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Bridge Rectifier Help

Discussion in 'General Electronics Discussion' started by Ad Astra, Feb 22, 2012.

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  1. Ad Astra

    Ad Astra

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    Feb 22, 2012
    Hey everyone!

    I am a relative newbie to electronics and was hoping to get the advice and suggestions of those who are wiser in the subject than I. I am putting together a demo of a Hoeken's linkage for my Machine Dynamics class, but I would like to motorize it to avoid tedious hand-cranking. For this purpose, I have purchased a low-rpm 24 VDC motor that I would like to be able to plug in and avoid having to constantly buy 12V alkalines to run the thing.

    Now, I have built a simple bridge rectifier using 1N4004 silicon diodes and a 120VAC/12VAC transformer in the past, but that was years ago and my requirements for this bridge are a little different than that one. So, I was hoping for tips or advice on a few things:

    1) For a rectified 24 VDC, I would require a transformer with 16-18 VAC output on the secondary windings, is that correct?



    2) What sort of VA rating should I be looking for on the transformer if I intend to use this motor (175mA @ no load)?



    3) I would like to maintain a steady DC voltage, so I know I have to use a capacitor for filtering, but how much capacitance would be required?



    4) If I wish to wire in a switch, should that be wired to the power supply or just the motor?


    Any help that anyone could offer would be greatly appreciated. Thanks!:)
     
  2. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    2. 10VA should do it. I figured it out for 350mA, but depends on your current requirements under load.

    3. 1000 - 3300uF should be more then sufficient and rather cheap at 24VDC
     
  3. Ad Astra

    Ad Astra

    2
    0
    Feb 22, 2012
    Thank you, jackorocko, for your answers. Just out of curiosity, how did you come to a value of 10 VA? Is there some sort of calculation you can perform in order to determine that, or is it just something that comes with experience?

    Also, how would I determine my current requirements under load? Should I assemble the whole model and use a couple A23's in series and read the current across the motor? Or can I determine it by estimating my torque requirements for the given linkage? Like I said, I haven't done anything more than basic electronics and that was a few years back, so I am, for all intents and purposes, a newbie at this. :eek:
     
  4. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    They rate transformers in VA because transformers don't theoretically use any power because the voltage and current are out of phase with each other. But, you figure it the same way you figure power. V * I

    I just doubled the current requirements and @ 24VDC that came out to ~8VA added a little more to make it an even 10VA. 10VA/24VDC = 410mA of usable current. Guess it really depends on the load. Someone with some more experience might be able to tell you how to figure out the full current per given load.
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    11,662
    2,697
    Nov 17, 2011
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