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wrote:
In article .com,
wrote:
Rewire the motor for 220 volts, but leave it connected to 110.

I have a used table saw with a 1hp motor I have run for several years.
All OK, but seemed a little underpowered. Come to find out the motor
was set for 220 volts but I was running it on 110.

Low voltage (brown-out) doesn't hurt a motor unless the motor is
heavily loaded. Then it draws excessive current to try and make up for
the low voltage. At half the rated voltage, the motor will stall
before it can hurt itself. If it were left stalled, it may get hot,
but since you wouldn't leave it that way, no harm done.

DO NOT DO THIS, unless you can carefully monitor the temperature of
the motor, and preferably the current going into the motor (you have
to monitor the current, because you can't monitor the temperature of
the motor windings, and those can get hot very quickly, before the
outside of the motor becomes dangerously high). Or unless you have a
supply of free replacement motors, and enjoy exchanging them.

A fixed-frequency motor is a constant power device: It will take more
current if the voltage is not sufficient, to create the power that is
needed by the attached equipment; it can't reduce its speed (other
than stall). So under moderate load, the motor will run at 2x the
current, meaning that the motor self-heating will be 4x larger than
usual. Unless you are super-careful, this can very very easily burn
up the windings, even if you power the motor down when it stalls.

A better idea is actually the following: The original poster said that
his garage is 90 feet from the house, and the power panel is at the
house, and he has only a 20A line connecting them. I suppose that the
20A line is 12-gauge, sufficient for 20A. At the house, install a
220V circuit, and connect the line to the garage to 220V. At the
garage, split the wiring up into 110V outlet/lighting circuits
(preferably two separate circuits), and a 220V circuit for the power
tools. Install a transformer that takes the 220V coming into the
garage, and splits it back up into two 110V circuits. This will not
be a small or dirt-cheap transformer, and there are difficult issues
with grounding, so this installation should be left to a professional.
This gives you two 20A 110V circuits (for example one each for lights
and for outlets), in addition to a 20A 220V circuit for larger power
tools - except that the total load is limited.

There is another idea, but I'm worried about bringing it up, as it can
be extremely dangerous if implemented wrong, and I fear it could never
be code compliant. If the original poster is lucky, the 20A line that
goes from the house to the garage has 3 wires in it: hot (black),
neutral (white), and ground (bare copper), all in an outer plastic
shield (like NM or UF wire). By using generous amounts of electrical
tape, one could relabel those wires to be two hot wires (black and
red, using the former black and white wire), and one neutral wire
(using the former bare copper ground wire). Now we have one 20A 220V,
or an Edison-circuit with two 20A 110V circuits with a shared neutral,
going to the garage. This circuit could then be used to feed a small
breaker panel in the garage, where it could be split up for example
into one 220V 20A circuit, and two 110V 20A circuits. In a nutshell
this is the same proposal as installing a new subpanel in the garage
and feeding it with a substantial line (for example 60A), except for
using a smallish line on a piece of cable that is not intended for
this usage. Small problem: The garage has no ground any more. This
can be cured by creating a "made ground", meaning a few ground rounds,
or (if available) a ufer in the foundation. Big problem: this is
completely in violation of the code; using the bare green wire for
neutral is code violating, and actually dangerous: the outer jacket of
the cable is not intended as an insulator, and if anyone who doesn't
know about this wire ever modifies the system in the future, death
becomes very likely.

Bottom line: I would just try running the tool on the 110V 20A
circuit; most likely it will work most of the time. And install a
battery-powered emergency light that comes on automatically if the
power fails (they are about $35 at the box stores); like this if the
jointer pops the breaker, the place doesn't go completely dark. And
don't forget to turn the tool off before resetting the breaker -
otherwise it will start up unattended when you turn power back on. A
magnetic starter might be a good investment here.

--
The address in the header is invalid for obvious reasons. Please
reconstruct the address from the information below (look for _).
Ralph Becker-Szendy

To a large extent what you say is correct. However, if you lower the
voltage enough, the motor could never hurt itself even if stalled since
it is not a PERFECT constant power device. Second, since the breaker
is limiting the current to 20 amps, which would be harder on the motor
- pulling 20 amps at 220 volts or 20 amps at 110 volts? (Acually, close
to the same since most of the heating is due to winding resistance,
thus equal current gives equal heating.)

In the case of the saw I mentioned, when it was wired for 220 volts,
the lights hardly flickered when I started the saw and when nearly
stalled, barely dimmed the lights. Now, wired for 110 volts, the room
nearly goes dark when the saw is started and I never get close to
stalling the motor under reasonably heavy load. This indicates to me
that when wired for 220 volts and run on a 110 volt circuit, the motor
CAN'T draw rated current, so can't hurt itself. After slogging through
some long, heary rips, the motor wasn't more than warm to the touch
when wired for 220.

However, if the OP can keep from blowing breakers, leave it at 110. If
not, try the 220/110 approach and see if the power is adequate.

If it is just a matter of starting current, one could rig up a series
resistance of some sort, like a 1500 watt heater, that was only in for
starting and then a switch bypassed it once the motor was up to speed.
A bit of a nusance, though.