Model Forum / General / Models / December 2006

right or wrong I use  an inverter on my mill to run machine and pump but I
change speeds with the belt not the inverter

Andrew

Mike,

A rapid summary - apologies if you already know this.

Inverters are generally designed for 230V single/three phase input or
415V three phase input, both generate 3 phase output (at variable
frequency) but they don't usually provide a voltage increase (in other
words 230V in results in 230V out).
Modern European 3 phase motors can usually be wired in star
configuration for 415V operation or delta for 230V operation; older 3
phase motors are commonly configured internally for 415V. If you want to
use an older 415 star connected motor with a 230V 3 phase inverter you
need to dismantle it to find the star point and reconnect the windings
in delta - possible, but fiddly and not for the faint hearted.

If you run from a 415V static converter (eg Transwave) the lathe motor
is used to "generate" a third phase; it's essential that this is running
before the suds pump is switched on (otherwise the suds pump may be
damaged) and you need to make sure that any controls (contactors,
transformers, etc) are not connected to the artificial phase. Because
the converter contains a 230-415 transformer you don't need to change
motors from star to delta.
If you use a rotary converter (effectively a static with it's own "pilot
motor") there is no need to observe these precautions.

You can run from a 415V 3phase inverter by providing a 240-415
transformer on it's input but there's a slight loss of inverter output
transient capability because of the single phase input. I'm currently
doing this with a Holbrook lathe and it works very well.

If you run from a 230V 3 phase inverter you need to wire the motors in
delta and connect them directly to the inverter output. Remember also
that in a 3 phase lathe there will be at least one 3 phase 415V
contactor, and probably a single phase 415 transformer to provide power
for the LV light; these will require rewiring/replacing. When I did this
on a Boxford (and a Chipmaster) I just used the inverter to drive the
lathe motor and had a separate single phase feed to the controls and the
suds pump (with a phase shift capacitor). Lots of fiddling about but it
worked well.

I really am sorry if all I've done is told you things that you already
know. The bottom line is that you CAN use an inverter to drive both
motors (providing they are both wired star/delta as appropriate for the
voltage) but if you use the variable frequency capability of the
inverter your suds pump will change it's speed (you may not want that).

Dave