capacitor charging

Thread Starter

clark.kent156

Joined Aug 17, 2019
50
question: can you use a 12v wall wart plugged into an outlet at home to charge a 12v audio capacitor? cant seem to find any useful info on this?
 

Ya’akov

Joined Jan 27, 2019
9,265
What are you trying to do? Why do you want to charge a capacitor?

The answer as it stands is “maybe”. Without knowing the goal and the specifications of the power supply and the cap, that’s the best you can get.
 

Thread Starter

clark.kent156

Joined Aug 17, 2019
50
just a little experimenting. drill with 6 inch disk on the end with magnets spinning close to another disk of coils, like for diy wind generator. the coils are rectified for dc, and can easily enough generate 12vdc. I have this car audio capacitor, 12v 1F. wondering if the little setup would charge it? in car environments, they charge them up first before install using the car's battery along with a test light or resistor. I assume this is to reduce the flow of amps as to not damage the cap. If it was very slow charge, wondered about the wall wart plug.
 

MrChips

Joined Oct 2, 2009
31,088
just a little experimenting. drill with 6 inch disk on the end with magnets spinning close to another disk of coils, like for diy wind generator. the coils are rectified for dc, and can easily enough generate 12vdc. I have this car audio capacitor, 12v 1F. wondering if the little setup would charge it? in car environments, they charge them up first before install using the car's battery along with a test light or resistor. I assume this is to reduce the flow of amps as to not damage the cap. If it was very slow charge, wondered about the wall wart plug.
It is not to prevent damage to the capacitor. It is to avoid starting a fire. An uncharged capacitor appears as a dead short.
Hopefully, you have never and will never short a car battery.
 

Ya’akov

Joined Jan 27, 2019
9,265
just a little experimenting. drill with 6 inch disk on the end with magnets spinning close to another disk of coils, like for diy wind generator. the coils are rectified for dc, and can easily enough generate 12vdc. I have this car audio capacitor, 12v 1F. wondering if the little setup would charge it? in car environments, they charge them up first before install using the car's battery along with a test light or resistor. I assume this is to reduce the flow of amps as to not damage the cap. If it was very slow charge, wondered about the wall wart plug.
As @MrChips says, an uncharged cap starts out looking like a dead short. So long as you can supply any current at all at a voltage higher than the current voltage of the capacitor it will charge until it reaches its rated voltage. But charging it to overvoltage can damage it.

There are two questions for you. First, have you tested your generator under load. The short circuit output may be nowwhere near the open terminal voltage. Second, can it under load produce a higher voltage than 12V? If so, you can potentially damage the capacitor if you don’t edit her limit the output of the e generator to 12V or provide a cut off mechanism for the capacitor to stop the charging when it reaches its rated voltage (probably at least 13.8V since it is intended for car use).
 

Thread Starter

clark.kent156

Joined Aug 17, 2019
50
you are correct. under load, the voltage drop way down. I can use a multimeter and that it does charge, just super slow. any solutions?
 

MrChips

Joined Oct 2, 2009
31,088
Let's do the math.

Charge Q on a capacitor C is given by
Q = C x V
where,
Q = charge in Coulomb
C = capacitance in Farad
V = voltage in Volt

Thus it would require 1C of charge to charge a 1F capacitor to 1V.
It would take approximately 1 second of 1A to bring the voltage up to 1V.

A 12V source feeding a 12Ω resistor in series would charge the 1F capacitor to about 12V in about 1 minute, about five times RC seconds.
 

MisterBill2

Joined Jan 23, 2018
19,461
Finally the explanation that the "Audio Capacitor" is actually a 12 volt application one farad capacitor. Probably it is intended to provide a low source resistance in the supply of an automotive sound system power supply.
So the short answer is that a small transformer type wall wart power supply will charge it eventually in a safe manner.
BUT first use your multimeter to verify that the output voltage of that small wall transformer is not above the maximum allowed voltage for that one farad capacitor. Probably it will be higher if there is no load.
And don't use a wall wart rated for much current, 500 milliamps or less is the best choice. And know that it will take several minutes the first time.
 

Thread Starter

clark.kent156

Joined Aug 17, 2019
50
So, turns out, aside of charging a cap with this setup, "anything" so far I attach as a load drops the volts way down. So, open circuit with NO load, meter reads about 25vdc. (The volts from the coils is rectified.) LED, resistor, ic reg, whatever is attached, bring the volts down to 5ish volts. What am I looking at here? This is just a fun little experiment. I'm not opposed to using boosters, transformers or whatever. Let's have your input. Thanks guys.
 

MrChips

Joined Oct 2, 2009
31,088
So, turns out, aside of charging a cap with this setup, "anything" so far I attach as a load drops the volts way down. So, open circuit with NO load, meter reads about 25vdc. (The volts from the coils is rectified.) LED, resistor, ic reg, whatever is attached, bring the volts down to 5ish volts. What am I looking at here? This is just a fun little experiment. I'm not opposed to using boosters, transformers or whatever. Let's have your input. Thanks guys.
Resistance.
The resistance in your source is too high.
What is your source?
 

Thread Starter

clark.kent156

Joined Aug 17, 2019
50
The experiment: Drill with 7 inch disk on the end with neo magnets, spinning close up to a stationary disk of coils of 22awg magnet wire. This is AC. Diodes on the coils rectify it to DC. With a multimeter connected, the open circuit voltage is 25v ish. It's rectified, so it's pulsed. I want to ad an low volt ic reg to this, and when anything is connected, it drops to 5ish volts. Pretty much the setup so far. I want to regulate the voltage out to steady it, then see how much I can step it up, using boosters, transformers, or whatever does the job. See what can become of it.
 

MisterBill2

Joined Jan 23, 2018
19,461
The performance of a component operated beyond it's ratings is not specified, and may include permanent damage. This is an unfortunate reality.
In this instance it happens that the impedance of the generator is quite high and so the voltage drop with any current draw is also high.
 

DickCappels

Joined Aug 21, 2008
10,246
You have to choose a trade-off. The smaller the capacitor the less energy is needed to charge the capacitor. But there is less energy stored in a small charged capacitor than in a large charged capacitor.

It boils down to only being able to get out almost as much energy as you put in.

To charge a bigger capacitor faster you need a generator with more output power.
 

Thread Starter

clark.kent156

Joined Aug 17, 2019
50
I'm wondering if the coils should be modified, like bigger awg wire, turns, etc. People do it all the time with home built wind generators and they can get good output.
 

DickCappels

Joined Aug 21, 2008
10,246
Maybe more in the direction of stronger magnets closer to the coils with iron plates to shape the fields from the magnets would help, but it may not be worth the effort. Even if you double to output current it would only cut the charging time in half while making it about twice as difficult for the vanes to turn... so that leads to thoughts of a larger blades.
 

MisterBill2

Joined Jan 23, 2018
19,461
Given that this was an experiment to learn, I suggest moving on, now that the lesson is learned. At least, I am guessing that the lesson is understood. The math to back up the results is clear, which is that all resistance causes a voltage drop proportional to the current flow, and also that current will flow to charge a capacitor. The generator portion proves that a changing magnetic flux passing through a conductor will produce a voltage.
So now that these are verified it is time to move on.
 

Audioguru again

Joined Oct 21, 2019
6,784
Why are you Building an electric generator that barely produces any current?
Use a DC electric motor instead of making it.

When you apply a load such as your huge capacitor to a motor as a generator then it will be difficult to spin the motor armature until the charging current produced by it is reduced.
A motor designed to use a low voltage should be used as your generator because to generate 12V it does not need to spin as fast as a motor made for 12V.
 
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