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Thread: Is my projector wiring correct?

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    Default Is my projector wiring correct?

    Thread updated, read post #5
    Last edited by Humphry; 11-05-2015 at 07:05.

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    swamidog is online now Jr. Woodchuckington Janitor III, Esq.
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    do not wire the dc grounds to the ac grounds!!!!

    Quote Originally Posted by Humphry View Post
    Hi all,

    My lasers display a 100% static beam when my laptop (control station) is plugged into a different AC phase/circuit to the laser power supplies. What is the fundamental issue here? When I unplug my laptop charger from the wall plug, or run the Pangolin FB3 via a USB hub to isolate the ground, the problem goes away.

    - My laser drivers utilize the + and - of each color channel, and do not use pin 25. I am a little confused on whether this could have any effect. I am not 100% sure if they are single-ended or differential, and again unsure if this would have any effect? One is CNI, one is Lightspace and one is Laserwave. Someone suggested I connect the -'ve ILDA colour signals with the central grounding point (AC Ground + DC 0v) in my projector?

    - The shield around my ILDA cables electrically connects projector chassis and FB3 case together, as I have soldered the shield to the metal DB-25 connectors. Is this correct?

    - Regards projector ground connections. I have followed Pangolin's projector wiring guide and connect all AC and DC grounds together. However, in my lightspace projectors when I connected DC 0v to AC ground, the power supply cut out and would not turn on until the connection was terminated, seems to be some kind of protection, is that even possible?

    I am really confused on what to do in this situation. To be honest, I don't even mind getting slight noise for beamshows if it means they can be 100% safe and guaranteed not to do crazy stuff.
    suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll say, like, plate, or shrimp, or plate o' shrimp out of the blue, no explanation. No point in lookin' for one, either. It's all part of a cosmic unconciousness.

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    Ok thanks for the response. Could you elaborate a bit more about what I should do?

    Quote Originally Posted by swamidog View Post
    do not wire the dc grounds to the ac grounds!!!!

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    Bill Benner wrote an excellent article on projector wiring. You can find it here: http://www.laserist.org/laserist2008...onnections.htm

    If you are in a location that has inadequate wiring (including poor grounds), then it is often advisable to connect all the DC grounds in the projector together at one point and then tie that to Pin 25 on the ILDA connector.

    However, you said you have already connected your AC ground to the projector case, which means any ground noise on the AC line will be present on your DC circuits as well (unless you have completely isolated all components, including the baseplate, from the projector case). This AC noise on your DC circuits can cause all sorts of problems.

    Then too, if the ground potential is different between the projector's AC ground and the controller's AC ground, you can have signal interference that way as well. (Down the ILDA cable) Note that this issue of poor/inadequate ground is quite common - we have experienced similar issues at SELEM for several years, until we finally solved the problem by pulling our own wire feeds directly from the 450 amp service entrance panel for the auditorium.

    At this point your choices are limited. You can either re-wire your projector to isolate the DC grounds from the AC ground, or you can use a ground-lift adapter to remove the ground connection from the AC line. Note that using a ground lift will leave you open to a nasty electrical shock if the hot wire on the AC input to your projector ever comes loose and contacts the metal case of the projector...

    Adam

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    Adam, thank you. I actually understand this now.

    Another problem I just discovered is that of my lightspace laser driver. It takes in -12v and 0v which I find unusual, and the -12v is connected to the negative modulation pins ie: ILDA pins 18, 19, 20 (negative colour signals). So I am getting -12v on ILDA pin 18, 19, 20 which is wreaking havoc to my laser system's grounds on all connected lasers. I think is a result of bypassing the maunfacturer's built-in "safety board" which I suspect counters this. Does anyone have any thoughts on if I have missed something, or perhaps a solution?

    Edite: Could I just swap out the power supply for a +12v power supply instead?
    Last edited by Humphry; 11-05-2015 at 07:16.

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    After reading your PM and now this message, I'm confused. Have you checked to see if the PSU is actually delivering -12 volts? (That is, measure across the output terminals?) Also, given that you were seeing positive voltage on ground (based on your PM), maybe you should isolate the PSU from everything before you check these voltages...

    I will be home tonight at 7 PM again. Maybe we should get together on Skype so you can show me exactly what you're describing.

    Adam

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