supply but like me, find that there is far more choice of 3 phase machinery out there, do bear the following in mind.
With 3 phase motor drives, inverters and phase converters, the key point when buying a machine is to establish whether the motor is wound for single or dual or voltage.

It is only a dual voltage motor – ie one that is wound to work from either a 230v OR 400v supply (by connecting in either star or delta mode) that can be made to run from an inverter on a 230v domestic supply.
An inverter will not transform the input voltage from 230 to 400v. Whatever voltage you put in, is what you get out so you need to buy a unit suited to one – or the other.

I have a late 3-phase Colchester Bantam 2000 and its original motor is wound only for 380/420v.
This precluded the use of adopting any inverter solution with only 230v single phase domestic supply available. (in any case, why would one need the speed variation provided by an inverter when the machine has a fully geared headstock? It’s a great solution if your lathe only has a 3-step pulley for speed variation, but otherwise ….?)

Be guarded with inverters. A great solution for machine builders but they do demand a high inrush current when powering up and have an inherent earth leakage of about 7mA.
(with 4 inverters in a machine drive system you are pretty much at the limit of what a standard 30mA domestic ring main RCD will tolerate)

Also remember that motor starting current can be 6x running current so cable sizing is important to get right if you don’t want the house lights dimming every time you start.
Also, the use of a D type motor-rated breaker is important too. (the normal B type domestic breaker will not tolerate the starting current)

If the lathe starts the motor from standstill each time you start the spindle drive, this starting current will be pulled every time you start the machine. By comparison, the Colchester Triumph motor, once started, remains running, with the spindle drive being stop/started by clutch – a much preferable solution – albeit a much bigger lathe. (bigger motors do have limits on the number of start/stops per hour due to resultant heat build up generated by the starting current)

If you have a machine with multiple motors (my mill has 4 motors) the inverter solution gets pretty expensive – and you run that risk with earth leakage problems.

I read with interest the comments about phase converters and it is true that in its basic form, this technology is a bit crude and not very user-friendly in some products. However there are modern digital phase converters in the market that auto-match to motor running conditions and minimise current draw on start-up. I use one as part of a 3 phase ring in my workshop to power two separate machines, one with multiple motors.

Also bear in mind that a 230v 13a domestic supply will provide you with 3kW max – about 4HP.

Good luck and read widely!
BTW, some really valuable comments in this thread re tooling etc