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Controling conventional high-Current DC motors with SCR's and the Launchpad

David Poston
Intellectual 315 points
Other Parts Discussed in Thread: MSP430G2553, LMD18201, MSP430F1611

I am trying to build a coolant pump for an engine lathe. I would like to know if there is a way to configure conventional rectifier diodes and SCR’s into a full wave circuit to power a 12 Vdc brushed motor sprayer pump. Can the MSP430G2553 MCU be used to control the firing circuit of the SCR’s? And, can the Launchpad be used to leverage high voltage and current servo motors on CNC type machine tools? I have single phase and three-phase power available at 480, 230, & 115 Vac.

 

  • 0
    Mastermind 7395 points

    You didn't specify the current for your design. Anyway, these days, SCRs have been in many application by MOSFETs and MOSFET H bridges if you need direction control.

     

  • 0 in reply to Avi Chami1
    Intellectual 315 points

    Sorry about that! I need a steady 5 - 6 amps @ 12 - 14 Vdc for the sprayer motor. I want to be able to vary the speed of the motor to control coolant flow. I have two other DC motors rated for 90Vdc at 1 & 1.5 Amps. How could the Launchpad be used to control a MOSFET H bridge?

  • 0 in reply to David Poston
    Mastermind 7395 points

    I didn't see MOSFET H bridges from TI for the applications you need. I found devices like the LMD18201, which can work at voltages of up to 55V and currents of 3A max. So it seems it would not fit your any of your requirements... but maybe a TI FAE can provide other solutions.

  • 0 in reply to David Poston
    Guru 227245 points

    David Poston said:
    I need a steady 5 - 6 amps @ 12 - 14 Vdc for the sprayer motor.

    For this you can use a VNH2SP30-E, a 12-14V automotion H bridge for up to 30A. It is used for PWM control. We used it with an MSP430F1611 and a timer-generated PWM to control the peltier cooling pads of a laser. (including pre-heating, as it is a complete H bridge that allows inversion)

    No idea for the 90V.

  • 0 in reply to Avi Chami1
    Intellectual 315 points

    I found a control transformer in one of the Junker NC machines where I work. It is rated for 1500 watts, and applying 110 Vac across the 480 Vac primary terminals gives 28 Vac across the secondary winding. Can the LMD18201 be controlled by the Launchpad?

  • 0 in reply to Jens-Michael Gross
    Intellectual 315 points

    Thanks for the tip! What eval board does the MSP430F1611 work on and can CCS v5 program it? I have been studying motor controls and servo and stepper motors and I see that PWM is used extensively, and it is very efficient.

  • 0 in reply to David Poston
    Guru 227245 points

    David Poston said:
    What eval board does the MSP430F1611 work on

    Don't know of one (doesn't say there is non). But basically every MSP with a Timer module (which means every MSP) can do the same. There are many threads in this forum about how to produce PWM with the timer.
    Note that the H-bridge is requires at least 3.25V as input high-level, so unless you power the MSP with >=3.3V (better 3.6V), you'll need some voltage conversion.
    PWM frequency can be 0 to 20kHz.

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