Help Powering CO2 Laser

[r691175002]

Hi,
I managed to pick up one of these units a while ago and have only just gotten around to getting it working.

After doing a bit of research, I've found a few references to the laser I am dealing with:
http://laserpointerforums.com/f43/starwarz-co2-power-47504-3.html#post656314
http://laserpointerforums.com/f43/starwarz-co2-power-47504-4.html#post666742
I am almost positive that the laser I have is one of the units sold here:
http://laserpointerforums.com/f39/5w-co2-laser-tube-rf-amplifier-150-delivered-23204.html

I've managed to dig up that the unit needs ~30-38V to the tube, 12V and 5V to the driver board but embarrassing as it is, I have no idea where to apply power.

I found a picture of the board with markings but it doesn't fully clarify how to power the unit:

This is what I've come up with, but I'm not all that confident:

How much heatsinking do I need on the RF transistor (The brass thing?).

Any help would be appreciated, I'd rather not fry such an awesome looking laser.

 

[Event_Horizon]

I had one of these. It worked for a short time before the oscillator died and I was never able to get it working again. The connections you've shown in your last image are correct. Both grounds are connected to each other.

The 5V input draws about 500mA, the 12V input draws about 2A, and the 30-38V input draws up to 10A. Make sure you have sufficient current capacity or you could damage the driver board. The PWM input draws only 2-3mA.

The power transistor needs tons of heatsinking. Running the thing without a heatsink for about 5 seconds heated it up to the point where it burned my finger when I touched it. I used a large heatsink meant for a Pentium 4 CPU and didn't have any problems after that (until the oscillator died and took out half the driver board with it).

 

[LSRFAQ]

From what I have seen, and from when mine died, they die for three reasons, not enough heatsinking. High RF VSWR from improper mounting, and trying to run a pulsed marking power supply 100% PWM for too long. The "MOD OK" light is there for a reason.

Most of those came out of high speed address label machines. So there was some cool down, with bursts of high power.

High VSWR is RF reflections by being mounted wrong or without the right shielding, or having a shorting loop couple energy back into the driver.
Shorting loops are formed by having a metal case too close to the laser or a all metal mounting strap that resonates with the 27 mhz RF. You have to mount the tube the way the factory did, with ceramic standoffs, at the right spots, not close up metal.

BTW< 27.125 is CB channel 14, and is also a industrial heating frequency. So you might wish to shield the laser a bit least 5 biker dudes come and track your signal down and beat you up.

I killed mine with high VSWR, while tweeking that matching coil on the head, and I'm a experienced RF guy and should have known better. Also don't run the PSU without the tube attached, instant meltdown.

About VSWR: Just assume your tube is the antenna. VSWR is a simplification of the concept, but it works.

From wiki:

When an antenna and feedline do not have matching impedances, some of the electrical energy cannot be transferred from the feedline to the antenna.[2] Energy not transferred to the antenna is reflected back towards the transmitter.[3] It is the interaction of these reflected waves with forward waves which causes standing wave patterns.[2] Reflected power has three main implications in radio transmitters: Radio Frequency (RF) energy losses increase, distortion on transmitter due to reflected power from load[2] and damage to the transmitter can occur.[4]

Matching the impedance of the antenna to the impedance of the feed line is typically done using an antenna tuner. The tuner can be installed between the transmitter and the feed line, or between the feed line and the antenna. Both installation methods will allow the transmitter to operate at a low SWR, however if the tuner is installed at the transmitter, the feed line between the tuner and the antenna will still operate with a high SWR, causing additional RF energy to be lost through the feedline.

End quote.

Mine had a much more massive driver, so I cannot help you with the pinouts. There is a guy in Cleveland that collects these, go ask on PL for help. He might see your post.


Steve

 

[HIMNL9]

Uhm, it can be used an antenna matcher / ROSmeter for match the tube and the oscillator, if the cable is not the proper lenght .....

Something like this one:

QUALITY - RECOTON CB 174B CB ANTENNA MATCHER - 100 WATT - eBay (item 390234939296 end time Oct-04-10 10:48:16 PDT)

Or anything similar ..... using it with a ROSmeter, you can tune your setup for the maximum power transferred (direct) versus the minimum possible reflected power to the oscillator.

A ROSmeter is relatively easy to build DIY, for the CB, but for the tuner/matcher is better to find one already built, if you don't have the needed RF instruments around for set it up.

 

[LSRFAQ]

A ROSmeter is relatively easy to build DIY, for the CB, but for the tuner/matcher is better to find one already built, if you don't have the needed RF instruments around for set it up.[/QUOTE]

Great idea, however...
I would not assume the amp is matched to 50 ohms. At least mine was not.
Steve

 

[HIMNL9]

Uhm, as far as i remember (are 15 years that don't play with CB ), antenna tuner is mainly for the resonance, not just for the 50 ohm load .....

I mean, if the tuner (that is basically an LC, or in the better ones, a CLC), reach to "match" the tube impedance at 27MHz with the board output impedance, it does not care too much if it's 50 ohm like in a CB setup, the main purpose is to obtain the better transfer of power from the board to the tube, with the minimum reflected power to the board .....

The only problem can be that the board is not planned as a CB amplifier, probably cannot hold a too high unbalancement during the tests ..... an artigianal tuner that "match" the impedance of the tube can be improvvisate, changing the L value, but during the tests, there is the need to use low power for not burn the RF transistor, and as far as i know, on that board there's no easy way for reduce the output power ..... not linearly, at least (maybe driving it with a PWM signal with only 5% ON time ?)

 

[Hemlock_Mike]

That's what I told him -- Set the PWM to minimum and slowly turn it up. Watch the meters for trouble.

HMike

 

[r691175002]

I doubt I have the technical knowledge to do any tuning, but I've got some nice heatsinks on all the trouble components and plan to power up the laser slowly via PWM. I still need to pick up a cheap power supply off ebay that can do the ~30V but after that I should be okay.

 

[HIMNL9]

36V is one of the "standard" industrial value, so you can probably find something in the industrial components.



EDIT: like this or this or this, as example ..... and, maybe from some electronic fairs, also second-hand units .....

And about the PWM driver, you can easily DIY one with a 555

 

[Hemlock_Mike]

My 3 assemblies all powered up without a problem but this model is different from mine having the final amp on the tube assembly. Too many people have had trouble with these but RF circuits are trickey sometimes.
Always start with the PWM set to minimum and slowly turn up the drive to the final / tube assembly.

HMike