Three way fridge - could it produce electricity whilst running on gas?

davo
davo Registered Users Posts: 21
Hello all, I know this is a little off topic from solar and wind but I hope somebody more electrically minded than me can help me out!
So I have an electrolux 3way fridge it can be run on 12v / 240v / propane. As I understand it the electric side of things is basically a peltier unit,right?
So I run my fridge 24/7 on propane,is there anyway I can get some electric out of the 12v unit while it runs on gas?
thanks in advance and apologies if this is a stupid question!

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Three way fridge - could it produce electricity whilst running on gas?

    In general, the three way refrigerators just use a simple resistance heater to replace the heat from the propane flame.

    Peltier units are usually less efficient and can only drop temperature something like 40F when pulling heat from the box (for a single stage Peltier).

    To turn heat into energy with a Peltier usually takes a much higher temperature gradient to get a useful amount of energy.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • davo
    davo Registered Users Posts: 21
    Re: Three way fridge - could it produce electricity whilst running on gas?

    Ok Thanks Bill perfect response!shame it doesnt work that way! I am interested in peltier units-I have a woodburner which has been lit sunce nov 1st so if you use peltiers and get a reasonable amount of power off them please post your setup so I can learn a bit more about how productive they are,I see lots of numbers online but its hard to work out what is fact! I think I could provide appox 200 degrees of temp difference quite easily.thanks
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Three way fridge - could it produce electricity whilst running on gas?

    So far, I have not read of anyone here that has obtained a "significant" amount of energy from a Peltier on a stove. One person here did, but did it by packing snow on the cold side.

    From what I have read, the high side of the Peltier has to be pretty close to its "melting temperature" to operate with room temperature cooling on the other side--You run a risk of damaging the device if you run it near its limits.

    Other issues can include causing cold spots in the stove/chimney which can build creosote/condense water.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Three way fridge - could it produce electricity whilst running on gas?
    BB. wrote: »
    To turn heat into energy with a Peltier usually takes ...

    There was a time when I would have agreed, but now I know about Seebeck...
    inetdog wrote: »
    Small quibble, but as a physicist I could not let it go:
    The Peltier effect, as originally discovered lets you directly use electrical energy to pump heat.
    The Seebeck effect, as originally discovered, lets you transfer heat to get electrical energy.
    Since both Peltier and Seebeck are long dead, they probably don't care anymore.

    To complicate matters, both the Peltier and the Seebeck effect are thermodynamically reversible, so one can reasonably argue that they are in fact exactly the same thing, the Peltier-Seebeck effect.

    But for convenience, you normally see the name Peltier for the thermoelectric heating/cooling application and the term Seebeck for the power generation application.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Three way fridge - could it produce electricity whilst running on gas?

    There are available and in use here in Canada, little "Seebeck" powered fans that sit on wood fired stoves and are supposed to blow heat around the room. The motor is very small, I've repaired a couple of them for a friend ( the bearing lube oil had dried up into a tar like material in the heat. I wonder why) and was amazed at how little power was required to turn the fan.
    But blow heat around the room? Hahahaha Now there's a joke. These fans do make owners feel better though, because when they look at the stove and see that little fan going around, it just has to be doing good things, it HAS to be, otherwise it wouldn't cost $149.00 Hahaha Dream on. The vertical airflow from convection far, far overpowers any slight airflow the little toy fan might be producing. But don't ever tell believers that. People of any religion don't appreciate being told their religion is a scam.
    http://stovefanreviews.com/
  • soylentgreen
    soylentgreen Solar Expert Posts: 111 ✭✭
    Re: Three way fridge - could it produce electricity whilst running on gas?
    davo wrote: »
    As I understand it the electric side of things is basically a peltier unit,right?

    Most 3-way fridges actually use some sort of Ammonia-cycle (see http://en.wikipedia.org/wiki/Ammonia_Refrigeration ) and no Peltiers are involved. What model do you have?
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Three way fridge - could it produce electricity whilst running on gas?
    Most 3-way fridges actually use some sort of Ammonia-cycle (see http://en.wikipedia.org/wiki/Ammonia_Refrigeration ) and no Peltiers are involved.

    This is correct! 3-ways operate on heat driving the ammonia cycle, not a peltier system. To do otherwise would require two different cooling systems for one fridge, and that to me, wouldn't make any sense at all.
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Three way fridge - could it produce electricity whilst running on gas?

    I was experimenting with Peltiers back in 1995. Neat items. I should have run with some of the ideas I had at the time, I would be able to afford a 100 kw PV system right now. :cry:
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Three way fridge - could it produce electricity whilst running on gas?

    Plenty of hobby kits out there for thermoelectric generators but very pricey and minimal output.

    The few RV units I have seen a ammonia based units either heated by gas or by a resistance heater. They don't tend to be particularly efficient
  • Ken Marsh
    Ken Marsh Solar Expert Posts: 114 ✭✭✭✭
    Re: Three way fridge - could it produce electricity whilst running on gas?

    Are you sure about the Peltier/Seebeck?
    Most of them are absorption units.

    But to answer your question, yes, it is possible to make a combined cycle heater.
    Back some 30-40 years ago the AGA (American Gas Association) developed and patented a
    combined cycle gas furnace that would put out something like a KW of electrical power while heating your house.
    Then they decided not to market it.
    It used a Rankine heat cycle, something like a closed cycle steam engine.

    The big deterrent to these type devices is the 15 lb pressure limit on steam devices used in residential applications.
    This would limit you to one or two percent efficiency.
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    Re: Three way fridge - could it produce electricity whilst running on gas?

    Got one of these as an xmas present. It works as promoted.

    http://www.thermologi.com/

    Attachment not found.

    So, not much electrical power for the input, but fun and useful. Could you run something off the pilot for a stove or fridge?

    Also, Wayne, how do you refurbish the ecofans? I've thrown out a few when they stopped working. Another I ran on a 1.5vdc wall wart for a while. It will turn freely, but won't turn under power (even with the voltage higher). Much snow?

    Ralph