Advice needed on flame powered THERMOELECTRIC FAN project

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  #1  
Old 07-31-13, 09:20 AM
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Advice needed on flame powered THERMOELECTRIC FAN project

I am organizing a parts list to build a peltier fan, using a TEC module to generate DC current using a small alcohol lamp as the heat source, a DC motor to swing an 8 - 12 inch fan blade, & 2 heat sinks to heat & cool the TEC. My problem: The only "how to" article I can find details use of a TEC1-07110T200, which is no longer available @ a reasonable price. The only high temp. (200 deg.C) TEC available for less than $20 is a TEC1-12706T200, which has different electrical parameters: (VMax = 15.2v/IMax = 6A/QMax = 51.4w/Tmax = 200 deg.C) I intend to use the recommended Mabuchi RF500TB motor (rated @ 1.5 - 6 vdc) which is used w/solar cells, & runs @ low amperage w/relatively high torque @ low RPM's. QUESTION: Is this Mabuchi motor a good match for the new TEC, or should I get a different motor? If so, please give details/specs of motor needed. The original builder (using the old TEC) measured a current of approx. 0.5 vdc at a very low amperage. Heat conversion to electricity is stated to be very low @ approx. 0.02%, so getting a motor designed to maximize the available electrical input is essential. His video shows his fan spinning rapidly enough to creat the desired breeze. Any assistance appreciated.
 
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  #2  
Old 07-31-13, 11:30 AM
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Maybe not relevant but some furnaces use 'millivolt' systems that convert heat from the furnace into electricity.

"using a small alcohol lamp" The device seems to measure 35 x 35 x 5.0 mm, can a small alcohol lamp heat the entire unit to 200 celsius? Try heating a similar sized piece of Aluminum and see if you can get it to 200 deg on the heated surface. The other issue is that it seems from the spec sheet even if you get the hot side to a uniform over 200 deg, you need to keep the cool side to below 133 deg. So keep heat from traveling from the hot to the cold side around the device will also be a problem.

As to the motor what you need to get it started is more than what you need to keep it going. So if you plan on having it automatically start then you may need to store some power to kick start it, otherwise you will have to start it by hand.

Good luck.
 
  #3  
Old 07-31-13, 04:50 PM
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It looks like the peltier devices are very similar, I'd bet they operate about the same. You are planning on using it as a generator so the max voltage and max current dont really apply (so you don't have to worry about it).

The key to getting the fan to spin is to pull the heat out of the "cool" side of the peltier as best as you can, you can even use the breeze generated from the fan to pull air through heat sinks attached to the peltier and the breeze will get stronger and stronger!
 
  #4  
Old 07-31-13, 05:03 PM
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Re: thermoelectric fan

Thanks geo8rge. I will try to address each of your points. 1) I don't think the furnace 'millivolt' system applies. The fan needs to be mobile & it's intended purpose is to cool me, not spread heated air around. 2) I believe the '200 C.' refers to the max. temp. the TEC will tolerate before it fries. The heat sink attached to the TEC's hot side spreads the flame's heat fairly evenly across the TEC. As I understand it, the electricity is generated from the temp. differential between the TEC's hot & cool sides (cool side has a much larger, more efficient heat sink). Because I want the fan to cool, the heat source needs to be as small as possible while still generating enough power to run the motor/fan. 3) I believe this design works because the original builder's fan appeared to run well using a similar setup, except for the different TEC. I just don't know enough about TEC's or DC motors to tell if the new TEC will power the Mabuchi motor/fan combo. 4) I think you are right - I will probably need to initiate fan rotation manually, but I can do that. 5) Can anyone tell if the new TEC will likely be able to spin the Mabuchi motor/fan combo w/enough RPM to create a breeze? I just don't want to spend $50 - $70 building this contraption only to discover the new TEC won't run the fan. Old TEC (TEC1-07110T200) specs: VMax = 8.5vdc/IMax = 10A/QMax = 52.7w/TMax = 200 C. I just don't know what all of these perimeters mean in terms of how they affect the operation of a DC motor.
 
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Old 07-31-13, 05:29 PM
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I just don't want to spend $50 - $70 building this contraption only to discover the new TEC won't run the fan.

That is an engineering or physics question I suggest you post on more appropriate msg boards. Your actual question is very likely solved in a university level physics text book as a standard question. Wikipedia has the math but no worked examples. So I suggest you find someone to point you to a worked example of a peltier junction. At that point you can determine what temperature difference you need to run the motor. That will determine if it is doable.

The millivolt thing is the same technology only in a different package specific to furnaces. It might work better as you are using a flame also. You might even find a local furnace repair person who will give one he pulled from a discarded furnace. Who knows. Try posting on the furnace board, they might know about the part and how you can get a possibly used one cheap or free.

For about twice your budget you can buy one pre built:
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Peltier junctions are used in those soda can mini fridges. You might find one at local second hand shops, ebay, or the town dump. It is likely the same part and will be all mounted and wired up.
 
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Old 07-31-13, 05:58 PM
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Thanks mnmattmn - Your words are encouraging. The cool side heat sink is much larger than the hot side (approx. 6" x 4" x 4") w/3 built in copper heat pipes & is designed to do exactly what you said - pull fresh air thru the cooling fins via the fan. If I understand you correctly - you're saying the difference in VMax (15.2v vs 8.5v) & IMax (6A vs 10A) between the two TEC's doesn't matter? There is one other parameter which concerns me: ^TMax (operating temp. differential) = 67 deg. C. for new TEC vs 62 deg. C. for old TEC. Does this difference mean I will need to get the new TEC hotter to generate the same power input to the motor? Now, if I can get one or two more electrical savants to vote 'yes' on this TEC /motor combination - I may gain enough confidence to pull the trigger on this build! I need a win. I'm 0 for 2 on my last 2 experiments.
 
  #7  
Old 07-31-13, 06:28 PM
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Thanks geo8rge - I tried to join the physics forum, but couldn't answer their qualification Q's. Apparently you need to know some physics before they will let you post. I'll look into the 'millivolt' thing & the 'furnace board'. I didn't know there was such a forum. My personal preference is to build what I need, if I can do so cheaply enough. But, if I get into the $200+ budget range, it would make more sense to just get a small gasoline generator & run a regular fan or maybe my window air conditioner. Appreciate your input.
 
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Old 07-31-13, 07:04 PM
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Honestly I'm not sure what the max delta T temp refers to, my guess is that its to protect against some sort of min load condition to prevent circuit damage due to temperature. I can't imagine why temp differential that small would damage anything but maybe it prevents thermal runaway or something like that.

You're going to have a hard enough time getting a big enough temperature differential from a gas lamp to get a steady breeze.

You could go with a battery powered fan and a solar panel battery charger, you might get as much power from the light generated from the lamp as from the heat...
 
  #9  
Old 08-01-13, 01:15 AM
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Thanks mnmattmn - I bought a 5" battery fan (the largest one I could find at the time) some years ago, but the motor has no torque & the breeze is pitiful, & if the power is out more than 6 hours I'm out of batteries. If I stockpile a drawer full of of alkalines, I run into the limited shelf life problem. I hadn't considered solar rechargeable batteries - if I can find a larger, breezier battery fan, I'll look into that idea in more detail. I considered attaching a fan blade to one of the little toy stirling hot air engines selling on eBay, but again, the lack of torque severely limits their utility as fans. It's all they can do to spin a small flywheel. Pakistan used to manufacture a beefier stirling fan powered by an alcohol or kerosene flame, & I have seen where one Australian company was selling a few of them, but again - at that price, I'm better off just getting a generator, though I think it would be fun to build one of those weird looking TEC fans. The one I saw on youtube looked like it put out an acceptable breeze. It whirled along at a decent clip for the entire 5 -7 minutes of the video, using an 8 - 10" 4 bladed home made aluminum fan & powered by a small alcohol lamp w/a flame not much larger than a candle flame. I appreciate your ideas. The solar/rechargeable battery thing may have possibilities. Hit me back if you think of anything else. Two heads are better than one!
 
  #10  
Old 08-01-13, 07:26 AM
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Info on thermoelectric effect.

Thermoelectric cooling, coolers, modules, heat sinks, exchangers, Peltier coolers, devices - TE Technology

http://www.textbooksonline.tn.nic.in...2-phy-em-1.pdf

Once again your question is very specialized, the right person could probably lead you to worked examples of what you want to calculate. I doubt anyone posting on this board has that expertise, the people that repair millivolt furnaces might.

Depending on the manufacturer you might be able to contact an engineer directly, so contacting the manufacturer might work even if what you are doing is a small project. If you live near a university I bet you can find someone who can point you to worked examples there.
 
  #11  
Old 08-01-13, 09:04 AM
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arbee,
What is the physical size of the units you're looking at? Peltier modules are more alike than different. The ones used in the consumer fans that sit on top of a woodburning stove & help waft the heat out into the room are common cheap devices you could buy of eBay for a couple bucks. Rather than get mired down in the physics and calculations I suggest you just throw one together as cheap as possible and see if it performs to your needs.
If you PM me your address I'll send you a couple Marlow SP5228 TE modules. They're about 24mm square by 3mm thick, with leads. I bought a box of em several years ago for a project that never gained traction. If they work for you, great, if not then you can look at larger units that put out more power.
Happy to support your project.
 
  #12  
Old 08-01-13, 12:23 PM
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Thanks geo8rge - I agree the math/physics of this application is esoteric. I have not been able to find a forum that discusses this application of TEC's. Since this is a forum for builders, I thought there might be a slim chance someone here might have messed w/TEC powered DC motors. My bad. There are no universities nearby, out here in the boonies, but there is a high school, & they must have a science instructor. Maybe I can get some leads from there. Also, I'll see what I can find out about millivolt furnaces. There is at least one U.S. co. that produces/sells high temp. TEC's. Maybe they will talk to me; but my experience in the past w/mfgers is they lose interest in spending much time on you, once they find out you're considering buying only one unit. And I understand their situation. In business, time is money. Thanks again.
 
  #13  
Old 08-01-13, 01:05 PM
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Thanks guy48065 - Your offer is most generous. I tried to look up the specs on your Marlow modules. but had no luck - even from the Marlow website. Do you know if they are high temp modules? The original TEC fan builder said anything that won't tolerate 150 - 200 C. will probable fry over time, even tho I'll be heating a heat sink & not putting the flame directly on the TEC. The TEC1 12706T200 module I planned to use is 40 x 40 x 3.5mm. The original TEC1 07110T200 module the builder used is 33 x 33 x 3.4mm. Since your modules are smaller, I might need 2, wired in series(?) to do the job. But I don't want to waste them. If they aren't hi temp types, I'll probable have to pass on your kind offer. The regular TEC's are only $2 - $4 on eBay & I can budget for them easily. It's the hi temp modules that run $18+, so I'll need to be reasonably sure they will work before I start this build. My experience has been that DIY projects - especially experimental ones - always end up costing more than you figured. Are you sure the ecofans (stove fans) use standard modules? I don't see how they survive the heat. Aren't standard modules rated @ only about 57 C. max temp.? Thanks again.
 
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Old 08-01-13, 03:36 PM
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If the hot side contact is an aluminum pad or small heatsink it will dissipate much heat before it can reach the TEC. I think it would be difficult to get 200c. at the TEC face.
 
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Old 08-02-13, 11:02 AM
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Thanks guy48065 - I checked replacement parts for ecofan. As near as I can tell, you are right. They use standard modules, not hi temp ones. If stove fans can get away w/standard modules, I don't see why my DIY fan can't use them also. I understand an alcohol flame burns @ approx. 1100 C. A standard TEC is rated @ 125 C max temp. But there is much heat loss between flame & the module's surface. I intend to use an alum 100 x 55 x 10mm hot side heat sink. That's large enough for 2 - 12706 standard TEC's wired in series. Even if they fry, they're cheap enough to be no great loss, & at least I'll know for sure that I need hi temp modules. My main concern now is that the lower heat differential allowed will not yield enough power to give me a decent breeze. If room temp is 95 F. the max temp differential allowed would be only about 85 C. Don't know if that's enough. Anyway, I think I'm ready to start collecting parts & get this show on the road. I appreciate all of your assistance. Wish me luck! I'll let you know how it all turns out.
 
  #16  
Old 08-02-13, 12:06 PM
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Best of luck to you. It's an odd project--using a heat source to run a cooling fan. Let us know if it's efficient enough to perform as you hope.
 
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