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Old 07-03-2009, 02:54 PM   #31
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Do you think a tool running at 240v works better than at 120v?


After considerable review, I have concluded that WFO is exactly correct, and I am completely incorrect about current loss in a dual voltage tool. As WFO explains, virtually all dual voltage motors are designed with two coils, which can either be connected in series or in parallel. As such, WFO is exactly correct, in that the current in each coil is identical regardless of whether the tool is operating at 120 volt (low voltage) or 240 volts (high voltage). My mistake was in assuming that tools were built with a single winding that could be operated at dual voltages, which is apparently not the case for conventional 120/240 tools.

I am curious, however, if there are any tools built to run on variable voltage with a single winding. It would appear that this would offer the opportunity to control the speed of the tool, i.e. with a variable speed router or drill. If that is a technique for controlling speed, it would seem as though those type of tools would have lower copper losses at high voltage (full speed) than at low voltage (low speed). Anyone have any ideas on this?

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Old 07-03-2009, 03:38 PM   #32
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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
While the resistance of the motor is changed by a factor of 4
R=E/I 120/13= 9.23 ohms 240/6.5= 36.92
The copper loss or IIR is the same
IIR 13 X13 X 9.23=1559.87 6.5 X 6.5 X 36.92 = 1559.87
The wattage of the motor is the same so the same amount of heat is created and the same amount of work is produced.

14 ga wire has a resistance of 2.525 per 1000 feet and 12 ga wire has a resistance of 1.588 per 1000 feet the difference in resistance will equalize the cable loss for the 2 voltages. So there is virtually no difference in operation. A 1/2 HP motor produces 1/2 Hp on either 120 v or 240 volt.
All I can add is this: My Delta tablesaw motor is placarded to read: 1 1/2 hp at 110V and 2 hp at 220V. It runs better than twice as good on 220, spins up way faster, doesnt even come close to bogging down like it does on 110V. I never bothered to ask it why it does this I just really appreciate it
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Old 07-03-2009, 05:15 PM   #33
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Do you think a tool running at 240v works better than at 120v?


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Originally Posted by skymaster View Post
All I can add is this: My Delta tablesaw motor is placarded to read: 1 1/2 hp at 110V and 2 hp at 220V. It runs better than twice as good on 220, spins up way faster, doesnt even come close to bogging down like it does on 110V. I never bothered to ask it why it does this I just really appreciate it
This brings up something else.
Depending on the windings I guess the torque-speed curve of the motor can be changed depending on the applied voltage and so can be better tailored to the task at hand. So it's not just hp, VxI, that determines operator satisfaction.

Now, can we render a verdict?
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Old 07-03-2009, 06:40 PM   #34
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Do you think a tool running at 240v works better than at 120v?


As stated above, a dual-voltage motor is simply two motors (so to speak) contained in the same frame. Lower voltage = higher current, higher voltage = lower current. Watts and HP is the same at either voltage.

Suppose we had a 2 HP dual-voltage motor that was driving a fan or centrifugal pump. East to start, and no chance of overload. During operation, I doubt if you could measure any difference between 115 volts and 230 volts. Input watts, shaft RPM, efficiency, winding temperature, etc. would all be very close.

If the same motor was used to power a table saw, it'd be a different story. A table saw, by its nature, is frequently overloaded. Sometimes to the point of stalling.

A typical induction motor has a breakdown torque rating of about 250% of full-load torque. Breakdown torque is the maximum the motor can produce before a rapid reduction in speed. Anyone who has ever ripped 2Xs on a table saw knows right where this occurs!

This 250% of full-load torque is accompanied by about 300% of full-load current. This is where the difference is noticeable. Our 2 HP motor, that is now producing around 5 HP, is drawing about 35 amps on 230 volts, or about 70 amps at 115. Reduced shaft torque (also known as HP) is more a function of percentage of voltage reduction that anything else. Therefore, at the lower voltage we're causing a greater number of volts lost (because of the higher current), and an even greater percentage of loss (because of basic math). This holds true on starting as well, not just overload.

Unless the wire is grossly oversized and a short distance from the source, the difference will be noticeable. Longer lengths of normal sized wire will have an even more pronounced effect on starting and overload performance.

If I have some spare time, I'll rig up a torque meter to a dual-voltage motor, and power it with a variac (to maintain an exact voltage at the motor terminals), and read torque vs. current at constant voltage and varying loads. Should be interesting!

Rob
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Old 07-03-2009, 06:58 PM   #35
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Do you think a tool running at 240v works better than at 120v?


OK so is that gooder or knot??????? Once the "test" is completed can you explain the results in English please
I vote YES for 220 for NO other reason than mine works gooder with it ROFLMAO
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Old 07-03-2009, 07:07 PM   #36
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Do you think a tool running at 240v works better than at 120v?


Sorry, I tend to get a bit technical at times. Maybe it's because I thoroughly enjoy winning arguments with electrical engineers!

I suspect the test will reveal about the same performance at either voltage (because it's laboratory conditions), but in real life you'll find better performance, cooler operating temperatures, and longer life at the higher voltage.

Rob
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Old 07-03-2009, 07:12 PM   #37
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Do you think a tool running at 240v works better than at 120v?


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Originally Posted by micromind View Post
Sorry, I tend to get a bit technical at times. Maybe it's because I thoroughly enjoy winning arguments with electrical engineers!

I suspect the test will reveal about the same performance at either voltage (because it's laboratory conditions), but in real life you'll find better performance, cooler operating temperatures, and longer life at the higher voltage.

Rob
You must have one humongous Variac.
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Old 07-03-2009, 07:34 PM   #38
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Do you think a tool running at 240v works better than at 120v?


Now DAT I unnerstand
Happy and SAFE holiday

A BIG THANKS TO OUR TROOPS FOR GIVING US THIS DAY
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Old 07-03-2009, 09:18 PM   #39
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Do you think a tool running at 240v works better than at 120v?


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Originally Posted by Daniel Holzman View Post
....WFO is exactly correct.....
To me, this proves that Daniel has one of the most brilliant minds on this forum.
However, I have shown this to my wife and she is skeptical. Perhaps she remembers the time I took on a bottle of tequila, and bottle of syrup of ipacac, and a toilet bowl lid and went 0 for 3.


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Originally Posted by Yoyizit View Post
You (micromind) must have one humongous Variac.
...now she wants to meet micromind.......
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Old 07-03-2009, 09:50 PM   #40
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Do you think a tool running at 240v works better than at 120v?


OOPS! Maybe I should explain!

A variac is a variable voltage transformer. There's a dial, usually on top, that you can set to a voltage and it'll maintain it. Provided the line voltage is stable. It's about the only way to vary an AC voltage.

I have two. Both are 240 in, max 260 out. The small one is 2 KVA, single phase. The larger one is 9 KVA, 3 phase.

Rob

P.S. Which one ya thing she'd like to see first?!??

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