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MORE Power!!! 120 vs 240 volts

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Forum topic by MRod posted 05-14-2008 09:41 PM 17449 views 0 times favorited 81 replies Add to Favorites Watch
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MRod

74 posts in 2715 days


05-14-2008 09:41 PM

Hi,

Question to you fine people:

If I change my current 120v 1 1/2 hp Table Saw to 240v (the Rigid tablesaw I have should be able to do both) will I get more power behind the cuts or does it not make a difference?

Thanks,
MRod

-- MRod, Henderson, Colorado by way of Brooklyn!


81 replies so far

View Bob #2's profile

Bob #2

3808 posts in 2673 days


#1 posted 05-14-2008 10:36 PM

Let me be the first to tell you that the power output will be the same.
Depending on the type of motor you may squeeze out a bit more on the 220 volt hookup.
It will be insignificant though.

Bob

-- A mind, like a home, is furnished by its owner

View RusticElements's profile

RusticElements

167 posts in 2377 days


#2 posted 05-14-2008 10:50 PM

Depends of the horse power rating of the motor. As a general rule, 240V motors are built to put out more power than 120V motors, but not always. Check the HP rating on both motors. It will either be on a metal plate fastened to the motor (the usual method) or stamped directly on the motor.

-- Michael R. Harvey - Brewster, NY - RusticElementArt.com - SpaceAware.org - AnConn.com

View che's profile

che

123 posts in 2678 days


#3 posted 05-14-2008 11:36 PM

No, changing a dual voltage motor to 240 won’t get you any more power.

There are some finer points to consider but if your a hobbyist woodworker (the saw is off more than it’s on) there will be little to nothing to gain by switching. However, If the saw runs for hours on end the higher voltage and lower current will keep the wires cooler and will reduce the voltage drop in the wiring which will get you a little more power at the motor.

-- Che.

View Catspaw's profile

Catspaw

236 posts in 2467 days


#4 posted 05-14-2008 11:50 PM

I think the benefit to going 240V is it is more efficient. You may not get more HP but you will use less electricity for the horsepower is has.

-- arborial reconfiguration specialist

View Bob #2's profile

Bob #2

3808 posts in 2673 days


#5 posted 05-15-2008 12:16 AM

Catspaw, I respectfully disagree with you.
As far as I know the charge for electricity is for Watts and that’s volts times amps.
It should be nearly the same regardless of the input voltage choice.

Regards
Bob

-- A mind, like a home, is furnished by its owner

View Al Killian's profile

Al Killian

273 posts in 2405 days


#6 posted 05-15-2008 12:49 AM

The only difference is if the motor is over 2 H.P. , then it will start much easeir and have alot less strain the motor. Smaller ones will not notice much difference.

-- Owner of custom millwork shop

View marcb's profile

marcb

762 posts in 2325 days


#7 posted 05-15-2008 12:54 AM

Bob,

Its more efficient in terms of voltage drop (you cut that in half), which can be significant in some places making 240 a much better alternative.

View Bob #2's profile

Bob #2

3808 posts in 2673 days


#8 posted 05-15-2008 01:42 AM

Marchb:
Explain that to me.
I really don’t understand?
Could you show me with arithmetic?

Bob

-- A mind, like a home, is furnished by its owner

View marcb's profile

marcb

762 posts in 2325 days


#9 posted 05-15-2008 02:55 AM

I’m afraid that I can’t remember the exact calculations to use. However I found this calculator on the internet.

http://www.rhtubs.com/voltage-drop_conduit-fill.htm

Running 120V over 100 feet of 14AWG at 15Amp gives you a voltage drop of 9.1 Volts, where as running 240 over the same wire gives you a drop of 4.6volts. If you have thin wires or long runs your motor can act a little wonky, so its better to run 240 in those cases.

View bayspt's profile

bayspt

292 posts in 2356 days


#10 posted 05-15-2008 03:08 AM

Che has it right. Higher voltage means lower current but it shouldn’t really make any differance at all. And technically if your wire is the correct size that shouldn’t make any differance either.

-- Jimmy, Oklahoma "It's a dog-eat-dog world, and I'm wearing milkbone underwear!"

View Bill Davis's profile

Bill Davis

226 posts in 2576 days


#11 posted 05-15-2008 03:51 AM

It will be some benefit though how much depends on the resistance in the wiring circuit. It will make the most difference if your wiring is undersized because since the 220 v motor draws half the current there will be only 1/4 the power loss in the wiring. Power loss in the wire is I^2 x R so if the current is halved the power loss is reduced by a factor of 4.

Let’s say the total resistance feeding power to the motor is 2 Ohms and the motor draws 10 Amps at 120 V and 5 Amps at 240 V. At 120 volts the power loss is I^2 x R or 10^2×2=200 watts lost in the wiring. At 240 volts 5 ^2×2 = 50 watts lost in the wiring. That is 1/4 the power loss. Now my numbers are made up and the resistance is way higher than you should experience in real life. It does illustrate however that there may be an advantage in using 240 volt wiring. Marchb said you cut it in half but in fact you cut in by 1/4th. Because you cut the power loss in the wiring that much it may actually therefore provide more power to the motor especially at motor starting where the starting current of a motor might be 10 times the running current. The I ^ 2 factor is significantly more important at the higher current draw at statrup.

View Bill Davis's profile

Bill Davis

226 posts in 2576 days


#12 posted 05-15-2008 03:53 AM

P.S. this question is like Adrondack chairs – It just keeps reappearing.

View Catspaw's profile

Catspaw

236 posts in 2467 days


#13 posted 05-15-2008 06:04 AM

Bob #2…see Bill Davis above.

240 motors start alittle quicker ‘cause they’re hit with 240 at start up. A motor will draw alot of current until it gets up to speed and starts generating counter emf. The quicker the start, the less current used for start-up. Also less voltage drop because the amperage is halved so less watts lost in the wiring. Although as Bill pointed out if the wiring is sized correctly, this drop is usually minimal.

These factors are what I consider “more efficient”. chances are you’d never notice a difference in your electric bill though.

I’ve heard that 240 saves on your motor life through less heat. But, I think that isn’t true because watts are watts. With 120, coils are wired in parallel, with 240 they’re in series. 120V/10A = 5A through each coil or 240V/5A, still through each coil.

What happens if you wire an adirondack chair for 240V?

-- arborial reconfiguration specialist

View marcb's profile

marcb

762 posts in 2325 days


#14 posted 05-15-2008 07:02 AM

Catspaw,

Its the voltage drop voltage that causes heat not whats running across it. Its been a long time since I read about electronics, but the voltage drop is how you size what wattage resitor to use.

View Catspaw's profile

Catspaw

236 posts in 2467 days


#15 posted 05-16-2008 12:15 AM

Marcb, it’s a combination of all things, V,I, and R and depends on what’s happening at any given time. Not quite sure what your resistor reference is though.

I would find this whole discussion quite fascinating (I have a degree in electronics), but, I’m guessing most woodworkers probably just want to know if it’ll sav’em money or giv’em mo’ power…..ooo OOO ooo oooo…(primal monkey noises.) We won’t have electricity soon anyway and we’ll all be using hand saws.

-- arborial reconfiguration specialist

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