How to ground?

Discussion in 'Homework Help' started by cpleng7, Jan 15, 2011.

  1. cpleng7

    Thread Starter Active Member

    Dec 18, 2008
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    Currently I am worked out with single phase full wave bridge rectifier. I am using the microcontroller to control the 4 SCR bridge.

    I want to ask is how to ground the part? now have 2 part, one is the controller part, with the voltage have step down using transformer to 9Vrms. since the SCR bridge rectifier is using the 240V and the optoisolator is used to isolate the 240V and 9V part. Should I ground all both of the part together? or I also need to isolate the ground part?
     
  2. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    Post your schematic.
     
  3. cpleng7

    Thread Starter Active Member

    Dec 18, 2008
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  4. Georacer

    Moderator

    Nov 25, 2009
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    If the upper circuit was independand and worked alone, you wouldn't have to ground it. But if you want it to interface with other circuits, they should all have a common reference point and thererore, yes, that point should be grounded.
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
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    I do not agree. The OP use opto couplers. To achieve galvanic isolation, and keep the high voltage part isolated in respect to the low voltage control unit. So by all means do NOT apply ground to the point marked with a blue square. It is wrong and will make your circuit unsafe
     
  6. Georacer

    Moderator

    Nov 25, 2009
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    I guess in high-power applications, where isolation is needed, your argument stands correct. But what I said isn't too different, since you don't need to "read" anything from a burning resistance (R11). I 'll agree though that I didn't put much emphasis on safety.

    If however you needed to take readings from electronic devices on the heavy load, how would you proceed?
     
  7. t06afre

    AAC Fanatic!

    May 11, 2009
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    The correct thing here would be to have two reference points (grounds). Then measuring on the controller unit (low voltage). The reference point will naturally be the grounding point. On the high voltage part some other point that make sense. As I said In this circuit. A common ground point is not needed nor recommended
     
  8. cpleng7

    Thread Starter Active Member

    Dec 18, 2008
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    so should I create another ground point for the high voltage side, if I wanted to see the graph from R11?
     
  9. t06afre

    AAC Fanatic!

    May 11, 2009
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    I do not use proteus. So I can not help you. But sure you can place a probe on each side on R11 and plot the difference. Or plot IR11*R11
     
  10. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    I second the vote for no ground. It would be a code violation for start, and a sure way to take a zap.
     
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