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Thread: Heat to make power?

  1. #1
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    Default Heat to make power?

    Some time ago I read or heard of a unit that truckers were using attached to the exhaust that made power 12/24 v. Anyone else hear of such a thing and if it exists would that be a nice trickle for batteries if attached to the wood stove?

    I have two of those fans that set on the wood stove and spin once up to temp. While I don't think they move enough air to really work I had one quit on me. Ever the consummate trouble shooter I got the meter out and tried to figure out what was up. The one that worked produced a small amount of dc volts like .09 and the one that quit on put out something like .003. Numbers are not accurate but you get the idea. My thoughts on how it works are dissimilar metals making the voltage. Why not a larger unit to trickle the batteries while you sleep?
    George
    Last edited by George Riddle; 01-17-2012 at 07:22. Reason: more info

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    Those fans are a thermocouple and the motors are very low voltage using the thermocouple for power. The problem is I have never seen a high voltage thermocouple, all are very low voltage. The highest voltage I have ever seen is on a boat in salt water, between the out-drives and the anode there was 5volts. They say a steel hull can be higher never knew anyone with a steel hull boat.

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    Did some further research and they are playing with thermochargers on laptop batteries to us the heat generated to help the battery last longer.

    DaleC, even 5 volts would trickle a little...

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    I think you're looking for a Thermoelectric Generator.

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    Thanks for the info RMoose. I binged Thermoelectric Generator and found this http://tegpower.com/pro8.htm an exciting unit for those off grid to charge your batteries while you sleep and/or heat your cabin with a wood stove. Very exciting for long dark Alaskan winters.

    George

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    George before you spend $300 on that, look up charging batteries your going to find 12-13v at 10 watts will charge a cell phone not a lot more. You would be better off with 3 cheap solar panels than that charger. There is so much info on charging battery's correctly it can't be all posted here.There are many videos on YouTube about making solar panels not what you are looking for but these guys know a lot about how to charge batteries and what is needed to do it.

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    DaleC,
    This was just a research idea of mine and thought small off grid folks would appreciate some info on using the woodstove energy while the daylight hours are minimum. If everything goes well I will be installing a $12K system at my lodge this summer to drastically reduce fossil fuel usage with the genset. Thinking like yours is always welcome to bring us dreamers back to earth with real data, thanks.

    George

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    George
    Dreamers are the ones that find the next great invention. But when I read that ad and saw what the generator did and how they advertised it as a backup power. 10w (bulb) you may as well light a candle get more light and another heat source be cheaper in the long run also. I consider that ad as a scam selling people who don't know what they are really getting and asking big bucks for it. Now back to wood stoves they make really good hot water heaters I know guys who supplied heat and hot water all winter for a family of 4 off 1 wood stove, now if you could make steam then you could turn a turbine and make electricity hmmm? Now if you have wind all the time then you have a way to may power that works, back in NY my friend it it till the utility put him out of business that's another story.

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    I dont know about you but our woodstove produces a good amount of wind up the chimney. I have often thought a turbine on the top of the stack could somehow create power?!

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    Be careful with that. You need that draft for the fire in the stove to burn properly.

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    As long as were are dreaming. What if you hook a copper line to your wife's pressure cooker with a pressure valve at "x" amount of # then run that to a car generator with fins on it to spin it to charge your battery.

  12. #12

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    George, you've been asking some of the most interesting questions lately! Unfortunately, you're up against some really thorny engineering problems. There's a big difference between what it's possible to do, and what it's possible to do in an efficient and cost effective way. Basically, if you're willing to accept incredibly low efficiency to get a tiny amount of power, the woodstove idea is one way to accomplish it.

    Realize that units designed for trucks are quite different from units for woodstoves. The truckers' waste heat recovery system you mentioned is a very expensive and overly complex piece of technology. The only reason they exist is that government regulations require constant incremental gains in fuel efficiency, regardless of the costs.

    The truth is that thermoelectric technology has been known for a couple of centuries (1821) and there are good reasons why it still gets such limited use. The problems with thermoelectric generation include:
    * inefficient (typically only 5%-10% efficient, and even recent discoveries only promise 18%-23% efficiency)
    * expensive (greater efficiency requires increasingly expensive materials, with costs outweighing the benefits)
    * limited lifespan (diodes prefer to work under a constant load, thermal cycling sharply reduces their lifespan)
    * cooling (TEG chips only work well with an extremely sharp thermal gradient between the two sides)

    As the technology improves, most of the uses are likely to be industrial, such as trucks and power plant cooling towers. The small amount of waste heat in other applications isn't enough for efficient operation, to overcome the high costs of the technology, without the incentive of government regulations requiring efficiency at almost any cost. (One exception is the 2007 partnership between BMW and Ford to improve automotive efficiency as part of the CAFE rules, but remember that cars are also inefficient, expensive, and have a limited lifespan!)

    I've seen studies on using the technology with cooking fires or home heating fires for third world development, and most of them agreed that it was a less efficient option than other alternative energy technologies. The main small scale use seems to be emergency preparedness (such as the "TEG Power" link you shared), since expense is basically ignored in such cases. (For example, many of us would never pay as much for a restaurant entree as we routinely pay for ridiculously expensive freeze dried meals.) Also, tiny cell phone batteries are much easier to recharge than larger 12V batteries used in a remote power system, not only due to size but by battery design.

    Here are some ideas if you want to try a small scale project: http://www.instructables.com/id/Char...g-Wasted-Heat/
    These small scale demonstration projects work by accepting very low efficiency, in exchange for lower costs.

    If you want to try creating a woodstove unit, remember you'll need a way to cool half of the unit. Vehicles use the engine coolant system because the movement of air under the vehicle doesn't create a sharp enough thermal gradient (the temperature difference between the hot side and the cold side) to generate the desired output.
    (A simpler approach might be using a Stirling engine (a TMG instead of a TEG) to run an alternator, but the units take up space and you lose a lot of power in the conversion from mechanical to electrical energy.)

    For the rest of you folks dreaming of chimney turbines, look up the "smoke-jack" sketch by Leonardo da Vinci, (which will then lead you to others' more usable 17th century designs). However, prepare yourself for a slow chimney draft and dramatically increased creosote buildup if you try something that blocks the stovepipe!
    Inspiration is simply the momentary cessation of stupidity.

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    Moderator Daveinthebush's Avatar
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    If a wood stove can produce heat, then it can produce steam. Could a woodstove produce enough to power a small steam generator to produce a sufficent charge?

    Vietnam - June 70 - Feb. 72
    Cancer from Agent Orange - Aug. 25th 2012
    Cancer Survivor - Dec. 14th 2012

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    As long were dreaming. How about puttting a copper pipe to the wife's pressure cooker and run it to a car generator with some fins on. To spin and charge the batteries

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    Moderator Daveinthebush's Avatar
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    I don't think we are dreaming here. Way back in the 60's people were taking truck radiators and mounting them on the back of wood stoves. Connected in-line with the water intake of the hot water heater it provided a boost for the water heater. I have even seen complete hot water heating systems based on such a heater system. A little searching and I bet we could find a similar system on the Internet.

    A friend back in NY used to pipe his hot water intake up to the roof and run it though a series of black PVC pipes and then back into the water heater. He saved quite a bit of money with the setup.

    If we don't use our imagination we will never get anywhere.

    Vietnam - June 70 - Feb. 72
    Cancer from Agent Orange - Aug. 25th 2012
    Cancer Survivor - Dec. 14th 2012

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    It wouldn't be to hard to set up a low pressure(100psi) steam system from a wood stove. Back in the Navy we would run copper lines in the exhaust of the gas turbines with a one way valve going in(coffee maker setup) to get steam to degrease the diesels. Could set up something similar for a wood stove but I would make sure to get good steel lines, copper needs almost constant water going through it or it burns up fairly quickly. Putting the lines in the firebox would be much better than in the chimney. Then its just a matter of a steam engine or turbine, few radiators to allow for expansion of the steam and a condensing tower so you can reuse the same water.

    ~Jerry

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    A chamber system with a hot water jacket around the fire box would probably be the ideal system. I have been kicking around ideas for a wood fired system to heat my driveway. I hate shoveling snow!

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    Quote Originally Posted by LuJon View Post
    . I hate shoveling snow!

    You and AKdoug are planning on traveling 100 miles to shove the snow off a roof, does AKdoug know this? LOL

    If not he does now. LOL

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    Quote Originally Posted by Daveinthebush View Post
    I don't think we are dreaming here. Way back in the 60's people were taking truck radiators and mounting them on the back of wood stoves. Connected in-line with the water intake of the hot water heater it provided a boost for the water heater. I have even seen complete hot water heating systems based on such a heater system. A little searching and I bet we could find a similar system on the Internet.

    A friend back in NY used to pipe his hot water intake up to the roof and run it though a series of black PVC pipes and then back into the water heater. He saved quite a bit of money with the setup.

    If we don't use our imagination we will never get anywhere.
    I am from AK but currently living down in New Zealand for a spell. Anyways, virtually every wood stove here has a "wetback" which is essentially a circulation system which runs through the stove to the hot water heater.

    http://www.righthouse.co.nz/products/hot-water/wetback

    Google "wetback stove" and you will get lots of hits. They are both commercially and home built but the commercially built ones are much better and effiecient. The one we have in our house now can easily heat the water for 2 people with no electricity at all. We have a pretty small wood stove by AK standards and it can heat up the hot water tank from cold to shower ready in about 4-5 hours. Many homes (especially in the rural areas) here have no electic or gas hot water - it all comes from the wetback. The first I thought when I saw these things here was why has this not been utilized in AK and other places as it works great and it is extremely simple to setup. There are no moving parts because if it is plumbed correctly the water should flow on its own as it is heated.

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    Quote Originally Posted by Rutting Moose View Post
    You and AKdoug are planning on traveling 100 miles to shove the snow off a roof, does AKdoug know this? LOL

    If not he does now. LOL
    LOL...he's got some lame excuse that he has to fly to the lower 48 for training ... Anyhow, shoveling a roof is far easier than a driveway, especially a 12x18 roof.

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