UPDATED: Mechanically Braked Motor not working

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Mike-W

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I would be grateful if a member with some knowledge of woodworking machinery motors could explain how my Electro magnetic motor on my Italian built bandsaw (Startrite/ACM) should work. I’ve not had a any problem before yesterday, but after having to replace the 2 amp internal fuse that protects the control circuitry twice I now find I cannot manually switch off the brake so to be able to freely turn the bandsaw by hand nor when turning on the saw to run will the motor run up, the motor hums as if it wants to spin up but will not turn – it sound to me as if the “positive brake - disc and plate mechanism” (as described in the sales brochure) is not disengaging as it should.

Looking at the connection box on top of the motor there are 5 wire’s, an earth , a black (L) and blue (N) approx 1.25mm2 onto the motor windings, these power up when operating the motor run switch. There is also a blue and red wire (approx 0.75mm2) that connects into a blue box within the motor connector box, there are two very fine wires that come out of this box and disappear into motor casing.
I have followed the circuit from the Brake Release switch into the motor connection box and the red becomes live when this switch is operated, a test lamp across red & blue (N) lights when the switch is operated as indeed the lamp also illuminates when the motor run switch is turned on.

The instructions have an exploded view of the motor and mentions a rectifier diode in the motor, it’s a poor reproduction and lacks any description of the numbered components.

I’m assuming from the bandsaw circuit diagram that any fault is likely to be in the connector box or in the motor as apart from the brake release switch on the bandsaw frame I don’t see any components controlling the motor braking.
The photo below shows the connection box and the blue box inside, i'm not sure what it is or what the two terminals in the middle (+ & -) should read on my test meter.... any ideas please?
 

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flh801978

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The blue device is a bridge rectifier it converts ac to dc as your brake needs dc
If you have 240v ac on the outer 2 terminals you should have approx 240v dc on the inner 2 which go to the brake

Ian
 

flh801978

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Just another thing I've noticed the top right terminal on your green block doesn't look to have a nut on it holding the crimp connection on
 

Mike-W

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Thanks Ian,
Its good to learn something new!
I'll check that with my multi meter after dinner.
Is that the same as what the instructions describe as a rectifier diode?
(In my distant past IIR rectifiers were used to convert AC to DC)

well spotted i put the nut back on after the photo was taken i had removed it to check the wiring run.
 

flh801978

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Disconnect one of the two inner wires on the bridge rectifier and check for continuity of your brake coil whilst you are in there with your meter
 

Mike-W

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flh801978":a5yh7fei said:
Disconnect one of the two inner wires on the bridge rectifier and check for continuity of your brake coil whilst you are in there with your meter
flh801978":a5yh7fei said:
The blue device is a bridge rectifier it converts ac to dc as your brake needs dc
If you have 240v ac on the outer 2 terminals you should have approx 240v dc on the inner 2 which go to the brake

Ian
Well i have checked the output on the Bridge Rectifier and am getting 115.3 volts DC,
going on to check the brake coil continuity and my meter is showing an open circuit.

I'm thinking this could be expensive....
i'll contact the current importers tomorrow and AES rewinds (the only motor repairers that i know of)
to get some idea of the way forward,
Thanks again Ian, it looks as if you have taken me straight to the fault.
 

flh801978

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If it is expensive you could remove the brake rotor if you don't need it to dead stop. My start rite has a braked motor but I have wired it so it coasts to a stop then applies the brake or if the emergency stop is triggered then the brake comes on
 

Mike-W

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I would certainly be interested in that option as i'm a solo hobbyist and therefore I don't think there is a legal requirement for my machinery to stop within 10 seconds.
I was wondering about fitting an un-braked motor if cost provide exorbitant.
Can I get back to you once i have investigated repair options please?
 

sunnybob

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Just a question, Dont know about braked motors, but is there a capacitor on the motor? your description of humming but not running is pure capacitor failure talk.
 

Mike-W

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sunnybob":1agu7nue said:
Just a question, Dont know about braked motors, but is there a capacitor on the motor? your description of humming but not running is pure capacitor failure talk.



Thanks Bob -
The motor is hard to turn with the brake switched to disengage, it should spin freely.
I have checked the capacitor any way and its close to the required value of 45uF as i have needed to replace a few on different motors recently.
 

Myfordman

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On some brakes there is a screw adjustment in the centre of the hub under a cover to adjust for wear in the friction plate. You might be able to adjust this to a position where the brake is off all the time.
Good luck.
 

Mike-W

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Well….
After a lot of chasing around i’ve got the motor fixed.
Yes the brake coil had got open circuit, it turns out the half wave rectifier was working fine.
I considered backing off the brake but my wife (the ‘H&S’ boss) insisted I got the brake fixed!
I was unable to find a rewind company in the south interested in fixing it. I did get a quote on a replacement coil and rectifier from Italy- (i was unsure at that point what needed replacing), this option was looking pricey .
Meanwhile I found a company ‘up North’ who could not have been more helpful, I took the motor to them and they rewound the coil and checked the motor over, i’ve now got it back on the Startrite bandsaw running as good as new.
The company- Richard Hough Ltd of Bolton (rhrewinds.co.uk) were very competitive, professional and fast- if any forum members are looking at woodworking machinery motor repairs in the future, i would certainly recommend them.
 
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