Inverse Marx generator

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just like irreversible thermodynamic processes, if you make the steps small enough, it starts looking reversible.

You can have two caps, C1 charged and C2 not, and transfer all the charge from C1 to C2, without loss. In fact, you can slosh the charge between them, back and forth, forever. Just don't use resistors.

John

It has to be identical size capacitors, otherwise 'all the charge' can't be transferred without adding/losing energy...

With switches and moving parts, you can make all KINDS of electrostatic charge-moving gizmos. The earlier "reverse van de Graaff machine" suggestion is just one of a large family of electrostatic motors. A favorite example of high voltage motor is the Oxford bell

"John Larkin" wrote in = message news: snipped-for-privacy@4ax.com...

What if you want equal charges on both?

Tim

--=20 Deep Friar: a very philosophical monk. Website:

Not so.

John

Easy.

John

just like irreversible thermodynamic processes, if you make the steps small enough, it starts looking reversible.

John Larkin, Please explain how you do that? Magic switch? Or magic perfect inductor ?:-) ...Jim Thompson

My original comment was in reply to a suggestion of using a rotating variable capacitor, a sort of "reverse electrophorus", where C varies. That will inevitably lose energy, similar to the electrophorus gaining energy from the mechanical separation of the plates.

Switching capacitors from series to parallel does not change each individual C, hence, neglecting switching losses, both charge and energy remain the same. I assume that is what you mean by a flying capacitor converter.

I like your use of the word "slosh".

"John Larkin" wrote in = message news: snipped-for-privacy@4ax.com...

charge

Without resistors? Prove it ;-)

Note: no dangling currents. Inductors carry charge, too, so that = wouldn't conserve it very well.

Tim

--=20 Deep Friar: a very philosophical monk. Website:

individual C,

What I meant was charging a cap with another cap. Without tricky = quasi-resonant or inverter circuits, you inevitably have to do this = (under the presumption that a constant DC output is desired), and this = inevitably leads to loss. But the 50% loss only occurs to the *change* = in energy, so if you make this change an arbitrarily small fraction of = the supply voltage, efficiency can be quite high. Hence why things like = MAX232 can be ~95% efficient despite pumping caps into caps.

When you mentioned a mechanical method, I envisioned a stack of = capacitors charged by the high-voltage source, then a rotor to ferry a = bit of charge at a time from the stack to a reservoir. The rotor would = be equipped with capacitors, and contacts would be present on each side, = so that the rotor is charged by the HV stack on one side, then connected = in parallel on the other side to deliver its charge. The rotor has to = be big enough, and insulating, so that arc-over doesn't occur at either = end of the rotor. The capacitors on the rotor have to be big enough to = deliver a useful amount of charge, enough times per second, to meet the = design current and efficiency specs.

Of course, no standing capacitor chain need be provided; the rotor can = simply mesh with series-connected contacts, providing all the = capacitance itself. Likewise, two or more rotors could be used, in = make-before-break mode, to eliminate the DC link capacitor. YMMV; a = standing cap bank would be wise for lightning collection, but = unnecessary for experiments (in either direction, step-up or step-down). = Three rotors in make-before-break would be quite suitable for supplying = a conventional (inductor based) converter, transforming, say, 1-10kV = into 1.5V or 12V or 160V, etc.

OTOH, when a capacitance is changed, work is performed. An = electrophorus works by applying force to seperate charges, increasing = the voltage. If capacitance falls linearly, voltage rises linearly, but = energy rises as voltage squared, so the energy rises linearly. The = difference comes from the work input, which by hand, feels negligible = against a 100g electrophorus. This might be confusing to perpetual = motion types, who are fond of electric or magnetic devices with forces = so weak, they seem to move of their own accord.

Tim

--=20 Deep Friar: a very philosophical monk. Website:

Note: I make the rules.

Connect an inductor across C1 until you've bled it down to half its charge. Now connect that inductor to C2 and charge it up to the same charge as C1 has. Now disconnect the inductor. If you keep the L shorted, you can save the residual energy for reuse later.

John

"John Larkin" wrote in = message news: snipped-for-privacy@4ax.com...

^ ^ ^ ^ Ha, so charge wasn't conserved after all. See? ;-)

Tim

--=20 Deep Friar: a very philosophical monk. Website:

All my cases involved controlling the charges on two capacitors. I never proposed violating conservation of energy. My point is that inductors can be useful in some situations.

John

The original suggestion came from Graeme Zimmer. He said "A constantly rotating Variable Capacitor with commutator contacts to apply the high voltage at Min Cap and then bleed off the converted charge at Max capacitance?"

Not the same thing at all.

Your "point" is, as usual, vagueness and subterfuge... and BS.

For amusement, newbies are invited to MATHEMATICALLY analyze this simple case...

Two equal value capacitors (C), one charged to Vo, the other uncharged (zero volts).

Connect together with a switch, start with a finite resistance value, analyze; then reduce the resistance, re-analyze; continue this analysis, approaching zero in the limit.

Then scratch your head in surprise... where did the energy go ?:-) ...Jim Thompson

Think nuclear battery, or lightning.

parallel. It's like an inverse Marx generator, or a synchronous C-W multiplier. How would you do it?

A *real* inverse Marx would charge a string of inductors in series, then connect them in parallel to get lots of output current.

That actually wouldn't be a bad topology for certain switching regulators.

That would work step-up, too, and avoid some capacitance problems.

Ooh, use step-recovery diodes for the opening switches!

John

Put a microcoulomb of charge on a 1 uF capacitor. Transfer it all to a 2 uF capacitor. The first state of the system holds twice the energy of the second. You can get that charge back onto the

Well, depends on words now. I can transfer "all the charge that's in C1 to C2" (ie, wind up with C1 at zero volts, and no energy lost) but the numerical amount of coulombs must change if the cap values are different, to conserve energy. I can move the charge back into C1, and return the system to its original state.

My point was that you can move charge between caps, without losing energy, but not by using resistors.

John