Rewiring a Motor for 240V

[Alan See]

I'm trying to convert my Jet 1100C Dust collector from 120V to 240V. I have the schematic that shows how to rewire the terminals on the motor. The problem is a can't seem to locate the terminals . I figured they were under the switch plate, but theyr'e not. Do I have to completely remove the motor to get to them? Has anyone done this?

[Rick Lizek]

I've always found them under the motor cover for the last 35 years so I don't expect them to be anywhere else. It would make no sense to have them under the switch as the switch is a seperate part.

[Alan See]

Errr.. Never mind! I figured it out. I was expecting to find posts, not wires. I see what I need to do now. This is my first motor re-wire. Is it supposed to smell like that?

Rick, I meant to say under ther switch box - which is mounted directly over the motor access, and acts as the cover.

Thanks, Alan

[Chris Padilla]

Why the rewire to 240 V?

[Richard Wolf]

I agree with Chris, why would you rewire from 110 to 220. Every article I have ever read says there is no advantage. The only advantage is if you are pulling to much power from one leg and dimming lights and TV in your house. I know I'm not a electrical genus so maybe someone else can jump in.

Richard

[Alan See]

The only advantage is that it will reduce the aperage draw on the main breaker to my sub-panel, Ive only got 50 amps to play with, so each amp is important. I don't expect the DC to work any better, I'm just trying to reduce the chances of everything going dark.
Alan

[Phil Ordway]

The motor will run cooler therfor last longer. Most users report more effective power.

[Ralph Barhorst]

The motor will run cooler therfor last longer. Most users report more effective power.

The motor will not run cooler on 220 volt. The same amount of current flows through the windings in both 110 and 220 volts. On 110 the two windings are connected in parallel each sharing half of the line current. On 220 the two windings are in series and therefore carry the entire line current.

If both connections are wired correctly you will not see a significant change in effective power.

[Bruce Branson]

Only electricians should answer electrical questions!Voltage and Current are inversely proportional.If you double one you half the other.If you half one you double the second one .For example my contractor saw pulls 18 amps at 120 volts and only 9 amps at 240 volts. The two legs of 120 are out phase with each other.

[Richard Wolf]

So Bruce, are you an electrian? You have given us the theory, but what are the advantages of 240 over 120, if any?

Richard

[Bruce Branson]

You can use a smaller breaker and smaller wire because only one leg hits the motor at a time.It is more cost effective that way because the horse power is the same.Amps x Volts =Watts divided by the power factor 746 = HP. So my saw has the same HP either way.The motor should run a little cooler but I have not seen any studies that said it would last any longer. The efficiency of the motor also comes into play some are marked some are not.No motor is 100% efficient.There are many places on the net to find the horsepower formula.

[lou sansone]

dear fellow ww's

By trade I have worked as an electrican for many years until by education I earned my electrical engineering degree and have worked in that field for about 15 years. The main advantage to running motors at a higher voltage is to lower the total amperage draw. Now for little motors under 5 hp it is a toss up. But as the motors get bigger it really becomes more important to lower the total amount of current. When you start looking at 50 + hp motors it really makes a big difference, not only in the size of the wire that has to feed the motor, but in all the switch gear that has to control that same motor. In fact motors in the 100+ hp range usually only come in the 460 range. Further more it is hard to find any motor over 10 hp in single phase for a similar reason.

I also agree with ralph, that there will be no gain in motor effency, that is a design issue that does not change simply by changing the voltage in a dual voltage motor.

but back the the original statement . " I only have 50 amps and want to conserve it". If you had 50 amps @ 240 you will have 100 amps at 120 volts( provided you balance the load and provide the proper size neutral ). You really will not gain anything by taking a motor that say used 20 amps @120 and now rewire it to use 10 amps @ 240. You still have used the same percentage of your total available power. Now if you mean that you "only have a wire that will carry 50 amps" then by all means you will gain something by using 240 volts rather than 120 volts. That is the theory behind high voltage transmission.

regards lou

[Ken Garlock]

The two legs of 120 are out phase with each other.

Bruce, this is a single phase application as is all residential wiring. What you have is a transformer on an electric pole that step down the high voltage to 240 volts. That 240 volt transformer winding is center taped and that tap is grounded. Across the winding, end to end, is 240 volts. from the center tap to either end of the winding is 120 volts. Since there is only one 240 volt winding in the transformer, and 120 volts id derived from that, there can be NO out of phase, period . The term out of phase is an electricians term that has no basis in fact.

You done hit my hot button

[Bruce Branson]

I worked at an Ohio Edison power plant starting in the late 70s.We used the term out of phase because if they were both the same leg your meter would read 120 volts instead of 240 leg to leg.The two hot wires alternate as return paths back to the power plant.They have to be 180 degrees out of phase with each other or the electrical point would be the same.We used to argue with the engineers all the time about the terminology.If you look at the internet site How Stuff Works and look up power grids they use the same terminology I do.They even have a diagram on about the 7th page of the section on power grids.I am a member of The Utility Workers Union of America local 457.

[Carl Eyman]

I always wire my tools using 1 hp or more as 240 volt. My observations are that there is less tendency to stall the motor on hard cuts. I agree with everything each of you has said. Lou, your explanation is the most straightforward I've found on this or any other forum. My question is isn't my experience explained by the fact that whatever the gauge of the wire from the power panel to my motor is there is less voltage drop at 240v than at 120? If the voltage drop is IR and I at 240v is 1/2 of I at 120v my voltage drop is less at 240. Thus the effective voltage at the motor wired for 240 is more than twice the effective voltage when wired at 120 and my effective power must also be higher.

I hope I haven't botched up my question too much.