Re: Table Saw motor upgrade

On Thu, 28 Aug 2008 01:21:11 -0400, blueman <NOSPAM@xxxxxxxxxx> wrote:

3. How big is the power "boost" when taking a given motor and rewiring
for 220v? Will the difference be significantly better than just
using 12 gauge vs 14 gauge cords?

i.e., will the difference be big enough to make the rewiring
worthwhile?

There is no power boost to the motor from the rewiring. Actually, the
coils inside the motor see exactly the same voltage in either case.
The coils in a dual-voltage motor are connected in parallel for the
low voltage case and in series for the high voltage configuration. The
voltage drop across each set of coils is the same in either case.

The only "improvement" from rewiring a dual voltage motor for high
voltage comes from a reduction in the amperage flowing through the
wiring that feeds the motor. The amount of transmission loss (voltage
drop and power loss) is a direct relationship with the amperage.
Double the amperage and you double the voltage drop in the wiring from
the transformer to the wall socket. Since the power dissipated in the
transmission lines is a function of amperage squared, doubling the
amperage increases the lost power by a factor of 4. Likewise halving
the amperage reduces the power loss to 1/4. However, this is only
significant if the power loss at low voltage is significant. In the
majority of installations, it is not.

In a few cases, transmission losses can be significant enough that
going to a high voltage configuration will show a noticeable
improvement in the motor performance. This can be seen most frequently
when the motor is at the end of a high resistance wiring path; either
very long wire runs or light gauge extension cords. It is most likely
to be apparent in the motor startup. Since the amperage draw is much
higher during startup cutting the loss in half can significantly
affect the power available to the motor during the startup.

With that said, a direct answer to your question about whether it's
worth it or not, is a big "maybe, but not likely". If you run the
motor off of a long, light gauge extension cord, then you'll probably
see a significant improvement. If your wiring is near code limits for
voltage drop, then you may see noticeable improvement. In all other
cases, it will be difficult to detect any difference in the motor
operation.

Tom Veatch
Wichita, KS
USA
.

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