Motor help required.

Hi guys, I need some advice / guidance from the electrical motor community. I recently purchased an old modified Burgess band saw. When i first got it it ran OK. But recently when I power it up the motor hums but does not move. If I turn the pulley wheel manually whilst the motor is buzzing it starts and runs OK. I disconnected the drive belt, tried again with the same result. Can anybody advise what might be wrong.

Thanks in advance, Alan.

Edited By alan ord 2 on 10/09/2023 18:29:26

Hey Al, It very much depends on the type of motor. It sounds as though you have a fault on the start windings, this could be numerous things. Does it have a capacitor on it , a round lump ? This may have failed. If it has a centrifugal switch this may be playing up, contacts, spring, or just broken. Open circuit start windings. Does it have brushes if so then the brushes or commutator is the fault. There's a few to start with. Good luck Noel.

Your symptoms are typical of a failed capacitor or a centrifugal switch problem. Some pics of the motor including the data plate would be helpful. The capacitor is usually mounted in a housing on the exterior of the motor. Some motors may have two capacitors and are described as capacitor start, capacitor run. Capacitor start will have one capacitor. The centrifugal switch is internally fitted in the motor and is used to switch the capacitor out of circuit when the motor is up to speed. If no capacitor is fitted then the motor could be of the split phase type which uses the centrifugal switch to switch a start winding out of circuit when up to speed. Your motor is unlikely to be split phase as the starting characteristics are poor compared to a capacitor start motor.

Mike

Thanks guys for the quick response. To be honest a lot of what you described went straight over my head. I will get some photos tomorrow and post them.

Thanks, Alan

To understand the set up better, read the thread on "Capacitor Selection".

The "Silly Old Duffer" post of 21:27 on 10/09/21023 shows very clearly the wiring circuit.

If you set the motor running, and then switch off, as it slows down you should hear a click.

This is the centrifugal switch remaking contact.

I am not an electrician, but my understanding is that when stationary, the centifugal switch makes contact, bringing the capacitor into circuit.

The start windings are then "live", but being fed via the capacitor, are out of phase with the main running windings.

This results in a torque which starts the rotor moving. As the motor speeds up, the centifugal switch opens taking the start windings out of circuit. The motor than runs on the "slip" between the magnetic field produced by the main eindings, and the field induced in the bars of the rotor.

In a motor that has seen use over a number of years, the capacitor could have failed, or the centifugal switch contacts may be burned and no longer making contact.

Replacing the capacitor (Note the comments about the voltage rating, it needs to be rated well above 250 volts ).

It is possible that no direct replacement centrifugal switch is available. If this is the case, either the existing one has to be repaired in some way (IF this is possible ) or a switch that is available, modified to fit. Again IF this is possible.

If you are unsure about what you are doing, involve someone who really does know\ what they are about.

You should be able to find a company that specialises in motor repairs, local to you.

When swarf got into the mmotor on my Myford, a local company managed to repair the damaged switch quite easily.

230 volts could prove fatal, or cause a fire.

Original Burgess bandsaw doesn't have a capacitor, haven't seen a centrifugal switch either.

Regards Ian.

BK3

Regards Ian

Alan, where abouts in the country are you ? There may be one of us close to you. Howards point is a good one - if having run the motor at it's rated speed, then turn it off and as it slows you MAY hear a click, this will be the centrifugal switch re setting, some are louder than others. I have a De walt band saw, it doesn't have a capacitor, this is as Ian has said. Noel

Hi guys, I have attached some photos of the motor. Don't know why they are not the correct way up. Maybe one of the moderators can correct and possibly advise me where I went wrong. The photos were the correct way on my PC.

Noel I am based just south of Doncaster.

Howard / Noel, after lunch I will try to listen for the centrifugal switch click.

Circlip, what do you mean BK3. I know very little about motor electrics.

Where is the centrifugal switch located? Can I access it by removing the motor end cap and how do I recognise it. Sorry for the dumb questions.

Regards,

Alan.

BK3 is a bandsaw model. Nothing to worry about ! From the pictures it doesn't use a start capacitor.! The motor is oldish so when working on it be mindful that old/rubber insulation on wires may disintegrate. A first step would be to check IF you have continuity on both sets of windings. For this remove the cover of the terminal block, NOTE WHERE the mains wires go. At this point you will need a multi meter or a friend with one to check that there is continuity on both the start and run windings. It looks as though there is a fault in the start circuit. A good picture of the terminal block will be needed if we are to guide you ! The centrifugal switch will be in the end cover where the terminal block is - Non Drive End. Noel.

Interesting situation????? Tried a couple of times to start and stop the motor and listen for the centrifugal switch click. Did not hear anything. Had to assist the start by turning the motor pulley. Tried a third time and this time heard a click as the motor slowed down. Retried the motor again and it started and ran without the need to turn the pulley wheel. Tried three more times and its now working OK. Sounds like I may have an intermittent fault.

Does the centrifugal switch need replacing?

Regards,

Alan.

So the evidence points to an intermittent problem and maybe that the switch is sticking.

My approach would be to disassemble the motor and check the centrifugal switch is sliding freely on the rotor shaft and clean/lubircate if necessary.

Andy

As with Andy, sounds like it became stuck. Clean and use light oil sparingly ! Noel.

Andy / Noel thanks for the info. I will check the centrifugal switch as you suggest. The motor did stick again but after a few cycles it corrected itself again so I do need to fix the switch.

Thanks all for your guidance.

Regards, Alan.