Can this motor be wired for 110v?

[BaronJ]

I have a 3/4hp 110v motor that only runs at 1750rpm. I use a larger pulley on the motor to double the speed right? It shouldn't hurt performance right?

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This depends upon what you perceive as performance.
In practice you can't get more power out than you put in. Yes you can double the speed by making the motor pulley larger but the torque will be less.

As an example 1 horse power is 746 watts so your 3/4HP motor will draw 560 watts. This is also the maximum output power less any losses. These losses are seen as heat. Its the reason the motor warms up. As you increase the load on the motor the losses increase and the motor warms up even more.

So when you have doubled the speed if you don,t try to take more energy out than you put in all will be OK.

 

[kd0afk]

I knew there was a loss somewhere. Thanks

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[dman]

3/4 hp is 3/4 hp and speed is a factor of hp. by that reasoning that faster motor has half the torque by default. since the 3/4 hp is more than the 1/2 hp i think you'd be clear with that combo assuming you can find the needed pulley, the difference in thermal losses won't be enough to need over 50% more power.

anyway, if you have heavy enough wire going to the main panel you might be able to make it a 220v circuit. i never saw a 15 amp common trip (220v) breaker so you would need more than 14 gauge wire, if you have 12 gauge you can get a 20amp breaker, put a sub panel into the area and use that to distribute the ground as ground as well as neutral and allow you to add breakers for 110v. basically when you have 2 circuits on opposite phases/polatiry you are allowed to share a neutral because the only current on the neutral is the difference current between the two hots, as far as grounds you can share grounds over multiple circuits and the sizing needs only be as large as the required for the largest circuit and not a combined value of all the circuits. i don't know how you have the wiring but there are several ways you may be able to convert to 220v without adding new wires in the case that the breaker isn't rated higher than the wires.

if that's not an option you can get an auto transformer. which is a single coil transformer and are found used on ebay for stepping up/down ac power. you may find them with many taps for multiple voltages. with an auto transformer that is only made for one step up/down there are 3 connectors. one for each phase in and an extra one for the step in voltage. you would use one of the conductors from the supply voltage to complete that circuit.

as far as the motor, i can't read the plate, i'm assuming it's a single phase? if it's 3 phase you need a phase converter and there are power inverting phase converters. i'm not sure if they make passive phase converters that way (but you can add an auto transformer) but a variable frequency drive would be available in a step up version with 110v in and 220v out (but these only put out 3 phase, leaving a phase open would be very bad). i'm having pretty good success with a cheap generic Chinese vfd on my knee mill.

there are several ways that you may be able to go but i can't say which is best without seeing your home.

 

[cfellows]

This is more of a question than a suggestion, so if you decide to try this, understand that you may blow a circuit breaker (or worse)

Since the white wire would normally be neutral and the red and black wires go to the opposite 110v polarities, wouldn't it work on 110v if you hooked the 110v ground side to the white wire and the 110v hot side to both the red and black wires? You would be doubling the amps but it still shouldn't be more than 10 or 12 amps under full load, right?

Chuck

 

[BaronJ]

3/4 hp is 3/4 hp and speed is a factor of hp. by that reasoning that faster motor has half the torque by default. since the 3/4 hp is more than the 1/2 hp

No it is not ! The speed of an induction motor is a function of the supply frequency and the number of poles the motor is wound with.

 

[BaronJ]

This is more of a question than a suggestion, so if you decide to try this, understand that you may blow a circuit breaker (or worse)

Since the white wire would normally be neutral and the red and black wires go to the opposite 110v polarities, wouldn't it work on 110v if you hooked the 110v ground side to the white wire and the 110v hot side to both the red and black wires? You would be doubling the amps but it still shouldn't be more than 10 or 12 amps under full load, right?

Chuck

Hi Chuck,
You cannot safely connect the red and black wires together ! That would cause a short circuit across the pole transformer.

 

[cfellows]

Hi Chuck,
You cannot safely connect the red and black wires together ! That would cause a short circuit across the pole transformer.

Baron, I'm talking about the red and black wires in the motor, not the ones from the breaker box or mains.

Chuck

 

[dman]

No it is not ! The speed of an induction motor is a function of the supply frequency and the number of poles the motor is wound with.

absolutely, that is what regulates the speed, but that's unreleated to what i'm saying.

hp is rpm*torque(in ft/lb)/5252... so if the power is equal and you half one factor the other must double. i understand that the power consumption and production depends on load and they don't constantly draw the rated hp without regard to load and bogging a motor will create slippage in the core and result in heat generating eddy currents and los of efficiency. i'm not saying bogging a motor to half speed would create the same hp and power draw.

what he asked is if he could substitute a 2 pole 3500rpm motor with a 4 pole 1750rpm motor and make up the difference with a bigger primary pulley. we are not talking about bogging a 3500rpm motor down to 1750 rpm... that would be silly. and what i'm saying is that if the rate of work is the same ( it will be if the second pulley effectively spins the same speed which is what our goal is in using a bigger pulley with a motor that has more poles) then the power consuption is the same and the motor rated hp requirement is the same so actually increasing the rated hp because he happens to have one will only give a surplus of power which isn't always a bad thing.

 

[RonGinger]

Chuck your idea might work depending on the motor, but all the motors Ive seen for 240v do not have the center tap wire. The white may simply be a shell ground- although that ought to be green.

If this were a 120/240v motor then it would work, but there would have to be more wires.

 

[Noitoen]

I've rewound thousands of motors in my time and insist, he should open the motor and inspect the winding connections. If they are in series, all he has to do is, disconnect this connection, solder 4 new wires and end up with a 120/240V motor in 30 minutes.

 

[BaronJ]

Baron, I'm talking about the red and black wires in the motor, not the ones from the breaker box or mains.

Chuck

Hi Chuck, apologies for my confusion. I thought you meant from the breaker box.
I hadn't realised that the wires in the motor were those colors.

Sorry. :wall:

 

[BaronJ]

absolutely, that is what regulates the speed, but that's unreleated to what i'm saying.

hp is rpm*torque(in ft/lb)/5252... so if the power is equal and you half one factor the other must double. i understand that the power consumption and production depends on load and they don't constantly draw the rated hp without regard to load and bogging a motor will create slippage in the core and result in heat generating eddy currents and los of efficiency. i'm not saying bogging a motor to half speed would create the same hp and power draw.

what he asked is if he could substitute a 2 pole 3500rpm motor with a 4 pole 1750rpm motor and make up the difference with a bigger primary pulley. we are not talking about bogging a 3500rpm motor down to 1750 rpm... that would be silly. and what i'm saying is that if the rate of work is the same ( it will be if the second pulley effectively spins the same speed which is what our goal is in using a bigger pulley with a motor that has more poles) then the power consuption is the same and the motor rated hp requirement is the same so actually increasing the rated hp because he happens to have one will only give a surplus of power which isn't always a bad thing.

Thanks for the clarification. Your post was a little unclear.

 

[BaronJ]

I've rewound thousands of motors in my time and insist, he should open the motor and inspect the winding connections. If they are in series, all he has to do is, disconnect this connection, solder 4 new wires and end up with a 120/240V motor in 30 minutes.

I saw your original post and was going to comment.

Yes I completely agree with you. An inspection of the windings would reveal all.

 

[kd0afk]

I just saw another motor that can be wired for both 110 and 220. The data plate states that. That's where I was getting fouled up. I thought a 220 motor could be wired for 110 but now I realize that it has to be made that way to be wired that way. Didn't realize it had to be made that way.

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[kd0afk]

I just ordered a step up/down 100 W transformer. I'll try that and see how it does. I will probably git rid of the plastic case and mount it in a box with a fuse and cooling fan.
I remember living in Germany as a kid all of our appliances were 110v so we had to use this 20 lb transformer.

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[Herbiev]

If the motor is 3/4 hp that is about 560 W so a 100 W transformer probably won't do.

 

[kd0afk]

It's 1/2 hp. But it's amps x volts. It's a 3.5 amp motor and at 220v it would mean I need a 770watt transformer? I just looked and found a 1000w up/down power converter for $50.

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[dman]

It's 1/2 hp. But it's amps x volts. It's a 3.5 amp motor and at 220v it would mean I need a 770watt transformer? I just looked and found a 1000w up/down power converter for $50.

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that sounds like a perfectly reasonable price..

the running amps are probably less than the amps rating. that could be starting current or max load current. i'd hate to think an asyncronous induction motor is 50% efficient, and the actual machine load will ahve something to do with the actual current. i mean there will be a minimum free spinning current. a stalled current, and a start current. when it's free spinning/no load it's doing no work, and when it's stalled it's doing no work. in these situations you have 0% efficiency. but in the right load range the motor should be quite efficient. but i'm not really sure how they come up with the ratings. the hp can be something like the power it produces without heating up. it may acutally produce more if the load demands it. and the current isn't necessarily the running current at the rated hp... either way it would help to have a somewhat bigger transformer than the math suggests if for nothing more than piece of mind..

 

[kd0afk]

I think the transformer would be the best option. I've priced motors and it seems that the higher the voltage the less expensive.

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[BaronJ]

Hi Guys,
The ratings on the motor plate are the full load current and voltage. There is often a temperature or temperature class rating code. This is the temperature that shouldn't be exceeded when the motor is running normally. There may also be other information on the rating plate such as HP, shaft size, rotation direction and wiring data. Sometimes there is information about the starting type CF or CSR.

The one thing that usually isn't on the rating plate, at least on smaller motors <3Hp is starting current, which can be three to five times the running current. The starting current usually only lasts for a very short time, but it is something to be aware of. I've seen motors mistakenly scrapped because feeding fuse or breaker has tripped.