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Thread: Needing some ground wiring help

  1. #1
    Join Date
    Aug 2011
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    Cape Town, South Africa
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    236

    Default Needing some ground wiring help

    Hi guys,

    Looking for some assistance with some long term signal/ground issues my laser projectors are experiencing.
    Happy to pay for your valuable time, as this has all been plaguing me for too long now.

    Questions include:

    - When I use multiple lasers (typically 4 or more on a single ILDA daisy chain with 100m ILDA run), then I get a static beam at about 5% - 20% power. This beam then disappears when I pull out the charger of my control laptop out of the AC power plug. The lasers and laptop charger are on the same power line, but this issue seems to be worse when they are running off separate AC breakers. It only seems to happen when I have multiple lasers daisy chained and never happens with just 1 or 2 units. I am going with Mr Brenner's single point grounding scheme, with ILDA pin 25 isolated from the other grounds. Does this mean I have definitely made an error in my grounding? Or do others experience this who know as a fact they have perfect grounding?

    - What do I connect the foil shielding of my ILDA cables to? Laser projector/controller case (and therefore AC ground), or just leave the shielding floating?

    - Do I connect my standard single-ended laser drivers to the R-, G-, B- pins, or ILDA pin 25? I use FB3's which by default tie R-, G-, B- and pin 25 together at the controller end anyway which just confuses me even more. Right now my laser drivers are connected to the corresponding negative colour value and NOT pin 25, and I worry that a loop could be present via the connection at the controller end, as they are separate within some of the projectors, but tied together in others. So should I tie all these pins together within all projectors, or does this make no difference and my problems lie elsewhere?

    - For the central point grounding scheme as per Mr Brenner, do I actually need to have a CENTRAL POINT (like a literal single point smaller than 1/2 inch where all ground wires meet at exactly the same place) or can I just make sure that all DC grounds are connected to AC grounds by using jumpers from the DC side of each power supply to the AC side. This would mean that the "central point" would be stretched over the ~20" length of AC cable that connects each power supply, as opposed to a literal 1/2 inch central point. Would there be a noticeable difference here?

    - Some of my laser drivers have ILDA pin 25 and DC ground tied together as part of their circuitry. What do I do in this case? Am I expected to make a buffer? Any alternatives?

    - When I use a continuity tester between some laser drivers DC and signal ground, it shows resistance of a few hundred ohms, but seems to never settle on a particular value. I assume this is due to capacitors, so can I assume that these drivers are "safe" in terms of keeping the DC and signal connections separate for sake of good grounding? I don't have a capacitance meter but can invest in one if it's going to help diagnose problems.

    Thanks in advance.

  2. #2
    Join Date
    May 2014
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    Barcelona, Spain
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    Default

    **For all projectors**
    -Check to be really sure if all metallic parts (case/heatsink etc) are connected to AC ground. (AC ground POWERCON pin connected to projector case via screw etc)
    -Check if AC ground is COMPLETELY electrically Isolated from DC ground (central grounding point). Is scanner block isolated as well? Several brands have galvo 'body' connected to DC ground. This could short DC-Ground to AC-ground thru scanner block screws.
    -Only if AC ground is completely isolated from 'central grounding point (DC ground)", connect inside projector: R-, G-, B- AND ILDA PIN 25 to CGP. You can short R-,G-,B- pins directly inside PJ's DB25 connector, and take a single wire to the CGP.
    -Connect negative main PSU pin, negative drivers pin etc and "0v" pin from +24V/0v/-24V Scanner PSU to CGP as well. When possible, avoid to wire negatives 'in series' between devices and going to CGP with single wire. Instead of this, provide single negative wire for each device and connect all together to CGP. This helps to avoid phantom DC ground between devices due wire resistance.
    -On the scanner driver: Do not connect pin25 (foil shielding) to the '0' ILDA INPUTS. Only +X-X and +Y-Y (usually red-white wires). Leave pin25 (which is now also tied to CGP) unconnected on the drivers '0' input.
    -Scanner driver heatsink is usually isolated from DC ground. But Check anyway to avoid AC-DC ground short like with scanner block.
    -Check for Mosfet on laser drivers as well. Back Metallic-body mosfets need electrical isolation.
    -For commercial already made DB25 ILDA cables: The shielding metallic part (surrounding pins) connects electrically to projector case when you plug-in the connector, and PJ case is AC grounded. So foil shielding is AC grounded as well. Only PIN 25 is DC ground.

    -Above should solve the problem.

    -If all above is done and still static beam when you plug Laptop to charger, that's for sure there's a phantom loop on the modulation inputs thru your DB25 cable.
    For testing purposes: Just isolate all projectors from AC-ground with 'special' AC-Adaptor with ground removed...and let us know
    https://www.ebay.com/itm/3-AC-OUTLET...-/131391739759
    Last edited by jors; 11-23-2017 at 01:13.
    Jordi Luque


    AtenLaser.com
    Barcelona

    "Let there be light"

  3. #3
    Join Date
    Nov 2008
    Location
    Cleveland Ohio
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    Default

    Try using an isolation transformer on the laptop. That won’t fix the real problem but will make the laptop vanish from the equation. Or. Use the laptop on battery. You got ground loop for sure. I had a ground problem caused by using a power conditioner. Still not sure why but taking it out of the system fixed my issue.

    Goggle ground loop. 0V, dc ground, ac Ground, chassis ground are all related but not the same. You can actually have different potentials on each with real current flowing. If you have the equipment on separate ac breakers you have a real potential for trouble. Maybe try driving the ilda signals with single open end shields to pin25 like high end audio or an optocoupler for the ilda signal from the laptop. Think jors said all that already. Above all use a gfi. You can get hurt in these situations if current flows and your in the middle

    https://en.m.wikipedia.org/wiki/Grou..._(electricity)

    I see they added we we both missed. Adding a resistor on the ground. ??
    The reason ilda is balanced lines is to prevent just this kind of stuff.

    Babble over. Just be really cafeful since you are on two different ac lines. I’m kind of afraid suggesting lifting the ground.
    Laptop to adat to ilda sounds like the real solution. Light cures ground loops.

  4. #4
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    https://www.sciencedirect.com/scienc.../9780750663700

    This book has 20 pages just on ground. Worth the read. I knew I had seen this recently.

  5. #5
    Join Date
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    Cape Town, South Africa
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    Default

    Hi all, thanks for the responses and help.

    My scanners do indeed connect 0v DC to the optical plate, so that dictates I should isolate ILDA pin 25 for the "less ideal but acceptable" wiring approach with pin 25 isolated, and AC/DC forming the central grounding point.

    BAD NEWS: However, I did a proper diagnosis of the system today and found that some of my laser drivers connect the -'ve modulation colour pins (R-, G-, B-) to 0v DC power (which forms part of my AC/DC central grounding point). These negative modulation pins are electrically connected to pin 25 in the Pangolin FB3 circuitry. So I believe that I now need to COMPLETELY isolate DC ground from AC ground as this is my only option forward.

    Crap, this is going to be a lot of work. I will ensure I wire them to one central point and not "in series" as you mentioned. Scanner drivers are at least isolated.

    - For the mosfets, is the risk that they short out pin 25 and DC Gnd with AC Gnd? If so I can just use a continuity tester to make sure. Or is it something less obvious?

    Thanks so much guys.

  6. #6
    Join Date
    May 2014
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    Hey Wait! before isolating entire PJ, which is recommended, it could also work well with AC+DC CGP but you must remove ILDA25 completely as you pointed.

    Ok, so disconnect completely R-, G-, B- from the drivers (which shorts to ILDA25 thru FB3), and connect all drivers negatives to your AC+DC CGP instead.
    Disconnect completely PIN25 inside your PJ from on board DB25 connector.
    You MUST always Isolate Mosfets from heatsink (which is connected to your AC+DC CGP). This is not tedious to do. Back metallic side of mosfet (TO-220) is usually DRAIN connection on IRF series.
    https://www.espruino.com/refimages/mosfets_pinouts.jpg
    If Mosfet is TO-220FP type does not need isolation (Black body all encapsulated)
    https://i.stack.imgur.com/vxxXy.gifP
    I'm pretty sure here is the problem.
    good luck

    Quote Originally Posted by Humphry View Post
    Hi all, thanks for the responses and help.

    My scanners do indeed connect 0v DC to the optical plate, so that dictates I should isolate ILDA pin 25 for the "less ideal but acceptable" wiring approach with pin 25 isolated, and AC/DC forming the central grounding point.

    BAD NEWS: However, I did a proper diagnosis of the system today and found that some of my laser drivers connect the -'ve modulation colour pins (R-, G-, B-) to 0v DC power (which forms part of my AC/DC central grounding point). These negative modulation pins are electrically connected to pin 25 in the Pangolin FB3 circuitry. So I believe that I now need to COMPLETELY isolate DC ground from AC ground as this is my only option forward.

    Crap, this is going to be a lot of work. I will ensure I wire them to one central point and not "in series" as you mentioned. Scanner drivers are at least isolated.

    - For the mosfets, is the risk that they short out pin 25 and DC Gnd with AC Gnd? If so I can just use a continuity tester to make sure. Or is it something less obvious?

    Thanks so much guys.
    Last edited by jors; 11-23-2017 at 07:15.
    Jordi Luque


    AtenLaser.com
    Barcelona

    "Let there be light"

  7. #7
    Join Date
    Nov 2009
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    Whanganui New Zealand
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    Default

    Might be the battery in the laptop.
    Sound guys struggle with the ground loop 50hz.
    Can you disconnect the battery?

  8. #8
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    Ferrite on the power cords?

  9. #9
    Join Date
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    Default

    Hi all,

    Thanks for the responses. The problem seems to stem from the fundamentals of my my ground connections. I have emailed Pangolin and hoping they can steer me in the right direction of a "rock solid" solution.
    Thanks Jordi for being particularly helpful via PM.

  10. #10
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    Just an aside... 100 meters on an ILDA run is right at the maximum of what the spec is designed for. Daisy-chaining 4 projectors at the end of that 100 meter cable is asking for trouble! If any of the diode drivers have low impedance inputs, you're screwed. (ILDA spec for input impedance is a minimum of 10K, but I've seen drivers from China that top out at 3K... Put 4 of those in parallel and you're in trouble.)

    Might want to look into a buffered splitter.

    Adam

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