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Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
Hi I'm trying to wrap my head around capacitors discharging. If i have a cap(1 F) in a dc circuit at 100volt/1 amp, if i disconnect the power quickly(1 sec) will the cap discharge 100 amps to the negative terminal.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
Well, first of all I assume this is hypothetical, since 100V at 1F is a pretty big capacitor at 10kJ (although it's not entirely impractical, maybe a series of supercaps if you want to make it, although balancing them can become difficult depending on the load and charging).
What happens when you disconnect the power supply briefly is the capacitor begins to discharge. It will follow the capacitor component law of I=C*dV/dt, so at 1A for a 1F capacitor, dV/dT = 1, so the capacitor will drain at 1V/second (at least near the beginning of the discharge when the curve can be linearized). So after 1 second, the capacitor will have roughly 99V left on it. For longer time periods, you would need to solve the differential equation since the linearized estimate would fall apart.
Registered Member #4266
Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874
thanks for the reply I was thinking about this circuit. If I turn off the switch and the TC is 1 sec , 100amps would flow, even though v1 is 100v/1 amp? The bit i'm not sure about is if the amps would increase
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
If you have a 1F cap charged to 100V then no current will flow until you attempt to change the voltage on the capacitor. If you just disconnect whatever power supply charged it up to 100V then nothing will happen, the capacitor stays at 100V and no current flows.
I'm not sure what's connected where in your schematic, if you put it inside [ code][/code] tags then the spacing that displays should be the same as the spacing you put in originally.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
That circuit will slowly bleed the capacitor when you open the switch. If C1 is at 100V and R1=100Ohms, it will drain at 1Amp (at least initially) and will follow the description in my previous post. The only way it'd drain at 100 Amps is if R1=1ohm with C1 at 100V.
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Capactor discharge amps in a dc cicuit
