Wiring a 120/240 motor to 240v, examined in detail. - Page 2 - Woodworking Talk - Woodworkers Forum
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post #21 of 41 Old 08-15-2016, 10:29 PM
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Quote:
Originally Posted by TomCT2 View Post
"..tripped out on thermal overload..."
no surprises there, Steve.

if the saw is just running, doing no "work" i.e. not cutting anything, it draws very little power thru the wires.

as the "work load" increases an electric motor demands more power, i.e. it sucks more amps through the wires. this is why overloaded circuits get hot.....

back to basics:
V(volts) = I (amps) x R (resistance) - Ohms Law
P (power) = V x I

a little substitution shows:
P = I x I x R

so, the amperage demand goes up by the square of the power (R is a constant; the resistance of the windings does not change.)

using 240 volts, the saw only draws half the amps (vs. 120v) - increasing power demands on the saw draw fewer amps at 240 - and it's the amperage that causes overheating.
Sorry, but that dog won't hunt. It's not only the amperage that caues heat, but applied voltage. Any load running on 120 volts at a given amperage, will draw half the amperage at 240 volts, BUT, power is volts times amps, the power is the same, and the heat is the same.

Now, IF the a saw is running on 120 volts on an inadequate circuit, the voltage will drop and the amperage will increase to the point the motor will start to overheat. Which brings us back to the notion that 240 is better than 120 ...... depends.

If you don't believe this, go find a saw running on 120, that works perfectly fine under max load. Now, unplug it, get a 250 foot roll of #12 wire and make a temporary extension cord to plug the saw into. Now run it under max load and see what happens.

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post #22 of 41 Old 08-16-2016, 09:18 AM
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Originally Posted by Alchymist View Post
Sorry, but that dog won't hunt. It's not only the amperage that caues heat, but applied voltage. Any load running on 120 volts at a given amperage, will draw half the amperage at 240 volts, BUT, power is volts times amps, the power is the same, and the heat is the same.

Now, IF the a saw is running on 120 volts on an inadequate circuit, the voltage will drop and the amperage will increase to the point the motor will start to overheat. Which brings us back to the notion that 240 is better than 120 ...... depends.

If you don't believe this, go find a saw running on 120, that works perfectly fine under max load. Now, unplug it, get a 250 foot roll of #12 wire and make a temporary extension cord to plug the saw into. Now run it under max load and see what happens.
You should have stayed out of this discussion. He is correct. It IS the amperage, not voltage that causes heat. Not voltage.

George
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post #23 of 41 Old 08-16-2016, 09:58 AM
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You should have stayed out of this discussion. He is correct. It IS the amperage, not voltage that causes heat. Not voltage.

George
Really? So tell me how much heat is produced without voltage? Power is VOLTS X AMPERES. So, without voltage, how much heat is produced? Do the math. To be correct, it is the flow of electrons that causes heat in the conductor, and without voltage, there is no flow. The higher the voltage, the more flow. Do I need to go into the power equations?

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post #24 of 41 Old 08-16-2016, 11:27 AM
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Originally Posted by Alchymist View Post
Really? So tell me how much heat is produced without voltage? Power is VOLTS X AMPERES. So, without voltage, how much heat is produced? Do the math. To be correct, it is the flow of electrons that causes heat in the conductor, and without voltage, there is no flow. The higher the voltage, the more flow. Do I need to go into the power equations?
No, you need to get into more equations that you do not understand.

You just need to understand electricity better.

George
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post #25 of 41 Old 08-16-2016, 11:37 AM
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Is it the flow of electrons, or the resistance to the flow of electrons that causes heat?


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post #26 of 41 Old 08-16-2016, 11:58 AM
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resistence

Explained here:
http://electrical-engineering-portal...ned-in-details

That's why in my opinion, it's better to wire a motor to 220 volts since the wires have less or 1/2 the current to carry than on 120 volts. Also in general, 240 volt circuits are dedicated to one receptacle. Often 120 volt circuits have more than one appliance/receptacles which also means more connections which are additional weak points.

In my case, I have a 1 HP dual winding compressor motor on a roll around piston compressor. It's wired to 120 volts because it needs to be located in different places .. in the shop, in the garage , or outside, depending. The other main shop compressor is a stationary 5 HP and is hard wired to 240 volts.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 08-16-2016 at 12:14 PM.
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post #27 of 41 Old 08-16-2016, 12:13 PM
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Quote:
Originally Posted by GeorgeC View Post
No, you need to get into more equations that you do not understand.

You just need to understand electricity better.

George
Ok, years as an industrial plant electrician, and many years as an electronics tech working on everything from computer mainframe design to Navy ECM systems to troubleshooting/repair on various military radars & even space shuttle equipment, how much do I need to understand better? Should I look into inductive and capacitance reaction formulas, use of the j operator, resonance formulae, wave propagation, dielectric constants, phase matching, and the like? Need some guidance here.

Quote:
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Is it the flow of electrons, or the resistance to the flow of electrons that causes heat?

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The resistance to flow is what causes heat. The lower the resistance to current flow, the less heat, and, yes, less voltage drop across the conductor. The old I= E/R.

Alexis de Tocqueville was a very smart man.

Last edited by Alchymist; 08-16-2016 at 12:43 PM. Reason: Typo
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post #28 of 41 Old 08-16-2016, 12:42 PM
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Quote:
Originally Posted by Alchymist View Post
Ok, years as an industrial plant electrician, and many years as an electronics tech working on everything from computer mainframe design to Navy ECM systems to troubleshooting/repair on various military radars & even space shuttle equipment, how much do I need to understand better? Should I look into inductive and capacitance reaction formulas, use of the j operator, resonance formulae, wave propagation, dielectric constants, phase matching, and the like? Need some guidance here.
And the significance of this post is???

George
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post #29 of 41 Old 08-16-2016, 12:51 PM
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Quote:
Originally Posted by GeorgeC View Post
You should have stayed out of this discussion. He is correct. It IS the amperage, not voltage that causes heat. Not voltage.

George
Quote:
Originally Posted by GeorgeC View Post
And the significance of this post is???

George
The significance is pointing out that it takes amperage AND voltage to cause heat. You intimated I didn't understand, yet the above quote is wrong. If it's not, show me where I'm wrong.

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post #30 of 41 Old 08-16-2016, 01:44 PM
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Quote:
Originally Posted by GeorgeC View Post
No, you need to get into more equations that you do not understand.

You just need to understand electricity better.

George
I am sorry George, but he is correct, and he does appear to understand electricity quite well. Without voltage, you do not have power, and without power, you have no heating. To better understand this, consider a super-conductor. Without resistance, there is no voltage drop, and without the voltage drop, there is no power consumed in the wire and no heating effect.

Ohm's Law closely ties current, voltage, and resistance together. Affecting one affects the other. Even though one of the common forms of the power equation is I^2 R, it is really the IV aspect that produces power.
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post #31 of 41 Old 08-16-2016, 02:10 PM
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Quote:
Originally Posted by TomCT2 View Post
"..tripped out on thermal overload..."
no surprises there, Steve.

if the saw is just running, doing no "work" i.e. not cutting anything, it draws very little power thru the wires.

as the "work load" increases an electric motor demands more power, i.e. it sucks more amps through the wires. this is why overloaded circuits get hot.....

back to basics:
V(volts) = I (amps) x R (resistance) - Ohms Law
P (power) = V x I

a little substitution shows:
P = I x I x R

so, the amperage demand goes up by the square of the power (R is a constant; the resistance of the windings does not change.)

using 240 volts, the saw only draws half the amps (vs. 120v) - increasing power demands on the saw draw fewer amps at 240 - and it's the amperage that causes overheating.
You're fairly close here, but there's one aspect that's led you slightly astray, and that is the powerfactor (phase shift between voltage and current). Not far, just slight.

With an idling motor, the only work it is producing is what's necessary to create the magnetic fields and overcome losses such as windage and friction. However, the current through the motor is surprisingly high, and is typically 1/2 of the normal full-load amps. So this begs the question, if the current is so high, why isn't it producing more power? That's because it is out of phase with the voltage. Only the portion of current and voltage that are in-phase are actually producing power.

As the motor slowly loads, the current changes very little (at first). What changes is the phase difference between the two. The powerfactor increases, and the amount of work or power in the motor therefore increases.

The wires leading to the motor are different, however. They do not have a phase shift between current and voltage (the voltage drop). They have a unity powerfactor, and all of the current times voltage (voltage drop) results in power consumption.
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post #32 of 41 Old 08-16-2016, 02:44 PM
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Originally Posted by Rick Christopherson View Post
You're fairly close here, but there's one aspect that's led you slightly astray, and that is the powerfactor (phase shift between voltage and current). Not far, just slight.

With an idling motor, the only work it is producing is what's necessary to create the magnetic fields and overcome losses such as windage and friction. However, the current through the motor is surprisingly high, and is typically 1/2 of the normal full-load amps. So this begs the question, if the current is so high, why isn't it producing more power? That's because it is out of phase with the voltage. Only the portion of current and voltage that are in-phase are actually producing power.

As the motor slowly loads, the current changes very little (at first). What changes is the phase difference between the two. The powerfactor increases, and the amount of work or power in the motor therefore increases.

The wires leading to the motor are different, however. They do not have a phase shift between current and voltage (the voltage drop). They have a unity powerfactor, and all of the current times voltage (voltage drop) results in power consumption.
yup. however, how the power factor varies 120 vs 240 is way beyond the bounds of messages on this thread....
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post #33 of 41 Old 08-16-2016, 03:16 PM
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Originally Posted by TomCT2 View Post
yup. however, how the power factor varies 120 vs 240 is way beyond the bounds of messages on this thread....
I don't believe the power factor changes with reconfiguring the motor. That's why it's listed as a single entry in the nameplate table. But I'm open to hearing if this isn't correct.
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post #34 of 41 Old 08-16-2016, 08:55 PM
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It isn't correct.

"When I have your wounded." -- Major Charles L. Kelley, callsign "Dustoff", refusing to recognize that an LZ was too hot, moments before before being killed by a single shot, July 1, 1964.
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post #35 of 41 Old 08-16-2016, 09:23 PM
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We need to leave these uneducated posters alone and let them pass their misinformation among themselves.

George
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post #36 of 41 Old 08-16-2016, 10:11 PM
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It isn't correct.
Why is it that the least knowledgeable are the most obstinate antagonists? You haven't made a single informative post in the entire discussion. All you’ve done is snipe. Are you incapable of the rational thought necessary to form an intelligent opinion on the topic? Do you think that waving around an expired GC license should cause people to penitently bow down and hang on your every asinine comment?

Grow up and act your age. If you have something of value to present, then present it. If not, STFU.
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post #37 of 41 Old 08-16-2016, 10:21 PM
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Well, or not.

I don't know why you're acting so obstinate, can't help you there. But I can recommend a good web developer that can help with your "web page".

"When I have your wounded." -- Major Charles L. Kelley, callsign "Dustoff", refusing to recognize that an LZ was too hot, moments before before being killed by a single shot, July 1, 1964.
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post #38 of 41 Old 08-17-2016, 09:10 AM
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This post is not aimed at any specific individual, just some observations. There is a lot more to AC - alternating current, than most people realize. To start with, the common everyday AC power that is used and abused by everyone is but a small subset of electronics, and electronics is a subset of physics. Our power grid is set a 60 Hz, which is but a very tiny point in the range of AC.

The theory alone behind AC is quite large, and mostly math. Two of the most important points in it are angle of rotation and it's sine, and two derivative points - ie, the numbers .707 and 1.414.

Then we get into the circuitry aspect, where frequency is just one factor in the myriad equations. Also to be considered are a host of other factors, two major ones being inductance and capacitance, and the resulting reactances.

When we start talking about motors, we must now add in the formulae from the realm of physics in the form of magnetic fields.

So it is no wonder that many people form incorrect opinions on how things work. Enough babbling, let me just say that whoever posted that a 240 volt motor will not run on 120, that's not always the case. I still have a 240 volt fan motor running on 120, and it's running at full speed. Just a matter of knowing the theory and the addition of one small component, and it's not a transformer.

Alexis de Tocqueville was a very smart man.
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post #39 of 41 Old 08-17-2016, 09:36 AM
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120 vac vs 240 vac
i have never seen any scientific data supporting that a dual voltage motor, configured for the higher of the two supply voltages, will operate with any improved performance.

IF a test were done that would have a dual voltage motor on the lower supply voltage and again on the higher voltage, with all of the correct circuit components to have the exact same voltage drop in both configurations, it would be extremely likely that the motor would perform the exact same in both configs.

the most common issue is, that in the lower voltage/higher amperage config, there is more voltage drop leaving less for the motor. if those situations were improved with larger conductors (less resistance = less voltage drop), the performance would improve greatly. motors suffer greatly when their power supply is not within 5% of nameplate ratings.

for all those that have expressed this concept before me, i am in your camp.
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post #40 of 41 Old 08-17-2016, 09:40 AM
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[QUOTE=TimPa;1452890]120 vac vs 240 vac
i have never seen any scientific data supporting that a dual voltage motor, configured for the higher of the two supply voltages, will operate with any improved performance.
/QUOTE]

That's because there is none.

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