Thread: How to change rotation direction of elec motor

There should be a schematic where you connect your wires that show how to reverse the rotation of the motor. If there isn't one then you probably cannot change the motor's rotation.

Paul

If the motor doesn't reverse by rewiring you can turn it around 180 degrees and mount it the other direction. You may need to build a new bracket, but that is generally pretty simple. Good luck.

I am no electrician, but the only motor I thought you could change the direction of rotation on was a DC motor.

Wattie, I might talk rubbish, so take it with a lot of salt. I grew up with electric motors (dad's factory) but what I knew is mostly forgotten.
My advice is to restore the original connection to the capacitor immediately while you find out how to change the motor's wiring if it's possible. Piece of cake with 3phase, can't remember how to do it in 1phase. If the motor is still running slower after you have changed back, you need to check that one section of the motor's wiring is not a) burnt already or b) disconnected, for example because overheating has melted a weak soldered connection. If this is the case, further use will just result in complete burning, while you might be able to save the motor if it is case b).

If all returns to normal, the reason of the slowing is that you messed up the earth connection and the motor was running at reduced voltage. No immediate damage done, but don't risk blowing everything up next time.

Cheers
Frank

I would suggest a 2 hour drive to get it done by an electrician makes far more sense than a similar ride in an ambulance or heaven forbid a hearse. Jon.

Originally Posted by Wattie

Hi All

I have just purchased a new 2.5 hp single phase electric motor to put on my dust extraction fan only to realise that it is running in the wrong direction.

I have swapped the wires running from the capacitor into the motor and this changes the direction of rotation but the motor does not spin as fast.

will i stuff the motor if i run it reversed ? or have i swapped the wrong wires around?

Any help would be greatly welcomed as the closest electritian is 2 hours drive away

Little boy,
Electric wires.
Blue flashes,
Boy's ashes.

thanks for your input every one, I think the safest and probably best solution will be to build a new mount for the motor and forget about rewiring it. Will get to it through the week.

Another question about the motor though, what revs should the fan run at? the motor runs at 2800 rpm
current set up is 3 1/2 inch pully on motor and 1 1/2 inch pully on fan.

by my calculation the fan should run at approx 6500 rpm with that setup. would that be fast enough?

By way of explanation the fan is one i picked up second hand and used to have a 3 phase motor on it. I only have single phase

The motor was missing though (thats why i dont know what speed the fan should run at)

The fan is 12 inch diameter with 6 inch out let and inlet

I just happened to have a 3 1/2 inch pully in the shed thats why i am using it.

The fan came with the 1 1/2 pully already on it. The belt guard looks like it was made to accomodate a fairly large pully on the motor maybe up to 8 inch.

Any ideas?

Most spin at 2850rpm, the old motor may have been a slow speed one.

Take note Some motors are reversable some are not ALL CAPACITORS ARE NON REVERSABLE put back how it was or the capacitor may explode

Wattie,

There are several types of motors using capacitors.
1. Capacitor start / Induction run
2. Capacitor start/ Capacitor run a
3. Capacitor Start/Run

The difference between 1 and 2 as opposed to 3 is that 3 does not have a centrifugal switch to switch out the start winding. This gives smoother torque in the motor.

All have 2 windings a start and a run winding. Reversing the ends of either the start or run windings will reverse a single phase motor.

As for speed, the speed of a motor is determined by 120 * frequency / number of poles.
So for a 2 pole machine ( which is the fastest, as a motor dont work with one pole) is 3000rpm (synchronous speed). For a motor to develop torque there must be a difference between synchronous speed and actual speed.

Most 2 pole motors run at 2800 to 2850 rpm. The difference is called 'slip'

What was the HP of the motor that came off? If it is the same as your single phase motor you will require the same size pulleys or risk running out of horsepower.

woodcutta

What sort of fan is it? Photo?

Not sure who made the fan. I was told the original 3 phase motor was probably 3 hp.

will post some photos as soon as i work out how

Originally Posted by woodcutta

What was the HP of the motor that came off? If it is the same as your single phase motor you will require the same size pulleys or risk running out of horsepower.

Provided that the motor's speed is also the same. It is quite likely that the old motor was 4 pole => 1400 rpm for better torque, as you said yourself. The pulleys' ratio in this case would have been double to achieve the same fan speed.