Motor issue – Atlas 7inch Shaper

[Me.Participant @me1]

Advice please –

I recently acquired an Atlas 7inch shaper, have used a few times and all was well – or so I thought.

After watching a You Tube clip of someone using the exact same shaper they happened to mention they thought there shaper was running back to front – the fast stroke on the cut stroke rather than on the reverse stroke.

I started mine and all was as it should be the motor running the correct way with the push stroke slower than the pull stroke – I then turned the shaper off at the wall and left knowing mine was okay.

Returning the next day I started the shaper again and low and behold it is now running backwards but not every time – I can turn it off then on a few times and each time the shaper is either running correctly or running backwards.

What is going on ? – How can it run correctly on some occasions and then run backwards on others – Is the motor at fault, Capacitor on its way out ???

When I say shaper I really mean the motor – its either running clockwise (incorrect rotation) or anti-clockwise (correct rotation).

[Frances IoMParticipant @francesiom58905]

start capacitor open circuit ? disconnected? or start winding open circuit?

[larry phelan 1Participant @larryphelan1]

I have a motor fitted to a disc sander which does the same thing.

Seems to depend on the humour it,s in.

Makes things “interesting ” though.

[Frances IoMParticipant @francesiom58905]

forgot – also check the centrifugal switch on the motor that switches the start winding out of circuit – if jammed open then start winding not powered – generally the motor will start rather slowly as the start winding is there to give a pulse of drive in the desired direction.

[duncan webster 1Participant @duncanwebster1]

In my limited experience if thd centrifugal switch is jammed open a single phase motor just won’t start

[Frances IoM]

On Frances IoM Said:

forgot – also check the centrifugal switch on the motor that switches the start winding out of circuit – if jammed open then start winding not powered – generally the motor will start rather slowly as the start winding is there to give a pulse of drive in the desired direction.

There isn’t any lag in the start of the motor – I turn it on and its running at the correct speed almost immediately. Would this mean the switch is stuck. Where would the centrifugal switch be situated. Is there any thing else that it could be.

I’ve never experienced a motor which runs in both directions after each turn on or off.

[Speedy Builder5Participant @speedybuilder5]

I had a very old (1930s ?)  1/3HP motor that wouldn’t start until you pushed a stick through the ventilation holes to push the start switch contacts together. That was fun!

[DiogenesParticipant @diogenes]

Is it single or three phase?

[Diogenes]

On Diogenes Said:

Is it single or three phase?

Its running off a 240V supply – I assume the motor is 3 phase motor as it has a capacitor fitted.

 

Just need to know why a motor would run in one direction when powered up then in the alternative direction the next time it is powered up.

[Pete RimmerParticipant @peterimmer30576]

A motor fitted with a capacitor is almost certainly single phase. I sometimes convert 3 phase motors to single phase operation by using a capacitor but only on lightly loaded things like my little drill grinder.

Does your switch have the facility to reverse the motor? No reason why it should on a shaper but you never know it might be faulty or falling apart. Otherwise, it’ll be the start circuit in the motor itself, most likely the capacitor. Could be you have a wiee afloat in the junction box but that’s a long stretch.

[Me.Participant @me1]

The motor is original to the shaper so I assume the cap is to.

As the 7″ Atlas was always a single phase supply to the motor I doubt anything is amiss there with the supply.

The switch is either on or off – its not a two way switch so that rules that out.

If the Cap is on its way out would this cause it to run backwards ?

My limited knowledge of power supply is exhausted so could do with a motor master to help with this problem.

[MacolmParticipant @macolm]

Small motors sometimes have a single stator winding with a permanent magnet rotor. They start in either direction. I had such a shoe polisher, a good feature to keep the brush effective.

With a single phase motor with a failed open circuit capacitor, if the remnance in the rotor were sufficient, it might start in either direction. The poorer quality the rotor iron, the more likely this would be.

[john fletcher 1Participant @johnfletcher1]

I’ve been around with motors since  1953 and never heard of this one. WITH THE MOTOR DISCONNECTED FROM THE MAIN ELECTRICITY SUPPLY. Unfortunately you didn’t tell us the make of the motor. As the Capacitor will be on the outside and so its normally easy to change. For a very simple and crude test, get your friendly Electrician with his 500 volt DC Megger to charge up the Cap for you, leave it for while, then short out (put the Cap leads together) you should hear and see a spark. Your friendly Electrician may have a Multimeter with Cap test facility on it, that will only be 9 volts and capacitors for mains use, should be tested at normal working voltage, in this case 400, but the multimeter is better than nothing. Next, the motor needs to be opened up to locate the centrifugal switch. the centrifugal switch, start winding and the capacitor form ONE of two circuits. The Run circuit 4 to 8 Ohms and start one up to 60 Ohms a lot depends on who the manufacture was. John

[noel shelleyParticipant @noelshelley55608]

The assumption is it is a cap start induction motor – the OP has not said anything to tell us what type of motor he has ? If it is indeed an induction motor and the start windings or the start circuit is faulty then the motor IF it can start to spin will run either way. It is odd and I’ve never come across such a situation BUT that does not mean that under  strange circumstances it is impossible.

The OP must tell us what he has, Ideally with a picture of the data plate, then maybe we can help.  Where is the OP ?    Noel.

[Me.Participant @me1]

Thanks John and Noel – I will post a picture of the plate for reference.

 

[Dave HalfordParticipant @davehalford22513]

A normal cap start motor cannot change it’s mind on which way it wants to run without the start coil being rewired. A failed start cap normally presents its self as a stationary hum as above.

If it’s very old as in Great War there may be brushes which are very obvious, but these reverse by rotating the brush carrier. These have no cap at all.

Could a Stienmetz modded 3 phase motor behave like this?

[Me.Participant @me1]

This is the plate from the motor fitted.

FYI – No humming from motor – no slow starting – no obvious cracks bangs or smoke – it just runs in a different direction each time its turned on – there’s no logic to the rotation 3 out of 4 try’s it turns clockwise the next few try’s it turns anticlockwise.

 

I do have another more modern 1/2 horse motor with a 1400 RPM, its 3 phase but I can fit a Cap to convert to run on single – would be nice to know whats wrong with the original one.

 

[Dave HalfordParticipant @davehalford22513]

That’s very clean for 1959 vintage.

[Robert Atkinson 2Participant @robertatkinson2]

Unfortunatly the data plate does no reveal the type of starting, just that it is a single phase squirrel cage induction motor. Can you post a picture of the entire motor including any wiring? Does it have a cylindrical item, a capacitor, attached?

Robert.

[Macolm]

On Macolm Said:

…

With a single phase motor with a failed open circuit capacitor, if the remnance in the rotor were sufficient, it might start in either direction. The poorer quality the rotor iron, the more likely this would be.

Macolm’s suggestion seems likely to me.

Electric motors need some arrangement by which the magnetic fields in the stator and rotor push/pull each other so the rotor turns.   There are several arrangements, but, bearing in mind this is a simplified generalisation, once the rotor of a single-phase is turning there is no need for a start winding or capacitors. But something has to get the rotor moving in the first place.

Early single-phase motors were pull-started with a rope, but apart from lots of dislocated shoulders and fatalities, the method had a nasty habit of burning out motors if it didn’t start first time.   Automatic starting systems were soon added.  Usually start and run windings phased 90° apart convert the motor temporarily into two-phase.One type is fitted with a centrifugal switch that disconnects the run winding once the motor is turning; if the switch fails the lightly wound run winding might burn out.  Other types limit current through the run winding with a capacitor, or two, which also provide the phase shift needed to generate push/pull magnetic fields.

Single-phase motors are not simple.  Conceptually more difficult than 3-phase, as anyone who tries to design one will find out!  They’re complicated electrically and mechanically, vibrate, and have poor starting power and torque.  Unreliable compared with 3-phase, and hard to reverse too.

I think remanence explains what’s happening.  The start winding, or start capacitor or the centrifugal switch has failed, but there’s enough residual magnetism left in the rotor to move it when the run winding is energised.  If the rotor moves at all, the motor starts.

At restart the way the rotor turns depends on how it was magnetised when the power was turned off and it alternates 50 times per second.

More information needed to fix it.

Dave

 

 

[Me.Participant @me1]

I will post a picture of the complete motor.

The machine was very well looked after by its previous owner and has had a complete rebuild in the past.

Im not overly concerned about changing the motor to an alternative but would like to keep it original if possible.

The capacitor being the easiest thing to change I think this would the best place to start.

[John HaineParticipant @johnhaine32865]

If it has a capacitor, they are pretty cheap, just change it!  If you switch it on (as it is) and let it run up to speed then switch it off, as it slows down do you hear a click?  That would be the centrifugal switch operating which would indicate a cap start unless the switch is kaput as well.  If the motor runs fairly quietly then no need to change it once the start direction is fixed.

[noel shelleyParticipant @noelshelley55608]

The click of the centrifugal switch is good to hear but not all motors make enough noise for it to be heard. Checking the wiring on the terminal plate/board will/should indicate if there is a fault on the start circuit. A motor of that age the centrifugal switch may well have failed.  A motor rewind firm will check the cap for you or just change it – if you know the value – it MUST be a motor start cap and note the voltage. Where abouts is the OP ? Someone may be near and be able to help.   Noel.

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