# Minimum size for nuclear batteries? **URL:** \ **Category:** Factual Questions\ **Created:** [June 16, 2014, 1:20am UTC](https://boards.straightdope.com/t/minimum-size-for-nuclear-batteries/690868 "2014-06-16T01:20:14Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [June 16, 2014, 1:20am UTC](https://boards.straightdope.com/t/minimum-size-for-nuclear-batteries/690868/1 "2014-06-16T01:20:14Z")
If I’m not mistaken, some satellites/probes (of the spacefaring sort) use nuclear generators that are not steam engines like the ones we have on Earth, but [something thermocouple something something magic something heat into electricity magic](http://en.wikipedia.org/wiki/Seebeck_effect#Seebeck_effect). Can this technology be downsized into consumer goods like cell phones or watches? Why don’t we see it more commonly used? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [June 16, 2014, 1:27am UTC](https://boards.straightdope.com/t/minimum-size-for-nuclear-batteries/690868/2 "2014-06-16T01:27:56Z")
[Is a battery small enough to use in an implantable pacemaker small enough for you?](http://en.wikipedia.org/wiki/Betacel) ---
**Author:** ![XT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/xt/32/456_2.png) [@XT](https://boards.straightdope.com/u/XT)\ **Post date:** [June 16, 2014, 1:31am UTC](https://boards.straightdope.com/t/minimum-size-for-nuclear-batteries/690868/3 "2014-06-16T01:31:44Z")
Actually…[yes](http://www.engadget.com/2005/05/26/nuclear-powered-cellphone-battery/). Well…how about, theoretically? 😉[Here](http://www.wisegeek.com/what-are-nuclear-batteries.htm) is a short article on how they work. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [June 16, 2014, 3:21am UTC](https://boards.straightdope.com/t/minimum-size-for-nuclear-batteries/690868/4 "2014-06-16T03:21:27Z")
The nuclear heat generator is pretty much naturally occurring (although the ones used in satellites and most consumer goods are refined a bit). The part that turns the heat into electricity is called a thermo-electric device, usually referred to in the consumer market as a thermo-electric cooler (TEC) or peltier device. They are commonly used to cool computer CPUs and also get a lot of use in portable picnic coolers (the type that plug into your cigarette lighter). Peltiers are kinda nifty little devices. Run a DC current through them and they become heat pumps, moving heat from one side to the other so that one side gets hot and the other side gets cold (they also generate their own internal heat, so you need to remove the heat from the hot side or the whole thing overheats). Reverse the current and the hot side becomes the cold side and the cold side becomes the hot side. They also work in reverse. Apply a heat differential to them, and they generate electricity. This is how they are used in space stuff. They aren’t all that efficient, but they are small and lightweight and have no moving parts. A typical peltier sized to cool a computer CPU will run you about 5 bucks or so. While they can be used to generate electricity (see the previous posts and links), they are much more commonly used as cooling devices. In addition to CPU and picnic coolers, they are also found inside of many imaging devices where they are used to lower the temperature of the imaging sensor to reduce thermally induced noise. Not only do they generate power for spacecraft, they are also often used to shuttle heat from one side of the spacecraft to the other, so that the side facing the sun doesn’t cook itself to death while the side away from the sun freezes. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [June 16, 2014, 9:25am UTC](https://boards.straightdope.com/t/minimum-size-for-nuclear-batteries/690868/5 "2014-06-16T09:25:03Z")
[Here’s](http://www.cnet.com/news/penny-size-nuclear-battery-keeps-going-and-going/) an article about a nuclear battery smaller than a penny, and they can supposedly be made much smaller than that. > [@](#): > > That makes it smaller than nuclear batteries used in space and military applications. Kwon says it might shrink to less than the thickness of a human hair if the right materials are used. Note that this kind of nuclear battery isn’t thermoelectric, but converts radiation directly into electricity; much like a solar panel but with radioactive particles instead of sunlight.