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Thread: adding TECs to my baseplate, advice needed

  1. #21
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    Quote Originally Posted by Nii
    Interesting you got that high with passive cooling. Thank you for the info.
    Its not really that high if you consider that a display projector is nowhere near CW. but we've had this debate here many times, and different people see things differently.
    For me, diodes are (comparatively) cheap and have long life spans, so going a bit hard on them is cost effective given that they'll still be obsolete and replaced long before they reach their MTBF.

    If you're selling modules commercially, you will probably take a different approach.

    I used thermal paste between module base and projector baseplate, and also between projector baseplate and heatsink. I was going to lap the faces of everything but ran out of time.
    http://www.facebook.com/SubsonicSystems
    http://www.frikkinlazors.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  2. #22
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    If you make an aluminum case for your module you could have it on top of the module and then heatsink and fan blowing air out of the top of the case. Don't know how well that would work, haven't seen a projector doing that.
    The best place for your TECs is under the module and on top of the base plate ie. between them. Cool the base plate by heat sinking and fans mounted on its bottom surface.

    Placing the tec's below the base plate and attempting to cool the whole base plate, as I said before, will not work well. Placing the TECs within the module and under each little diode mount is difficult because these little mounts need to be adjusted in position and when secured could crack the brittle TEC.

    Placing the TECs on the top surface of the module introduces a few problems. The fans that will be needed to draw the considerable heat off the hot side of the TEC will have to dump that warm air outside of the case to avoid warming the inside of the projector and negating the advantage of the TEC. This cooling air turnover will bring potentially dirty air through your optical components. Secondly, the heat transfer from your diode depends on the cross sectional area of the heat conductor/the path length. Sending this heat to the edges of the module base, up the thinner walls and across the top of the module to the fans is a long and narrow road.

  3. #23
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    Quote Originally Posted by planters View Post
    The best place for your TECs is under the module and on top of the base plate ie. between them. Cool the base plate by heat sinking and fans mounted on its bottom surface.

    Placing the tec's below the base plate and attempting to cool the whole base plate, as I said before, will not work well.
    I see, so the point is when the TEC is below the baseplate the cold side is affecting the baseplate, when between the baseplate and module base it's the hot side which is compensated by heatsink below that area of the baseplate. Got it.

    Placing the TECs on the top surface of the module introduces a few problems. The fans that will be needed to draw the considerable heat off the hot side of the TEC will have to dump that warm air outside of the case to avoid warming the inside of the projector and negating the advantage of the TEC. This cooling air turnover will bring potentially dirty air through your optical components. Secondly, the heat transfer from your diode depends on the cross sectional area of the heat conductor/the path length. Sending this heat to the edges of the module base, up the thinner walls and across the top of the module to the fans is a long and narrow road.
    Agreed. I jut remembered that the commercial DPSS module I disassembled once which did it that way actually had the whole diode and optics upside down, on the plate the TEC was attached to.

    So I guess if TEC will ever be needed, it's best to engrave a hole on the bottom side of the module plate so it will be sandwitched between the module base and top side of the baseplate?

    Quote Originally Posted by norty303 View Post
    I used thermal paste between module base and projector baseplate, and also between projector baseplate and heatsink.
    You mean the white thermal compound which solidifies and sticks to what its applied to, or the grease? I've only been able to find the white stuff in tiny tubes.

    I was going to lap the faces of everything but ran out of time.
    lap?

  4. #24
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    Lapping is the process that machinists and opticians use to produce super accurate, conforming surfaces. This usually means plane-plane, flat to flat surfaces, but it doesn't have to.

    Take your base plate and your heat sink and your module base and examine them with a straight edge. They are often far from flat. The thermal contact will be very poor, grease will help, but not much. Now, take an abrasive (auto supply, telescope making supply) powder and add a little water or just get a premixed paste or slurry and rub the intended contacting surfaces against each other until the finish becomes uniform over the entire contact area. 600 grit or smaller as a final finish will produce good thermal contact if the surfaces are now flat. Adding grease will only make it even better. If you went all the to 2000 grit and a nearly mirror like finish, then you can even skip the grease!

  5. #25
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    Quote Originally Posted by planters View Post
    Lapping is the process that machinists and opticians use to produce super accurate, conforming surfaces..........600 grit or smaller as a final finish will produce good thermal contact if the surfaces are now flat. Adding grease will only make it even better. If you went all the to 2000 grit and a nearly mirror like finish, then you can even skip the grease!
    Fleabay link to this type of paste would be really useful.

    Despite the advertising ....Thermal grease/paste has similar thermal conductivity to "CONCRETE" and relies on the layer being very thin, so this last option sounds really good.

    Cheers

  6. #26
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    Quote Originally Posted by Nii
    You mean the white thermal compound which solidifies and sticks to what its applied to, or the grease? I've only been able to find the white stuff in tiny tubes.
    Grease. I buy big old syringes of it quite cheaply from Maplin (sort of UK RadioShack)

    I killed an old scanner/printer, but dismantled it and took out the glass plate before I scrapped it to use as a lapping surface. Grit paper clipped on the edges.
    http://www.facebook.com/SubsonicSystems
    http://www.frikkinlazors.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  7. #27
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    Quote Originally Posted by norty303 View Post
    I killed an old scanner/printer, but dismantled it and took out the glass plate before I scrapped it to use as a lapping surface. Grit paper clipped on the edges.
    Any reason to use the glass from a printer rather than a regular window or picture frame glass piece or was that just what you had on hand at that time?

  8. #28
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    I had it on hand and I guess there's a chance they might take extra care to make the bed of the scanner flat. It was a decent thickness anyway, so possibly more resistant to flexing.
    http://www.facebook.com/SubsonicSystems
    http://www.frikkinlazors.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  9. #29
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    Any reason to use the glass from a printer rather than a regular window or picture frame glass piece or was that just what you had on hand at that time?
    If you are willing to take the time to lap the contact surfaces and I would recommend it, then don't forget the base plate. You can purchase flat ground plate which is quite flat but it will cost more. Stock, mill plate almost always has a significant bow that can be seen with a straight edge.

    Sandpaper on a flat mounting surface is a convenient technique for the smaller components and I even describe it in one of my earlier videos. In order to flatten the contact area on the base plate using the material to be mounted and a paste abrasive to do the lapping saves a step because both surfaces are being brought into compliance at the same time. It is not actually necessary to make them both flat, just complementary.

    I use the water based Clover, silicon carbide compounds. The grease based compounds work better as they persist longer between recharging the abrasive between surfaces, but they are harder to clean off. Generally, start with around 100-200 grit and cut the grit size in half for each subsequent grit. Randomize your stroke, change hands and "walk around the barrel" as all the telescope makers will remember. Finish up a grit with a few unidirectional strokes. Finish up the next grit with a few unidirectional strokes at a 90 degree direction to the previous grit. This way you can tell when every single previous scratch has been removed without needless, extra, blind work.

    This whole process is actually quite fast and typically can be completed in less than 10 min./surface. Don't jump up in grit size beyond a doubling to save money or time. This will enormously increase the necessary time to remove the coarser scratches. It isn't linear. A speed trick is to run all the surfaces you need to lap through each grit stage together, to save clean up.

  10. #30
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    That's very valuable information. Thanks planters and norty.

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