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Thermoelectric Toast

Use thermoelectric effect to heat more efficiently
  [vote for,

This was inspired by lurch's pointing out that in off grid homes, an electric toaster is too strong a peak load for many systems.

So, instead of using simple resistance to create heat for toasting, use the Peltier–Seebeck effect to move heat from the outside of the toaster to the inside. The number of watts of heat produced will be greater than the number of watts of electricity consumed, due to the absorbtion of heat from the outside.

Of course, even if it's more energy efficient than a regular toaster, it will still require a largish amount of energy, expended in a short amount of time.

To smooth out that load, I'd recommend including in the toaster some largish electrical capacitors: when you want to toast bread, they start charging; when fully charged, they discharge very quickly into the heating elements.

Sure, one *could* use batteries instead of capacitors, possibly relying on the household bank of batteries that nearly all off-grid homes use for when their solar / electric / wind power isn't available, but discharging batteries excessively quickly can cause two bad effects: electrolysis of the electrolye (the water in the battery acid turns to H2 and O2), and heat creation in the batteries (boiling of electrolyte, melting of the casing, etc.). In fact, this is one of the big reasons why some off-grid homes poorly handle peak loads.

goldbb, Feb 08 2009


       Why have it in the toaster ? unless it's the only high-load device you own.
FlyingToaster, Feb 08 2009

       OK, so a toaster is around 500-1500W, and lets assume 1 minute to toast a slice of bread...   

       That's 30-90kJ of energy, which ain't a small amount. Personally I'd like to see a small flywheel (500kJ/kg or 2/10/20kJ/kg for regular/super/ultra-capacitors according to Wikipedia).   

       Assuming 100kJ energy required to make up for conversion losses, you need a 200g (1/2 lb) flywheel, maybe 400g/1lb assuming it's not from NASA (or equivalent) and to make up for losses. The unit could be plumbed in between any high-drain device and the supply, damping out the peaks. You would have a DC motor and the flywheel (preferably lubricated for life and sealed in a moderately good vacuum, potentially with a coolant mechanism for the motor) The 'in' terminal would have a chopper working to limit the supply to a user specified wattage, with the output feeding off the flywheel if the drain is greater than the supply. You may have to overspec the flywheel to avoid voltage drops unless you wanted a boost capable chopper (nasty large extras required).   

       The alternative to this would be to fit a larger system similar to this between the batteries and the supply, avoiding the need for extra AC-DC-AC conversion.
Skrewloose, Feb 08 2009

       I'm fairly sure the thermoelectric effect isn't used very much because it's so inefficient, especially to move large amounts of heat. You sometimes get it in mini fridges, but usually a compressor cycle heat pump is more efficient. And unless the outside of the toaster is very warm to begin with, there won't be much advantage to this.   

       But it would be quite easy to make a toaster slowly absorb energy and release it in one go. You could have several ways of storing it. I'd have a place to put water in, and have it slowly electrolyse into hydrogen and oxygen, and when you want toast, it explodes. May take some adjusting to get a perfect browning though.
mitxela, Feb 08 2009

       ya need a toaster that is more efficient. really, how much of that 500-1500 watts is actually absorbed by the bread?   

       it seems like current-generation toasters are more space-heaters than bread cookers.   

       many more efficient methods of toasting bread spring to mind, for example:   

       -insulating the toaster and using exhaust (moisture laden) air to pre-heat incoming air.   

       -narrowing the radiation spectrum for optimal absorption (must we see that it is operating?)   

       -using microwave absorbent plates, insulated on the outside, pressing against the bread - zap them and the bread gets a pointblank heating to desired temp (as measured by plate resistance, exhaust opacity, and/or exhaust humidity). of course, moisture would escape through tiny perforations, which incidentally adds the option of installing 'blessed virgin mary' patterned plates for perfect anomalous toast each time.   

       -or eliminate the toaster altogether, and use pre-packaged toast™ ("good toast, fast."). it comes in packs of two, and only requires mild heating to average toast-eating temperature. i know, i know - how the heck do you get great prepackaged toast? well, its claim is to be good toast, not great, so problem solved.
TIB, Feb 09 2009

       ...Or just make an 'off-grid' toaster for your 'off-grid' house. This toaster would have a pull-out drawer which you'd load up with small bits of paper, kindling and charcoal. You'd put your bread in the slot, and minutes later, with a fragrant smell of woodsmoke, your toast would pop out (the pop-up mechanism is triggered by the bending of a bimetallic strip heated up by the fire).
hippo, Feb 09 2009


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