4 ms·

> "Why not no battery in the device?" How about a nuclear battery, aka radioisotope thermoelectric generator (RTG)? This would be sealed in (carefully!) and wo

> "Why not no battery in the device?" How about a nuclear battery, aka radioisotope thermoelectric generator (RTG)? This would be sealed in (carefully!) and would last the lifetime of the device, with no need for charging, ever. Would need special steps/handling to ensure safe disposal at end of product life, however.

M3L0NM4N 3y ago
What about a fusion reactor, generating its own hydrogen molecules to power nuclear fusion through electrolysis from the water vapor in the air. There isn't really a theoretical limit to how small a fusion reactor can be, although clearly this would not achievable for a long time.
- ungamedplayer 3y ago
  Totally planned obsolescence.
- eru 3y ago
  If you want to go totally crazy, you can use a black hole as a power source. The laws of physics don't give you a minimum size for them either. However for black holes the smaller they are, the more power they emit in terms of hawking radiation.
  - SV_BubbleTime 3y ago
    I’m pretty sure there was a Rick and Morty close to this.
  - Dylan16807 3y ago
    Fusion is silly but at least possible. Unless you have an idea for keeping the black hole inside the phone?
    - eru 3y ago
      Yes, I do: use a bunch of carefully controlled magnets to spin your block hole in a circle inside the phones. Black holes can hold charge, and thus electromagnetism works on them. (Not really useful for a phone, of course. But manipulating black holes like that is not any harder than manipulating an equally massive lump of ordinary matter.)
  - thfuran 3y ago
    The power scales to such an extent that a black hole light enough to be in a phone is just an explosion.
    - eru 3y ago
      Yes. I tried to find the calculations, but couldn't find them. Google Bard to the rescue (and cutting out the actual calculations she gave): > Therefore, a black hole needs to be at least 9.49 × 10^{22} kilograms in mass to emit 100 watts of Hawking radiation. This is about the mass of the Moon. No clue whether those numbers check out. EDIT: poking bard a bit more gives this correction: > However, for a black hole to emit 100W in gamma rays, it would need to be very small, with a mass of only about 10^22 kilograms. This is much smaller than the Moon, which has a mass of about 10^25 kilograms. But poking more and more makes me less and less confident, because bard seems to believe that bigger black holes emit more than smaller black holes.
Dylan16807 3y ago
You can't really have more than 4-5 watts of heat in a phone, so even with the friendliest heat source don't expect more than a quarter watt of electricity.
ChuckMcM 3y ago
This is challenging because you probably don't want a phone that is hot all the time. There is however a very interesting technology which uses beta radiation and what are essentially "solar cells" to generate electricity directly[1]. Basically you could paint some Cesium 137 on to a solar cell and it would generate power 24x7! [1] Beta Voltaics a new kind of nuclear battery -- https://en.wikipedia.org/wiki/Betavoltaic_device https://en.wikipedia.org/wiki/Betavoltaic_device
- Dylan16807 3y ago
  Currently single digit efficiency so it's still going to be unacceptably hot.
  - ChuckMcM 3y ago
    I think you meant "big" rather than "hot"? It's decay rate is low enough that it doesn't even melt itself when not cooled (and it melts at room temperature). Adding precision here, a 'thin layer' would not melt itself, you could probably keep a 10+kg chunk liquid. But the low efficiency means you need a lot of surface area between the Cs137 and the silicon lattice, so it one could calculate the number of sq meters of "battery" surface you would need to power a device and then see if you could topologically fold that into a relatively small area. Cs137 also can produce a small amount of gamma radiation which you'd want to shield against so the whole thing might end up in a lead box. (not great for making it light :-)) It would be a fun engineering challenge and a good use of nuclear waste but difficult to sell politically because the association with "nuclear." And yes, it isn't actually practical at this level. Looking at where folks are looking at this seriously it seems to be more of a spacecraft thing (long duration probes far from the Sun kind of thing)
    - Dylan16807 3y ago
      Being big is also a problem, but I did in fact mean heat. "Not melting itself" is not the threshold we need to meet for a phone. We should probably consider 5 thermal watts the limit. If we have a 30% efficient betavoltaic panel, then we can produce 1.5-2 watts of device power within that limit. If we have a 5% efficient panel, then we're only getting a quarter of a watt. A quarter of a watt can stop an idle phone from draining, but you'd only recover about 1% of a normal phone battery per hour. By the time we're considering external devices, I think "battery bank with a solar panel" beats betavoltaic on the technical merits even when we're ignoring difficulty and radiation. Even a tiny panel built into the back of a phone generally wins.
Savely 3y ago
Imagine Samsung battery incident on another level!

M3L0NM4N 3y ago

What about a fusion reactor, generating its own hydrogen molecules to power nuclear fusion through electrolysis from the water vapor in the air. There isn't really a theoretical limit to how small a fusion reactor can be, although clearly this would not achievable for a long time.

ungamedplayer 3y ago
Totally planned obsolescence.
eru 3y ago
If you want to go totally crazy, you can use a black hole as a power source. The laws of physics don't give you a minimum size for them either. However for black holes the smaller they are, the more power they emit in terms of hawking radiation.
- SV_BubbleTime 3y ago
  I’m pretty sure there was a Rick and Morty close to this.
- Dylan16807 3y ago
  Fusion is silly but at least possible. Unless you have an idea for keeping the black hole inside the phone?
  - eru 3y ago
    Yes, I do: use a bunch of carefully controlled magnets to spin your block hole in a circle inside the phones. Black holes can hold charge, and thus electromagnetism works on them. (Not really useful for a phone, of course. But manipulating black holes like that is not any harder than manipulating an equally massive lump of ordinary matter.)
- thfuran 3y ago
  The power scales to such an extent that a black hole light enough to be in a phone is just an explosion.
  - eru 3y ago
    Yes. I tried to find the calculations, but couldn't find them. Google Bard to the rescue (and cutting out the actual calculations she gave): > Therefore, a black hole needs to be at least 9.49 × 10^{22} kilograms in mass to emit 100 watts of Hawking radiation. This is about the mass of the Moon. No clue whether those numbers check out. EDIT: poking bard a bit more gives this correction: > However, for a black hole to emit 100W in gamma rays, it would need to be very small, with a mass of only about 10^22 kilograms. This is much smaller than the Moon, which has a mass of about 10^25 kilograms. But poking more and more makes me less and less confident, because bard seems to believe that bigger black holes emit more than smaller black holes.

Dylan16807 3y ago

You can't really have more than 4-5 watts of heat in a phone, so even with the friendliest heat source don't expect more than a quarter watt of electricity.

ChuckMcM 3y ago

This is challenging because you probably don't want a phone that is hot all the time. There is however a very interesting technology which uses beta radiation and what are essentially "solar cells" to generate electricity directly[1]. Basically you could paint some Cesium 137 on to a solar cell and it would generate power 24x7! [1] Beta Voltaics a new kind of nuclear battery -- https://en.wikipedia.org/wiki/Betavoltaic_device https://en.wikipedia.org/wiki/Betavoltaic_device

Dylan16807 3y ago
Currently single digit efficiency so it's still going to be unacceptably hot.
- ChuckMcM 3y ago
  I think you meant "big" rather than "hot"? It's decay rate is low enough that it doesn't even melt itself when not cooled (and it melts at room temperature). Adding precision here, a 'thin layer' would not melt itself, you could probably keep a 10+kg chunk liquid. But the low efficiency means you need a lot of surface area between the Cs137 and the silicon lattice, so it one could calculate the number of sq meters of "battery" surface you would need to power a device and then see if you could topologically fold that into a relatively small area. Cs137 also can produce a small amount of gamma radiation which you'd want to shield against so the whole thing might end up in a lead box. (not great for making it light :-)) It would be a fun engineering challenge and a good use of nuclear waste but difficult to sell politically because the association with "nuclear." And yes, it isn't actually practical at this level. Looking at where folks are looking at this seriously it seems to be more of a spacecraft thing (long duration probes far from the Sun kind of thing)
  - Dylan16807 3y ago
    Being big is also a problem, but I did in fact mean heat. "Not melting itself" is not the threshold we need to meet for a phone. We should probably consider 5 thermal watts the limit. If we have a 30% efficient betavoltaic panel, then we can produce 1.5-2 watts of device power within that limit. If we have a 5% efficient panel, then we're only getting a quarter of a watt. A quarter of a watt can stop an idle phone from draining, but you'd only recover about 1% of a normal phone battery per hour. By the time we're considering external devices, I think "battery bank with a solar panel" beats betavoltaic on the technical merits even when we're ignoring difficulty and radiation. Even a tiny panel built into the back of a phone generally wins.

Savely 3y ago

Imagine Samsung battery incident on another level!