How can I build a Dynamic brake for a 1/3hp single phase 110/220v 50/60hz AC motor for cheap?


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shanren2 years ago

Hi there, I got the same question here, I'm making a EDM wire cut machine. the motor doesn't stop immediately when the reverse relay triggered during the reciprocation. I am planning to make a brake shoe wrap on the surface of the one end of the wire roller which drived by electromagnetic rod.

Do you mean a DC injection brake  ?
.  http://www.google.com/search?q=DC+injection+brake
There are some circuits around, but its a very not easy thing to do without a lot of experience. You have to totally isolate the motor from the supply before injecting DC (often from a big, low ESR capacitor) If the motor isn't designed for it DCIB can cause it to explode from the deceleration forces.
Hopper1974 (author)  steveastrouk8 years ago
I am not sure what kind it would be.  Since the motor coasts about 2 1/2 revolutions before it comes to a hault.  Over time it heats the motor up to much and then starts to disrupt the timing postion on where it is suppose to stop.  I am assuming this is due to the heat issue.  The revolutions before stopping become longer and longer in revolutions.  It then locks out the machine when it gets to far out of time with the safety circuit. 
lemonie8 years ago
Are you using the motor for drive at the moment and what is it powered by and driving? Do you want to store the energy generated or lose it as heat?

L
Hopper1974 (author)  lemonie8 years ago
Using it as a drive motor.  Using it with 110v but would also need it to be powered for 220v.  The motor is mounted and is driving a gear box.
Could you be really-specific about the motor and gearbox, exactly what type they are makes a difference. I do expect someone or I can answer it with full details.

L
Hopper1974 (author)  lemonie8 years ago
It is a universal type motor I guess.  The gearbox is a oil bath style gearbox with a side output to drive a drive shaft which goes to an assembly on a machine.  Total run time would be 8-10 seconds at a time for each stop position.  The gearbox gears are a planetary style gear assembly.  The original motor (old style 50+years)  was a continuous duty 1/3 horse motor.  All the new motors that are continous duty that I have tried work but they don't stop on a dime like the old style motor.  Someone told me that the old style motors used regenerative braking built into the motor itself.  The new style I am trying to use has an external capacitor to start it but it winds down instead of stopping on a dime.  Trying to figure out a simple circuit to build to make it stop on a dime using the start windings to brake it.  The motor since it is 110 or 220 has 2 run windings inside it.  Motor I am using is a Leeson motor.  Gearboxes I am using are national brand and also a GE/Westinghouse brand gearboxes.
Ah right, you want to stop the motor rather than brake what's connected to the output?
I wonder whether you'd be better with a motor brake if you want it to stop on a dime? Dynamic brakes do not work well at low speed, they'll not give you the hard-stopping you'd like. Steve' will probably know better than me on this question.

L
Hopper1974 (author)  lemonie8 years ago
The old national motor has a carbon brush block inside that enables it to stop perfectly.  The GE and Westinghouse motors only have a dual switch setup but nothing as for a mechanical brake but the still stop on a dime.  I am thinking it might be because of the centrifugal weight mechanism for the switches that help it stop.  The output on the gearbox is just a splined shaft that has timing cams mounted on the shaft end then at the end of the shaft it connects up to a weldment assembly to move it up and down by an arm that is connected to the shaft and then to the weldment assembly.  The motor that I am trying to use is 1750 rpm at 110v and 1425rpm at 220v.  I think the gearbox has a 14:1 ratio for the gear reduction on the output.  There is a company out there that is using a motor brake setup on there motors but they tend to fail and not work as they should.  That why I am trying to see if a dynamic brake will work instead.
The brush block it's self won't brake, there may be a switching mechanism that acts with the electricals (inc. brushes). I don't see an electric-brake giving you a hard-stop unless it's powered perhaps? Comment back to Steve' I think he may know better on this.

L