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using a RMH to heat an area and charge a battery

Devon Olsen


Joined: Nov 28, 2011
Posts: 1002
Location: SE Wyoming -zone 4
    
    6
so i was thinking, a RMH is great for heatin an area without using electricity, but it requires a consistent input, you have to put wood into it every once and a while and though the time between fueling can be greatly increased with a feed tube, you still have to be there every once and a while to do this
well what if you need to heat a space that you cannot get to for a day or more at a time?

what if you used the rocket mass heater, coupleed with a cold exterior wall to power one of these:
http://www.wonderhowto.com/how-to-use-peltier-module-create-free-electricity-from-heat-220628/
and therby charged a battery, the battery runs a thermostat for a water heater or an air thermostat so that once the RMH dies out the thermostat kicks in, keeping the area warmed for an additonal "x" hours and reducing your need to be there as often, ideally the theory is that by doing this you would only have to fill the RMH feed tube once or twice a week, this way you don't need to be there as often to keep said space warm...


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Ernie Wisner
volunteer

Joined: Oct 16, 2009
Posts: 788
Location: Tonasket washington
    
  23
That is a great idea!
Where is more information located? I would like to read up on it.

For a box stove that would rock I am not so sure about the rocket. firing every 20 hours might make for a better use else where. Whats the voltage that thing generates can it charge batteries? since it is depending on temperature differentials could it be used in a house or boat to run LED lighting. Seems for some applications this might be a really great thing. Do you have more info on it?


Need more info?
Ernie and Erica
Wood burning stoves, Rocket Mass Heaters, DIY,
Stove plans, Boat plans, General permiculture information, Arts and crafts, Fire science, Find it at www.ernieanderica.info


Devon Olsen


Joined: Nov 28, 2011
Posts: 1002
Location: SE Wyoming -zone 4
    
    6
googling thermoelectric generator should return some results for sure, i haven't studied them a ton and the general idea is that they are not the most effecient of generators, but would make good use of the heat at the top of the barrel in a RMH i would think
i heard someone sy you lose more heat/insulation in an area by having this exposed to the outer air so its best to simply use the lower variations of your heat source vs your heated area for generating electricity
with how hot RMH's get i think it would still work pretty damn well

this file seems a little buggy for me but the first page that i was actually able to see looked very interesting, i believe they used one of these things on a semi truck... maybe it'll work for you though...
www.hi-z.com/documents/Hi-Z.Brochure.2006.pdf

[disclaimer, i think these numbers are totally fucked]
in the bottom video he was gettin approximately 6.5v out of 800F i think, thats what i got from it anyway, so if a RMH got to 800F, which would be a very low temp for a RMH i would think,
so at 6.5 watts per second at 800F, you have 390 watts per minute and 23400 watts per hour, if you produce that steadily you are getting 561,600 watts from 24 hours
to convert this to volts you use the formula W/Amps=V
for shits and giggles because i know nothing about amperage really lets go with 30 Amps
so in a 24 hour period at 800F you would produce, with the same set up he had, 561,600/30 = 18,720 volts, i am assuming it only takes 12 volts to charge a 12v batterly so that is a lot of volts, i think i may have fucked that up somewhere along the way

also keep in mind that the numbers here are based off of a blow torch and an ice-water bath so a little different numbers to be sure and the wider gap in temperatures the more electricity you would produce, ideally, your low temperature would be 70F in the greenhouse during the winter and the high temp would be the RMH, so like 1100F? about a 1000 degree temp difference for producing electricity...
Roy Clarke


Joined: Feb 05, 2012
Posts: 121
Devon Olsen wrote:
in the bottom video he was gettin approximately 6.5v out of 800F i think, thats what i got from it anyway, so if a RMH got to 800F, which would be a very low temp for a RMH i would think,
so at 6.5 watts per second at 800F, you have 390 watts per minute and 23400 watts per hour, if you produce that steadily you are getting 561,600 watts from 24 hours
to convert this to volts you use the formula W/Amps=V
for shits and giggles because i know nothing about amperage really lets go with 30 Amps
so in a 24 hour period at 800F you would produce, with the same set up he had, 561,600/30 = 18,720 volts, i am assuming it only takes 12 volts to charge a 12v batterly so that is a lot of volts, i think i may have fucked that up somewhere along the way

also keep in mind that the numbers here are based off of a blow torch and an ice-water bath so a little different numbers to be sure and the wider gap in temperatures the more electricity you would produce, ideally, your low temperature would be 70F in the greenhouse during the winter and the high temp would be the RMH, so like 1100F? about a 1000 degree temp difference for producing electricity...


You are right, those figures are total tosh.

If he was getting 6.5 Watts at 800ºF, he was getting 6.5W and that's it. Time doesn't come into it except he would get 6.5 W.min in a minute and 6.5W.hr in an hour. According to those figures if he ran it for a day he's talking of a 1/2 megawatt output (or some other invalid contortion).

I just hope he keeps away from steam heating.

you could look here http://donkey32.proboards.com/index.cgi?board=discuss&action=display&thread=457
Devon Olsen


Joined: Nov 28, 2011
Posts: 1002
Location: SE Wyoming -zone 4
    
    6
thanks for that link and reply, it seems that TEG's are not very cost effective to say the least...
Roy Clarke


Joined: Feb 05, 2012
Posts: 121
They are useful though if you are traveling, have a stove, and want a little electricity at night. Batteries can be heavy, and solar cells don't work well in the dark.
Devon Olsen


Joined: Nov 28, 2011
Posts: 1002
Location: SE Wyoming -zone 4
    
    6
well my thinking behind it was to use the heat to store power in a battery so that i could continue to keep the area electronically heated through the use of the stored energy in the batteries
i was wanting something that could easily be put in place and would not require any fancy construction such as a windmill(which i could build myself but that too much construction to fit my needs) would suffeciently produce the needed electricity and be fairly cheap, which it doesn't seem to be

another option for keeping a greenhouse heated beside simply building a walipini or similar concept of greenhouse i suppose would be what CRMPI has going on for their tropical greenhouse...
Ernie Wisner
volunteer

Joined: Oct 16, 2009
Posts: 788
Location: Tonasket washington
    
  23
how are these things made? can they be fabricated at home? It might work if you can make the thing at home and if you can take advantage of the temp difference between the sea and inside the hull. it also looks like the greater the difference the more power is created. I dont know how it all works out, sounds interesting and i would love to get my hands on one of the units or make my own. it could be a nice way to add blowers onto a stove at the very least. then i wouldn't worry so much over the power going out and folks depending on funky fans and such to run a stove.
Roy Clarke


Joined: Feb 05, 2012
Posts: 121
http://www.ecofan.co.uk/ here is a ready made fan

Here are lots of links to get you started on a home made setup.

You can apply heat across them to get electricity out, or you can apply volts to pump heat.
Devon Olsen


Joined: Nov 28, 2011
Posts: 1002
Location: SE Wyoming -zone 4
    
    6
now, why didn't i think about that... thanks Roy!
tel jetson
steward

Joined: May 17, 2007
Posts: 3097
Location: woodland, washington
    
  53
Roy Clarke wrote:http://www.ecofan.co.uk/ here is a ready made fan


my folks had one of those. neat gadget. worked relatively well on their wood stove. I think they're relatively easy to burn up, though. the ecofan has a bi-metal strip on the bottom to lift it up off the stove as the temperature increases to protect it from getting too hot. my folks' quit working because it got dropped and the fan bent just a little bit so it wasn't balanced anymore. there wasn't enough juice to spin the fan after that. point being, in order for these things to work at the very low current created, parts have to be very light weight and so they're quite delicate. I wouldn't want to rely on one.

there may well be burlier options that can handle higher temps and a bit of abuse.


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Roy Clarke


Joined: Feb 05, 2012
Posts: 121
tel jetson wrote:...... in order for these things to work at the very low current created, parts have to be very light weight and so they're quite delicate. I wouldn't want to rely on one.


I think that's the main point with these fans, very low power in means very low air moving out. I have a Stirling engine type, also low power. IMO they are a waste of money and are a placebo. The air movement created by the convection of the stove is way greater than the fan, and not having the fan going produces no noticeable difference.
tel jetson
steward

Joined: May 17, 2007
Posts: 3097
Location: woodland, washington
    
  53
Roy Clarke wrote:I think that's the main point with these fans, very low power in means very low air moving out. I have a Stirling engine type, also low power. IMO they are a waste of money and are a placebo. The air movement created by the convection of the stove is way greater than the fan, and not having the fan going produces no noticeable difference.


hmm. my folks' wood stove was mostly used for heat during power outages and more as entertainment the rest of the time, as they had central gas heat. I wouldn't say that the ecofan made a huge difference, but it was definitely noticeable. it did create a very gentle warm breeze that could be felt a couple of feet in front of it. and it was silent, unlike the electric stove fan that was also installed. but, somewhat like a catalytic insert, it was at best a stopgap for an inferior design - the standard wood stove.

Ernie seems to want to build one of these contraptions on a boat. it's a neat idea, and may well work fairly well. my main concern is that the few I have experience with are very fragile. and I don't think that's very compatible with a boat. if it were me and my boat, I would want my equipment to be sturdy. it may be possible to build a Seebeck device that meets that criterion, in which case it seems like a pretty solid idea if the materials are affordable and available. low voltage, sure, but voltage. my suspicion, though, is that sturdiness and affordability are not features available for a thermoelectric generator. in which case, they're a neat gadget with limited utility.
 
 
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