Something is not right - Omtech 60w

I just got my Omtech MF 1624 up and running. I did a mA power test at various percentage powers and read the mA meter on the power supply. Here are the results plus what Omtech said it should be.
My Reading Omtech Info
12% 2 NA
15% 4 NA
20% 5 4
30% 4 5
40% 8 7
50% 11 10
60% 14 16 (at 65% - 75%)
70% 16
80% 19 19
90% 21 20
100% NA 23

What in the world is happening in the 20-40% range? I ran it twice and got the same result. 15% and 30% are at 4mA and 20% is at 5mA.

Also, judging by the results and the Omtech data, I should not run the laser at greater than 60% to ensure longer tube life. Correct?

I don’t know if it helps you, but here my (old) power test from my OMT 60 Watt machine.
It is likely that the values are a little worse today, I have used my machine a lot.
Are you using the controller to test or LB?

.txt must be converted to pdf

LB-Powertest - Ark1.txt (97.8 KB)

I used LB for the test. How would you do it via the controller? What difference would it make?

On my machine with a clone Ruida, like you, I can run all kinds of tests without LB, but it is of course much faster and easier to use LB for that.
What have you set your min. power to? and how do you test?
My values come from a test with max.min. same setting and same time, minimum 10 sec. I read mA on my external ammeter and cross check on OMT’s own ammeter on the power supply.

I ran the attached file one layer at a time. It had time to stabilize the mA reading.
Miliamp Test Pattern.lbrn2 (17.5 KB)

Your test file looks normally/ok for me.
I will make and document an extended thorough test and send it to the OMT for a comment.
But, stop at 80%, there is no need to go over 80%, I have “proven” in some tests that my 60watt tube (50-55watt?), Do not give more useful output after about 75%.
I assume that you have always run with proper cooling.

I do not know how much spread there is, or must be, in a CO2 tube but when the values are below their own specifications they should respond.

COâ‚‚ laser tubes do not have tidy current flow, particularly at low power levels:

The green trace is the tube current at 10 mA/div corresponding to a grayscale test pattern (inverted: black = 0%):

Below about 20% power, the tube current consists entirely of off-scale-high pulses, not the relatively steady current at higher powers. Various meters respond to those peaks in different ways, but small differences in the spike distribution can overwhelm whatever averaging the meters apply.

So, what’s going on is you can’t depend on the meter readings for more than a general guide to the tube power levels on the low end. The real test is what the beam does to the material on the platform, which is where all those Material Tests come in handy.

More details on my blog:

Are the displayed values stable? The mA meters on the lps has to sample… it needs to be a stable reading to be trusted.

Ensure you really have a 60W tube… It’s based on length with a dc excited co2 or glass tube co2. If your tube diameter is 55mm, then it’s length needs to be ~1200mm to produce 60W. Mine was labeled 50W and was 880mm in length… it measured 43W… not 50W as advertised.

Not so obvious here, but a K40 is rated at 40W but it’s tube length, ~700mm is only that of a 30W device. If you run 20mA on a K40, thinking it’s a 40W tube, you are running it around 25% over it’s maximum rated current. Many set the power to 18mA, so it lases at 18mA anytime if lases. This is also 20% over the maximum current value of 15mA for a 30W tube. The main failure here, is the analog tube is driven like a ssl (diode).

Most of these machines, such as mine, is just about a meter wide, you can’t shoehorn a 1m tube in the machine anyway.

If you use percentage power, based on mA, it’s not really accurate, so to speak… Most of us have found there is a limit, below the maximum tube current that gives maximum output wattage of the device. Many assume twice the current, twice the output power, but we can see that isn’t the case.

A lot of this has to do with a co2 tube being a negative resistance device, meaning an increase in voltage doesn’t directly relate to an increase in current. In other words Ohms law doesn’t apply with these devices.

If you set it up to 50% power based on a mA reading, you’re likely setting it to percentage current, not percentage of it’s output power.

Either way, setting up the lps to only supply your selected maximum current or wattage out. It is then you have it calibrated for percent control from Lightburn (or any other software). In any case, it’s not absolutely linear, but it’s close enough. It’s not like we have a choice, as it’s all we have.

A lot of this I don’t buy into… If you need a 100W of power, you’d be dumb to use a 100W machine, as a 130 or 150W would run cooler or with less current. Like a stereo, if you needed 20W of power for the job, you’d be dumb to buy a 20W amplifier… you’d likely pick up a 30W or more so you wouldn’t be driving it at maximum.

If you run it within it’s specifications, it should do fine… you may need 100%, I have, and I’ve used it. I didn’t buy a 40W because I needed a 40W. I do need about 30W do do most operation.

If I buy a car that will do 100m/h, but the dealer tells you don’t drive it over 60 if you want it to last… I’d call bs on that… This is how you make something cheap and pass it off with bogus values… it’s corrected by stating don’t run it where it’s rated.

Most good tubes advise you of it’s life along with a working current and a maximum or don’t exceed current. Many also have lives in the 8k to 10k hour ranges, they also don’t tell you not to run it above 60%…

I cut pretty consistently at @70%, but push it up as I need it. However I expect a reasonable tube life even at 80 or 90%.

I notice has wattage on his chart, is that measured or assumed?

I do mine and take watt meter readings at each step… it’s time consuming, but I get a kick out of it and a good idea of how my tube is performing.

I’m not an electrical engineer or a physicist, but I’ve spent about >55 years fiddling with electronics … What I can measure I believe.

Good luck


??? - If you have found “Watt” in my chart then that is a mistake, everything is in LB% and mA.

Without a suitable instrument, it is not possible to determine the output power in Watts of a laser machine.

If I have understood it correctly, then @1Vince is in contact with Omtech and it is they who have given him the values that they think their tube should present.

My reading was the mistake… not yours… I was thinking an 80W tube, but in reality it’s an 80% value… :pray:

Sorry about that…

I was hoping more people would get a watt meter … it’d be great to compare what we have.

I think @ednisley has used thick acrylic to test relative power out… but he’d have to confirm…


…no problem my friend :+1:

…you may be thinking of the test I did and showed once it was with 16mm acrylic and clearly showed that there was no more/additional effect after the 70%.

I would also like one, but the price for it is a bit too high for the limited use I have for it.

That’s about what I saw with a grayscale pattern punched into acrylic:

The green trace shows the tube current at 10 mA/div:

The current should increase linearly, but there’s definitely compression at the high end, and the trench depth flattens out above about 60%, so pushing the tube harder doesn’t produce much benefit.

When I get my shop back together again, I want to conjure a simpleminded geometric beam absorber equipped with thermistors and a cartridge heater for calibration. It won’t be lab-grade accurate, but maybe it’ll be close enough.

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Thanks everyone for your input. The “Omtech” info I presented comes from the owners manual that came with machine.

…then you must contact them if you think you have not received what you paid for.

It is even less than in my test, very nice and convincing test you have done.

Must have been you … I remember knowing I can’t reasonably afford 16mm acrylic… :grimacing:

You’d have seen this with a watt meter… but I get it…

Have you watched this video, from Russ, using his dohickey ? I’ve got this and a Mahoney meter.

It’s about a 1/2 hour… you probably know the first 9 1/2 to 10 minutes…


…he’s just my hero :+1:

Thank you