darthgently Posted September 26 Share Posted September 26 (edited) 1 hour ago, K^2 said: Fine grain entropy is conserved. Coarse entropy is growing. To paraphrase a Calvin and Hobbes strip: “My head hurts, I think I’ll go take a nap now” I think this is the one I had in mind: https://www.gocomics.com/calvinandhobbes/1989/10/29 Edited September 26 by darthgently Quote Link to comment Share on other sites More sharing options...
K^2 Posted September 27 Share Posted September 27 8 hours ago, darthgently said: To paraphrase a Calvin and Hobbes strip: “My head hurts, I think I’ll go take a nap now” Legend has it, the topic of reversibility of time is what drove Boltzmann insane. So if all you got is a headache, you got off easy. Quote Link to comment Share on other sites More sharing options...
Terwin Posted September 27 Share Posted September 27 10 hours ago, K^2 said: Legend has it, the topic of reversibility of time is what drove Boltzmann insane. So if all you got is a headache, you got off easy. To be fair, if you discover proof that the universe is not compatible with the rational mind, then the only rational thing to do is to disconnect from the universe... Quote Link to comment Share on other sites More sharing options...
darthgently Posted September 27 Share Posted September 27 11 hours ago, K^2 said: Legend has it, the topic of reversibility of time is what drove Boltzmann insane. So if all you got is a headache, you got off easy. Quote Link to comment Share on other sites More sharing options...
farmerben Posted October 5 Share Posted October 5 How do you convert a DC voltage into a different DC voltage? I'm thinking about the adapters that plug into a 12V cigarette lighter in a car, and have a 5V output. They don't heat up that much, so I don't think its just a resistor drop. Quote Link to comment Share on other sites More sharing options...
darthgently Posted October 5 Share Posted October 5 1 hour ago, farmerben said: How do you convert a DC voltage into a different DC voltage? I'm thinking about the adapters that plug into a 12V cigarette lighter in a car, and have a 5V output. They don't heat up that much, so I don't think its just a resistor drop. Google around on “DC to DC converter”. If voltage is like water level the DC-DC converters are like canal locks between differing water levels. Sort of Quote Link to comment Share on other sites More sharing options...
magnemoe Posted October 5 Share Posted October 5 4 hours ago, farmerben said: How do you convert a DC voltage into a different DC voltage? I'm thinking about the adapters that plug into a 12V cigarette lighter in a car, and have a 5V output. They don't heat up that much, so I don't think its just a resistor drop. Most common is to change the high voltage into high frequency pulses. To go from 12 to 5 you have 5/12 of pulse being on. You then use one or more capacitor and coils to even out the power so its constant. Power supplies for stuff like computers does the same for AC, I assume they turn it into DC first before doing this tricks to avoid the 50 Hz interfering with the fast pulsing. Quote Link to comment Share on other sites More sharing options...
darthgently Posted October 5 Share Posted October 5 1 hour ago, magnemoe said: Most common is to change the high voltage into high frequency pulses. To go from 12 to 5 you have 5/12 of pulse being on. You then use one or more capacitor and coils to even out the power so its constant. Power supplies for stuff like computers does the same for AC, I assume they turn it into DC first before doing this tricks to avoid the 50 Hz interfering with the fast pulsing. What he said. To relate to the canal lock analogy the pools of the locks would be similar to that caps and the rate of lock cycle the pulses. But if you know caps and coils then skip the analogy. Quote Link to comment Share on other sites More sharing options...
farmerben Posted October 5 Share Posted October 5 canal locks are a lousy analogy Quote Link to comment Share on other sites More sharing options...
darthgently Posted October 5 Share Posted October 5 (edited) 1 hour ago, farmerben said: canal locks are a lousy analogy Yeah. I agree. Maybe a hydraulic ram is better. But my first suggestion was to look into DC to DC converters. That was good advice Edited October 5 by darthgently Quote Link to comment Share on other sites More sharing options...
AngrybobH Posted October 7 Share Posted October 7 On 10/5/2024 at 5:43 AM, farmerben said: How do you convert a DC voltage into a different DC voltage? I'm thinking about the adapters that plug into a 12V cigarette lighter in a car, and have a 5V output. They don't heat up that much, so I don't think its just a resistor drop. Car power port chargers usually use a quick and dirty method to drop the voltage down(and cheap ones can cause push button start cars to not start because of noise). They use a zener diode. It allows current to flow through the diode the wrong way at the fall over voltage. A 5v zener will leave 5v on the circuit and flows the rest to ground. A little wasteful but it gets the job done. F to V converters (frequency to voltage, comes as a single chip, reversible, super cheap) can do like what @magnemoe was saying. Cheapest way is a simple voltage divider if you know the input voltage is constant(ish)(12v----58% of ohms total----5v output ----42% of ohms total----ground). There are also DC/DC converter chips sold in chip form(these are used in just about everything). Expensive DC/DC converters add all the circuits for reduction in noise and clean output. The choice comes down to what you are powering, how many watts you need, and how clean you need the power. Additional concerns might be what environment you are running it in and how long you need it to work for. 100 amps continuous in a harsh environment with a super clean output for a decade is a very expensive problem. Quote Link to comment Share on other sites More sharing options...
farmerben Posted October 7 Share Posted October 7 https://en.wikipedia.org/wiki/DC-to-DC_converter I understand Impedance in LC circuits. The only complicated part is the switching mechanism. I'd like to plug one into an oscilloscope and see what the output really looks like. It is surely not a flat voltage on the load. Quote Link to comment Share on other sites More sharing options...
darthgently Posted October 7 Share Posted October 7 (edited) 43 minutes ago, farmerben said: https://en.wikipedia.org/wiki/DC-to-DC_converter I understand Impedance in LC circuits. The only complicated part is the switching mechanism. I'd like to plug one into an oscilloscope and see what the output really looks like. It is surely not a flat voltage on the load. If the final filter capacitor is big enough it can be darn flat. It also depends on how stable the load is also of course Edited October 7 by darthgently Quote Link to comment Share on other sites More sharing options...
magnemoe Posted October 7 Share Posted October 7 6 hours ago, darthgently said: If the final filter capacitor is big enough it can be darn flat. It also depends on how stable the load is also of course If the switching frequency is fast as in MHz you don't need an large capacitor. You need an large one converting from AC to DC but if smart and only needing 12 V out you could adjust the pulse length to the incoming voltage who is known and predictable. And yes its easier solutions, for an led indicator light you simply add an resistor so voltage over led is correct. Quote Link to comment Share on other sites More sharing options...
darthgently Posted October 7 Share Posted October 7 2 hours ago, magnemoe said: If the switching frequency is fast as in MHz you don't need an large capacitor. You need an large one converting from AC to DC but if smart and only needing 12 V out you could adjust the pulse length to the incoming voltage who is known and predictable. And yes its easier solutions, for an led indicator light you simply add an resistor so voltage over led is correct. Depends on the stability of the load, but yes, agree overall Quote Link to comment Share on other sites More sharing options...
farmerben Posted October 14 Share Posted October 14 Do staircases work in Martian or Lunar gravity? So do you want much larger steps to leap up to, or are staircases governed by the flexibility of the average person and need to be the same size? Quote Link to comment Share on other sites More sharing options...
kerbiloid Posted October 14 Share Posted October 14 LEM was having them. LK-700 project was having them double (the vertical upper one and the on-strut lower one). Spoiler Quote Link to comment Share on other sites More sharing options...
Terwin Posted October 14 Share Posted October 14 2 hours ago, farmerben said: Do staircases work in Martian or Lunar gravity? So do you want much larger steps to leap up to, or are staircases governed by the flexibility of the average person and need to be the same size? I think step size is related to average leg or stride length. Then again, kids with more energy can jump up multiple steps with shorter legs, while older people with less energy can struggle for the one step at a time, so perhaps not? Quote Link to comment Share on other sites More sharing options...
magnemoe Posted October 14 Share Posted October 14 2 hours ago, Terwin said: I think step size is related to average leg or stride length. Then again, kids with more energy can jump up multiple steps with shorter legs, while older people with less energy can struggle for the one step at a time, so perhaps not? Yes also if you are in an heavy and stiff space suit. I say they just use normal steps as we are used to them. You can skip if you want to or not say carrying something heavy or bulky. Now its some stupid steps like at my engineering school up from the parking lot. Steps was 1.5 standard step wide for some reason. why not make it shorter? Quote Link to comment Share on other sites More sharing options...
darthgently Posted October 15 Share Posted October 15 5 hours ago, magnemoe said: Yes also if you are in an heavy and stiff space suit. I say they just use normal steps as we are used to them. You can skip if you want to or not say carrying something heavy or bulky. Now its some stupid steps like at my engineering school up from the parking lot. Steps was 1.5 standard step wide for some reason. why not make it shorter? Perhaps the steps at the engineering school were a lesson in disguise: Consider the user in all your designs Quote Link to comment Share on other sites More sharing options...
farmerben Posted October 30 Share Posted October 30 What is the difference between crushed glass and sand? Can you use them interchangeably in concrete? If you were to spread crushed glass on the environment, would that be worse than spreading sand? Quote Link to comment Share on other sites More sharing options...
AckSed Posted October 30 Share Posted October 30 3 hours ago, farmerben said: What is the difference between crushed glass and sand? Can you use them interchangeably in concrete? If you were to spread crushed glass on the environment, would that be worse than spreading sand? Mostly, there's no difference. Irregular grain size is the biggest issue, and that can be screened out. Here's someone making sand out of glass: Quote Link to comment Share on other sites More sharing options...
kerbiloid Posted November 1 Share Posted November 1 (edited) https://en.wikipedia.org/wiki/Glass_wool https://pmc.ncbi.nlm.nih.gov/articles/PMC4246535/ Don't touch the glass wool with bare skin, it will be itching. The glass grains are sharp crystals, like the regolith is, while the sand grains are smooth due to water and wind erosion. Edited November 1 by kerbiloid Quote Link to comment Share on other sites More sharing options...
magnemoe Posted November 1 Share Posted November 1 5 minutes ago, kerbiloid said: https://en.wikipedia.org/wiki/Glass_wool https://pmc.ncbi.nlm.nih.gov/articles/PMC4246535/ Don't touch the glass wool with bare skin, it will be itching. The glass grains are sharp crystals, like the regolith is, while the sand grains are smooth due to water and wind erosion. its nice insulation as its fire proof unlike most loose material. Fun story, back then it was new some guy my father knew tried use it as an makeshift Santa Claus beard. It was not conformable. Quote Link to comment Share on other sites More sharing options...
AckSed Posted November 1 Share Posted November 1 Oh yeah, there'd also be organic contaminants in the form of food residue, glue and paper/plastic labels, and metal, which is already mag-separated here, but for mortar or cement you wouldn't really care. Quote Link to comment Share on other sites More sharing options...
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