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The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

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Old 07-24-2012, 05:43 AM
niceguynorthwales niceguynorthwales is offline
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Default dc brake for ac three phase motors

hello to all, new to this site.
i was hoping someone here could help, we have a machine with a three phase 415v 3 kw motor, the starter for the motor was fitted with some form of :homemade: dc brake, however the starter was practically demolished during a move.
i know there are ways of making your own dc brake, does anyone know the circuit and components required, we would be deeply grateful for any assistance.
thankyou
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Old 07-24-2012, 05:47 AM
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strantor strantor is offline
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When you say DC brake, are you referring to an actual physical brake attached to the motor, like an eddy current brake, or are you referring to some sort of DC injection scheme?
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Old 07-24-2012, 08:42 PM
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BillB3857 BillB3857 is offline
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We had a machine with 50/100 hp, 3600/7200 RPM, 60/120Hz direct drive spindles that used a low voltage high current transformer feeding a bridge rectifier. When the spindle was commanded to stop, a timer circuit 1) insured drop out of main A/C contactor, 2)supply low voltage DC to two leads of the motor for a fixed time 3) drop out and release DC to motor. It was also interlocked to prevent attempts of starting the spindle during the braking cycle.
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Old 07-24-2012, 10:07 PM
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GetDeviceInfo GetDeviceInfo is offline
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another application I've worked with saw arbors where a rectifier is connected across the lines in the motor terminal box. The DC pulls off a spring loaded brake when powered. On loss of power the brake brings the arbor to an accelerated stop condition.
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