[D.Kreft]

On Feb 26, 3:37 pm, (Captain Howdy) wrote:

Have you not ever hooked up a dual votage electic motor, if you ever come
across one see the amp specs at 110v and at 220v, Whoever told ya that this
only works when transforming or inverting was just trying to mess with your
mind.

I'm not an electric motor expert, but I do hold a degree in Electrical
Engineering (I suppose that one could argue that my EE profs were all
out to mess with my mind). Granted, I'm not an EE by profession, but I
do have enough edukashun and real-world experience with electronics to
have something of a clue as to how these things work.

From what I understand about dual-voltage electric motors, they
achieve their dual-voltage capability via alternate wirings in the
motor itself or via an internal transformer (such as would be found in
a computer power supply or home electronics box) which is used to
convert the to the desired level. Some devices, like laptop computer
power converters do this voltage sensing automagically so that you
don't have to flip as switch as you would on a typical desktop
computer power supply or home audio receiver.

So even here, you're still talking about using a transformer to handle
the voltage conversion. The reason that a doubling of input voltage
results in a halving of input current is simple--because assuming
negligible losses in in the transformer itself the law of the
conservation of energy (from the first law of thermodynamics) applies:

Pin = Pout

Substituting VI (voltage * current) for each side:

Vin * Iin = Vout * Iout

Then divide both sides by Vin:

Vout * Iout
Iin = -------------
Vin

So yeah, doubling Vin leads to a halving of Iin. There's nothing new
here.

Ultimately, though, we're still dealing with DC inputs so this
comparison to dual-voltage AC motors, while entertaining, isn't
entirely relevant and does more to support my point than detract from
it.

-dan