Safe power setting for glass tube

[Bruno Piancatelli]

Hello Again, I´ve had this doubt for some time now. When I first got my machine the supplier recomended me that I should not exeed the power setting above around 65% if I wanted the tube to last what it is supposed to last.
This is a 60W chinesse tube.
The thing is that reading through the forum and looking for information to confirm this, I haven´t found any comments about this being so.
Im not talking about using at 100% but I wanted to know if it would make any difference from using at 65% than using at 80%?
does anyone have any experience on this subject?
Thanks!

[Henri Sallinen]

Hello Bruno,

I myself got the recommendation that I shouldn't use the machine at 100% power, but instead use 90%. 65% sounds a bit too low to me.

[Allen Rawley]

Hello,

The short answer is, yes 65% control setting at the operator control panel will greatly extend the lifetime of the laser, at the cost of reduced laser output power for your jobs.

However, typically the proper way that this is regulated is not by the operator panel (or your PC), but by the power supply potentiometer setting for current. The proper setting for the majority of laser power supplies from China is 28-30 mA. You can read this in the power supply manual provided from the power supply manufacturer.

Once the power supply is properly set, then at the operator panel (or PC) you run the laser from 0-100%. I made up a set of instructions for my USA customers to perform this setting http://tinyurl.com/lqs2wgr .


The long answer and insights are below:

With any CO2 gas laser (RF or glass tube), if it is operated at less than maximum power then the life will be longer than if operated at maximum power. For example, if I am selling a laser machine to a manufacturer running a production line who needs 80 watts of power for his process, then I typically recommend +20%, so they purchase the 100 watt in their machine.

For the glass tube lasers it is the same physics. However, I have seen the sellers of glass tube lasers have a variety of approaches. Below are several of the negative experiences I have had over the years:

1. A glass tube laser is rated for 130 watts by its original manufacturer. This is the so-called agreed upon power level that includes the warranty for its lifetime. The warranty may be eight months or so. The maximum power that this laser can output is approximately 150 watts. The way to get 150 watts from it is not from the control panel, but from the power supply potentiometer Next, I have seen the laser machine assembly houses in China (or the distributors/agents for the glass tube lasers) then sell the laser as a 150 watt laser. Laser power supply comes in with a 34-37 mA. The result is that the laser arrives with great output power (150 watts) but the operating life is significantly reduced.

More often then not, my experience in buying Chinese machinery is that the assembly houses do not set the power supply properly and the current is not usually set properly.

2. An 80 watt laser does not output 80 watts, but has a few watts less than 80 watts.

3. A 90 watt laser sold on eBay is actually an 80 watt agreed upon power level with a capability of 90+ watts with the improper power supply settings.

As a response to these issues, I developed a low cost laser power probe to measure the CO2 laser power. The device helps me to purchase laser tubes that meet their specifications, and return the ones that do not. There are videos on youtube. Search CO2 laser power meter probe if you are interested.

[Dave Sheldrake]

Pretty easy to make a calorimeter with nothing more than a block of aluminium of known weight (mass) and a digital cooking thermometer.

The specific heat capacity of Aluminium is 0.9 J/g/K

Heat the block with the unfocussed beam for 10 seconds then simply check temperature.

(Mass * Heat Capacity * Temperature Change) / Time In Seconds Beam was applied = Power in watts

The result isn't the most accurate but without a proper power meter it's pretty close.

Dr Lindsay Wilson explains it so much better below.

http://imajeenyus.com/optical/20130423_measuring_laser_power_thermally/index.shtml

Digital Cooking Thermometer £2.99
Block Of Aluminium £0.50
Drill the same size as the probe £0.56
Black Thermal Paint Can = £2.49

Total £6.54 or about 10 bucks.

cheers

Dave

ps: Don't try suing a laser manufacturer based on the read out from a 10 dollar Callo, when they turn up with their £10,000 power meter from Ophir the judge is going to laugh :)

[Bruno Piancatelli]

Very interesting responses!
I´ve been using at 65% but actually dont want to push it to 90% either. so I think I´ll be using a setting in between those numbers to be happy with.
Thanks!

[Martin Boekers]

Hmmm I have run my at 100 power (RF Tube) most of the time. I haven't noticed an issue with it, I have replaced tubes. Typically about every 4 years. These machines get a lot of use. If this is true those with 30 or 40 watts are really at a distinct disadvantage..

[Bruno Piancatelli]

Hmmm I have run my at 100 power (RF Tube) most of the time. I haven't noticed an issue with it, I have replaced tubes. Typically about every 4 years. These machines get a lot of use. If this is true those with 30 or 40 watts are really at a distinct disadvantage..

I think we are talking of another quality and type of tubes. the one I have is the glass cheap chinesse, and the question was reffering to those.

[Martin Boekers]

I think we are talking of another quality and type of tubes. the one I have is the glass cheap chinesse, and the question was reffering to those. Sorry didn't mean to jump in like that. There was a reference about glass and RF that's why I responded. Not sure if at high watts the laser gets hotter and water cooling may effect it? I guess if they burn out faster the thing to consider is the cost in engraving time as opposed to the price of a tube. Good luck with your laser! Many here have been exploring the Chinese lasers with success.

[Dave Sheldrake]

When I first got my machine the supplier recomended me that I should not exeed the power setting above around 65%

Your supplier is telling porkies Bruno, when a glass DC tube fires far higher than normal voltage is shot into it(well above what you will ever run it at). While running it at 100% will reduce the expected life of the tube in the bigger picture it won't actually make much difference (a job run at 50% power taking twice as long as a job running at 100%) (not quite the exact maths but close enough).

Chinese PSU's aren't usually adjusted very well at the factories (on the basic machines anyways) and can run over the maximum limit for a tube so keeping inside of 90% power can help reduce the risk of burning a tube out, when tubes fail due to high current it's a product of dissolution of the materials the electrodes are made of that causes the biggest issue, over pumping the gas isn't so much of a problem in real terms.

Both RECI and EFR have a maximum warranted current, if you exceed that then you can degrade the tube early and have no warranty.That said, if you are running at high end (85 - 90% power all the time) then as Martin said consider the tube cost Vs the increase in productivity.


With any CO2 gas laser (RF or glass tube), if it is operated at less than maximum power then the life will be longer than if operated at maximum power

RF excited lasers are designed to be run at 100% power.


For the glass tube lasers it is the same physics.

Not even close to the same sadly.

cheers

Dave

[Alexa Ristow]

I started off trying to save tube life by limiting usage of 100% power on my Glass tube 60W Chinese. I then started getting busy enough that job time became an issue. At this point mathematics kicks in. If a tube costs $1000 and lasts a 1500 hours then tube cost is 66 cents per hour. If I had to push it and drop the life to 1000 hours then tube costs is 100c per hour. The question is whether or not the extra speed is worth 34c per hour..............

Now...
Some threads lately have pointed out that you can overpower certain material such as MDF. With experimentation, I can actually cut faster at 80% power than with 100% power. Never mind the logics, production line cutting backs this up.

I now am more aware of utilising the power settings for efficiency than worrying about power settings for costs,

Regards,

Norman and Alexa.

[Dave Sheldrake]

I can actually cut faster at 80% power than with 100% power. Never mind the logics, production line cutting backs this up.

Very true, it's a combination of outgassing (Carbon Dioxide sucks up IR laser beams, think of it as global warming on a tiny scale ;)) carbon production (why do you think they line NBC suits with carbon) and ineffective air assist (too far away or not enough pressure / flow)

In the case of laser cutting the laws of diminishing returns are very well illustrated, double the power rarely if ever results in double the speed until you get to some very high end tubes / sources.more usually it's a 2:1 ratio,

40 watt glass cuts 3mm ply at 14mm per second
60 watt glass cuts 3mm ply at 16-17mm per second
80 watt glass cuts 3mm ply at 20mm per second

It only really changes when you get to big body tubes with high power levels 150 - 240 watts due to the bigger beam input focussing down to a smaller spot for the same given lens system (increased power density)

cheers

Dave