Ground Connections

[gottaluvlasers]

Hey everyone-

this is more of a "lets see who does what" question than a conceptual question...

How do most of you connect your grounds in your projectors? And in the way that you describe your wiring, have you noticed any problems??

1) I know some connect every single ground together and then to ILDA pin 25. This includes all DC power supply grounds (or com's) and all AC grounds (including earth and chassis ground). Any of you do this?

2) All AC grounds together to one centralized grounding location then to earth/chassis ground. and all DC supply grounds (com's) to one location and then to ILDA pin 25?

I read Pangolin's projector wiring guide and it seems to me that it is suggested that #2 above seems to be the more proper and safer way?

It seems like such a simple concept. but i think this is where the most questions seem to arise. Do most of you keep AC grounds and DC "Grounds" (common's) separate? or is "ground" a "ground?"

-Marc

[buffo]

1) I know some connect every single ground together and then to ILDA pin 25. This includes all DC power supply grounds (or com's) and all AC grounds (including earth and chassis ground). Any of you do this?

Hey Marc;

I do this with my projector, and it works fine. However, I do understand that this method creates a ground loop between the projector and the computer with the controller. Nevertheless, thus far I have not had any issues with signal interference as a result of this loop. Most of the projectors at SELEM were wired this same way (with a few notable exceptions).

2) All AC grounds together to one centralized grounding location then to earth/chassis ground. and all DC supply grounds (com's) to one location and then to ILDA pin 25?

There is a part of this second scheme that you have left out. For it to work, you must also isolate your lasers from the AC ground, since nearly all lasers have their cases connected to DC common. This means isolating them from the base plate (since the base plate is normally screwed or bolted to the metal projector housing, which will be grounded to the AC ground). Or, alternately, you can isolate the entire base plate from the rest of the metal projector housing (which is equally difficult).

I read Pangolin's projector wiring guide and it seems to me that it is suggested that #2 above seems to be the more proper and safer way?

Yeah, Bill gave a presentation on this, at SELEM 2008 I think... Anyway, the point is to avoid creating a ground loop, and the only way to do that is to separate the AC and DC grounds inside the projector. But this creates all sorts of problems from a construction standpoint (as explained above), which is why most people simply say "screw it" and connect all the grounds together. If the wiring run between the projector and the controller is fairly short, you shouldn't have any problems. I've never had an issue even with up to 150 ft of ILDA cable between the two, though it could be that I've just been lucky. But shorter cable runs are definitely better.

Another thing you can do to minimize the risk of problems is to power the projector and the computer with the controller off the same 110V circuit. Even if you have to run an extension cord from a power strip out to the projector, at least the length of the ground loop will be minimized to double the length of the cable between them.

A worst-case scenario might be if you have the projector plugged in to an outlet on one side of the room with the host computer plugged in to an outlet on the other side of the room that happens to be on a different circuit, with a long ILDA cable between them. Then the loop could be quite large, since you don't know where the wiring for the two outlets goes on it's path back to the panel.

Even so, I've only heard of a handful of stories where people have had trouble with such arrangements. And in a "the show must go on" type of situation, you could always break the ground connection at one end to eliminate the loop and see if that gets rid of the interference. Of course, doing this opens you up to all sorts of electrical shock hazards should the hot AC wire in your projector ever come loose and happen to touch the metal case, so it's obviously not recommended for normal operation.

Adam

[gottaluvlasers]

Adam-

PERFECT answers!! thanks man!!

i do mine the way you do yours also. I connect every single ground, common, whatever (AC and DC) all to ONE central location and then that also connects to ILDA pin 25.

isolation i think is still the "standard" but i dont know of anyone who wires it that way. Funnily enough, I think gene (phredy1) had a problem with this method about a month ago. He had some weird audio hum from his computer sound. he lifted ILDA 25 and boom...audio hum went bye bye.

-Marc

[buffo]

Yeah, audio is a bitch when it comes to ground loops. We used to have this problem with 60 cycle hum in the audio ever time we had a LEM. Since all the computers were on different power circuits and they all connected to the mixer via RCA cables (which have the outer shield at ground potential), we had a massive ground loop. I finally solved the problem last October with a set of active direct boxes. Basically, they're powered isolation transformers that physically separate the computers and the sound mixer from the power amps and the speakers. Works like a charm!

Adam

[Phredy1]

isolation i think is still the "standard" but i dont know of anyone who wires it that way. Funnily enough, I think gene (phredy1) had a problem with this method about a month ago. He had some weird audio hum from his computer sound. he lifted ILDA 25 and boom...audio hum went bye bye.

-Marc

I did have a nasty ground loop audio hum problem and lifting pin 25 solved that problem. My question is what is the disadvantage to having pin 25 lifted? Since I removed the pin 25 ground wire I have noticed a slight "shake" in laser output. Hard to describe in words, but similar to if the projector was on a bouncy floor. I tried a ground lifted AC power cord for the projector and it did not help.

Here is how I run my system:
Laser: Laptop --> USB to DAC --> 50' ILDA to laser projector
Audio: Same laptop --> USB sound card --> RCA's to mixer --> balanced XLR's to active speakers

Gene

[buffo]

Gene;

Your problem is a classic ground-loop. The *ideal* solution would be to install a direct box in-line between your computer and your mixer. That will eliminate the audio loop. Then you can re-connect ILDA pin 25, which should resolve the "shake" you're experiencing.

Note, however, that a good dual-channel direct box will set you back around $160...

Adam

[dave]

Note, however, that a good dual-channel direct box will set you back around $160...

Or go to a car audio store and get a isolation transformer for a fraction of the price..

[dave]

the only way to do that is to separate the AC and DC grounds inside the projector. But this creates all sorts of problems from a construction standpoint (as explained above), which is why most people simply say "screw it" and connect all the grounds together.

I have never had any issues separating ac from dc ground inside the projector. None of the CNI, laser-wave, Arctos, Kvant, lasers I have played with have their cases at ground potential..

[buffo]

go to a car audio store and get a isolation transformer for a fraction of the price..

I tried a cheap, passive audio isolation transformer first. It worked, but it also reduced the amplitude of the incoming signal too much. Even with the mixer wide open, I couldn't get enough signal to the amps to produce much more than maybe 1/3 of normal max volume. At a LEM, 1/3 volume is just not enough!

Then I tried a more expensive (but still passive) direct box. Same result. Got rid of the hum, but also lost enough signal that I couldn't get the volume up where I wanted it.

The active direct box was just the ticket though. Now I can max out the amps, and no 60 cycle hum anywhere...

Adam

[LaserGuy216]

I use #2.. all ac to ac ground,(with filter), all dc to ilda ground... the only proble ive ran into is that if you use an outlet that has no ground your image will be shaky.... only when you then use an grounded adaptor plug and ground to the house pipes or earth ground..... now my case isnt grounded to anything... i think i need to ground it to something.... but then i need to isolate my lasers.... hummmmm ....

what should i do??