Co2 not firing at min setting

Community Laser Talk
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I have a 60 watt Chinese blue and yellow machine that looks a lot like the first omtec. It’s around 2018 made. I’ve fitted a new trotec 7813 controller and life’s been good with it. But my min setting for the tube was around 12%. So I’d normally opt for a line setting at 15% when I just want a pencil type line for marking out stuff etc. recently I’ve had an issue that it’s not firing at 15% at all but intermittently . when it does it’s very bright inside the tube by the outlet but week in the middle of the tube. Even at 16% it’s now randomly stopping and starting during a run. The tube is original so I know it’s on borrowed time but the machine sat a lot from last owner. At 85% where I do all my cutting it’s working fine.

My question, is this the first signs of the tube going bad or do you think I need to start chasing intermittent shorts or power cable issue. Maybe power supply going bad?? It’s weird to me that it is ok on higher settings.

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All of which resembles a tube going bad.

The claimed lifetimes seem hopelessly optimistic, with seven years being on the outer edge. Unlike fine wine, the tube’s gas mixture does not age well, regardless of its total power-on time, and can go bad on the shelf.

IMO, you should replace the power supply at the same time, because those components definitely deteriorate with age.

Several folks report lifting a defective tube out of its crate, so don’t assume anything is right with the replacement hardware and test for beam quality as part of the initial setup.

3

Thanx for the reply, I know it’s way past its sellby date. Just wasn’t sure if not firing at low setting was a thing of a bad tube. Obviously I knew about it not putting out power at higher settings but this one is fine in that area so was confused by it.

Not sure how I would check beam quality?

On a new one. I was going to get a mcw power supply and tube so I could upgrade to a 80watt so if I change tube I’ll do both. Hopefully being a more bigger brand in the market I’d assume there will be good quality but then who knows.

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There are physical changes in tube size as the power increases.

Few of these allow for the ability to lower the tube to the optical alignment position of the original. If you go from a 50mm tube diameter to an 80mm, you have the be able to lower the tubes alignment path by 15mm (1/2 the diameter change).

Not like you can’t do it, but larger tubes may not lase at any lower of a power percentage.

The only use for higher power is to cut thicker material. You usually loose out at lower power levels.

I’m on my third tube and I haven’t replace the lps.

I and I’m sure many others, don’t have deep pockets like @ednisley does, with the ability to change out the entire lps → tube section at once.

I grew up in the fix it electronics, where you replaced the ORU (Optimum Replaceable Unit), that would be what fails not the whole chain of components.

With this stuff you may get a lps worse than the one you have. That would leave you with two unknowns.

The beauty of this, is it’s your choice.

Good luck.

:smiley_cat:

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My machine has big spacers in the holders so I think there good for 80mm but I’ll double check. Plus the adjustable up and down and I’m pretty sure there at the top with the 50mm tube but again a good idea to check.
On the lps I’d agree if you was changing same tube for tube with no issues but the advise given hold good weight when I’m getting an intermittent non fire, although this is likely to be the fault.

If I was going to spend 350 on a std tube I might as well pay 500 get upgraded tube and lps as a package. Makes me feel like I’m getting something extra for my spending. No big pockets but it makes you feel it was worth spending if you get an upgrade. Lol.
I dont need as such for it to fire down low as such. It’s just mine had stopped firing at that level so want to know if that was the tube dying. The other bonus of the bigger tube is as you saying being able to cut deeper but again I prob don’t need that too but it would also means I could cut the stuff I am cutting at either a faster speed or with less % power which should make it last better instead of having to push it to 85% all the time to cut 3mm ply.

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That’s likely due to the tube, not the power supply, because CO₂ tubes generally don’t fire below 10% (-ish) power. Whether that’s 8% or 15% or whatever depends on the tube, its age, the coolant temperature, and probably the moon phase.

I did some simpleminded experiments a while ago:

TL;DR: The minimum power is whatever it is and using a few more percent to guarantee ignition seems prudent.

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Yeah I know of the min power. My original question said I know my min is 12% so I use 15 but even at 16% it’s started being intermittent and like a switch whilst using it. I’ll go to 20% lol :joy:. But I just need it to mark the ply not cut or engrave it for my use. I layer up ply so I mark the wood where the upper piece has to go for great alignment

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If you can run at 20% power with a 60W tube, then we’ll assume a 12W output. Which seems is rather high, from your comments, for what you do.

Now increase this to an 80W tube that only lases at 20%, meaning the lowest you can get is 16W or an increase of 30% from what you have.

It sounds like you’re shooting yourself in the foot.

We are all used to digital systems, but the lps → tube combination is not a digital device but an analog one. Most analog devices work best in a working range of the design, I.E. they don’t perform as well at the edges. Continued use of an analog device at it’s maximum, is asking for a failure.

Same with running this type of operation with a tube.

Be wary anytime you are running one of these at extremely low power levels, especially around it’s lase point. I’m on my third, it lases at about 10%, but is in TEM01, not usable for work, but is OK for an alignment. The tube works fine in the 15% up range, as far as I can tell :thinking:

Just be warned that big tubes have their own issues, as do their power supplies.

The <=1mS response time specification relates to how fast it will reach 90% of it’s specified voltage within that time. This determines how fast the machine can run and still maintain control of the lps. One reaches a higher trigger level faster than the other, but has less MTBF (Mean Time Before Failure).

lps-voltage-current
lps-voltage-current1762×762 164 KB

Take you time and understand what you’re getting or buying.

I beat one tube to death driving it hard and running it at warmer temperatures… the other I treated with kit gloves… both lasted 2 and a half years.

Use it as long as can, even if it appears to loose power.. You’re going to pitch it or, like I do, put it on a shelf as art…it really is…

Good luck… main thing is to have fun..

:smiley_cat:

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I see your point on min level. As I wasn’t aware a 80 watt would be so high min. I assumed it would be closer to 12 my one fires at. I was using 15 so it was t bang on the lower limit. I’ll do some more research before replacing.

Thing is I don’t think this has ever worked as a 60 watt anyway since I brought it second hand. My 20 watt diode would do things at the same speed as this would and when you see guys cutting thick hard wood in one pass, no chance it cuts 3mm ply in 28/85%\2 and still a bit sticky in places. 10mm oak in 6/85%\6. Tottaly burnt edges. My main used is engraving in oak chopping boards and it’s doing that just fine so I will run it till it stops doing that for sure.
Funny thing is it’s working ok today at 15%. But it is 2 degrees cooler on the water temp.

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It might not, but you really shouldn’t be looking at so much power as anomalies occur and they are considered normal, such as low laser currents.

Commonly, larger tube lase at higher minimum values, but it’s not written it stone.

Really you don’t whose at fault or if there really is a fault. Both the tube and the lps are analog devices and you’re depending on a gas mixture to lase. Add in the complexity of what happens at a different temperature, various component tolerances and the overall stability of this operating at the edge of it’s operational ability.

My 43W tube lases at 9.8% power, normally, however, in winter when the temperature drops into the 50F range, the machine will lase at just over 8.5%..

A wise person uses these where they are in a stable operational range.

You can’t really compare how these operate. A tube is analog and a diode is digital.

For a 50% power, a tube just stays on at 50% power. A diode is on 100% power for 50% of the time. How that impacts the material can make a difference.

:smiley_cat: