Real time capacitor voltage

Momentory

Joined Sep 4, 2022
86
I have a simple circuit

- capacitor 15v - 1000uf
- coil of enamelled wire

If i set the battery to 12v so the capacitor will be charged 12v, then i decide to low the voltage of the battery to 4v then the capacitor will take time to get 4v

My target is get the same voltage of capacitor as same as the battery at once( real time) so if the battery is 12v so the capacitor is 12v, if the i low the voltage to 5v so the capacitor instant be 5v

Could be this done?

crutschow

Joined Mar 14, 2008
32,903
The capacitor will go to whatever voltage you set the supply to, but not instantly.
The time to get there is determined by the output-resistance/current-rating of the supply.
So what supply will you be using?
What is your purpose in doing this?

Momentory

Joined Sep 4, 2022
86
The capacitor will go to whatever voltage you set the supply to, but not instantly.
The time to get there is determined by the output-resistance/current-rating of the supply.
So what supply will you be using?
What is your purpose in doing this?
dc solenoid
Yes is the problem i want it to be instant adjustable

WBahn

Joined Mar 31, 2012
29,164
The short answer is no, you can't get the voltage of a capacitor to change instantly -- doing so would actually violate the laws of physics since the energy stored in a capacitor is a function of the voltage across it and since energy can neither be created nor destroyed, the capacitor voltage can only change as fast as the energy stored on it can be moved elsewhere.

What is the actual problem you are trying to solve? What is it that you are trying to accomplish with this circuit? What is the purpose of the switch and inductor?

Momentory

Joined Sep 4, 2022
86
The short answer is no, you can't get the voltage of a capacitor to change instantly -- doing so would actually violate the laws of physics since the energy stored in a capacitor is a function of the voltage across it and since energy can neither be created nor destroyed, the capacitor voltage can only change as fast as the energy stored on it can be moved elsewhere.

What is the actual problem you are trying to solve? What is it that you are trying to accomplish with this circuit? What is the purpose of the switch and inductor?
I am trying to make a solenoid
According to the voltage the solenoid kick will be stronger or less

If i set the voltage to 12v and did not click the switch to release voltage to the coil and changed my mind to make the voltage 5v instead of 12v, so i will low the voltage supply to 5v and here begin the problem
"I do not want to wait till the voltage of capacitor go down to 5v"

drjohsmith

Joined Dec 13, 2021
789
I am trying to make a solenoid
According to the voltage the solenoid kick will be stronger or less

If i set the voltage to 12v and did not click the switch to release voltage to the coil and changed my mind to make the voltage 5v instead of 12v, so i will low the voltage supply to 5v and here begin the problem
"I do not want to wait till the voltage of capacitor go down to 5v"
how about putting a load across the capacitor, say a resistor, which dumps the charge,
you could even fit it into a switch system, so switch in one position alowed voltage to be changed , with load, in other dumped capacitor into the coil..

Papabravo

Joined Feb 24, 2006
20,385
I am trying to make a solenoid
According to the voltage the solenoid kick will be stronger or less

If i set the voltage to 12v and did not click the switch to release voltage to the coil and changed my mind to make the voltage 5v instead of 12v, so i will low the voltage supply to 5v and here begin the problem
"I do not want to wait till the voltage of capacitor go down to 5v"
Tough rocko's. If you have the capability you might want to examine the mathematics behind RC and RL circuits. If you were to do that you might have a better chance to approach the performance, you desire without throwing spaghetti onto the wall to see what sticks. Your present approach is doomed to lead to disappointment.

If the mathematics is too difficult for you then using a simulator might be a viable alternative.

ApacheKid

Joined Jan 12, 2015
1,268
What is this "adjustable voltage battery"? can you tell us exactly what you have? two batteries? a power supply with two voltages? how about a photograph?

Last edited:

ElectricSpidey

Joined Dec 2, 2017
2,593
If you charge a 1uf cap to 12 volts then change the voltage to 5 then push the button...the solenoid will not even notice the 12 volts because the time it will remain at that level will be very short.

Different story perhaps if you use a much larger cap.

Papabravo

Joined Feb 24, 2006
20,385
If you charge a 1uf cap to 12 volts then change the voltage to 5 then push the button...the solenoid will not even notice the 12 volts because the time it will remain at that level will be very short.

Different story perhaps if you use a much larger cap.
That is kind of what I implied by suggesting a familiarization with the mathematics behind such circuits. It is hard to see what is happening based on intuition alone.

LowQCab

Joined Nov 6, 2012
3,454
There is no need for a Capacitor, unless your Power-Supply is very weak.
Why does the "Pulse" to the Solenoid need to be adjustable ?
.
.
.

WBahn

Joined Mar 31, 2012
29,164
I am trying to make a solenoid
According to the voltage the solenoid kick will be stronger or less

If i set the voltage to 12v and did not click the switch to release voltage to the coil and changed my mind to make the voltage 5v instead of 12v, so i will low the voltage supply to 5v and here begin the problem
"I do not want to wait till the voltage of capacitor go down to 5v"
How long does it take for you to change the voltage from 12 V to 5 V? How long after you change the voltage to 5 V to when you "click the switch"?

I can almost guarantee you that either of those is more than long enough for the capacitor to stabilize at the new voltage?

What is the purpose of the capacitor to begin with?

"Trying to make a solenoid" is not very descriptive of the problem you are trying to solve. What is the purpose of this solenoid?

MisterBill2

Joined Jan 23, 2018
15,654
First, this is not really a valid inquiry because we are given only a bit of information. So really any detailed attempt to answer is a waste of effort. A lot more explanation is required as to just what is really wanted. So here is a answer without details:

The solution is to use a power supply that can both sink and source current. The TS will need to purchase that device because of being unable to design it. That could be as simple as a supply with a shunt regulator.

But if the actual requirement is "instant adjustment" then the TS is simply out of luck, because that does not happen.