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Resistance within a vacuum

  1. Apr 12, 2004 #1
    Hi I'm new here to physicsforums. I have been pondering this for a while since I am into car audio. Would an amp be able to function without frying under lower resistance than predicted within a vacuum? My whole idea is that maybe if I I vacuum sealed my amp I could connect alot more speakers to the amp and not have the sort of heat dissapation that destroys some electronic components. I came to think one night without the oxygen there the extra transfer of energy wouldn't be possible and therefore the whole system would not be able to short out instantly. Sortof like how vacuum sealed light bulbs work. Now I know the amp would still adventually break but maybe I could squeeze more out within that time limit. Thoughts ?
     
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  3. Apr 12, 2004 #2

    Janitor

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    I have read that there are three ways to dissipate heat: convection, conduction, and radiation. By vacuum sealing, you are eliminating convective cooling, so it seems to me that the amplifier will run hotter than it would in open air. Am I missing your point?
     
  4. Apr 12, 2004 #3
    Well the point is to completely eliminate the heat dissapation- without needing the usage of convective cooling, thus eliminating the extra energy consumption in the first place. This would totally stop the electric that is transfered to heat at the begining of the "short" so there is not immense heat transfer to destroy the electronics immediately. Even though natural denaturing of the circuitry will take place, the effects would be slowed down drastically under even lower resistance levels. That's my idea sorta.
     
  5. Apr 12, 2004 #4

    ahrkron

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    I think you would get the opposite effect.

    You want to get as much heat as possible out from your electronics. When in contact with air, part of the heat is transfered to the air molecules. Air around your equipment gets hotter and your hardware cools down (i.e., your electronics are not fried by "hot air surrounding them"; it's the other way around!). This is why some equipment is cooled down using water flow: the liquid "takes away" the heat generated.

    Air is a very poor heat conductor, but it allows for some heat transfer anyway. If you take that away, all heat generated within the circuit will have no way out.
     
  6. Apr 12, 2004 #5
    That's not how electronic components work. First and foremost, heat kills. You don't want to remove you amps ability to cool itself on the false asumption that it will improve performance. Would you remove your cooling fans and heatsink from you computer? Well, if you have an Epia MB it wouldn't be a problem; however, most other computers... Resistors work by converting electrical energy to heat energy and disipating that heat energy to the environmnet. Transistors (all semiconductos for that matter) operate differently as temperature changes. Most amps have compensation circuitry, but I gar-on-tee the compensation circuitry wont handle operation in a vacuum. You should take a look around the web for information on how OpAmps, semiconductors, resistors, capacitors, and inductors work. For instance, the OpAmp gain is a funtion of the feedback resistance compared to an input resistance. Heat the bugger up and your resistances are going to shift in a non linear fashion by different amounts thus changing the OpAmp gain. Capacitors (electrolytic especially) die much more quickly in high temp conditions. Heat energy causes semiconductors to "conduct more" for lack of a better term thus increasing the likelyhood of overdriving your amp.

    There's a reason amps come in aluminum cases with fins. They need the cooling to operate correctly.
     
  7. Apr 12, 2004 #6

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    It would be interesting to hear from some 'rocket scientist' on how the circuitry in a spacecraft is designed to keep from overheating and ruining things, out there in the vacuum of space
     
    Last edited: Apr 12, 2004
  8. Apr 12, 2004 #7
    Most of that equipment is designed to operate under extreme conditions. More design, and testing goes into an electronic component designed for space than used in an automotive amp. Also spacecraft designers shield the crafts from the direct sun light. Space is a pretty cold place if you block the sun's heat radiation from affecting your sensative electronic equipment. In space direct radiation is the heat sink.
     
  9. Apr 12, 2004 #8

    russ_watters

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    Mostly radiative cooling. The space shuttle cargo bay doors are left open to radiate heat for example.

    The space suits of astronauts on the moon were cooled by ice sublimation: they sprayed water onto the heatsinks.

    Alien, I'm not sure where you are getting this idea that a vacuum reduces electrical resistance...
     
    Last edited: Apr 12, 2004
  10. Apr 13, 2004 #9

    Cliff_J

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    Alien509 - Besides killing things faster with the vacum seal, you also need to factor in the SOA (safe operating area) of the transistors used to construct the amplifier. Its like a redline on an engine, if you exceed it by too much, poof!

    You would be much better off by focusing on getting as much heat away from the amplifier and its internal components as quickly as possible. Things like more thermal mass, more heatsink area, lots of fans to circulate cool air, and a liquid cooling system would allow the electronics to perform at a higher level for a longer period of time, even if you're just going for a 30 second burp at a soundoff. How much better, and how much you'd gain is another story, and it probably isn't too much.

    Companies make larger amplifiers for a reason, and its called physics. :)

    Cliff

    P.S. You competing? What org & class?
     
  11. Apr 13, 2004 #10

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    Yep. After I posted last night, I got to thinking the same thing. Use reflective foil to keep sunlight off of the parts of the spacecraft you want to keep from getting too hot. Roll the spacecraft like a BBQ spit if need be to even out solar heating. Take advantage of the fact that in any direction where there is no sun or nearby planet, the temperature is near absolute zero, so that radiating heat away is a good way to rid heat generated by components of an electrical circuit.
     
  12. Apr 13, 2004 #11
    ok I am no rocket scientist and I may be wrong but here is my reasoning. I'll be refering to the amp as the system within the vacuum. I was taught once that in order for heat to be transfered there has to be some other atom(s) to take on that "inertia" from the orginal source. The "inertia" being the energy transfered kinetically from the system. Simply put I think heat is the result of electric being converted to kinetic energy outside of the system. Now my reasoning for thinking that the system could operate more efficiently within a vacuum is that the oxygen would not be there to accept the energy. With the vacuum there would not be "excited" oxygen atoms blasting the atoms of the sytem out of alignment and taking on extra electricity. Therefore the need for cooling would not be necessary and the system would keep operating despite resistance levels.

    My theory is that light is the only form of energy that can move through a vacuum because it follows a different set of rules than electricity. Light is something that I and many others do not completely understand yet. Theory about space is, those machines up there do not have to worry about cooling themselves. Even if they had heatsinks using direct radiation where would that heat transfer be going to? The next question is why would energy tryto make its way from the system with nowhere to really go ? I think it would be a waste of a hunk of metal if you ask me.

    Ok now like I said I maybe wrong. Speculations?
     
    Last edited: Apr 13, 2004
  13. Apr 13, 2004 #12
    Alien,

    I think you're confusing heat generation and heat dissipation. To produce sound, your amplifier uses electrical energy (from your car's battery when the ignition is off, and from the alternator when it's on). Only a little bit of that energy gets turned into sound; the rest gets turned into heat. It would be nice if amplifers were perfectly efficient, and all the energy got turned into sound, but that's not how it is. Anyway, that's how the heat gets generated and nothing you do to the space around the outside of your amp is going to change that.

    Now to keep your amplifer from getting too hot, you need to get rid of that heat. As other's here have said, there are only three pssibilities: conduction, convection and radiation. In a vacuum you lose the first two, so that would just make things worse.
     
  14. Apr 13, 2004 #13

    NateTG

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    Alien - it might be helpfull to think of it this way:

    A bunch of energy is flowing into and out of the amp down the wires. Some fraction of the energy is 'used up' in the amp, and causes the amp to heat up. This heat is there whenever you're using the amp.

    Since electronic equipment (generally) works better when it is cooler, this heat is not desirable in the amp - that's why people are talking about heat dissapation.

    Wrapping the amp in vacuum prevents the heat from dissapating, and you will lose efficiency, and probably the amp if you try to run it that way.

    If you want to overdrive the amp, you should plan to put additional cooling on it instead of a vacuum. Even then, you may only be able to get a small increase in performance moreover, the amp will not be designed to operate under those condidtions, so you may end up breaking it.
     
  15. Apr 13, 2004 #14
    Ok well thankyou all for your input. I might try a few experiments soon to test my theory. I have a old sterio with a broken tape deck that I could test with whenever I get around to doing it. The second question I raised was what electrical effect would be on the speakers themselves. I just couldn't help the thought especially with vacuumed sealed light bulbs and how that whole ordeal works. I know the simple suttle solution would just be to add a ton of cooling to the hardware but I am looking for a little bit more. Thanks again. More speculation welcome.
     
  16. Apr 13, 2004 #15
    Hi. I am a new user from India and am now promoted to 11th std. I am reading many Physics books and am getting a lot of doubts. I hope any of U will be able to clear my doubts.
     
  17. Apr 13, 2004 #16
    It might help you to consider a little more carefully why light bulbs are "vacuum sealed". The problem with light bulb filaments (ask Edison) was that the filaments burned out too fast to be practical. Removing the air prevents oxidation of the filament. That's why they burn out immediately when the bulb is cracked - air rushes in, the filament burns & opens the circuit.

    My friends & I doubled our vacuum tube life when we added a small battery operated fan to the cabinet. It draws cooler room air over the tubes and keeps them from getting so hot. It's true that radiation from the filament to the glass walls cools the filament but it's convection of air around the glass that keeps the glass cooler. For longer life, use a fan to cool the electronics.
     
  18. Apr 13, 2004 #17

    Cliff_J

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    Not sure what you're looking for at the speakers, but there is nothing magic happening.

    If you can make the amplifier produce more output voltage AND it can flow the necessary current to maintain that voltage, more power is delivered to the speaker. In turn, hopefully the speaker can turn the additional power into sound, and it needs all the help it can get at cooling (look at like JL Audio's W7 and how many patents are about cooling the motor structure. The cooler you keep the speaker, the lower its resistance and in turn this results in an ability to receive more power.

    Here's a tidbit for you: A doubling of the same number of speakers driven with the same amount of power with the exact same signal will result in a doubling of output (3db gain). So if you quadruple the number of speakers but wire for the same final impedance load to the amplifier (same power) you will end up with a 6db gain. Sure you could wire all them in parallel instead and chase 12db, but fried transistors or a loss of 12db are far more likely.

    Repeat: TINSTAAFL!

    Cliff
     
  19. Apr 20, 2006 #18

    Mech_Engineer

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    Ok, this is getting painful so let me shed some light for you Alien. First and foremost, let me state that your "overdriven" amp will definitely fry if you put it in a vacuum.

    This is obvious, but you don't have to be a rocket scientist to understand basic heat transfer concepts.

    First of all, your light bulb theory is flawed because you're not understanding that for your amplifier to be able to cool itself in a vacuum "like a light bulb", it would have to GLOW like a light bulb as well, at very high temperatures (around 1000C). Light bulbs use a Tungsten filament because Tungsten won't melt until about 3400C, where as your amp won't survive past 200C. Also, light bulbs create heat just like your amp, through resistive heating. So read on...

    Heat will be created in your amplifier through resistive heating, Q=I^2*R, where I is the current travelling through the conductor (in this case, electronic components of the amp) and R is the resistance of that conductor. The result of this simple equation is power, in the SI system Watts.

    No matter what the conductor is surrounded by, the same amount of heat will be generated. This heat energy will build up in the conductor by raising the internal energy of it, and thus raising its temperature. Normally, this energy can be disspated through the use of conduction, AKA heat flow through a heatsink or heatpipe to a cooler temperature, and/or through convection, where a flowing fluid blown by a fan or through natural buoyancy can carry the energy away. These can be used in conjunction by having a heatsink that conducts heat away from the components, and then uses a large surface area (fins) to utilize convection.

    Not allowing convection or conduction to occur by surrounding the amplifier with a vacuum will cause it's temperature to increase dramatically because the only form of heat transfer still available will be radiation, which is far less effective than the previous two, especially at low temperature differences.

    This basically means that your amp will get hotter and hotter until the radiative heat transfer away from it equals the heat generation inside it. With even a small amplifier (say, 750W, it's generating about 750W of heat which must be dissipated), if the inside of your car is 75C (not likely without AC full blast) your precious amplifier would have to be at about 583C! Of course, components would have melted long before it ever reaches this temperature rendering the amp useless, but this shows you just what the problem will be.

    This is kind of true, but you're confusing heat transferred away with heat being generated. Just because there is no way to remove the heat does not mean it will stop generating it!

    I'm not sure what to say about this except that it is an incorrect conclusion.

    Except for the "more efficient" part, this is true, but the fact is the heat will still be generated with no place to go (except through radiation), melting your amp.

    :grumpy: Uh, what?

    First of all, light is pretty well understood, so I'm not sure who "many others" are or what it is that's not understood. Secondly, space vehicles have very small power consumptions so they don't require very much cooling, but more importantly RADIATION is the dominant (and only) form of heat transfer up there (other than perhaps sublimation of solid coolants, but that is another topic). The black of space is effectively at absolute zero, 0K or -273.15C. This makes it easy to utilize radiation for cooling purposes. This isn't done very much, however, because as I said satellites are pretty efficient and don't generate a lot of heat. Therfore, they are usually shielded from radiation with thin foils, which reflect radiation from the sun and insulate against the cold.

    It has a place to go, radiate to it's surroundings.

    And that is that, you have heard from a professional that says your experiments will undoubtedly end in failure so good luck with that whole vacuum chamber thing, you're going to need it. :uhh:

    If you want your amps to run more efficiently, cool them MORE with fans or colder air. However, as stated previosuly, amps will not take much overdrive before cooking, they are rated with a max power rating for a reason. There really isn't any good way to "overdrive" an amp anyway, it's just destroying it.

    The most important question you can ask yourself:
    Q:If simply surrounding electrical components with a vacuum helps with efficiency, why hasn't it already been done?
    A:Because it doesn't. PERIOD.

    ------------------------------------------------
    Brian
    Mechanical Engineer, U.S. Department of Energy

    Bachelor of Science in Mechanical Engineering
    University of Arizona, Tucson
    ------------------------------------------------
     
  20. Apr 20, 2006 #19
    Ummm, not necessarily. A typical solid state amp running class B or A/B will run most efficiently when in full clip. Now, that isn't saying anything about the power supply of the amp. The power supply needs to be able to deliver the required power to the output transistors. Obviously the power supply will be taxed more heavily. But when the output transistors are 'full on' they are dropping little voltage across themselves. This limits the amount of power that can be dissipated in them. As long as the load on the amp does not drop below the manufacturers spec, most decent quality car audio amps can run in full clip all day long.
     
  21. Apr 24, 2006 #20

    Mech_Engineer

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