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Old 06-29-2009, 08:29 PM   #1
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Do you think a tool running at 240v works better than at 120v?


My brother and I had an interesting conversation, I purchased an old DeWalt radial arm saw wired for 240v and on the way home we got into discussing it can be wired/run at 120v as well. The motor says wired at 240v it draws 6.5 amps, if wired for 120v it draws 13 amps. The saw is wired for 240v from the factory.

On the long ride home came the discussion will the motor run better at 240v or 120v? Person A said 13 amps at 120v is the same as 6.5 amps at 240v they're the same and the motor will run the same. Person B said using 240v you have 2 opposite legs with push & pull and the motor runs better, why else does it come wired for 240v from the factory?

What's your thoughts or can you explain how different the motor will run wired either way? Thanks

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Old 06-29-2009, 08:39 PM   #2
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Do you think a tool running at 240v works better than at 120v?


Person A is correct. Having it wired for 240V allows you to use smaller gauge wires.

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Old 06-29-2009, 08:44 PM   #3
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Do you think a tool running at 240v works better than at 120v?


Voltage drop is also less when wired at 240V.
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Old 06-29-2009, 08:51 PM   #4
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Do you think a tool running at 240v works better than at 120v?


It won't make a noticeable difference. It might not make any difference at all. Power out = efficiency x power in.

Correction; I-squared-R loss will be 4x greater at 120v, so the efficiency is better at 240v. This is why cross-country xmission lines run at very high voltages.

Last edited by Yoyizit; 06-29-2009 at 09:28 PM.
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Old 06-29-2009, 08:55 PM   #5
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Do you think a tool running at 240v works better than at 120v?


I don't know with technical certainty, but I don't believe it matters. I think it just gives you a second wiring option for machines that use up a lot of juice and won't fit on a 120v 15 or 20A circuit. So instead of having to wire a 120v 30A circuit, you can do a 240v 15A.
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Old 06-29-2009, 09:11 PM   #6
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Do you think a tool running at 240v works better than at 120v?


Requires 13 amps at 120 volts, so for him a 15 amp circuit would work 14 ga, 20 amp 12 ga, is better. It's about wire size. It's cheaper to run smaller gauge wires than heavier gauge. I will always use the 220 v if given the option. Some tools require it, usually 3 hp or greater and have the thermal safety switch/voltage drop shut down. BUT... 220v breakers cost more and take up more slots in the panel. So, maybe it's a toss up on the cost? bill

Last edited by woodnthings; 06-30-2009 at 07:54 AM.
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Old 06-29-2009, 09:18 PM   #7
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Do you think a tool running at 240v works better than at 120v?


Motor wil perform the same both ways.

13 amps is a good size draw and will require larger supply wiring then the 240 to run properly.

If it is to be used in the field, the 120 option would make more sense but you would need to use at least 12 gauge cord and try to plug into 20 amp circuits to be safe.
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Old 06-29-2009, 10:18 PM   #8
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Do you think a tool running at 240v works better than at 120v?


Quote:
Originally Posted by Yoyizit View Post
It won't make a noticeable difference. It might not make any difference at all. Power out = efficiency x power in.

Correction; I-squared-R loss will be 4x greater at 120v, so the efficiency is better at 240v. This is why cross-country xmission lines run at very high voltages.

The reason that high voltage is used for transmission lines is because the higher the voltage the lower the amperage the smaller the wire needed.
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Old 06-29-2009, 10:30 PM   #9
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Do you think a tool running at 240v works better than at 120v?


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Originally Posted by jerryh3 View Post
Voltage drop is also less when wired at 240V.
Only if the same size wire is used and it would have to be a significant length to make a noticeable difference.
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Old 06-29-2009, 10:49 PM   #10
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Do you think a tool running at 240v works better than at 120v?


Being a guy who owns a table saw that can be wired for 120 or 240, I can say that it definitely works better on 240. It seems to get up to speed faster, and it runs cooler.

Also, I would think that since the current drawn at 240 V is less, there would be less self-inductance in the windings, which may be why it is able to start faster. But that's just speculation on my part.

And by the way, 120 V "pushes and pulls" with a hot and neutral just like 240 V does with two hots. Current flows to AND FROM a neutral just like any hot wire. The idea that the neutral is some kind of dead, limp stand-around is one of the most wide spread misconception about AC.
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Old 06-29-2009, 10:51 PM   #11
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Do you think a tool running at 240v works better than at 120v?


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Originally Posted by hayewe farm View Post
The reason that high voltage is used for transmission lines is because the higher the voltage the lower the amperage the smaller the wire needed.

Riiiiiigggght..... Because of the IČR losses.
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Old 06-29-2009, 11:21 PM   #12
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Do you think a tool running at 240v works better than at 120v?


Cost is the reason, I2R losses can be lessened with bigger wire lowering "R" or higher voltage lowering "I", it can also be lessened by lowering the frequency.
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Old 06-30-2009, 12:41 AM   #13
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Do you think a tool running at 240v works better than at 120v?


In theory it doesn't make any difference. In real life, any dual voltage motor will start quicker, have more power, and run cooler on the higher voltage.

Especially if it's a any distance from the source. Like more than 40'.

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Old 06-30-2009, 04:18 AM   #14
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Do you think a tool running at 240v works better than at 120v?


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Last edited by jerryh3; 06-30-2009 at 04:22 AM.
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Old 06-30-2009, 12:47 PM   #15
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Do you think a tool running at 240v works better than at 120v?


http://en.wikipedia.org/wiki/Push-pull_amplifier

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