[MonoNeuron]

Hi Guys,
I want to buy a 100 or 150 watt laser tube but I can't find out what the minimum power output is. The lady I am in touch with at Coletech doesn't seem to understand what I want.

eg.

The RATED power output is 150 watts
The ACTUAL power output at full power is probably 180 Watts when new.

If I apply 5 volts to the control side of the PWM power supply then I will get the actual full power of the laser.

If I apply <1 volt to the control side of the PWM power supply then what will I get and how low can it go and still have a stable beam output ?

Will I get 20 watts or will it be more like 60 watts.

I need to know this because I still want to engrave stuff and also cut thicker stuff at a faster rate. This will determine if I get a 100 watt laser or a 150 watt laser.

I can still use my 30 watt laser for glass and paper and card stock etc but then I can use the 100-150 watt laser to cut 10-20mm wood and ply or Acrylic at a greater rate.

Any thoughts on this anyone?

regards
Richard.

[Tweakie]

Richard,

I don't think there is any evidence to suggest that the input voltage to the control side of the PSU and the laser output power (in watts) is a linear function. Certainly when using a variable resistance (0 to 5 Volt) the tubes do not operate below a minimum current (around 5mA) and I assume (although I have never tested it) that this is achieved, internally, by pulsing. Therefore, If the PSU is externally pulsed (PWM) at the control side to set the current then there is the possibility of inserting a 'tickle pulse' which could allow the tube to function below the 5mA region and give a wider 'range' of power settings (at least better minimum settings for higher power tubes).

Tweakie.

[MonoNeuron]

Hi Tweakie,
I'm not really trying to find out an exact power rating. I'm just after a ball park figure of about how much it will drop from full power and still be usable.
I hope someone here has a 100 watt laser and can tell me this from experience.

It's actually hard to find this info out. I think I read somewhere a few years ago that they will drop to about 30 watts and still be stable and if so then that will be great. I'm not sure though and that's why I'm asking.
:-)
Thanks.
Rich.

[zax15uk]

Rich,

There is no reason a 100/120W tube can't be used for light engraving and cutting paper etc.

As Tweakie suggested if you use a PWM driver at high frequency you can get extremely low output.

Zax.

[MonoNeuron]

Hmmm. Interesting.
Does this mean I can set up the glass tube like a RF tube and have a tickle pulse generated to pre-ionize the gas?
I think someone here on the Zone posted something about tuning the power supplies to the tube but he didn't go into specifics.

If someone knows how to do this then that would be really good information to all users of the glass tube lasers.
Can anyone offer any insights on how to do this?

Thanks for the info guys. It's really helping my understanding of how things work.
Rich.

[MonoNeuron]

Double post.

[MonoNeuron]

Damn computer locked up and I posted too many times. :-(

[zax15uk]

Rich,

Yes absolutely, the tickle pulse keeps the tube near lasering potential and by feeding PWM frequency you can get very short intense bursts from it with pseudo variable power output.

The tickle pulse also has the benefit that the laser fires much faster than would otherwise be possible so the response time is reduced. It also extends tube life since the initial 'surge' current to a cold cathode is actually what causes most of the electrode degradation.

If you purchase a good quality PWM laser PSU with the tube this function will be built in.

Zax.

[MonoNeuron]

That's good news Zax.
I am going to buy a laser from Coletech in the next few months so do the Chinese power supplies have this function built in?

I have one for my 30 watt glass laser tube but never really got around to using it as the laser was pretty much depleted by the time I got it set up.

Can you tell me how to tune them in?
Thanks.
Rich.

[zax15uk]

Rich,

It's difficult to say based on the posted specs. The response time is listed as =<1ms which is respectable. 0.5-0.6ms is possible if the ballast resistance is minimized but fine tuning requires it to be matched with a tube.

I would ask them for the PWM input frequency range?

You should be able to get sufficiently low output even without the tickle pulse 'standby' feature. If your table has a good XY speed it would give great power range for engraving (with the right lens) and cutting thick material.

Zax.

[MonoNeuron]

That's good news !

I typically use a 50 mm lens for my setup which gives me a good all 'round performance for the 30 watt tube. I have a 3 inch and a 1" focal length lenses that I seldom use as I find the 50mm one the best performer and also my magnets fit under the head when engraving.

Shirley from Coletech sent me all the manuals and some pictures yesterday on the 100 and 150 watt tubes but I have to say the docs are pretty sparse on info. Just enough to get you going.
The pictures are worth a look and the tubes look very well made and it even looks like there is a port/tube for regasing near the output coupler. That would be handy when it runs out of puff but finding a regasing place in Australia will be near impossible and I wonder if the places in the US would do it even though you bought from China???.

thanks for th insightful info.
Rich

[MonoNeuron]

I received these photos from Coletech the other day and just thought I would post them here for others to see what you get for your money.

Rich.

[zax15uk]

Very nice --- these are by far the best Chinese glass tubes I have seen.

Zax.

[Litografa]

Not bad at all!!! Not revolution, but at least good evolution in right direction!

[MonoNeuron]

Yes, I agree. The glass - metal seal does it for me. I would think the rated hours would be close to what they say it would be and not the fraudulent ones some sellers come up with like 10,000 hours for epoxy connected tubes.
(Maybe it's 10,000 hours before the tube decomposes which would be the actual LIFE of the glass in the tube. :-)
Been stung once and reluctant to cop it again.)
Rich.

[MonoNeuron]

Quote : "I would ask them for the PWM input frequency range" :endquote

Shirley says the PWM of the tubes is 20Khz.

[zax15uk]

That should work ok with the right driver.

I would expect the life to be a lot better, but also the output to be stronger compared to the cheapo glass tubes.

Zax.

[tdiaz]

That looks like the RECI tube I have, and have worked out a table with voltage settings, to get me various power settings:

http://17500mph.com/photos-3?g2_itemId=1266&g2_page=8 and the next have some photos of the setup.

This is how I have it now, with a meter inline, a large knob so I can turn it with more detail. I pick a voltage and that gives me the output level desired when triggered.


See a larger one, here: http://twitpic.com/2pcljs (click the photo header to see a larger one)

Using this RECI tube and the "100W" power supply from Light Object, and the attached power setting table, I get the same output each time.

[MonoNeuron]

That's great Tdiaz,

Seems an all round capability. If I don't use the extra wattage then the tube should last a while longer than rated.
I think I will be getting the 150 watt one in the next few weeks, or maybe even tomorrow as the Aussie dollar is about even with the US dollar and I won't lose anything through the exchange rate.
If I buy direct through Coletech I can save $100 than eBay order but you have no comeback if something goes wrong.

[MonoNeuron]

Do you only do cutting or have you tried engraving as well with the tube?
The only problem I can see with this setup is you don't have PWM for the output.
I need it for mine but at least you have given me the info I wanted.
Thanks.
Rich.