# 120v vs 240V

4909 Views 21 Replies 11 Participants Last post by  DaninVan
I do believe there's been past threads on that. But sure, let's start a new thread continuing on from
http://www.routerforums.com/tools-woodworking/118089-ripping-2-thick-figured-maple.html#post1638441
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Let me start off by saying that I don't care what the electrical metering says, I want to know what's happening at the motor shaft ie measured torque or alternative realworld condition.
I think I opened a can of worms...
https://en.wikipedia.org/wiki/Horsepower#Shaft_horsepower_.28shp.29

Well see? That was easy!
https://powertestdyno.com/product/electric-motor-test-systems/
Dan I didn't read ,but to me if the current consumption is to high , how do you supply enough current with a single 120V 20 amp plug/circuit , when my table saw draws 22 amps ?
To me you need a second wire taking half the load
Right, Rick, but that wasn't the point in question. Charley suggested that by switching a dual voltage motor to 220V that the motor output would/could increase to 2HP from 1.5HP
My point isn't really electrical but rather physical...I want to see the comparative outputs on a dynamometer, not an ammeter.
Right, Rick, but that wasn't the point in question. Charley suggested that by switching a dual voltage motor to 220V that the motor output would/could increase to 2HP from 1.5HP
My point isn't really electrical but rather physical...I want to see the comparative outputs on a dynamometer, not an ammeter.
Dan I can't answer your question but I would bet money Charley knows what he is talking about. He thrives on stuff like that.
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You'd think with the millions of motors out there that this question would have been asked and answered with empirical test results run on actual motors in service, not with electrical theory.
I just can't find it....but this question gets asked A LOT!
The companies that test and rebuild motors, and run them on dynamometers, must think a question like this is silly. It's what they do everyday.
Some users will experience a measurable increase in actual power at the shaft when they change a dual-voltage motor from 120 volts to 240 volts. Others will not. Here's why:

When the motor is operated at 120 volts, the amperage draw is double what it is at 240 volts, given the same load on the shaft. If the wire size from the breaker to the motor is marginal for the 120 volt current draw, heat losses in the wire will reduce the actual voltage seen by the motor, especially on long runs. This loss in line voltage under load causes a measurable loss of power to the motor. The motor will not be able to deliver its rated horsepower. These heat losses go up as the SQUARE of the current. So, if we double the current, we have 4 times the heat loss.

If the wire feeding the motor is generously sized for the length of the run, the heat losses are insignificant, even at 120 volts, and the motor operates as designed whether it's wired for 120 volts or 240 volts. So, the guy who is feeding his 1.5 HP dual voltage motor with a 40 foot run of #14 wire will see a noticeable increase in power when he changes that setup to 240 volts. The guy who is feeding the same motor with 20 feet of #10 wire won't see any difference at all.

There are good reasons other than the power gain to use 240 volts instead of 120:
1. You're paying for the heat that's lost in the wire. You're losing 4 times as much at 120 volts.
2. Your electrical load is more balanced at 240 volts. This could make a difference in your bill if you have "demand" charges.
3. Your motor will run cooler at 240 volts. That's always a good thing.
4. Your motor will start up quicker.
5. You can safely and EFFICIENTLY operate your motor on a smaller wire. (Should be #1)

A dual-voltage motor has 2 sets of windings. On 120 volts, they are wired in parallel. On 240 volts, they are wired in series. As long as the frequency (60 Hz) is the same, I think they get the same number of "kicks" per second either way.
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SORRY ZERO WILL SEE ANY TYPE OF ACTUAL POWER INCREASE FROM THE MOTOR.

This is a known fact, I just cant be drawn into this more than this post this is something for 15 years has been debated on forum to death and the answer has been found. Will it hurt anything not at all so by all means change it over to 240V all mine are converted over.

Below is just one exert from one of the hundreds of papers from people, scientists and companies that have studied it. And a few post on a thread in a forum are not going to wipe out 4 years of my schooling getting a BA in Electronics studying Motors, Electrical and Electronic Circuits and Transform Analysis, the math to go with it and the lab experiments to prove what you are saying just doesn't translate into real power gains.

Now below is a dumbed down explanation, not my words. I guess I can pull the white papers, but it just says the same thing in a far more technical, hard to understand way.

Trying to come up with a scenarios where a user would see a power gain has more to do with everything BUT the MOTOR and going to 240V in itself which is exactly what the many posts already have and will continue to try to state for the people that just do not understand or want to believe there is no power gain. Or prove there are power gains. The motor itself will never produce more power, hopefully everyone can agree on that. The only thing debatable are things the previous poster mentions as length of wire and some other nice points he made that may allow the 240V wired version of the motor to see it's max power using 240V over 120V, but it a very, very small amount and for 99.9% of instances it will not matter.

So yeah we can make up a scenario where 220V will give you more power when a 120V motor is switched over, but that's not reality. You can skip to the last paragraph that I made bold of this post to state a scenario just like that.Even in the worst conditions a 10% increase on a 1.5 HP motor is NOT going to make a difference in cutting anything, especially 2" thick maple.! A 1.5HP motor will never gain .5 HP going from 120 to 240V not even under the worst conditions we can come up with. Most homes and shops are not large enough nor wired poorly enough to encounter these issues..

You won't save money
A common myth surrounding 240V vs 120V is that the machine now uses only half as much power. Remember, a motor draws a certain amount of current, which is volts multiplied by amps. So if we double the voltage, we cut the amps in half. Unfortunately, the power company measures your electrical usage (and charges you) in watts, not amps. DO we really need get inot power formulas, I think not.
You won't get more powerThere are some motors that do produce more power at higher voltages. Your power tools don't use those motors. Your motor produces the horsepower it's rated for. Really, can you imagine that a company's tool can produce a higher power rating and they wouldn't tell you about it? Your buddies who tell you their saw is more powerful, starts up quicker, etc, are engaging in wishful thinking unless their tool is long way off from the panel box (See "why would you do it" below).
There's no point in "balancing" the legs.One of the stranger justifications I've seen for converting to 240 is that, because it uses both legs, the load is "balanced". The idea is that a 10-amp 120v load puts 10 amps on one leg and nothing on the other. On the other hand, a 5-amp 240V load puts that load of 5 amps on each leg, using a smaller portion of each leg. However, keep in mind that a 100 amp panel allows you 100 amps on each leg, for a total of 200 amps. Since a 240V load uses both legs, you're putting that 5A load on each one. So a 10-amp 120V load uses 5% of your panel's capacity (10/200) while the 5amp also uses 5% of the capacity (5*2/100).
You will cut down on your panel's physical capacityEach 240V circuit breaker takes up two slots in your panel, whereas a 120V breaker only takes one. In most shops, where only one or two high loads run at once, slots for circuits are more of a premium than amps.
You (probably) won't increase your motor's lifeYes, a higher-amp motor runs hotter which cuts the expected lifetime. But we rarely run our equipment long enough for heating to be an issue. And if we cut our motor's service life from 30 years to just 25, is that really worth getting worked up over?

Why would you do it?
There are really only a couple reasons to bother with converting
You can use smaller wires in the circuitThe amperage your motor draws determines the kind of wire you need to run to it. Too high of an amp load will cause the wire to overheat. But larger wires are more expensive, harder to work with, and may not be available. For example, if your motor draws 25 amps @ 120V, rewiring to 240 will drop the load to only 12.5 amps. That means you can use 14/2 wire instead of 10/2, although you should probably use 12/2 to be safe. Of course, that only matters if you're installing a new wire. If you have an existing wire, rewiring for 240V means you can fit a bigger motor onto the same existing wire.
You will lose less power along the way (and you might notice it)If your tool is located quite a ways from the panel box, higher voltages experience less drop during the voyage. Let's look at a fairly typical example. Let's say you have a 120V motor that draws 10 amps. The total wire length to the tool is 50' of 14/2 wire. The voltage drop for that situation would be 3 volts or 2.5 percent. Changing that motor to 240V would reduce the drop to 1.25 percent, in other words completely and totally not noticeable.

If, however, we quadruple that length to 200' we also quadruple the loss, i.e. 10% versus 5%, which now might be noticeable in a 10hp motor, but in the real world NOT anything smaller.
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I'll jump in here and say what I probably said last time we had his discussion - I run everything I can on 240. I think it's more efficient and in the case of my air compressor, a 40+ year old Craftsman twin cylinder model, switching to 240 made all the difference in the world.

A friend gave me the compressor sometime in the late 70's but it didn't have a motor. It's supposed to be a 2 HP compressor but all I had on hand was a dual voltage 1.5 HP motor. I mounted the motor, wired for 120 with about 8' of #14 SJO, and started using the compressor. It worked ok but I had to let the air in the tank get down to about 25 lbs. or the motor would stall. So when it shut off after filling the tank I would just unplug it and then plug it back in when I needed more air, assuming it was 25 lbs. or lower.

So I figured that maybe on 240 it might perform better. Wired it for 240 and lo and behold it would cycle on and off without having to drain the tank first. Now this is partly due to using a 1.5 HP motor on a compressor designed to use a 2 HP motor but what it told me is that whatever the difference between running 120 vs 240 my compressor now ran like it was supposed to (still using it).

One more - I bought a DeWalt RAS in the mid 70's and hooked it up 120 v, just like it came from the factory. The motor ran fine but I noticed that it took a few seconds to spin up to speed and on thick cuts I had to be careful not to stall it. Same thing - I wired it 240 and it now spun up very quickly to speed and I could now cut without stalling the motor.

I'm aware there could be all kinds of other factors but none really matter to me - changing to 240 on both of those solved a problem and produced more power in real world settings. I'm sold - run everything you can on 240!

David
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Well now that we've all been properly schooled with the dumb version, the debate is over for me before someone blows a gasket . . .
I could be wrong but in Dovetails last point he talks about power yet gives his results in volts. I believe that the losses would be better expressed in watts. According to my calculations, the losses are 12.625 watts compared to 3.15625 watts at 50 feet of 14/2. The losses are 4 times, not double. At 200' it would be 50.5 watts compared to 12.625 watts. As he suggests, the loss is still negligible, the difference being only 37.875 watts. This doesn't include wire in the motor. I have no idea how many feet of what gauge wire are in a motor and whether this is negligible too. I do know that heat means losses, so if the motor runs cooler it is running more efficiently (wasting less power).

I used 10 amps compared to 5 in my calculation.
I do believe there's been past threads on that. But sure, let's start a new thread continuing on from
http://www.routerforums.com/tools-woodworking/118089-ripping-2-thick-figured-maple.html#post1638441
Ohms law clearly states that voltage and current are directly proportional, in other words if you half the voltage the current (in amps) will double, and because watts equals volts multiplied by amps, the watts will be the same and if you divide watts by 746 the answer will be in horse power. I know that Ohms law refers to direct current but it's close enough for alternating current unless precise accuracy is required which is not the case so far as routing or saws are concerned.
In summary, I agree with a previous post maintaining that horse power will remain substantially the same between 120 and 240 volts, so long of course that the motor is designed for dual voltage.
After thinking about it some more, I have to agree that Dovetail is right about not getting any more power out of the motor at the shaft. The motor will increase current draw to compensate for any lower voltage it might experience, but power output at the shaft will remain the same.
When the motor completes a cycle, ie the tank has reached the set pressure, the pressure switch shuts off the motor and the unloader valve bleeds off the built up pressure in the compressor head. If it doesn't, on the next cycle the motor has to overcome the pressure in the head causing the motor to stall. Sounds like what you were experiencing.
It's a quick cheap fix.
Right, Rick, but that wasn't the point in question. Charley suggested that by switching a dual voltage motor to 220V that the motor output would/could increase to 2HP from 1.5HP
My point isn't really electrical but rather physical...I want to see the comparative outputs on a dynamometer, not an ammeter.
I said this ONLY when talking about the specially designed motor that comes in a Delta Contractor Saw. It is made to run on 120 volts AC at 1 1/2 hp so it can be used on job sites on standard US 15 amp 120 volt circuits that are common in new homes.

Take the saw back to your shop where you have a 240 volt circuit, change the motor wiring to 240 volts and the same motor will produce 2 full horsepower. Most motors produce the same horsepower when connected to either voltage. The specially designed motor in the Delta Contractor saw gives you 1/2 hp more when connected to 240 volts. This is true on my son's 34-444 Delta Contractor saw and has been true with other Delta Contractor Saws that I've seen. Again, this is not a normal dual voltage motor design. It is special for the Delta Contractor Saws. I had a photo of the motor label on my son's saw, but can no longer find it. Only on the motor label will you see that extra half hp listed when you change the saw over to 240 volts. The motor is made differently than most dual voltage motors which produce the same horsepower on both voltages.

Charley
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I personally would use 220v only for the lower current draw. Higher amps = a little more heat, heat kills motors over time.

Would it even be noticeable on a table saw? Probably not, since it is not a tool that is heavily loaded for long times. On an air compressor? Definitely it would make a difference.

Anyone who argues for power savings, lower bills over time,etc probably won't even see enough savings to cover the costs of buying the new plug and receptacle.
Dang yer hide, Charley! Now I have to go out to the shop, pull the saw out (clean off the dust) and check My Delta saw motor label.

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Sort of wants me to go back to all hand tools.
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