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How to connect HeNe laser DC supply with three input wires--red, black and purple/violet?

whatthephoton

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hi,
This is my first post and first laser (other than those $2 diode laser modules from Aliexpress), a helium neon one I got for about $40 w/ power supply. The problem is the power supply has three wires on its input. I assume black is ground, red is +Vcc, but am not sure what to do with the purple/violet wire. The info plate on the power supply has been partially spray painted black to obscure the info, for whatever nefarious purpose I don't know. The info I can see: Data Logic, output 1500VDC @ 0.5mA. It looks like model is 111-1500-5-? but I don't find anything relevant despite many search keyword variations (I also searched laserpointerforums for general hene power supply info mentioning a third wire but didn't anything useful). I guess that Data Logic is the same as Datalogic which was Spectra Physics (wikipedia, /wiki/PSC_Inc.). I think the voltage should be 24V but am not sure and will take the approach of just increasing the DC input from 0V up to where the laser starts lasing as per Sam's ...laserhps.htm#hpstoc (sorry can't post links as a new user) "...voltage for such a supply if not labeled or listed below can be found by driving it from a variable DC source..." ... after I figure out this purple wire business.

So, does anyone know what to do with this third purple wire? I read Sam's laser page on HeNe laser power supplies and it mentions "Violet wire loop enables CDRH delay (cut to disable)", but this is not a loop on the supply I have, at least not that I can tell. It also mentions many DC supplies having a third wire that's yellow. I suppose it is some kind of enable line that needs to be tied either to ground or some positive voltage (5V TTL? +Vcc?). I'm hesitant to tie it either high or low for fear of causing some logic gate in the power supply to source or sink too much current and burn out (but I will try via a 1k resistor if nobody replies to this).

p.s. Three other newbie questions, in case anyone knows:

1. Can I assume that the sticker on the laser is probably correct, that the laser is <5mW (perhaps even 3.15? which is marked near the output), and that I don't need to use laser goggles with it?

2. Based on the pictures I'm attaching, are there any exposed parts I shouldn't touch (that are high voltage)? Obviously not the end where the high voltage (yellow) wire is attached, but what around that is charged, what other surfaces farther away would be at high voltage?

3. The power input connector is some kind of Dupont connector. Can anyone identify exactly what so I can order the mating connector to crimp onto my power supply leads?
 

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Anthony P

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-Black and purple together to ground. Red to +12v. Treat both ends of the tube as live. They are PROBABLY not lethal, but the will make you swallow your chewing gum.
-I would cut off that connector and use something you have lying around or can get easily. It is not high voltage. Any DC connector will do.
- That tube is definitely <5mW. I would guess 1mW or maybe 1.25mW.
 

whatthephoton

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Thanks a lot for the input. Could I put a switch between the purple to ground and use it to turn the laser on and off? How do you know the purple should be grounded? The reason I ask is I was looking through Sam's "HeNe Laser Power Supplies" page and 4 out of 9 DC power supplies listed under "Sample Color Coding of DC Input Power Supply Bricks" have the extra wire going to some +V (4-12V in different cases) to enable the laser.
I think the seller said it's 24VDC. If I start at 12V and slowly ramp up is there any way to know when I've hit the correct voltage?
And how long after switching off the power could I touch those high voltage areas without getting a shock? Or it's so long (hours) that I should manually short them to ground?
 

Anthony P

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You are correct, I am not certain. This is an educated guess based on decades of experience with multiple similar devices. It would be nice if the label was legible. Reach out to Paul1598419, he has some experience with these types of devices.
It looks to me as if it was removed from a piece of equipment like a bar code scanner. It also appears that the tube and supply were not the original pairing.
Have you tried asking the seller your questions?
 

whatthephoton

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Ok. Sounds reasonable. I can try first with the purple free, no connection, bringing up the voltage to 12V and see what happens. If no lasing starts I can try grounding the purple through a ~1k resistor, just to be cautious. The seller did say it was removed from some device, it was functioning and he had used it on some small optical bench set up. I don't know if the tube and supply were not the original pairing. I did email him to ask about the purple wire and input voltage but he didn't reply. I guess he doesn't want to be bothered by it anymore.
 

whatthephoton

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Followup: I built a case to keep me from accidentally touching the exposed high voltage. Then I connected the black and red wires to a variable DC power supply (black to ground) and also connected the purple and black together. Then I slowly cranked up the voltage from 0. At just a bit over 15VDC there was a faint clicking/sizzling sound and the laser turned on. I did not try to go up to 24V, which is what I think the seller said it runs on. I tried manually separating the purple from ground and got the same clicking/sizzling sound during which time the beam flickered then went out as the contacts broke completely (presumably a de-bounced switch would cleanly switch the laser on & off).
A few questions in case anyone's still following this:
1) So, it turns on at a little over 15 VDC. Is there any reason to run it at a higher voltage? Is it bad for the power supply or tube to be at the edge of the laser's turn on voltage? How high can I go with the voltage, as in, how do I know when I'm about to go to high and damage the power supply? A 15.0VDC will not work (I don't remember the exact turn on voltage but let's say, 15.5V) and the next common voltage I find is 18VDC. I'm pretty sure 18VDC is not going to be over the supply's max. voltage input but I'd like to know how to tell when the voltage is getting too high.
2) can I use the purple wire to turn it off and on as rapidly as I want? Either with a switch manually, or say with a relay of some kind so I could pulse the beam at a millisecond rate? Or does switching a tube rapidly off and on shorten it's lifetime? (assuming a tube can even switch on and off that fast).

IMG_5676.jpg

IMG_5681.jpg
 

Anthony P

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Cool enclosure. Glad you got it running. Again, it would be nice if the label were legible. It tells you input voltage. Are you looking to actually switch on and off rapidly or just modulate intensity? When you switch the low voltage on it activates an igniter circuit in the power supply. This creates an extra high voltage pulse to get the gas ionized and then shuts off once conducting. After that the tube runs at its nominal HV. I don't know what effect it would have to pulse that. Optical output intensity can be significantly modulated with a small transformer in line on the HV+ line. I can get more detailed on that if you are interested.
 

whatthephoton

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Thanks. It's an acrylic (Staron) sheet base, walnut ends, 4mm styrene sheet top (heated and bent over a laser-cut form). The big gap is to allow air flow/cooling, if needed.

IMG_5242.jpg


It is really too bad the power supply label is illegible.

I don't have a specific pulsed mode use case in mind. I was just wondering for future reference. For the most part I think just turning it off and on is enough. I originally got it to make a Bath Interferometer for telescope making but then read that $1 red laser diodes were sufficient for that purpose. So now I'm not sure. I found some lists of "neat science experiments you can do with a hene laser" and might try some of those for fun. I would also like to try to compare the beam properties of this hene laser to a laser diode to see in real life how they differ (like coherence length, beam shape, not sure what else).
 

Anthony P

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My favorite book on HeNe projects is "The Laser Cookbook" by Gordon McComb.
 




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