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Thread: Questions on abuse - Rohm vs. Opnext

  1. #21
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    Ahh... if only I could create a battery pack that could provide that voltage and current, while being able fit in this box along with the other stuff. Even the bigger box I bought the other day is only 6" X 3" X 2". The next few years may see some cool advances in battery tech that might allow this.

    So, the other day I came up with the only power scheme I can see working, and fitting the space. The LD and driver will be powered from a single 14500 Li-ion, the TEC and home made driver will get three NiMH AA's if I can get the right unit (Melcor sells a TEC in a size I could use, with the right V and I requirements to run it at 80% Vmax), and the fan will run from two 9V batteries in parallel... still not sure if it'll be an underdriven 12V fan, or a regulated 5V.

    After a little playing around, I have the entire layout of all components figured out. Believe it or not, it's all going to fit!

    Now, I just wonder if a company like Melcor is willing to sell me just one or two TEC's. I get the feeling they might not, but will investigate. Also gotta' start learning about how to make a basic TEC driver.

    Doctor - Looks like a LM338 will be the choice, as I'll need about 2 Amps. I know basically nothing about building regulated supplies yet, but now I know the first few components needed. Thanks for the tip!

    Edit: Some clarifications on the battery choices. As for the LD, a single, AA size Li-ion can easily handle the current draw. However, it cannot come close to driving a TEC. A protected cell would instantly shut itself down under that load, and trying to abuse an unprotected one in such a way would make for an expensive, 'one use only' laser. Three of 'em in parallel could safely do it, but three NiMH in series produces roughly the same V, are cheaper, and can easily handle 2.5A to the TEC. Fast self-discharge issues are solved by using Sanyo Eneloops. Now for the fan... two 9V's in parallel straight to a 12V fan, underdriving it, should give enough runtime to enjoy myself a few times, but probably more so if it's regulated down to use a 5V fan... which I'm liking the sound of more and more, as it would allow full rpm's, and I could even stuff a little fan speed control into this thing! There's just enough space for it!

    Muah haa haa haaaaa!...
    Last edited by PNjunction; 06-04-2007 at 17:36.
    Alas, poor diode. I fried him well.

  2. #22
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    Ok... life required a temporary break from spending so much time planning this project. Although it will be on the back burner until getting close to the actual construction, the heat will remain on at a slow simmer.

    Sometime after last posting, it became more and more apparent that some design problems in my original plan were going to cause a few headaches. These issues have been dealt with, and the new plans allow for other improvements as well. I'm psyched!

    The diode driver will use two 123's instead of a AA Li-ion, giving more V, more capacity, and less worry. The double 9V's for the fan are also being scrapped in favor of three 123's for similar reasons. And the best part... the redesign can now fit 7.2V worth of nice, high current NiMH's for the TEC.

    Speaking of which, I REALLY want either the CP 1.0-63-06L, or CP 0.8-63-06L from Melcor. They look like the perfect combination of voltage and current, Q, and if I use a Meredith mount and block, the sizes are a great match. I gotta' get one of these.

    More to come
    Alas, poor diode. I fried him well.

  3. #23
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    John -----

    I learned how to turn an Opnext into a 0.177 mw LED today

    Dump 380 ma at it --- The power meter never registered its death..........

    Mike

  4. #24
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    Sorry to hear that Mike... It still hurts me to hear of a dead LD... God knows my stash of dead LD's only gets bigger the more experiments I do... Hope you get better luck on your coming trials

    GL;
    DDL

  5. #25
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    Mike - Sorry to hear that as well! And thanks for posting something that actually has to do with the title of this thread.

    Yeah, 380mA is a lot to dump into these things. Might've blown chunks right off the facets, or caused melting. Do you have a good, powerful microscope? It'd be interesting if you can actually see damage. Also, you've mentioned about wanting to take the can off to get the most out of a diode. This dead one would make a great candidate for practicing your technique.

    Now, if nobody minds too much that I continue this thread as it pertains to my harebrained project, then I shall take the liberty... it's probably better than littering the place with various topics every time I have a question, new idea, or just reporting on something. Speaking of which...

    I have a practical application question along the lines of "how many Watts does it take to cool X amount of mass to Y degrees below ambient?". To be more specific about it... is a TEC with a Qmax around 12 or so, enough to get a diode, module, and a small Al heatsink nice and chilly?

    I'll soon be getting a cheap TEC to experiment with, but since it won't be of the same specs as what's intended for this project, it'll be tough to make a direct comparison.

    BTW, for anyone interested, it appears TE Technology Inc. will sell directly to the public, but at a minimum order of $85 USD. However, I quite like the sound of their view on moisture protection, and they have a couple offerings I'm interested in. Anyone up for a small group buy?
    Alas, poor diode. I fried him well.

  6. #26
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    Quote Originally Posted by PNjunction View Post
    is a TEC with a Qmax around 12 or so, enough to get a diode, module, and a small Al heatsink nice and chilly?
    TEC's of 2W Qmax will cool an overdriven DVD diode to well below freezing, even while warm ambient air passes over them. If you have a large module on the TEC you'll want more, so keep it SMALL. That way you can glue it on with metallised epoxy and get good thermal contact and save money and time and awkward hardware handling.

    The moisture-proof TEC's won't help. First, you have to seal the whole case, so there won't be enough water molecules in there to be a problem. Second, the water-proofing seal reduces the cooling effect, as it will conduct some heat back to the cold side. I described the best way already, in detail. I've looked at all the alternatives I could think of or that were told to me by others. Don't try to predict the numbers, just make the smallest simplest sealed unit you can, and measure what you get.

  7. #27
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    Quote Originally Posted by The_Doctor View Post
    TEC's of 2W Qmax will cool an overdriven DVD diode to well below freezing, even while warm ambient air passes over them.
    Wow!... Cool!... no pun intended. The one's I'm looking at (due to their 15mm X 30mm footprint) are approx. 11 - 12W Qmax, so it sounds like even running it slightly low should give good results. Great to know they can produce that much cooling with so little power.

    Well, thanks again, Doctor. That certainly does save me some time and money experimenting with an Ebay TEC to find that out. Guess I could still do that anyway, and then make a cold beverage plate with it... although I have been enjoying my ale a bit closer to room temperature these days.

    BTW, the moisture protection comment was just in regard to just the TEC itself. The case enclosing the cold side still certainly needs to be sealed as well. That link to TE Tech seemed to say some interesting things on the subject, assuming it's not all marketing hype. Since this thing is intended to be used outdoors, I liked what they were saying about using their use of epoxy sealant. Hopefully, the performance loss from potting is minimal. According to their data, the loss on a 40mm X 40mm module was 2 degrees C at Qmax. Loss increases with a smaller footprint, but I'm assuming that the desired performance will still be easily met. Heck, while I'm assuming, I'll even go so far as to guess that some of that loss is mitigated when running at less than max drive.

    Anyway, there are some more assorted issues to work out during the "design phase" (lol), and am looking forward to next stage... the buying of more parts.
    Alas, poor diode. I fried him well.

  8. #28
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    Bad news... my 16X Rohm burnt out today. Guess that goes toward the original purpose of this thread, so I present to you... "Requiem for a dead diode". aka. Laserium Defunctorum... to be sung in Gregorian Chant style.

    Desiderium laserium concubius
    Evoco genero
    Refero referre rettuli relatum
    Me laserium defunctorum


    REALLY have to work on my Latin.

    Well, it braved over 300mA for a longer time than many others have reported, without once complaining. Well, I guess laser diodes only complain once really, but nonetheless, I'm quite upset about the loss. It was a great little diode. Might have to put a slightly stronger resistor on the next one, or use alkalines.

    Alas, dead diode. I fried him well.

    Edit: That's now my new sig.
    Last edited by PNjunction; 07-03-2007 at 14:39.
    Alas, poor diode. I fried him well.

  9. #29
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    Awe Man Sorry to here yet another diode has gone to the
    great " PN junction in the sky ". Sorry , Couldnt help it..

    I do feel your pain tho.. Ive had several diodes that I liked well and they have passed on without any reason for their departure..
    Same with an old girlfriend I had once.
    Well, anyway, too bad they didnt let the magic smoke out like in other semiconductors. At least we coulda had a show..
    "My signature has been taken, so Insert another here"
    http://repairfaq.ece.drexel.edu/sam/laserfaq.htm
    *^_^* aka PhiloUHF

  10. #30
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    Quote Originally Posted by marconi View Post
    Awe Man Sorry to here yet another diode has gone to the great " PN junction in the sky ". Sorry , Couldnt help it..
    LOL!

    Quote Originally Posted by marconi View Post
    Well, anyway, too bad they didnt let the magic smoke out like in other semiconductors. At least we coulda had a show..
    And one stinky laser. I've somehow managed to not let the smoke out of any LED's so far, but came darn close once with a high power 5mm. I hear it's a fairly pungent event.
    Alas, poor diode. I fried him well.

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