laser tube problem

[geekinesis]

Hi there

I was cutting some acryllc when I smelt something strange from the machine other than the usual acrylic smell.

The laser lost power and there was also no register on the amp meter even though the dial was turned up to about 40 percent power

I checked the tube and found the end had detached, as in the picture.

I know the tube is now shot, but what else could be wrong? even if the end of the tube is detached (all the glass is still intact and no leaking water)

Is there something wrong with the electrics as well? If the tube is broken would the power going to the tube still register?

[Tweakie]

Sorry to hear your bad news.

That looks like it has got very hot, which it should not have done, so perhaps check your water circulation. (It is always wise to have a flowswitch in the circuit just in case circulation stops).
When the end water jacket becomes detached the correct gas mix has gone and it's bye bye tube. Something caused this to happen and you must find out what and correct the problem before you risk damaging the replacement tube.

Tweakie.

[geekinesis]

Hi
The water temp in my tank was about 29 degrees when the tube blew. But I guess that means the tube temperature could have been much higher and not being cooled sufficiently. I normally aim for about 23 degrees water temp.


I usually cut pAper at 10 percent power. This was cutting acrylic instead on 40percent. I notice sometimes as well that the power can fluctuate a bit using the potentiometer on the machine. So it's possible it was runnng at a higher power briefly which tipped the temperature.

How long does it take for the power supply to lose it's charge so I can replace the tube?
Is it several minutes or longer?

[Tweakie]

How long does it take for the power supply to lose it's charge so I can replace the tube?
Is it several minutes or longer?

Wait at least 15 minutes then short the HT to ground with a wire (with 1Megohm series resistor) firmly connected to ground at one end and holding the wire with a well insulated probe. Always keep one hand in your pocket when doing anything like this. This will dissipate any residual charge. As said before always treat high voltage with great respect (the green side of the grass is much better looking).

The water temp in my tank was about 29 degrees when the tube blew. But I guess that means the tube temperature could have been much higher and not being cooled sufficiently. I normally aim for about 23 degrees water temp.

I don't see anything wrong with 29 degrees temperature but that part of the tube looks as though it got a lot hotter than that to fry the epoxy.

Tweakie.

[zax15uk]

I would guess there was limited or no flow around the mirror, possibly from air trapped?

Once the circuit is open (as it would be in this case) the current meter will read 0. It is unlikely your PSU is damaged, but sorry you will have to replace the tube and check the coolant flow.

Zax.

[geekinesis]

thanks for the advice

If i leave it a few days, would i still need to ground the power supply before changing the tube?

I am thinking that maybe the epoxy seal was weak for some reason, letting the water jacket loose, which then allowed heat to build up, which then caused the melting of the ret of the epoxy.. Or an air bubble as you suggest.


Is it ok to add some dye (food dye) to the water so that bubbles show up more clearly?

[geekinesis]

ps

The tube was at least a year old when I bought the machine a year ago.

So at 2+ years I was probably close to buying a new tube soon anyway. I thought it would last at least 6 more months though as it hadnt lost any power (until now)

[zax15uk]

If the seal was weak you would lose the gas mix quickly and the laser would just stop, it looks to me that this was a catastrophic failure due to over heating. If the pump was running and the water temp in range the likely cause is insufficient local cooling due to trapped air or some form of blockage.

It should be ok to add a small amount of food coloring (does anyone know if it is non conductive?) if necessary, most people are using a mix of distilled water and anti-freeze which has a dye added.

I would just follow Tweakie's suggestion to be sure. Put a 1Mohm resistor in one end of a croc clip lead, connect the other end of the croc lead to the PSU and touch the free end of the resistor to the other PSU lead. Simple and safe.

Zax.

[geekinesis]

Ok will do. So to ground the psu where should I attach the clip? The wires from the PSU to the tube are insulated around the tube join.

Now I need to install the new tube when it arrives so will probably be back for more advice.

[myrko]

You need to check the output curent

show this link

CO2 Laser Tube products, buy CO2 Laser Tube products from alibaba.com

at the end of the page you have a array with current values for each power tube.

ex: for a 40w the max curent is 18mA.. = 100% power on the controller.
Limit curent placing a resistor at the input (pin 5 or 6) of the laser power supply.

!! never put more curent because it decrease the lifetime verry quickly.. !!!!!

most common chinese laser manufacturer don't ajust well the max output current.
The result, is tube broken... !!!!