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Thread: Single point wiring scheme...

  1. #1
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    Default Single point wiring scheme...

    I am trying to figure out how to wire my project so I have read the wiring guide from Pangolin. I understand the advantages of using a single point grounding scheme, but I am not sure when to use it. In my projector I have 3 power supplies: a 15V supply (for flexmods), a 5V supply (for 473 and 532 DPSS), and a +/- 12V supply. The +/- 12V supply powers a stanwax ilda interface board which controls the power to the other two power supplies. So my question is should I connect the grounds of all the power supplies together? There are no phantom grounds. It seems as though keeping each supply's grounds separate would be better, and then use multiple independent single point wiring schemes.

  2. #2
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    Quote Originally Posted by laser_freak View Post
    multiple independent single point wiring schemes.
    Multiple single? That doesn't make sense.

    I will try to answer your questions with a diagram as there's a lot of complexity.

    Click image for larger version. 

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    On the above diagram...

    All AC grounds should be joined together at position (E) connected to the incoming AC earth wiring and grounded to your projector baseplate which must be electrically coupled to your projector case. That is, run a separate wire from this point (E) to each of the AC powered items Earth points (star wiring).

    All DC grounds should be wired to a similar point (G), but one that is isolated from the baseplate (i.e. the AC ground). That is, run a separate wire from this point (G) to each of the DC powered items ground points and to each and all of the ground points on the DC output of the PSUs (star wiring).

    In the example wiring, 2 lasers (red and green) are powered by DC and 1 laser (blue) by AC. This should show you how the DC and AC grounds are treated independently. And also how the AC Live (L) is passed through the relay (in a similar way to the brown wires coming from Stanwax's board (i.e. one wire goes back to the main AC (L) and the other to the Live points on each laser's AC powered PSU.

    This choice of AC and DC separated grounds requires the PSUs and galvo block to be electrically isolated from the baseplate. Use silicone pads and nylon spacers and nylon machine screws as required.

    AC kills! Before plugging anything in, test the continuity between the projector baseplate and case and the AC Earth pin of your power plug. There must be continuity!!! Then test the continuity between the AC Live and the projector baseplate and case. There should be no connection/continuity!!!

    Same for AC Neutral to baseplate and case. Check for continuity between DC Ground and AC Earth/Ground. There should be no connection/continuity. Check for continuity between DC Positive and each of the 3 AC terminals. There should be no connection/continuity. Check for continuity between DC Negative and each of the 3 AC terminals. There should be no connection/continuity. Check for continuity between DC Positive and DC Ground. There should be no connection/continuity. Check for continuity between DC Negative and DC Ground. There should be no connection/continuity.

    Plug in, stand back and switch on. If no loud explosion, then carefully test the case is not AC Live by testing the AC voltage between the case and a known good AC earth point. There should be no volts!!!

    I hope this is clear and makes sense. Let me know if you need further explanation.

  3. #3
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    Thank you for the explanation, however I think I should rephrase my question with a diagram.
    The below diagrams only consider the DC wiring aspects as I have the AC wiring all sorted. There is no scanner in my setup and therefor no scanner supply in the diagrams below.
    Here is the wiring scheme I think the Pangolin guide recommends (one big central DC grounding point):
    Click image for larger version. 

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    And here is the wiring scheme I am wondering would work, or if there are any disadvantages to it compared to the above wiring scheme.
    Click image for larger version. 

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  4. #4
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    Quote Originally Posted by laser_freak View Post
    ...here is the wiring scheme I am wondering would work, or if there are any disadvantages to it compared to the above wiring scheme.
    Click image for larger version. 

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    Because you're not showing the signal wires (which are also DC) on your diagram, in principle this is fine. However, if you are running these off the same colour correction board or DAC, they're not truly isolated from each other. The differences in ground potential between each of the 3 DC circuits could cause noise in the signal lines as the difference tries to neutralise/balance out across the signal lines which are electrically coupling those 3 DC circuits.

    Now I'm no electronics guru, so I think that's right, but I defer to more knowledgeable folk here for confirmation.

  5. #5
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    Hmm, that's an interesting point. The reason I want to keep the color correction board isolated is because the flexmods I am using do not have differential input. Therefor I need to connect all of the negative outputs that go to the flexmods from the differential color correction board outputs to ground. If I were to also connect the color correction board's ground to the rest of the projectors ground I think I would create a ground loop since the negative color outputs from the color correction board would be indirectly connected to the color correction board's ground.

  6. #6
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    Quote Originally Posted by laser_freak View Post
    Hmm, that's an interesting point. The reason I want to keep the color correction board isolated is because the flexmods I am using do not have differential input. Therefor I need to connect all of the negative outputs that go to the flexmods from the differential color correction board outputs to ground.
    You don't need to ground your signal wires. Keep these separate from your DC power wires. Except, I know that in the case of the FlexMod, you need to run 2 wires to the same point, 1 for DC ground and 1 for signal negative. That's OK.

    Quote Originally Posted by laser_freak View Post
    If I were to also connect the color correction board's ground to the rest of the projectors ground I think I would create a ground loop since the negative color outputs from the color correction board would be indirectly connected to the color correction board's ground.
    There is unlikely to be a difference in ground potentials because of the other steps taken to eliminate this, so a ground loop here is unlikely.

  7. #7
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    Thank you for the help taggalucci! I'm going to wire my projector today.

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