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Thread: Theremo-electric energy recovery

  1. #36
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    Default Re: Theremo-electric energy recovery

    Hi Will

    My take on it is that the stove could pound out 100W 24/7 whereas the same 100W solar panel might actually produce that same 100W at only peak hours and none at all for about half the time. So the actual benefit of the stoves 100W system might just be equal to a panel array of maybe 400W

  2. #37
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    Default Re: Theremo-electric energy recovery

    Makes perfect sense for this application.

    I'm sure you've seen this website: http://www.tegmart.com/teg-module

    There's chips for up to 300 degrees C. And energy harvesting converter modules. I'll be exploring this stuff myself,
    Will

  3. #38
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    Default Re: Theremo-electric energy recovery

    They look great but man are they expensive. I can get ten generator modules for about the same price that will work for experimental purposes.

  4. #39
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    Default Re: Theremo-electric energy recovery

    P1130653.jpg

    I got a little silly with the air intake on the first of the test beds.

    P1130669.jpg

    Above is the third prototype minus the front door and prior to welding. There's a couple spacers holding up the flat plate which has the two aluminum pieces on it for the chips. Those are leaving once I get things welded up.

    The square tubes coming up through the plate are the pellet fill tubes. The big hole underneath the diamond shaped hole is the ash drawer.

    Anyway I'm just about ready to stick some chips on this thing and see what melts first ;-)

    I'm a fair hand in a machine shop so I can sorta play with the design a lot and who knows, maybe eventually I'll come up with something cool ;-)

  5. #40
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    Default Re: Theremo-electric energy recovery

    Quote Originally Posted by Boston View Post
    P1130653.jpg

    I got a little silly with the air intake on the first of the test beds.

    P1130669.jpg

    Above is the third prototype minus the front door and prior to welding. There's a couple spacers holding up the flat plate which has the two aluminum pieces on it for the chips. Those are leaving once I get things welded up.

    The square tubes coming up through the plate are the pellet fill tubes. The big hole underneath the diamond shaped hole is the ash drawer.

    Anyway I'm just about ready to stick some chips on this thing and see what melts first ;-)

    I'm a fair hand in a machine shop so I can sorta play with the design a lot and who knows, maybe eventually I'll come up with something cool ;-)
    That air intake is just - wow! I'm supposed to get my membership set up in the local laser cutting outfit in January 2018 so I'll be looking to design and create something like this. It's purpose will probably be for an air intake of some sort like yours is.
    Will

  6. #41
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    Default Re: Theremo-electric energy recovery

    Thanks Will, it actually wasn't that hard to program. The leaves had various constraints based on certain dimensions and I think the only correction I had to make was that I used the wrong radius on one of the arcs.

    I used a sharp overhead mill with a acuright CC 5 D controller. Sounds fancy but I only needed two axis.

  7. #42
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    Default Re: Theremo-electric energy recovery

    I purchased 20 chips 40x40 which produce 4.8V 669MA at 100 temp difference. I also picked up the charge controller, 100A 12V battery a fuse and couple12V fans. As luck would have it. So I'm thinking 10 in parallel with 4 sets or 10 in series should mimic a 100W solar panel reasonably well. I have room for 80 chips in the current design. I'll let you know if I melt anything LOL

    Oh and here's a question, these things are only about 10% efficient, so you never want to stack them. But, I should be able to wire them in series and not see that 90% loss, right ???????

    I used a piece of 1/2 aluminum as a hot sink base which I've made adjustable in hight over the hottest part of the stove so i can make changes if things get too hot. I'm still working out if I want to use CPU coolers or a 4"x4" piece of aluminum tube stock filled with cold water as a cold sink. If I got with water cooling it adds complexity, the fans are relatively cheap but have a small footprint for their size.

    I can machine down the surface of the aluminum, both sides, but I'm going to get some deformation no matter what I do once I apply heat. So it might be better to go with smaller segmented cold sinks over the common heat sink. Otherwise I'd have to let one or the other float so as not to tear apart the chips.

    Anyway if someone could respond to the question about wiring these things in series I'd be most apreciative as an answer does not seem to be easily found elsewhere online

    Cheers
    Last edited by Boston; 12-21-2017 at 05:22 PM.

  8. #43
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    Default Re: Theremo-electric energy recovery

    The reason that I deleted the suggestion to hook the chips in series was that I didn't know how much resistance there was through each of them. If there is too much, then... (I am NOT an electrical engineer) If there is too much resistance, when hooked in series, the power loss could be problematic. That is my concern and I don't know enough to properly evaluate that concern.

    So having reestablished my in-expertise, I will proceed to pontificate on efficiency. 10% efficient means that if you apply 100W of heat to one side, it will produce 10W and you will have to remove 90W from the other side. Stacking them would reduce the temperature drop across each chip in the stack. If you stacked two chips and had 100 on one side of the stack and 0 on the other side, the temperature in the middle could be 50. You would only have a 50 temperature drop across each chip. You still might get 10% of the energy per chip for a total of 20%, but the heat flow would be a lot less. Im guessing they would model like resistors, so two chips, twice the resistance to heat flow (ignoring the extra interface), half the heat flow, so you would only have 20% of half the heat flow heat flow. (That has to be wrong, because 10 chips would extract 100%, which can't work).

    What is FAS steel? If epoxy and not in the hot zone, then OK.

    There are usually better ways, like wind, solar, engine driven alternator etc.
    When you are converting waste heat to power or in this case tapping a small amount of heat to run the heater, the simple, almost passive nature of the device is the more elegant solution.
    Last edited by MN Dave; 12-21-2017 at 10:45 PM.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  9. #44
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    Default Re: Theremo-electric energy recovery

    I'm not stacking them.

  10. #45
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    Default Re: Theremo-electric energy recovery

    Totally agree about not stacking them - IIRC, they are quite fussy about clamping pressure, how even that is across each device, and surface flatness. The segmented cold side heatsink idea probably has some merit in this application, but just keep in mind that the hot side needs to stay flat under each device. I think some systems use springs under the clamping screws, so that pressure stays the same as things move - see if there are any "application notes" on the manufacturers website. Most electronics manufacturers are very good at telling you how to get started, and what not to do.
    As long as each string has the same number of devices, and thermal input, I cant see any proplem with putting them in series. If you wanted to be really safe, a diode (like an electrical non return valve) in series with each string might be a good idea. Again, manufactures app notes would normally have some guidance on this sort of thing.

    Pete
    Don't underestimate the power of stupid people in large numbers!

  11. #46
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    Default Re: Theremo-electric energy recovery

    Hey E that's a great idea. like a diode bridge in a transformer. I'll pick up a couple, so any thermal variation ( which you just know I'm going to have ) doesn't do just what your suggesting and confuse the circuit.

    I picked up a 20 amp charge controller and a fuse but the diode is a great idea. ( looked it up and it looks like a series of blocking and bypass diodes would be ideal.

    Oh and a number of the systems I looked at had spring fittings as attachments between the hot and cold side. I was going to use the same system. Also I think I'm going to first try some liquid filled tube stock aluminum with pressure relief of course as a cold sink. I'll measure a few things and then try the system with some CPU coolers instead of the liquid filled rig and see how they compare.
    Last edited by Boston; 12-22-2017 at 03:29 PM.

  12. #47
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    Default Re: Theremo-electric energy recovery

    The latest configuration is 6 groups of 10 chips, 10 wired in parallel should bring me up to 6.9A at 5V over a 100C range with three groups in series for 15V at ~7A or roughly 100W, About what a 100W solar panel might be expected to put out.

    Todays word is MPPT or maximum power point tracking

    I used a pretty thick piece of aluminum for a heat sink, 1/2 and I'll have to get this latest prototype up and running before I'll know how well the heat is being distributed.

    The plate is 6061 10" x 21" x 1/2
    Surfaces on the last prototype that will be in contact with the plate where roughly 250F 625F and 350F
    So when I light this thing on fire i'll be looking for more even heat distribution along the plate floating above these heat sources. I have a 1" chunk of 12"x ~7' I think it's 7075 but I'm not entirely sure. Which would likely help even out the heat.

    I'm hoping to avoid using expensive MPPT components and simply use the diodes blocks and bypasses to control the signal

  13. #48
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    Default Re: Theremo-electric energy recovery

    Ok the blocking diodes lose to much energy. Something like 0.7W each. Rumor is they may not be necessary anyway in a system designed to operate 24/7 I might try one at the battery but that'd be about it.
    The bypass diodes I can reduce to groups of 5 in the system, in case there's uneven heating.
    Last edited by Boston; 12-23-2017 at 03:22 PM.

  14. #49
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    Default Re: Theremo-electric energy recovery

    Good gracious, this is complex and therefore intriguing and sure hope it works out for you! Not by any means an engineer of any sort, so my understanding is poor but I would guess your setup will likely be optimized for your particular application and an exact replica wouldn't necessarily work well for another application (i.e., a different brand, type and heat output stove). I could see a small industry for a specialist to go in, assess a client's desired application, and design/build a working unit. A related industry would just pre-build the unit with a stove, exhaust, etc. application. Good luck!

  15. #50
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    Default Re: Theremo-electric energy recovery

    It's mostly for off grid living but the system could be adapted to any heat source, an exhaust pipe could be modified to make it work ;-)

    Since I'm still waiting for the welder to get back into town I ordered all the electronics and redesigned the hot sink so it can slide up and down so I can hopefully adjust the heat a little even with the stove going at high medium or low.

    Only thing left to get is the extruded cold sinks, I thought the stuff we had laying around would work but it's just not the right size. I designed the thing to have separate cold sinks for each group of 10 chips. Hopefully that'll keep each group operating at at least something like the same temperature.

    If the fan and cold sink plan doesn't work all that well I'll try liquid cooling and see how that goes.

  16. #51
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    Default Re: Theremo-electric energy recovery

    Sorry, but I have more food for thought than design advice to offer. In fact, my thought is pretty hungry. I have chosen to burden you with it anyway.

    To keep the temperature nicely distributed you might want some sort of heat transfer fluid. Toluene and Xylene have convenient boiling points, (231.1F and about 284 F) but at this point you are dabbling in heat pipes, and if you can seal water under a vacuum, or just vent steam and torque the plug while it's boiling, you have a pretty good temperature range of 50 to 550 F.{edit 2 links there} There are flat plate heat pipes for cooling electronics. Unfortunately, I have just told you everything I know about them. I had a much better reply before the old PC decided to reboot.

    I know that this can distribute very evenly, but not the details. So, Thick plates, gun drilled holes, some tubing, but how to connect and plug... With a few days of light reading, a clever machinist like you just might pull it off.

    https://www.1-act.com/resources/heat...es/hik-plates/
    Last edited by MN Dave; 12-28-2017 at 09:54 AM. Reason: *Sigh* nobody ever reads my links.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  17. #52
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    Default Re: Theremo-electric energy recovery

    The basic idea of a heat pipe / heat distribution looks great.


    Some useful links:
    https://www.1-act.com/merit-number-and-fluid-selection/

    https://www.1-act.com/working-fluids/

    It appears a heat pipe could be fashioned with water for a working temperature up to 150 C.

    I'd just forget about using toluene or xylene as the working fluid though. Even in off the shelf heat pipes I can see corrosion eating a hole in the heat pipe some day and the fluid leaking out - especially on a boat.
    Will

  18. #53
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    Default Re: Theremo-electric energy recovery

    I have considered a liquid coolant system but I'd likely keep it stupidly simple. A pump, a flat plate with baffles assisting circulation some tubing, Something I could carve out of a chunk of say 1" aluminum plate a gasket under a cover with a pressure relief valve and maybe an off the rack transmission aluminum radiator of some convenient size. That would be on the cold side.

    On the hot side we have a guy who blast fuses metals just down the road. I could fuse a thin coper sheet to the bottom of the aluminum, or at least that's one idea I had. I'm not sure what happens to heat transfer between metals using this method of attachment. Normally I'd simply leave +0.001 tolerance, bake one side and freeze the other assemble and then let them fuse as they reach ambient room temp. But you only get one shot at this kind of assembly. Hmmmm, I'd cut some grooves in the bottom of the aluminum plate for the rod. I'd be better off using square bar on the thermal fusing.

    anyway I'm bitching at a supplier now for the cold sinks, lets see if he caves and sends me free stuff ;-)
    Last edited by Boston; 12-28-2017 at 03:27 PM.

  19. #54
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    Default Re: Theremo-electric energy recovery

    Explosive bonding will give you just about the best thermal interface that you can get between two metals. There aren't many places that do that. I don't understand the hot/cold fusing idea. You don't mean a shrink fit, do you? Diffusion bonding between Cu and Al would generate a lot more brittle intermetallic at the interface, which would tend to break. You would need a third material like a thin Ni foil at the interface to prevent that. I don't really see any advantage to the copper cladding aside from the wow factor.


    Stupidly simple may be the more elegant solution, and one heck of a lot less expensive. I was thinking of heat pipes in general principal, but for the DIY assembly, skipping the wicks, high pressure seals and general complexity, would make sense. Locating the radiator above the boiler plate and trading an expensive pump for gravity feed is pretty reliable. A high boiling liquid like antifreeze is easy to work with. Boiling might separate the components, but you don't care in a closed system.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  20. #55
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    Default Re: Theremo-electric energy recovery

    I thought of gravity feed system. I could cut the cold sink side the same as I'd described before, use heat sink as the cover and put a thin fan over it and under the radiator. I'd still need to segment the cold sink side to reduce the variation in thermal expansion between the two sides. But the radiator could be a common component. The problem is the design so far is a big flat plate sitting atop the stove. If I want it to naturally circulate I'd need to set it up vertically

  21. #56
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    Default Re: Theremo-electric energy recovery

    I think I should have started with Wikipedia this time. There is so much crap there that I tend not to bother much on these subjects anymore. This time, it was a mistake. It talks about working fluids and metals compatibility. Doh! With water and aluminum, you get some noncondensible gas production, which must be H2 (corrosion). I suspect that the corrosion inhibitors in automotive antifreeze will take of that. Copper works with water, so if you do want to try cladding, it goes on the inside where you can't see it. Aside from the minor bugaboo about flammability, xylene... well, I am a safe distance away. just be careful where you point the relief valve. https://en.wikipedia.org/wiki/Heat_pipe

    If I mentioned PERC, tetrachloroethylene, don't try it. it might react violently with Al. Some of the obscure stuff is hard to remember late at night. Methyl (wood) alcohol is also very corrosive to Al.


    More design information:
    You might just need a spreader, see p. 13:
    http://semi-therm.org/wp-content/upl...-2016.pptx.pdf
    Similar from NASA:
    https://ntrs.nasa.gov/archive/nasa/c...0150018080.pdf
    Somewhere in these it says that wicks can move fluid uphill.
    Last edited by MN Dave; 12-29-2017 at 12:54 PM. Reason: don't brush the toutch pad while typing
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  22. #57
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    Default Re: Theremo-electric energy recovery

    Well the idea is to get even heat across the entire plate. So I used a really thick plate ( 1/2"). Which might just naturally covey heat more evenly across the entire surface since it takes so long to heat up or transfer through the 1/2 and across the entire 21" length and 10" width. The whole thing is modular so I'll weld up the stove and then just put the plate on it and see how evenly it heats. Take it from there instead of spend a week modeling the heat distribution

  23. #58
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    Default Re: Theremo-electric energy recovery

    OK so my last test, the stove ran at 85,000BTUs/hr and burned perfectly clear.

    So on to the thermo electric generator part.

    It's one part hooked up in both parallel and in series to achieve a 100Watt "look" at the charge controller.

    One single part, the generator chip which is a

    SP1848
    SA
    27145

    It has no UL listing on it, so the question is, if I only have one part repeating in the product, does it need a UL listing ?

  24. #59
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    Default Re: Theremo-electric energy recovery

    Well the project is coming along nicely. The stove is working perfectly and now it's time to fit the chips. Lets see if I can do this melting the least number of chips possible ;-)

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