Silly question about capacitors

[MileHigh]

Dieter:

If it made economic and/or technical sense to harvest back-EMF it would be done.  But in general it doesn't make sense so it is not done.  To say that something like back-EMF is "never really examined" is not true at all.  There is a huge amount of material to learn if you want to learn about electronics and a wise person would not make judgements or pronouncements without first understanding all of the issues.  I am not directing this comment specifically at you, it is a comment that applies to everyone.

MileHigh

P.S.:  And I will defer to comments by MarkE below about how back-EMF is being harvested and recycled in a lot of applications nowadays.  I am also on a learning curve that I will never get off of.

[MarkE]

Surrounded by scary formulas. I made more simple experiments. The two caps, empty, where connected in a loop, then gently heated to about 45 deg. C., then I doubled their capacitance by unconnwcting them, still warm. Now one has 12 mvdc, the other -12mvdc charge.


Of course I don't think that the thousands of intelligent and educted scientists made a baf job so I have to reveal the truth about caps after 10 Minutes of experiments  , it's just that science is very if not only profit-oriented, so certain aspects are never really examined. Example given the back emf is usually seen as a nasty, dangerous thing that needs to be eliminated, eg. by heat dissipation, instead of  harvesting it to save energy. After all, they want us to consume electricity since one reactor gives about 1/3 billion $ in a year.

BEMF is recycled in virtually all high efficiency power converters and motor drives.  It is a necessity of smaller packaging where we can't afford the space needed to dissipate the wasted heat of dissipative BEMF discharge circuits.  40 years ago people threw away a lot of power in order to save component cost.  That all changed about 20 years ago.  Only in the lowest end consumer products do we see low efficiency power converters and motor drives.

[MarkE]

Dieter:

If it made economical and/or technical sense to harvest back-EMF it would be done.  But in general it doesn't make sense so it is not done.  To say that something like back-EMF is "never really examined" is not true at all.  There is a huge amount of material to learn if you want to learn about electronics and a wise person would not make judgements or pronouncements without first understanding all of the issues.  I am not directing this comment specifically at you, it is a comment that applies to everyone.

MileHigh

It really is done everywhere now.  Virtually all stepper motor drives that are in everything from 3D printers to robotics are full bridge drivers that recycle BEMF.  All high efficiency motorized appliances use one form of bridge driver or another that recycles BEMF.  Virtually all switching DC-DC, and DC-AC converters to recycle BEMF.

[dieter]

Today probably, yes, but for some 30 years it wasn't an issue. Would it be wise to say, Science is not financed by economy? Conclusion?


Anyway, what I have said about the -12 and +12 Mvdc charge may be caused by my body, acting as an antenna. Since I had them in my pocket while I was sitting in front of a heater fan.


Basicly I was referring to a document, I think it was "the secret life of capacitors" from the download section, that discovers a relation between self-charging and wheather changes, in pressure or temperature.
BTW Milehigh, I didn't say "something like a back-emf is never really examined", as you impressed. The idea of harvesting it wasn't really examined, at least for a long time. Thats a fact, just watch some older schematics, how they used to deal with bemfs between some cmos chips.

[Vladokv]

Energy is lost as heat. Condesators heat up dramatically at high current. Look at induction heating - condesator  in LC tank heats up dramaticaly. Polyester condesators with no electrolyte heats up! Currents in that very moment are enormous and so energy losses are. Your setup looks like Colpitt oscillator with very low inductance(and straight wire have inductance). Current jumps back and forth maybe and million times(some miliseconds) before come to stop.