# Rate of change of voltage over time?

Discussion in 'General Electronics Chat' started by vead, Aug 17, 2016.

1. ### vead Thread Starter Well-Known Member

Nov 24, 2011
712
11
Hello
I am not sure the examples, that I am taking is correct. I have taken values just for my understanding. Example:Capacitor is connected to 20 V battery. Voltage of capacitor increase or decrease at the particular movement of time. I want to find out voltage across capacitor at any moment of time

From the graph, it can be seen that voltage before 5 second will less than 20 V and voltage after 5 seconds will less than 20 V.

How to find out voltage at specific time?

2. ### Marley Member

Apr 4, 2016
252
61
Of course it depends on the resistance of the 20V source.
See this. Not sure why your graph goes back to zero?

If the source has a reactive impedance it gets a lot more complicated!

I'm sure there are mathematical geniuses out there who can give you a formula for that!

3. ### AnalogKid AAC Fanatic!

Aug 1, 2013
7,089
2,002
Your charts are not correct for a capacitor connected to a battery. A battery will charge the capacitor up to the battery voltage. The capacitor voltage will then sit there until the capacitor is disconnected from the battery.

There are two common equations for determining how a capacitor's voltage changes with time. One is based on the capacitor being connected to a constant voltage source through an impedance. The other is based on the capacitor being connected to a constant current source.

ak

4. ### MrSoftware Senior Member

Oct 29, 2013
1,145
334
Strictly from a math point of view (assuming you have data and don't care that it came from electrical components), then this thread covers creating an equation to fit the line pretty nicely:

http://math.stackexchange.com/questions/121212/how-to-find-curve-equation-from-data

When you have real data, and you figure the equation for the curve, then you should be able to plug a time into the equation and come out with an approximate voltage for that time.

Last edited: Aug 17, 2016