Silly question about capacitors

[dieter]

This is pretty much the opposite of what I've learned yet. Resistance causes heat loss but has no "slow down effect", and I've never heared of cooling elements for caps, tho they obviously are common for transistors or ICs...

The cap in a simple ac/dc supply that smoothens the rectified current is in heavy duty to do exactly what we discuss here, but they are as uncritical as a cap can be.

It just doesn't make sense, sorry.

[MarkE]

This is pretty much the opposite of what I've learned yet. Resistance causes heat loss but has no "slow down effect", and I've never heared of cooling elements for caps, tho they obviously are common for transistors or ICs...

The cap in a simple ac/dc supply that smoothens the rectified current is in heavy duty to do exactly what we discuss here, but they are as uncritical as a cap can be.

It just doesn't make sense, sorry.

Dieter, plug the circuit into any SPICE simulator as vasik041 did.  The amount of time that it takes for the second capacitor to come with 0.1% of 50% of the starting voltage is 6.9 RC time constants.  Increase C or R and the absolute time to stabilize to within any particular percentage of the 50% asymptote stretches out.

You can find capacitor with heat sinks easily.  Go take a look into your local power utility substation.

You are absolutely wrong about what you think about electrolytic capacitors.  Very often more capacitance is used than would be required to meet charge storage requirements in order to stay within ripple current requirements.  Ripple current requirements are set by internal temperature rise considerations.  There is lots of information on the web sites of the various electrolytic capacitor makers such as Nichicon and United Chemicon.  http://nichicon-us.com/english/products/alm_mini/pict_f.htm

[dieter]

Ok, I may be wrong there and yes, some caps may not be charged and uncharged too fast, otherwise they may be destroyed.


But I came to an other explanation that works for me:


Since we connect the 2 caps in series, the total capacitance will suddently be only 50% anymore. This happens faster than SOL, but immediately. The charge in cap A is now too high for its capacitance and quantum mechanics, those impatient dudes, can't wait til those lazy electrons have moved trough the slow wire. So they simply kick 50% of the charge "out" somehow. The remaining half, that now still fills Cap 1, will then slowly flow to cap 2 until they re equalized. Now they are still 50% full each, but as soon as you seperate them from eachother, they will double their capicitance, resulting in 8 Volts= 25% of the energy in each one.


Now I just have to find out, where the 50% has gone. So you say that's where the heat is caused, by forcing electron charges into the dielectric surroundings?


EDIT: okokok, but what happens when we increase the capacitance of an empty cap? Could't that be at least a good way to collect charges, eg. from the surroundings?
Ok, a silly question again but phew, I can test that right now.


EDIT 2: Wait a sec, who said the initial charge of cap 1 (16v) is the max capacitance? Maybe the reaction is the same no matter how full the cap is and immediately altering the capacitence cannot be compensated by charge flow in the cirquit? When this causes heat, does then heat cause a charge?


I actually just reallize that I don't know anything about caps.

[MarkE]

Dieter, yes you are wrong as the linked reference explains in Item 2.  Electrolytic capacitors must be applied such that they do not suffer excess ripple current which in turn would cause excess internal heating and premature failure.

That is certainly a creative interpretation you offer.  The accepted theory previously explained is backed by careful experiments.

There are machines that vary capacitance.  If a voltage is placed across them, they emit E/M radiation.  More commonly, these machines act as stress or fine position sensors.

I don't think anyone said that the capacitor was charged to its upper voltage limit, only that it was charged to a particular voltage.

[forest]

sorry, I was not clear enough. Take two non-polar capacitors in paralell (maybe would be good to use two electrolytic to form non-polar to have bigger capacitance from start and lower leakage to air), charge them to the same voltage  (because of being parallel), then disconnect and connect them in series and measure. what is going on ? energy rise ?