Re: [CAD_CAM_EDM_DRO] Bridgeport motor question

rivet3man wrote:

>I'm preparing a series1 (BOSS) Bridgeport to fit PC-based controls.
>The main spindle motor is a US motors 2hp, & though the rating plate
>gives a connection diagrams (9 wire) for 220 and 415 volts there are
>actually just the 3 wires coming from the coils and I believe it was
>set for high voltage. I want to run it from 240Volts via an invertor.
>I'm going to see if I can unearth the actual winding terminations,
>but
>if I get too far out of my depth it'll be off to the rewind shop on
>Monday for them to do it.
>My question is, as understand it the US style 9-wire dual voltage
>motor is star connected for both voltages. More usual here in the UK
>is 6 wire, with star connection for high volts & delta for low. If it
>looks easier to reconnect this motor for delta than to unearth all
>the
>terminations to parallel the windings, will that be just as good?
>
>

The standard dual-voltage 9-wire motor doesn't bring out the center
of the wye of the "inner" winding set, so you don't have access to all
the terminals to make it a delta winding. If you can find the place these
wires are tied together deep in the stator and bring them all out, then
you coul do that. But, switching the motor from wye to delta changes
the voltage of the motor yet again. Assuming a plain, single-voltage
wye motor is set up for 208 V L-L, it will need 120 V L-L to run
in the Wye connection. A 415 V wye motor would then run nicely
on 240 V L-L, if you have access to the terminals.

Without unearthing and splitting that center tie, you cannot reconnect
the motor as a delta connection.

The trick with the European motors is that the common supply voltages
are not a 2:1 ratio, but a square root of 3 ratio. In the US, there is
a muddle of voltages available, and 208/230 are close enough that one
winding setup can handle the whole range. In the US, 415 is almost
unheard of. 208 V is used mostly in office buildings so 120 V power
for lights, office equipment, etc. can be derived from the same transformer
as the 208 3-phase power. There would be no purpose in having 415
V power, and so the high-voltage supply is almost always 460 to 480 V,
and often is pure delta, with no connection to neutral permitted.
(On the other hand, a lot of industrial lighting runs off 277V, using
the line-neutral connection from a 480 V Wye transformer.)
Jon