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Testing an old 20watt laser diode (fiber coupled)

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LAN_403

EEYORE

Mon Oct 13 2008, 04:49AM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Hello
I never let the value drop below 6.5k ohms. I also lightly sanded both surfaces and put heatsink compound down. I didnt debur but did sand down the holes well. Should I attempt a thourough polishing of both surfaces? I should have left the indium foil on...Ill try the 1/2in drill bit idea tomorrow. At least the laser seems to work! It actually seems to begin lasing around 10amps (at least burns stuff at 10amps). At 31amps, it really rocks! Burns the crap out of stuff! My flatpac seems to work great for this too! I am using a 1.5ohm load resistor, a 0.1ohm 100watt current limit resistor, and some ultrafast 37amp diode across the laser diode. The load resistor needs better heatsinking, but is okay for just a couple of seconds. I put some ICs in the unfocused beam and they instantly flamed! Cooked some sausage as well as some crackers...And its and 808nm laser! Now I just need a huge vanadate and KTP crystal!
matt

Steve Conner

Mon Oct 13 2008, 09:46AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Of course the temperature will rise sharply.

A TEC is designed to have a high thermal resistance, for best efficiency when it's working. That makes it a lousy conductor of heat when it's turned off.

If it conducted heat well, it would be driving with its handbrake on, so to speak. The heat would leak back through from the heatsink as fast as it tried to pump it away. This does happen with any TEC beyond a certain Delta-T, and it causes thermal runaway which will cook your laser. But poor thermal conductivity delays the onset of runaway.

The Peltier effect is another heat transfer mechanism quite separate from regular thermal conductivity, so the low conductivity doesn't hurt it, but it needs electric current to drive it.
So don't be shy, stick a couple of amps through it while keeping an eye on the thermistor resistance.

EEYORE

Mon Oct 13 2008, 02:41PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Hello
there is no built in Tec in this laser package. It just has two large power lugs and a thermister.
matt

Carbon_Rod

Mon Oct 13 2008, 11:23PM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

A TEC kit for that power rating is not as easy to find (usually $3k to $7k).

An aluminum block water cooled CPU kit, and mini-fridge is not hard to find.

EEYORE

Tue Oct 14 2008, 12:20AM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

I expected a rise in temperature, but not nearly like this. I have many other high power lasers (3watts or so) that have no active cooling. They have a little rise in temp. but not much. I know this laser is MUCH more powerful, but the heatsink is many times the mass of the other ones. I figured it would last more than a minute at least before needing some kind of active cooling. I wanted it to stay simple. Im willing to bet the surface quality sucks. Should I attempt to "polish" the laser diode? I plan to sand down the heatsink better. I tried putting an ice cube on the heatsink. It really didnt do much while the laser was on, but cooled it down with the power off.
Matt

Steve Conner

Wed Oct 15 2008, 09:55AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Oops, my bad, I think I got you confused with some other guy who had a big laser with a TEC.

rp181

Wed Oct 15 2008, 12:17PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

ya, this happned with me to and IGBT, heat travels too slow...
sand it, and if you can, mill it.

EEYORE

Wed Oct 15 2008, 04:50PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

Steve McConner wrote ...

Oops, my bad, I think I got you confused with some other guy who had a big laser with a TEC.

No problem! Youve been more than helpful as is, and that explanation was very informative anyways! I think this thread will be very useful for others that come along later with a big laser diode.

I will get some sandpaper today and sand both laser diode and heatsink down as smooth as I can. Maybe some good quality thermal compound is also in order? (Just have some old crap from a few years ago).

Im looking to replace the current power resistor (for current limiting). All I can find are wirewound resistors. Well, thats the only kind I can find with nice terminals for connecting the fat wires I want to use. The only non-inductive power resistors are t0-220 and t0-247 type with thin leads. Thats a pain trying to connect them securely to 8awg wire! Anyone reccomend a place to look? I tried digikey, mouser, ebay. (Ebay has lots of "non-inductive" wirewound resistors). I dont see how a wirewound resistor can be non-inductive?

Thanks guys!
Matt

Bamacoiler

Wed Oct 15 2008, 08:09PM

Registered Member #1628 Joined: Wed Aug 06 2008, 08:48PM
Location: Huntsville, AL USA
Posts: 95

mattrg2 wrote:

I dont see how a wirewound resistor can be non-inductive?

Arcstarter

Wed Oct 15 2008, 10:24PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Bamacoiler wrote ...

mattrg2 wrote:

I dont see how a wirewound resistor can be non-inductive?

I know that doesn't help but that is one(just for proof :P)

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