Why High Voltage?

If you have a machine tool that has a dual voltage motor, is there any reason (other than saving money on the wire to the machine since it can be a lower gauge due to the lower amp draw) to run it at the higher voltage?

I have a buddy that has a table saw that he swears accelerates to speed faster now that he has it wired for 220. (used to be 110V) I would think it would not matter what voltage he ran.

-Joe

about current draw would be my guess
less voltage drop for that startup instant due to wire size of 220 setup at the wall

engineers will show up and tell us the math

That table saw uses less energy at 220 volts than it does at 110. It gives the motor more torque because it has more energy ( amp's)because of the higher voltage...

The 110 line might have given it 15 amps.
When you run 220 it might have 30 amps.
It's like trying to jump start a car with a cheap set of jumper cables..
The wire in the cables is too small and you cannot provide enough energy to run your car and turn the other car over at the same time.
So you have to stand there while the power builds up in the dead battery.
When you hook up a good set of copper jumper cables, you can start the other car right off the bat! Why? because there is more power being delivered to the other car with the good set of jumper cables..

Two issues: cost and voltage drop.

When you go from 110/120 to 220/240, your amperage consumption drops. Power company charges you for amperage, not voltage.

Voltage Drop: when a motor first starts, it is essentially "shorted" for a very short period. You know "motor starters"? Motor starters are basically circuits that will bypass a fuse or breaker for a very short interval allowing the motor to spin up at very high amperage, then returning "monitoring" to the fuse or breaker.\

Anyhoo...motor "shorts" which pulls a huge whack of amperage. Anytime ANY current passes through a wire, you have voltage drop. Voltage drop is a function of amperage. More amps, more drop. More drop...less amperage (self limiting at a given voltage).

Your friends' perception of higher acceleration derives from this phenomena. During the short spin up cycle, 220vac delivers more available high amperage because the OVERALL amp draw at the higher voltage is lower, so the drop is lower and so the amp limiting is reduced.

Now... there is an underlying assumption here. You get all your 220vac performance improvements IF you wire with wire sized for the 110vac hp requirement. Voltage drop is a function of amperage AND a function of the wires resistance. Resistance at a given voltage goes up as diameter goes down (think, water pipe). Go with the smaller diameter (220vac amperage rated wire) and now your voltage drop at startup (inrush it's called) is basically the same as your 110 scenario.

One of other benefit. The heat produced by a motor is a function of the SQUARE of the current used. The current used is a function, of course, of the load--but what most people don't get is WHY. When you load a motor, it wants to slow down--this increases the angular distance of the magnetic field in the rotor to that of the stator. THIS causes current to go up---which brings more force into play (thus the motors tendency to speed back up) but produces MUCH more heat.

So....if you have, for example, a 1hp table saw you won't notice any appreciable difference in performance if you are ripping 3/4" Eastern Wimpy Pine. On the other hand, if you are ripping 2" bubinga, on 110 you'll trip the thermal overload on the motor every 5-7 minutes of cutting. DAMHIKT

Switch to 220, and the thermal overload problem because much less prevalent. Needless to say, a cooler motor is a happier, longer lived motor.

Hammer...hate to disagree...but you're kinda backwards on this. A 1HP rated motor will never give you more than 1HP. The HP rating is what stays constant.

One HP = 746 Watts. A watt is one Volt x 1 Amp. Remember the HP of your motor is 1hp no matter what voltage you run it at.

So...746 / 120 v = 6.2 Amps
746 / 240 v = 3.1 Amps

However, you mostly see good quality motors (i.e., ones that produce a true 1Hp at the spindle) rated at 15A on 120vac and 7.5A on 240vac. This is because the efficiency of the motor. The point, however, remains.

If HP is constant, all other things (efficiency) being equal, a 120vac voltage will draw twice as much amperage as a 240vac.

Note, however, that some motors as an unintended consequence of their overall design tend to be a little more efficient at 240 than 120 (ie Baldor and Leeson)

I do not understand the cost argument. Last time I checked my electric bill, the power company charges my by the kilowatt hour which is a measure of energy.

Energy is power times time. Electrical power is the product of voltage and current. If I wire the machine for low voltage it will draw twice the amps, but the power (P= VI) will stay the same. As long as I use it the same amount of time, the energy used would be the same regardless of the voltage the saw was wired for, so I do not see the cost benefit.

Do motor starters “bypass a fuse or breaker” The few that I have played with seemed to have an overload circuit in series with the contactor, so I don’t see the bypass. Now if you rewired a motor for high voltage and did not half the size of the overloads I could see how you would trip them less, but I do not think that is what you are supposed to do...

The voltage drop argument works if you leave all the feed wire at the same gauge as the low voltage level. I thought the reason for running higher voltage was to reduce the amp draw and therefore the wire gauge that you needed to run.

Hammer: one more thing. Your point about the jumper cables is dead on. Automobile starters consume tremendous amperage.

The voltage drop through the cheap cables is vastly higher because they are so much thinner (and sometimes made of aluminum)--this chokes the current available to the starter. So you have let the charge "trickle" into the battery as you point out.

The big beefy copper cables, of course, don't have this problem because their crosssection and composition lowers resistance significantly at the target amp draw.

Correctly installed motor starters DO NOT bypass the fuse or circuit breaker!

A motor starter incorporates a contactor to switch the motor on and off, and an overcurrent relay with a long time constant, to provide running overcurrent protection. The current setting of the relay is usually set at or slightly above the normal full load current, and protects the motor against sustained overloads or stalls. The long time constant prevents the overload from tripping from the starting current, which can be up to SIX TIMES the running current.

The fuses or circuit breakers ahead of the motor provide short circuit protection, and need to incorporate enough time delay so as not to trip during startup.

The only place where you might see a "bypass" system set up on a motor starter would be on a reduced voltage or "soft starter", where the motor is started on reduced voltage to limit the startup current spike, then a contactor is closed to bypass the soft starter and apply full voltage once the motor is spinning. Setups like this are usually only seen on large motors, or in installations where voltage drop is excessive.

If you are talking little single phase motors, the 115/230 switch makes a significant difference. The same motor on 115vac will launch the sawblade with a rolling start, the motor on 230vac will launch the sawblade to full synchronous speed seemingly faster than you can blink your eye. I too was very impressed.

My opinion is that the tipping point of benefit is around 3/4hp...below that just stick with 120vac, above that consider 230vac operation.

In industry, the savings is in the copper...go into a plant and wonder why the insulation hasn't melted off the "little" #12 wires feeding a 480vac motor....it draws half the amperage as it would in your house on 230vac.

Matt,

Your description is very similar to the one my friend gave. It is a ~1hp Powermatic saw. I just do not understand why it works better with the 220.

-Joe

the motor starters and other equipment are expensive too, and take up space. they're saving a marginal amount in efficiency, tons in bulk.

Harrar

A 1HP rated motor will never give you more than 1HP. The HP rating is what stays constant.

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I disagree
A 1 HP motor means a motor you can give a constant load of 1HP(If cooled sufficient) If running idle it has a much lower HP so also amps are lower
If a motor is 10 HP it does not mean it GIVES 10HP whenn running,it means the max continues load is 10 HP (So you can TAKE max 10HP) And for some period of time it also can be higher as 10Hp

Its cost of installation, pure and simple. Copper and breakers cost more for greater Amperage.

Most commerccial and residential distribution wire is rated 600 Volts but the current capacity for 230 Vs 460 service doubles meaning double the weight of copper and doubling the current capacity of ever protective device in the system. Installation costs for a large 230 volt distribution can be substantially more than for a 460 vole system.

Conductor size dictate how many Amps it will carry. That's why power companys erect 500,000 volt distribution towers: so they don't have to string 4 diameter (no exaggeration) conductors from the power house to the city.

It's a peculiarity of the US electrical system that we have two common distribution voltages. 115/230 single phase and 230/460 three phase. That's what we have grandfatered in, so that's what we're stuck with.

If the conductors are sized correctly starting and running performance in motors and other loads is identical regardless of voltage.

""""Your description is very similar to the one my friend gave. It is a ~1hp Powermatic saw. I just do not understand why it works better with the 220.""""

ok try this one
10 psi
1/2 pipe
1" pipe
5 gallon bucket
you still got 5 gallons when bucket is full
but the big pipe gets you there faster because less resistance in the pipe

I was always told to think of voltage as pressure and amps as flow. So in your explanation, you aren't changing the voltage(10psi) only the flow by decreasing resistance.

Power consumption is still the same.

wippin boy seems close. voltage is pressure, amperage is a measure of the amount of electrons.
five gallon bucket
10 psi (110v)
20 psi (220v)
which is going to fill up the bucket faster?

watt=voltage x amperage

Hammer is wrong, but also somewhat right.

The energy consumption is the same, barring a minute difference in wiring losses to the motor.

However:

The maximum instantaneous current capability is larger at the higher voltage, so start current can be significantly larger. (wire resistance same, voltage 2x higher ~= 2 x fault current)

And, the motor will actually draw less start current and run current in general at the higher voltage. So the same start current generally results in a faster start at the higher voltage.

So you would expect a somewhat snappier start.

As far as energy savings..... forget that, you won't notice.

But, Harrar:

Your winding currents are the SAME at 220 as 110 under the same conditions. The difference is only that at 220 the windings are in series, while at 110 they are parallel.

So the heating deal isn't going to do anything at 220 it didn't do at 110, for same currents.

The difference you are seeing isn't due to exactly what you said, it is due to the fact that the 220 tends to have the ability to dump MORE current into the motor, and allow it to power thru your tough wood faster.

It is almost surely the TIME issue that you notice for heating.

Even though the 220 currents can be higher, and hence have MORE losses, it isn't for as long, due to decreased voltage drops. With less drop, you are not bogging the motor as badly.

AND, if the wire size is the same at 220 as at 110, the exact same wire voltage drop is only half the percentage drop, so the net effect on the motor is quite a bit less. But, if you pull the same percentage drop at 220 as at 110, you are pulling double the current if wires are the same.

The 220 will give more perceived power, in general, but it is not noticeably more "efficient" overall, because the wire losses are small in any case unless you habitually overload the wiring..

2slow you are correct on what the power company bills for. They do not bill for current as stated in one post.

The primary reason for higher voltage is as stated by several posters is that the size of the distribution equipment and wiring is reduced. The wire size can sometimes be reduced by a factor 2 of and sometimes 4 by doubling the voltage. Why is this? Because sometimes (especially on long runs) the wire is sized based on volage drop not on amperage capacity. A 22 volt drop at 220 volts is 10 percent. A 22 volt drop at 440 is only 5 percent. Thus if a 10 percent drop is permissable and amperage vs wire size is not the issue then the wire can be 1/4 the size at 440 as at 220 volts. If voltage drop is the criteria then wire size can be reduced by the square of the ratios of the voltage.

And that leaves the last issue. Why does the 110 / 220 volt motor perform better on 220? And it absoulutely does. I have a radial arm saw that will almost not start on 110. I am not sure that this is the only factor but at start up a motor draws a lot of current and there is some voltage drop in the shop wiring as well as the power cord of the equipment. I will bet that the same size shop wire and equipment cord was used for both voltages. Therefore, there would be twice times the voltage drop at 110 volts. Note that this is 4 times the voltage drop when analyzed as a percentage of supply voltage.

Power company charges you for amperage, not voltage.

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Your dead wrong on this one unless the power company on the third coast is very diffrent then most power companies. Power is sold by the kilowatt hour in all jurisdictions that i am famialier with.

isn't a watt =voltage x amperage?