HGM won't lase

[buffo]

Chris Leubner? Ah... Yeah. Hmmm. How to put this?

How about, "Don't trust him any further than you can throw him."

The guy used to have a good rep, but lately it's mostly trash. Ask Steve Roberts and he'll give you an ear full. Heuursciences is not anywhere near as trustworthy as he once was.

Adam

[mixedgas]

And Chris's best friend is a HGM factory trained engineer like my best friend is? Who still services them even though HGM is long gone?

I dont know how many times I have typed a varient of the following paragraphs, but here goes:

Straight poop: A hgm5 is designed like all other opthalmic/derm/dental lasers for 3.2 watts delivered to the target for up to 30 seconds, followed by a cooldown. Its mission in life is to provice pulses from 100 mS to 1-2 seconds and in some cases CW at about 500 mW average power for a eye doctor, although in some cases they use up to 2 watts pulsed. They also get used for dermatology and dental work at somewhat higher powers. It is inherently a modified 68B tube with shorter brewster stems (less lifetime with that) and a Larger bore (more lifetime, less gain, instantly multimode by definition) . Its PSU in normal service runs up to 32 amps pulsed. Out of the factory new they can do as high as 4-5 watts for a few seconds until the gas heats up. IT is, in its origional configuration, designed to reduce the need for cooling water and a large frame argon by running pulsed,and then cooling down, ie the medical proceedures only take a few minutes and then it drops to idle. This is LOW DUTY CYCLE operation.

CW, its good for 500 mW for a long, long time, or a 750mW to 1 watt in show mode with boosted cooling. Ie at 18-20 amps CW with boosted cooling. And I mean BOOSTED cooling. Some do more power at these currents, remember the medical conservatism is built in to avoid lawyers.

A factory 68 cooling system has 2 huge squirrel cage blowers that are almost as big as the laser. Most laserists add two more fans to that. Ie approaching 1000-1200 CFM when loaded and with clean fins. A few tubes are exceptional and will do much more power at the 18-20 amps. Since many people who buy them are not aware of the pulsed mode, they often think oh well, I can really cook this monster. That is a mistake. Because they are so overbuilt for medical safety reasons, they can take some serious abuse. Thats why you hear, oh "I got 3 watts outta mine". Most of those users never watch the hours, and just leap to another laser when they die. Ie they dont care, as long as they are making $$$ they are happy. Few of these users own power meters either, and belive that when another laser hacker set up the laser for them, the 3 watts stayed 3 watts as long as they used it. SO watch out for rumors.


The model 5 PSU is very compact and needs more air across it when doing CW, The idea from the factory is the big metal frame (and its a heavy sucker) will adsorb a lot of heat in the doctors office and keep things cool. remember, 15 seconds at say 3 kilowatts is a lot different then CW at 2 kilowatts. Tube amps x tube volts = a lot of power so 175V X 22 amps = 3,850 watts you have to get rid of. You want the tube core to not exceed 700' F , and hopefully be cooler then that.

As with all small to medium frame argons, tube life is inverse exponetial with tube current, ie higher currents kill them much much much faster. Over in Sam's FAQ, I have the 60X/532 life vs current chart posted,you might want to go take a read. Its basically 3 60X size tube cores in series with a bigger bore and larger gas returns, so the same current density in the bore, so you can scale that chart up to your laser in your head.

Newer medical HGMS, such as PC-EDO, dont even drop to idle, they just wink out and are reignited each pulse. The newer ones are filled with very little gas, so the power is higher, but CW rapidly kills them. I have seen a newer pulsed HGM do 6 watts for 30 seconds on a test bench, followed by LONG, LONG, cooldown. And oh did the computer yelp alarms while that test was happening.


When you get yours, PM me and we will go through the tests, then you call me and I'll walk you through how to cool it.You will need a amp-clamp, a good battery powered voltmeter (half the electronics float at 200 VDC) and a medical footswitch to get started.
A BIC pen cap with the lid sliced off so the beam comes through will take the place of the fiber, and you should have goggles.

I have never posted the mods, as a request of my medical friends, the reason being they dont want to see hacked lasers blow somebody's retina to shreads if returned to medical service. In fact my buddy usually asks for the med computer module so they DON'T go back to medical service.

The HGM as delivered is a light mode laser, when the med comp is removed, a jumper is installed, and the laser goes to the max current limit when lit ads there is no current feedback circuit, The max current pot becomes the current control, and this is dangerous to the laser if not respected and kept turned down by the operator. A few people have devised complex resistor networks to provide a variable current control. You can also add a LEM current sensor(30-50$) in place of the light card and have some current feedback and thus have a real upper limit to protect things.

Steve

[DZ]

I had an old omnichrome that arc'd down a return path. I had always heard that once that happens, its difficult to get it to arc down the bore again. It stunk since it was once of the little mixed gas omnichrome 643's...

[Xytrell]

It was an ignitor air gap issue as suggested by Mixed gas in a PM. Working perfectly now, thanks!

[LesioQ]

A... what ? An air gap ? Shed some light on this idea, please !
Piotr.K

[mixedgas]

A... what ? An air gap ? Shed some light on this idea, please !
Piotr.K

HGM (parent company of ALC) on medical systems used a small resonant tesla style ignitor that arced to a isolated cooling fin as the ignitor via a small air gap. If the gap is too small, no ignition, if the gap is too large, no ignition. Gap must be "just right" In reality that coil is a standard lawn mower ignition coil. A optoisolator drives a scr that dumps 220V at 2-6 uf into the coil. This keeps the pulse out of the high side switching fets in the psu without a diode. Its close to the cathode end of the tube. The magnets being in series with the tube on the anode end also helps

Steve

[mixedgas]

It was an ignitor air gap issue as suggested by Mixed gas in a PM. Working perfectly now, thanks!

We aim to please,or is that we please to aim....

Steve

[GooeyGus]

Still waiting for my HGM unit to come... I paid over two weeks ago and the guy hasn't shipped yet. He sure is taking his time....

[Laser Zone]

Have you tested to see what ohms you have across the magnet ?

[mixedgas]

Have you tested to see what ohms you have across the magnet ?

its lasing, ignitor air gap was wrong.

Steve