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Using 130 Volt DC Motor w/TRIAC Controller

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bobledoux

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I want to power a permanent magnet 130 volt DC motor using a mains powered TRIAC based controller like the Vellemann K2636.

These controllers are intended for universal AC/DC motors, like those in electric drills, that have wired field and armature coils.

Is it sufficient for me to run the controller output through a full wave bridge rectifier and into the motor? What about the reverse diode across the motor leads?
 

dknguyen

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The "reverse diode"? Do you mean the flyback diode in anti-parallel to the inductive load? This *ONLY* works for inductive loads with unipolar current flow (like single-direction motors). For bipolar current, it will not since it will cause a short circuit in the other direction. Bidirectional motor drivers should have these built-in anyways (the diodes are anti-parallel across the switches to provide a similar current path between the motor leads, except now it does not interfere with the bi-directional current flow).

I think you would need to add a large smoothing capacitor across the diode rectifier output to make it DC rather than whatever the controller outputs (does it output sinusoidal AC or some kind of DC to drive the universal motor? You say triac, so right now I am assuming sinusoidal).
 
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bobledoux

Member
Let me try again:

I have a triac controller running a sewing machine motor. Its an AC/DC universal motor.

Today I decide, "Gee, I'll disconnect the universal motor, run the power supply
output through a full wave bridge rectifier to give me DC, and replace my old motor with a permanent magnet DC motor."

Will it work?

Do I need to do anything else to make it work?
 

tcmtech

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Most Helpful Member
It should work if the DC motor is in the same opperating range amps and volts wise. But
I would definitely do Like DK says and use a filter cap too! Some PM DC motors running off unfiltered DC derived from a simple rectified AC source can generate a bad back ground hum when loaded. Yours may or may not do it.
 

dknguyen

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Most Helpful Member
If the triac controller works the way I think it does, then a bridge rectiifer followed by a large smoothing capacitor to rectify the triac output to a DC voltage should work. (smoothing capacitor is probably not needed if the AC frequency is very high, but mains 60Hz and 120Hz is too low).

But from my understanding, a triac crudely chopping the AC waveform shouldn't be able to drive an AC motor. BUt you didn't say AC motor, you said AC/DC motor. It would be similar to a PWM signal used to drive DC motors, but instead of chopping a constant unipolar DC voltage, you are chopping the cycles of a bipolar sinusoidal voltage (which becomes unipolar when you rectify it).
 
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Ubergeek63

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If the triac controller works the way I think it does, then a bridge rectiifer followed by a large smoothing capacitor to rectify the triac output to a DC voltage should work. (smoothing capacitor is probably not needed if the AC frequency is very high, but mains 60Hz and 120Hz is too low).

But from my understanding, a triac crudely chopping the AC waveform shouldn't be able to drive an AC motor. BUt you didn't say AC motor, you said AC/DC motor. It would be similar to a PWM signal used to drive DC motors, but instead of chopping a constant unipolar DC voltage, you are chopping the cycles of a bipolar sinusoidal voltage (which becomes unipolar when you rectify it).
nope ... triac controllers are phase drives and the capacitor will charge to the full peak voltage when you pass 45% "duty cycle".

Dan
 

dknguyen

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THat is true. Didn't think about that. BUt wouldn't it be effective if he used the triac controller between 0-50% duty cycle? THen his average DC voltage would always increase with duty cycle (if in a somewhat non-linear fashion).
 
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Ubergeek63

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THat is true. Didn't think about that. BUt wouldn't it be effective if he used the triac controller between 0-50% duty cycle? THen his average DC voltage would always increase with duty cycle (if in a somewhat non-linear fashion).
That is why our phase drives drive a 16mH 20A inductor and a 2300uF 400V capacitor.

I still push to replace that turkey with a PWM with an LC filter at 20KHz instead of 120Hz,

Dan
 
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