220v conversion question

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On 09/01/2009 08:35 AM, Doug Miller wrote:

I agree it will draw half the current. Assuming properly sized conductors such that voltage loss is negligible, why would 6A at 240V behave any differently than 12A at 120V? In both cases we're drawing 1440W.
Now it's possible that the motor itself could be designed such that it runs more efficiently at 240V than at 120V. This isn't necessarily the case here, but if it is it would be due to the motor design, not the higher voltage as such.

It's true that electricity will follow all possible paths, but the higher the resistance of a particular path relative to the other paths the less electricity will flow through it. The safety ground is a low-resistance path, so most of the electricity will flow through it rather than through the operator.
Older electric dryers and kitchen ranges using 3-pin plugs generally run their control circuitry and lights at 120V using the safety ground as a neutral. Not ideal, but it's not unusual either.
Chris
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Higher voltage.

Quite true; OTOH, at 120VAC 60Hz, it takes only a few tens of milliamperes to interfere with heart rhythms, thus *any* current flowing through the operator is a potential hazard.
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On 09/01/2009 11:08 AM, Doug Miller wrote:

Huh? Voltage is just potential. You need power to do work, and the amount of power (and thus the amount of work that can be done) is the same in each case.
Faster startup implies that the mechanical work of spinning up the motor is done in a shorter amount of time. This means either the motor is more efficient at 240V or else it's drawing more power. In both cases this would be due to motor design, not simply higher voltage.
Chris
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Yes, that's right. That's why the motor will start more quickly with higher voltage.
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On 09/01/2009 01:02 PM, Doug Miller wrote:

I hope that's supposed to be a joke.
Chris
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Ok, again, I am no electrical expert but in my coloring book world of looking at electricity, You have less resistance up to the motor using 240 vs 120. Each of the 2 wires carrying 120 volts is carrying 1/2 the load up to the motor than the single wire in a 120 volt application.
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Leon wrote:

No, each of the wires in a 220v circuit is carrying the same current, one carries it in, one carries it out, just like with 110.
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That would suggest a direction to the current flow, and with AC we know that isn't the case.
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On Wed, 2 Sep 2009 05:27:19 -0700 (PDT), Robatoy

There is a direction to the flow in AC. It just reverses every 50th or 60th of a second. But at any given instant of time, the current is flowing in a specific direction. During that instant, one wire in, the other out. The next 50th/60th of a second, the in wire becomes the out and the out becomes the in.
Tom Veatch Wichita, KS USA
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group) and I quote you:

That is incorrect as a statement. There are those moments when the direction reverses when nothing flows in any direction at all. (Unless you want to open that can of worms called power-factors and phase anomalies where current and voltage are out of step with each other. But we need a lot of very sharp crayons to explain that to the Neanderthals.)
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On Wed, 2 Sep 2009 09:56:47 -0700 (PDT), Robatoy

OK, I'll give you that one. 8)
It's true that 100 or 120 times per second (50 or 60 cycle) the sine wave model of current amplitude crosses zero, and with zero current, there can be no flow direction.
Tom Veatch Wichita, KS USA
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Wow! An AC pissing contest. Don't piss on a live circuit! ;)
nb
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From the Anti-FAQ, for everyone's edification.
5.1 HOW DO I WIRE MY SHOP?
As my friend Doug, the journeyman cabinetmaker, says: there's only four things you gotta know about being an electrician:
S--- flows downhill, Payday is on Friday, It may be s--- to you but its bread and butter to them, and Every asshole is a potential customer.
Oops! That was about plumbers. Forget it. Anyway, Doug is just jealous of plumbers 'cause they make more money than cabinetmakers, just like Tom.
Actually, all the regulars and most of the newbies on the wreck are electrical experts. That's why any thread on wiring and electricity gets so many responses. Most of us work with electricity all the time. After all computers and power tools are electrical, and so's the TV we watch Norm on. If you want to change the plug on your tablesaw, you still need to know everything about wiring and amps and volts and watts and volt-amps and wire gauges and phases and power factors and impedance and resistance and plug configurations and panel sizes and capacitors and motors and switches and electrical codes.
But that's OK, don't be afraid. You can trust any wiring and electrical advice from anybody on the wreck, apply it and be absolutely sure that it will meet code and be perfectly safe. No point in getting ripped off by electricians or consulting an inspector. Just ask away on the group and you can be sure of getting a whole lot of accurate and consistent responses, just like when you ask any math question of all the rocket scientists on the wreck.
Luigi
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Well, if we also bring relativity and quantum mechanics into this discussion, it would be fair to say that at any given time the current might be flowing in any direction you'd care to choose, and what's more, we have no way of telling so!
--
The best argument against democracy is a five-minute conversation
with the average voter. (Winston Churchill)
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On Thu, 3 Sep 2009 19:24:16 +0000 (UTC), snipped-for-privacy@sdf.lNoOnSePsAtMar.org (Larry W) wrote:

Doesn't matter, it's all relative.
Tom Veatch Wichita, KS USA
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To have zero volts and some current - all it takes is phase shift.
Phase angle between voltage and current is well known.
Eli the Ice Man Voltage leads current in inductive (E L I ) L is inductive ICE Current leads voltage in a capacitive circuit.
So if you attach a motor to the AC lines - The voltage will go to zero before current does......
Martin
Larry W wrote:

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On Wed, 2 Sep 2009 05:27:19 -0700 (PDT), Robatoy

120 times per second (60 each way)
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It was a coloring book explanation.
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Power is proportional to the *square* of the potential.

Not more efficient, but does have more *power* available, all else being the same.
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On 09/01/2009 01:37 PM, snipped-for-privacy@gmail.com wrote:

You forgot the whole "divided by resistance" part. and Potential divided by resistance is current.
P=(V^2)/R = V*I
As Tom Veatch indicated, in the typical case when you rewire the motor for 240V you are also increasing the resistance so that the final power ends up the same.

Again...why would this be the case? The available electrical power of a motor drawing 6A at 240V is exactly the same as one drawing 12A at 120V.
Chris
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