@Abe_Fouhy ok the panel supports various steps of current control. Likely a digital pot function in place of an actual pot. That means that you could use this panel with your new setup. It kind of gives you an indication of current and post position similar to the digital meter + pot in a standard K40. The value in the display has to be a relative setting as there is no actual current input to this panel.
I do not see an “enable” function and the “D” function on the LPS is disabled (see your picture). This makes this machine really unsafe since there are no interlocks and no water protection.
The K function has only one wire on the connector which suggests to me that it gets ground up on the pcb. This could also allow erroneous “test” events.
If it was me I would not keep this panel because:
… you can get this and better control from a 10 turn pot and the digital voltmeter. See my post on replacing pot.
…There is no lasing current indicator, it must assume that the current setting = the actual laser current which is not actually true.
…Its unsafe …
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The resistor may be a ballast resistor to help control the current to the laser. When the tube ionizes the voltage drops and the current increases and this resistor helps takes up the slack . I don’t see the need for this in a switching supply. By inspection it looks like a switching supply so that resistor confuses me. If this is not a switcher a new supply would give better results and does not need this resistor.
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I would love to see this supply close up :).
Where is this resistor connected from the cathode to gnd???
Can you tell me its value?
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Thanks for the pictures and info. although I cannot read the traces and chip #s on the pcb as its out of focus 
Yea it was really hard to find a spot to focus my camera, the room is a bit dim. You’ll soon have better info with it in your hands 
I’ll check the ohm value in a bit, I am starting to wonder about this little machine.
Everything I read here shows me that the previous user upgraded these components, is the head LO like yours? In the process of upgrading he may of blew a PS and replaced it with a switching and kept the resistor, i don’t know. I couldn’t tell you the difference by looking at the two.
I am leaning toward a panel redesign to put some digital/analog volt and ammeters there as I think it will be really helpful for me to learn how the laser cuts/engraves according to the power levels. Also more data is always better. Plus if they are analog I could make this a cool steam punk laser setup haha.
@Abe_Fouhy
I agree that you would be better off fixing all this stuff especially adding the safety features…“PLEASE” with a more functional adn COOL panel.
I appreciate the info as I have seen these digital panels but did not know what they did … not impressed :(.
Getting that D supply would be awesome … after seeing that close up picture I realized I worked with one other, @Chris_Menchion , that has the same supply. It was difficult to get working right.
I noticed that on the back of the supply the frame gnd looks disconnected. Be careful around an un-grounded HVLPS …
Where in the world do you live …
I live in Oregon, yea I was wondering about that! Ungrounded PS’s in general need to be grounded, but this machine looks sketchy on the electrical… it’ll be good to get it all cleaned up with new documented hardware with UL listings. 
And yes, I am putting interlocks on first thing too!
@donkjr some questions I forgot to answer:
I have everything fused using automotive blades. This post has details and part numbers of fuse holders.
I simply connect mine to a PC so nothing needed special to interface.
I will find the reference to the cabinet extensions.
BTW there a many k40 panel designs on thingiverse.
In case I have not shared earlier. Here is the main index for all the conversions, designs etc I have done.
@Abe_Fouhy Nice I am in Utah. These machines especially need good gnding because of the lethal HV.
Some cabinet extensions:
I was thinking of making one from PVC with a flange to mount it.
Absolutely, btw - does my laser head look like an upgrade or standard part? My mirrors are silver, and I know that others are gold, so I didn’t know if the previous owner may of hooked me up.
Checked your site, looks like I will be on that quite a bit more. That fuse block is exactly what I was thinking about!
@Abe_Fouhy it looks a standard but with a port for air assist and laser pointer bracket added.
Ok cool. You don’t by chance have a sweet hack for testing the power of the tubes with one of those calibrated oven thermometers (http://www.2laser.com/laser_power_meter_probe_and_laser_monitor) do you? Ie a standard one wire sensor enclosed in 1/4 copper tubing and then temp converted to power in watts?
No I don’t (yet) the problem is the surface has to be one that absorbs 10,600 NM consistently and then you need a calibration means.
I have done a few experiments with peltier devices and that produces an output but nothing serious yet.
The real question is why do you want to know the power and what do you do with the # when you get it?
Oh I want to know the power to create a engraving and cut chart on my tube. From some basic research it looks like 100% power may not actually give you more cutting depth and that every tube is different. A few experiments I saw said that at 85% was their optimal cutting depth and had a lot less electrical noise generated, giving a bit more life to the tube, while another was down at 70% being their max. They could both jack up the power, but it didn’t yield better results.
I was just thinking if we had a cheap DIY meter we could all get a good baseline on where the power curve is on our tubes and save some life out of them. We could then take the data and create a power chart ring around our pots on the control panel to show engraving depth/cut depth and speed or chart for quick reference on materials we would like to cut.
I didn’t even think about the peltier, that is a great idea! Does it have to be an absorption material or could we use a IR transmitter/receiver to absorb the spectrum around a beam and plot that live while cutting to a controller to interpret the voltage map?
@Abe_Fouhy
The digital meter gives me a position on the pot that I can return to so that I do not have to pulse the laser to get to a specific current.
The problem is that lasers are a consumable and that over time at the same current they output different power. That is why there is an adjustment. Over time you will have to increase the current to get the same output until at max current you cannot get enough power.
Then also the quality of engraving and cutting is dependent on many factors other than power: the original image quality and tuning, the type of material, the moisture in the material, the response of the material to 10,600 nm, speed just to cite a few.
Laser failure mode is also many factored:
…From heat damaging the enclosure, seals and especially the output mirror. As the gas ionizes it creates heat that has to be removed so running cooler is better.
…From the gas leaking down (all tubes leak all the time).
I can’t see how electrical noise has anything to do with failure???
Manufacturers recommend to keep current below 18-20 ma. This is only because the tube is rated for 1000 hrs including a de-rating over time. To get this life the tube can actually operate initially @ >24 ma and higher max power. Essentially its design output starts at a higher power than is needed and therefore it takes longer to get to an unacceptable level.
I don’t know that its practical to expect all these conditions can be consistent enough that everyone can use the same data effectively. Its a “your results may vary” kind of problem. Perhaps we can get some range of value though.
I agree that it would be nice is there was a cheap way to measure light power. BTW its a pain to go through a power measurement even with a lollypop every time you do a job :).
This post is perfect for me, as I am an engineer at heart and love to over complicate the issue. This is essentially saying to me, fix your machine, do some lasing then let’s try to see if there is really a problem with something rather than assuming with you 2 days of lasing haha.
@Abe_Fouhy in regard to measuring light output.
I tried using IR sensors and there is a few basic problems:
- They do not have any response in the FAR region 10,600 nm.
- Its hard to keep them cool and not fry them. I even used a water drop to attempt attenuation.
- The sensors that do have response in the Far infrared by definition are slow. i.e thermo-couples. Heat changes are generally slow so the devices like are in PIR sensors and peltier don’t have the needed response.
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Don's Laser Cutter Things: K40 Dynamic Laser Response testing
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I settled on looking at the current from the tube while operating and syncing that with the printing. I was using this to try and characterize optical response to better understand PWM control for engraving. I was not trying to measure power.
Some recent information I have received suggests that the light output may not be well represented by the ionizing discharge current and my conclusions may be off by 130 us or so. Appendix C: Laser Response Characteristics
I do think that a relative indication of power is possible if we put a fixed duration of power into a peltier. I do not know what the light will do to the raw surface (ceramic) of the peltier and if that will create an error over exposures. One idea is to thermally glue an anodized block of aluminum to the face of the module. Anodizing is a good Far IR absorb-er and it is hard.