Can this small motor be reversed?

[HollowpointParticipant @hollowpoint]

I have a small motor I salvaged from a scroll saw I would like to use for a project but it is running anticlockwise. I need it to run it clockwise.

I've opened it up and from my research it seems all I have to do is change the brown live wire from the centre (B) to the left (A) Leaving all other wires as they are. Is this correct? It seems too simple? I don't want to blow anything up!

[HollowpointParticipant @hollowpoint]

[Robert Atkinson 2Participant @robertatkinson2]

Would need to see the motor data plate to be 100% certain, but NO moving the wire will not work.

You need to reverse the connections to the start winding. Only one end of this winding is visible in your photo, the grey wire connected to terminal "A" . The problem is that the other end is inside the motor somewhere. You will have to dissasemble the motor and investigate. Even then it may be buried in the winding and unreachable.

EDIT: As a general rule to reverse any type of electric motor electrically you need to swap or move TWO connections. One noticable exception is some special motors that have two sets of windings, one for each direction. These were / are used in valve actuators and the like.

Robert G8RPI.

Edited By Robert Atkinson 2 on 04/07/2022 21:07:18

Edited By Robert Atkinson 2 on 04/07/2022 21:17:14

[noel shelleyParticipant @noelshelley55608]

Robert has it ! You need to find the other end of the start winding, It will need to be found and brought out. May be easy to spot – may be not. Good luck. Noel

[duncan webster 1Participant @duncanwebster1]

That's not actually correct, you can reverse a Parvalyx motor by just swapping the live from one connection to another. When I get home I'll find the diagram and post a link. Can't work out how to do this on a phone.

[HollowpointParticipant @hollowpoint]

Thanks for that. Unfortunately the motor doesn't have a data plate which is why I thought I better ask.

It was this YouTube video that suggests you can swap just the one wire.

**LINK**

[MacolmParticipant @macolm]

It may not apply to the motor in the photo, but sometimes the shaft and end plates can be swapped on the frame (ie the windings reversed with respect to everything else). The shaft then projects the other way, and thus rotation is reversed. Usually works for shaded pole motors.

Edited By Macolm on 04/07/2022 22:13:19

[noel shelleyParticipant @noelshelley55608]

IF lower A is the start winding L1 and it's tail N must be to LowerC ? Run must be lower B and lower C ? swaping upper B and C will reverse the start and the run will keep it spinning ? Noel.

[John HaineParticipant @johnhaine32865]

https://www.model-engineer.co.uk/forums/postings.asp?th=133409

**LINK**

[duncan webster 1Participant @duncanwebster1]

Posted by duncan webster on 04/07/2022 21:31:56:

That's not actually correct, you can reverse a Parvalyx motor by just swapping the live from one connection to another. When I get home I'll find the diagram and post a link. Can't work out how to do this on a phone.

see this. I think what is happening is that there it is a capacitor start and run motor, and there are are 2 identical windings. Swapping the live feed changes which winding is fed through the capacitor, and so changes the direction of rotation. Of course we don't know that the OP's motor is like this.

[EmgeeParticipant @emgee]

Agree with Duncan changing the live from B to A will reverse the motor as per Parvalux.

Emgee

Edited By Emgee on 04/07/2022 23:25:51

[V8EngParticipant @v8eng]

Some motors have a wiring diagram fixed inside the connection box cover.

[john fletcher 1Participant @johnfletcher1]

I think the answer is NO. You would be very fortunate to locate the common connection, experience is what is needed here, also you say there isn't a name plate so is the motor RPM going to OK . To locate the common connection you will need an ohmmeter, your motor will have a higher resistance for the start winding and much lower for the run, maybe around 6-8 ohms. Leave well alone, at the moment you have a useful motor but might finish up with a scrap one. Parvalux three lead AC motors are altogether different both windings have the same resistance. John.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, the fact that this motor has a blue, brown and a grey wires, suggests to me that it is not like a Parvalux motor, which I always though their AC motors have black and white wires only on a three wire one. You need to check the resistance as John Fletcher 1 has said and I would think the blue wire will be common, meaning the resistance between blue and brown, and blue and grey would be the same, however if any of the other two wires are common you will still need two pairs that are the same resistance, but you will need to remove those top three wires to be sure to get true resistance readings and if the resistance readings are significantly different, it probably means it can't be reversible by just swapping the A and B wires.

Regards Nick.

[Robert Atkinson 2Participant @robertatkinson2]

The difference is if it is a capacitor start or capacitor run motor and the parameters of the windings. I admit I had forgotten about the parvalux style. These are capacitor run with identical windings and can be reversed. Most capacitor run motors don't have equal windings so need two wires swapped.
The OP's motor appears to be capacitor start. This is based on the physical desgn and size of the capacitor, so is just an educated guess. If capacitor start then agin two wires to reverse.
A resistance measurement between the 3 connections might give a clue if it is capacitor run or start or even if windings are the same. If the resistance between A and B is different to the resistance between B and C it cannot be a balanced capacitor run motor. If they are the same it might be, but even then it's not 100%, the inductance of the two windings would have to be measured to be sure.

With no information just moving the wire has a risk of letting the magic smoke out.

Robert G8RPI.

[MacolmParticipant @macolm]

If you can lay hands on an old fashioned halogen security lamp, best 500W or else 200W minimum (and no more than 500W), include it in series with the mains feed. If the motor (wired as is, and without mechanical load) runs, and the light does not come on at full brightness, then it is (fairly) safe to try it with the brown wire moved to the "grey" position. If it now runs the same but in reverse you can try it without the lamp in series. If at any stage the lamp comes on full, switch OFF immediately.

[duncan webster 1Participant @duncanwebster1]

You can check if it is capacitor start rather than capacitor run. Connect a voltmeter across the cap and start the motor. If it is cap start you'll get a voltage which very quickly disappears as the centrifugal switch opens, if it's cap run the voltage will persist.

[MacolmParticipant @macolm]

As Duncan Webster says you can easily check if there is a start switch. If so, and it is on the neutral side of the winding, you can rewire, and problem solved.

If it is a run capacitor, check for nearly equal winding resistances, and if so, likely simply a case of moving brown wire, but see my previous post to do it safely. If unequal, it is a case of completely reversing one winding with respect to the other.

I do suggest the halogen (filament lanp) method to reduce risk. I had assumed these would be banned from sale by now, but I find both Toolstation and Screwfix still offer replacement lamps (250W, 400W and 500W). Toolstation also seem to have the halogen. security lamp housings. For anyone who occasionally has to fault find or investigate workshop power electrics, this could be a good and cheap investment. Without a housing, it should be OK to solder on to the caps of the bulb, since if used correctly for this purpose it will never get to anything like full temperature. Of course, a suitable mounting and safe configiration is necessary.

[john fletcher 1Participant @johnfletcher1]

The lamp limiter as it is know as in the repair trade and as described by Malcolm above, is a very simple and useful electric test gadget, well worth making. For mine I have 4 BROWN batten lamp holders mounted on a length of wood, 13 amp plug and lead one end, 13 amp socket outlet and three terminal the other for the load so that I can insert an ammeter, all covered by a bit of stainless steel mesh over the bulbs to let the heat out and to stop the bulbs from being broken. These Gadgets were well know in the radio, tv rand electrical repair trade in the 50', simple and reliable. John

[SillyOldDufferModerator @sillyoldduffer]

My guess is swapping the wires won't cause magic smoke or reverse the motor. But I don't know for sure!

I think it's a capacitor start and run motor where the start and run windings are identical and one end of each is wired together inside the motor and brought out to terminal C,

The circuit 'as is' and with the proposed change could be:

Swapping just the capacitor as shown in the lower circuit risks magic smoke because it depends on how beefy the top winding is, and we don't know. No problem if both windings are physically identical, but the capacitor connected winding might be wound with lighter gauge wire in expectation the current through it is limited by the reactance of the capacitor.

The reason I don't think swapping the capacitor will reverse the motor is that the start of the two windings, marked by solid filled triangles, isn't changed by moving the live connection, so current still flows in the same direction in both coils. As moving the capacitor doesn't change the direction of the current, I think the magnetic fields flow in the same direction, albeit the phase is different. Therefore I expect the motor to rotate in the same direction, and possibly be reluctant to start.

To get the motor to reverse, I'm fairly sure one of the windings has to be reversed. This can only be done by opening the motor up, finding the join, separating the two windings, and swapping one of them over.

Dave

 

Edited By SillyOldDuffer on 07/07/2022 12:15:58

[Robert Atkinson 2Participant @robertatkinson2]

SOD said

"The reason I don't think swapping the capacitor will reverse the motor is that the start of the two windings, marked by solid filled triangles, isn't changed by moving the live connection, so current still flows in the same direction in both coils. As moving the capacitor doesn't change the direction of the current, I think the magnetic fields flow in the same direction, albeit the phase is different. Therefore I expect the motor to rotate in the same direction, and possibly be reluctant to start. "

The capcitor introduces a 90 degree phase shift in the current. Thus moving the live reverses the phase relationship between the two windings and the motor WILL reverse direction.

The problem is the capacitor also introduces an impedance in series with the winding. Depending on the detail design of the motor, which we do not know, the windings may or may not be different to compensate for this. If the windings are different then the currents will be outside the design parameters which may or may not cause damage or / and poor performance. Motors DESIGNED to be reversed with just a single wire cange to different sides of a capacitor will have identical windings. This however introduces compromises, the windings are likely to use thicker wire and be heavier and costlier. Performance is likely to be reduced compared to a single direction motor.

Question for OP, are there any markings on the capacitor? What are they?

[Author]

Posts