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DC motors and speed control

Discussion in 'Power Electronics' started by Josh47, Feb 25, 2021.

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  1. Josh47


    Feb 9, 2021
    I bought a 120vac to 0-90vdc 400w motor speed controller from Amazon and I was wondering if there was anyway to modify it to get more amperage from it. It has a internal 8amp fuse. I posted a pic of the scr's and 3 diodes. Rest of the board is control with a small transformer and 2a full wave rectifier. Is the power of this unit limited to 400w because of the diodes because they are only good for 6a? The scr's are rated for 25amp. I know heat sink and trace size also needs to be rated correctly as well. Any suggestions?

    Attached Files:

  2. Bluejets


    Oct 5, 2014
    400w/90v approx 4.5A.
    If you need bigger, buy a bigger unit, best way.
    Kabelsalat and Harald Kapp like this.
  3. Josh47


    Feb 9, 2021
    I guess... this one was just 45 bucks and fast shipping. Just kinda wanted to know why it's only 400w when the components are rated higher. I'm going to be using it on a 1/2hp 90v motor so it will be pushing its limits. Then again the motor is geared and shouldnt be to much of a load I Hope.
  4. Bluejets


    Oct 5, 2014
    Many pieces of equipment have descrete devices rated at higher levels than the working levels.
    It's simply to give some overhead, not necessarily for a higher output.
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    @Josh47 : did you realize that you hijacked an old thread from 2015? I moved your question and the replies so far to this new thread.
  6. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    Well, It's only 400w because.. it's just $45.:D

    Horsepower is not inherent in the motor, it is developed by loading on the motor.
    If you haven't much of a load then there is no problem. I would use the 400w drive and limit its output current with something like a MDL-6 fuse for protection.
  7. Technomaniac


    Oct 31, 2020
    You might have 25 amp SCRs and such, but that kind of rating sometimes requires a generous heat sink, normally missing in the compact Chinese gear.
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