For a first order approximation, under 'steady-state' conditions, you
_are_ basically correct. Needless to say, considering only 'steady-state'
conditions is not really meaningful for analysing a table-saw. :)
The differences occur due to a variety of 'lesser' factors, including:
1) parasitic losses that are not directly related to applied voltage,
2) "stiffness" of the power _source_.
3) speed of response to varying load conditions -- when a motor is trying
to play 'catch up' to an increased load, it draws more power than it
does handling that same load at steady-state. The longer it takes to
get back to steady-state, the more 'excess' power consumed.
4) 'non-resistive' (e.g. 'capacitive', and/or 'inductive') components of
the load. (capacitance, inductance, and resistance react in _different_
ways, in parallel vs series circuits -- different from _each_other_, I
mean. e.g. in series, resistance 'adds', but capacitance 'divides')
5) 'power factor' -- pretty much equivalent to #3
More commonly, it is the other way around, a device is slightly _more_
efficient at the higher voltage. On a _good_ day, it may approach 2%. :)
However, there are no 'guarantees'. It depends, _entirely_, on the design of
the specific device.
Consume more power? The first guy to respond to the question was spot
on. Has everybody who attemps to reply actually run a bunch of tool on
both 120 and 240? Same tools? Tried both ways? If you use a gawdawful
heavy cord direct from the service panel, maybe you couldn't tell the
diffence. In the real world, with similar gauge wiring, you'll find the
saw will start quicker and bog less. Since it bogs less, it runs
You're supposed to size the wire for the current and the length of the run
so that the voltage drop at max load is allowable. If you do that then saw
should not be "bogging" due to voltage drop in the wiring under heavy load.
Reply to jclarke at ae tee tee global dot net
Correct. As I mentioned in a different post, in an ideal world, every
application of a power tool would have copper coming to it of such size
that the maximum load of the tool wouldn't produce a discernible voltage
drop. This would include the cord provided by the manufacturer of the
tool. In the real world, I've been happier with tools running on 220.
I've spend a lot of time with most of them both ways. You pay's your
money and takes your choice. My advice is, if the tool stays in one
place all the time and 220 is handy, use it. YMMV.
J. Clarke wrote:
More consumption in the 240 volt mode. Makes sense. Doesn't work out
that way. The rotating motor functions as a generator. Its generated
emf opposes the supplied emf. Its ability to counter the supplied
voltage is what limits the net draw. If there's voltage drop in the
line, (which is more pronounced in the 120v mode) then the motor is
less effective as a generator, less effective at opposing the applied
emf and generates more temp rise. Motors run best at full rated
voltage. However you want to supply this, the result is the same. On
120 volt, use the largest gauge wire. For a given gauge, 240v will do a
better job of keeping your motor spun up to the full rated RPM and
therefore do the best job of generating counter emf.
The actual motor wire carries the same current on either voltage. You are
changing from parallel to series connection of the windings.
The drop mentioned is in the feed wire. If it were very large wire, the saw
wouldn't know the difference, but when more current is drawn and the saw
starts to bog down, then the current goes up even more and things snowball.
By keeping the voltage up by drawing less current on 220 and having less
sag, you allow the motor to do its thing and produce rated power at rated
At lower voltage (sag) and higher current, heating rises in the motor
because of IR drop in the windings. This is true at either voltage, but
starts at higher loads because of less drop in the feed.
Every answer you get will be academic. The failed capacitor has nothing to
do with what voltage you run. The best reason to run 220 is to be able run
more tools on the feed without having to increase the feeder wire size.
On Sun, 13 Jun 2004 00:36:05 GMT, Brandt in western Canada
I have a 1 HP-110V Crapsman TS, whenever I saw hardwood lumbers the circuit
breaker trips. I also encountered the tripping problems with my 1-1/2HP-110V
compressor whenever the compressor loading. I rewired both machines to 220V and
the problems gone forever.
I learn these tips from helpful posters here. By rewiring it to 220V you really
have nothing to lose.
As I understand it, your single pole (120v) 20 amp breaker trips under
a heavy load, more than 2400watts. By rewiring to 220 (or 240) volt,
you install a 2-pole breaker, probably 20amps PER leg. That kinda
makes you supply equivalent to 40 amps (~4800 watts) . Supplying the
saw with as much as double the current, certianly would make the
breaker trip less.
loadOn Sun, 13 Jun 2004 11:49:07 -0600, in rec.woodworking you wrote:
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