Class A and the environment

[rif]

Nelson Pass has commented on environmental concerns in a few of his articles, and that got me thinking of possible "solutions". Some are funny and not serious, but overall I am -- is there anyway to put the unused/not needed energy associated with class A to use before it's wasted as heat?

1) Is there anyway to avoid creating heat -- class A draws the same power regardless of audio needs -- if you crank up the volume or drive a difficult load it should in theory reduce the heat dissipated. Is there anyway to put that unneeded juice to use before the transistors convert it to heat? Power the room's lights? (I'm only half-kidding -- what kind of an impact would tapping the unused energy have on audio qaulity?)

2) If it has to produce heat, is there anything usefull to be done with it? Use water cooling and save the hot water in the house's hot water tank? Make a hot tube in a spare room? Let the heat sinks go up to 100 deg C and run a steam engine (OK, now I'm kidding, but it would be fun!)?

3) When shutting down, can the energy stored in the caps be put to use instead of being bled off as heat? Charge some batteries, return the power to the grid?

Have some fun brainstorming

[phase_accurate]

Let the heat sinks go up to 100 deg C and run a steam engine (OK, now I'm kidding, but it would be fun!)?

A Stirling engine would run at lower temperatures (and generate less noise than a steam engine)! Why not drive some appliances that way ?

regards

Charles

[GRollins]

The power not dissipated in the amp when playing music is dissipated in the speaker; some nearly insignificant fraction goes into sound waves, which still end up as heat. Granted, it's not "wasted" in the sense that it's accomplishing a stereo's intended purpose, but thermodynamics still applies.
I water cool two pairs of Aleph 2s. I had considered running the heat into the water heater in the next room, but the problem there is that you're commiting yourself to at least the operating temperature of the water heater. Depending on various other factors, that may or may not suit you. In my case, it wasn't going to work well.
Of course, there's always the old standby--heat the house in the winter. That leaves the question of what to do in the summer hanging, though.
It's not really enough heat to cook with, although it might do for warming leftovers. Pizza, anyone?
The basic problem is that heat is the most degenerate form of energy and you're up against entropy when trying to do something with it. In household use, there just aren't that many useful outlets. It's too much to be comfortable, and too little to be put to work.
Unless you have a really big system.
There. Now you have a perfectly good rationalization to present to your wife/significant other as to why you need more amplification.

Grey

[batee]

Energy in caps is negligible compared to overall consumption. 1F at 50V contains 2500J = 2500 Watt Seconds. Not even 1 Watt Hour (3600 Watt Seconds).

Seems like it's an efficient heater. In the winter, the heat wouldn't have to be converted, but you'd still have to find a way to distribute that energy efficiently. For ultrasmall dwellings, a small fan might do it. For larger homes, I think I'd try to get the heat into the HVAC intake so the furnace had to do less work, or water cool the and use the heated water as a supply for the water heater. In the summer, if it were a separate enclosure vented to the outside, at least it wouldn't increase the cooling bills. In the more extreme case, a heat pump could be used to convert the heat and then used to cool the house.

A more practical solution would be to build efficient speakers, use a smaller amp, and turn it off when you're done.

Another approach to lowering energy requirements would be to capture other available energy (solar, wind, tidal hydro, extension cord to neighbor's exterior outlet, hot air coming out of the neighbor's dryer vent, whatever) and use it to power the amp.

I think Nelson provided the ultimate solution: Use lightbulbs instead of resistors. Brilliant!

Bryan

[dnsey]

A Stirling engine would run at lower temperatures (and generate less noise than a steam engine)! Why not drive some appliances that way ?

And why shouldn't one of these appliances (or the only one) be the amp itself? Of course, some additional energy will be required, but this seems a fairly constructive form of positive feedback

Anyone care to calculate the losses / efficiency?

[cowanrg]

energy is never wasted. it merely changes forms.

[rif]

Originally posted by GRollins
The power not dissipated in the amp when playing music is dissipated in the speaker;

Are you sure? That doesn't doesn't right to me.

Originally posted by cowanrg
energy is never wasted. it merely changes forms.

Depends on how you define wasted. Creating something and then throwing it away without using it is wasting. At worst we're wasting energy, at best it's an inefficient use of energy (but worth it!)

[LBHajdu]

Peltier elements could be used to transform some of the heat back into current to feed the output stage. This would make a loop, some energy will always be lost, so you still have to feed the amp some power however it would be much less.

A 5” by 5” peltier element could supply something like 5 amps, however the heat difference between the two sides would have to be something like 150C.

Just in case someone here has never heard of peltier element, they are ceramic plates if you apply hot to one side and cold to the other the produce electricity almost lie a solar cell. If you apply current to it, then the produces a heat difference between the two sides (this is how it’s most commonly used. If you plan to use it to produce electricity, you have to buy the type that is optimized for that.

[janneman]

Originally posted by rif


Are you sure? That doesn't doesn't right to me.

It's true. A really, really efficient speaker transforms 5% of the electrical input into acoustic output. The other 95% goes into heating the voice coil and associated parts.
So if you crank up the amp to deliver say 20W into that speaker, 19 watts are converted to heat. Plus whatever the amp dissipates at that point.

Jan Didden

[Swedish Chef]

A Peltier element used as a TEG (Thermo-Electric Generator) typically has an efficiency of < 10% (depends heavily on the temperature difference following Carnot's formula).

While energy isn't wasted what we in Swedish call exergy is. Exergy is the "quality" of the energy with electricity and petroleum fuel being close to 1 (you can convert it to almost any other form of energy with very little loss). Heat has a terribly low exergy. You can convert 100W of electrical power into (almost) 100W of thermal power but you can not convert that 100W of thermal power back to 100W of electrical power.

/M