642 Dual

[mikkojay]

it also doesn't make as good thermal contact with the diode as a machined press-fit in a block of AL would

Yeah, I thought about adding a little paste, but unfortunately it was after they were together. I did however tighten the retaining nut a few degrees past hand-tight, so they are snugged in there very tightly. I'll post back with any updates, and probably start another thread for the box build.

The little grocery scanners are also coming along well, I need to finish those up too. So many projects, it's great not knowing which one to work on next!

Oh, and a special thanks to Andrew for answering so many of my endless questions when it comes to these diodes- you are most definitely PL's diode wiki! Thanks!

-Mike

[mikkojay]

I'm very interested in the one driver for multiple diodes idea. It was said on another thread that it is not a good idea. How did you get it right? i blew my dual red, didnt even get to see a nice red beam. Great work!

This is the third (actually a rebuild of the second) dual red I have built using 2 diodes on one Flexmod driver. The first two used open can reds, and I didn't use a series resistor or anything. I just adjusted for the current I wanted (x 2), hooked them up and it worked. Call it dumb luck, I don't know- it has been fine for me. I always try to be careful and use a grounded iron, grounding strap, etc. The first one I built is still kicking just fine in my RGB graphics projector, and that one is being driven at the upper end of the open can's rating I am sure. Two drivers would be just fine, and probably preferable, I just figured I would stick with it while it's working for me.
-Mike

[MechEng3]

My quad setup really heats up the resistors in line...does you unit have this issue? They are 4.3 0hm. Nice laser! You will love the mix with 473nm.

[mikkojay]

My quad setup really heats up the resistors in line...does you unit have this issue? They are 4.3 0hm.

I'll have to check- I actually put one inside the holder with the Lasorb, but that was a bit of a squeeze, so the second one I actually mounted externally- I can check that one. I put a little extra black tape blob on it all because the heat shrink tube I used was just a little too small in diameter to slide over the bird's nest I created. Maybe a bit lower value might be in order?

Like I said earlier, this is the first dual I have used series resistors on. I will have to make sure they aren't getting too hot, especially if I have one inside one of the holders- I don't want any more heat in there than necessary.

Update- I just went and ran a test- I ran it for about 10 minutes, and the resistor (external one) did get warm. Also, the holder with the internal resistor did get just a hair warm, while the other one was room temp. I know what I will be doing this afternoon-

Thanks, Mike

-Mike

[mikkojay]

OK, here's the latest- I ditched the 4 ohm resistor in the holder and changed the external resistors to 1 ohm. They barely get warm. My meter is out of cal and I am sure is not really accurate, but it does give me some decent ideas of before and after readings.

After switching to the 1 ohm resistors, my combined laser output went up by about 8%. I also did a before/after cube measurement on the "thru cube" laser, and the cube seemed to "eat" 9%. I don't know about the angle side.

I tweaked the gain up while watching the meter another 8% just because I know that I was originally very conservative with my initial current setting. The beam is very nice, so I am going to call it good for now before I get carried away and start working on my other todo list.

Happy Halloween
-Mike

[drlava]

What is your power supply voltage while they are operating? I would not expect a significant output change with a resistor swap like that. 1 ohm resistors will give you about 300mV of diode voltage compensation, since you're using matched reds it should still be ok.

[mikkojay]

Just went and checked- 4.93vdc. I am using a small switching p/s that is rated 5VDC @ 2A.

[decix]

Opnext HL6385DG have an operating current of 280mA an certainly do get warm after a while of operation. You should really watch the temperature, what I see from your pics there is not enough heatsinking for these cuties. I built a lot more aluminium around mine.

[mikkojay]

Hi Decix,
That's a pretty setup! I noticed that when mine was on for a long time the modules did get slightly warm, but by no means hot. Since my next projector design is completely open, I may just ensure that there is good airflow past the module and call it good. Another good side effect of analog modulation in the way we use these is duty cycle. I am hoping that if I observe a bit of warmth after 20 minutes of full power CW, in reality the way my ultimate use of this module will be, it might see about 50% of that power (in duty cycle terms). I hope that would mean that the red could be catching its breath and cooling down during blank periods, which is a plus.

-Mike

[decix]

Just warning you because I already killed one of those... 120 EUR up in smoke :-) But I rather think it was a power supply peak, not temperature.