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klugesmith

Sat Mar 02 2013, 08:22PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Ash Small wrote ...
...I've also been thinking, as E=1/2CV^2, does it make more sense to connect capacitors in series, rather than in parallel? (more voltage, but less charge, but energy is a factor of V^2)

Ash, you ought to know better. The stored energy in a capacitor bank is not changed by converting from parallel to series connections, and neither is the maximum power output.
The capacitance, resistance, and inductance between the bank terminals change by a factor of N^2. One configuration or the other might be a much better match for a particular ETG bridge or coilgun coil.

It's hard to argue against experimental results.

Ash Small

Sat Mar 02 2013, 10:06PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

klugesmith wrote ...

Well, I know that 1/Ct=1/C1+1/C2+1/C3.....+1/Cn, and the equation I quoted above contains a V^2 function, and I did find it puzzling that energy is a function of V^2. I also assume that the 'C' in the equation I quoted stands for charge (C=Coulombs). I'll have to look into this in more detail.

Hanzie

Sat Mar 02 2013, 11:04PM

Registered Member #6534 Joined: Sat Sept 08 2012, 12:22PM
Location: The Netherlands
Posts: 32

I believe the 'C' stands for the capacitance in Farad. Could be wrong though.

Ash Small

Sun Mar 03 2013, 12:11AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Hanzie wrote ...

I believe the 'C' stands for the capacitance in Farad. Could be wrong though.

You could be right, but conventionaly, capacitance is expressed in terms of 'F'.

'C' generally stands for Coulombs, from what I remember.

EDIT: In the example I gave in my previous post, 'C' stands for capacitor (C1, C2, etc.).

Ash Small

Sun Mar 03 2013, 12:57AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Ash Small wrote ...

Hanzie wrote ...

I believe the 'C' stands for the capacitance in Farad. Could be wrong though.

Maxwell

Sun Mar 03 2013, 02:02AM

Registered Member #8497 Joined: Tue Dec 04 2012, 06:24PM
Location:
Posts: 74

C is most definitely capacitance in:
energy=1/2*C*V^2

C is used in electrical schematics to denote a capacitor.

DerAlbi

Sun Mar 03 2013, 04:13AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

We need seven posts so clarify that you cant charge capacitors in parallel, then wire them in series and end up with more energy than before -.-
great job.
Does someone to accompany me? I take a walk - cant stop crying about this -.-

Yandersen

Sun Mar 03 2013, 06:18AM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

Yeah, those guys need to pay a visit to school one day...

Energy of capacitor is
E=C*U*U/2,
where C is a capacitance in Farads.
The charge capacitor holds is expressed in Coloumbs:
q=C*U
When two caps are connected in series, the charge each one holds does not change - the effective capacitance becomes two times smaller. So as chain holds doubled voltage, the capacitance is halved.
Addition for curious ones:
q=C*U=I*t,
where I is a current and t is a time. I found that derivative very useful:
dU = I*dt / C
It shows for how much volts (dU) cap's voltage will change for some period of time (dt) if cap is being charged with a constant current (I).

Wizzup

Sun Mar 03 2013, 10:30AM

Registered Member #3302 Joined: Sun Oct 10 2010, 02:21PM
Location: Finland
Posts: 42

I will build a new chamber with a similar design than the old one but I will use iron rod instead of nylon, 5mm wall thickness should hold inside anything I put in there. I will post pictures and a diagram of its structure when its ready and a video of it shooting a steel projectile through some stuff :)

Ash Small

Sun Mar 03 2013, 11:17AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Sorry about the mix up. As I said, according to international convention, F stands for capacitance (Farads) and C stands for charge (Coulombs).

C=F*V

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