# Designing a capacitor bank

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1. Feb 20, 2016

### mike younes

im stuck on figuring out how to design a capacitor bank
i have nothing to start with, its part of a project, and i want its input to be 12v (storage).

im trying to google capacitor banks and trying to simulate my own using pspice but i keep getting floating nodes and missing resistors or inductors that are not used in most capacitor banks online.

to design the bank is all i need, so i can build it later

Thanks

2. Feb 20, 2016

### BiGyElLoWhAt

So, basically just a battery? What kind of power do you want? That's the only thing I would see using a resistor for. You need to be more specific if there are specific applications that you have in mind. There really isn't much to a capacitor bank.

3. Feb 20, 2016

### mike younes

basically yes a battery. im not really experienced in the field. i want the bank to be such that it takes 12v input. so what i need to know is just how to place the capacitors and what capacitances they must have. when simulating using pspice, the simulation is not running, i dont know whats wrong in it. i wanted to do a trial and error until i get an output of 12v. im not sure im doing this right. any help is greatly appreciated.

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4. Feb 20, 2016

### BiGyElLoWhAt

I'm not sure what purpose the inductor or resistors are serving.

Essentially, a capacitor bank is just a bunch of capacitors in parallel, and how many and what size is determined by your output, not your input.

5. Feb 20, 2016

### BiGyElLoWhAt

So what are you looking in your output? That will determine any resistors, and also how many capacitors and what size. How much energy do you want to store? How much Power does your output need? etc.
Notice the output. You can charge pretty much any capacitor up to 12V using the input. q=VC, so q/C=V. Capacitance (C) is a constant, so the amount of charge is what changes with the Voltage.

6. Feb 20, 2016

### BiGyElLoWhAt

I suppose looking at the image, not sure how your program works, above c2 and c3, there's a break in the line, as well as to the left of r3 and the inductor, underneath r2, underneath v1, to the right of r1, above r4, I think that's it. I could have missed something. Perhaps that's where the errors are coming from.

7. Feb 20, 2016

### mike younes

i just need it to output 12V efficiently, nothing more. i was trying to use trial and error in pspice to get this but the simulation is giving me errors.

8. Feb 20, 2016

### BiGyElLoWhAt

Then just use capacitors, nothing else. How long do you want it to output 12V for? Use that to determine the size of the capacitors. Do you calculus?
As for the errors, you don't have a single complete loop in that whole circuit.

9. Feb 20, 2016

### mike younes

should i add resistors in series with the capacitors in the circuit for it to work?

10. Feb 20, 2016

### mike younes

this is what i have now after connecting all dots right

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11. Feb 20, 2016

### BiGyElLoWhAt

Depends on what you want. Capacitors in Series will let you ramp up the voltage, whereas capacitors in parallel will let you get a lot of current out of it. Also, you're only inputting 2V? Even if you ramp that up to 12, you're going to have a Voltage drop across R5. With a circuit like this, I would have to analyze it. I can't intuitively tell what it's doing. So you're going to have a voltage across the capacitors of $2V - I_{battery}R_5$

Is this an introductory electronics course?

12. Feb 20, 2016

### mike younes

yes it is. my problem is just that i cant simulate the circuit. maybe theres missing resistors in series or in parallel with the capacitors?

13. Feb 20, 2016

### BiGyElLoWhAt

I don't really understand. What are you trying to simulate? Just the V_out?

Try something like this:

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14. Feb 20, 2016

### mike younes

yep, thats what i need most in a capacitor bank right?

15. Feb 20, 2016

### BiGyElLoWhAt

Depends. Sometimes you want V out, sometimes you want I out. Either way, I think you're over-complicating the assignment. The inductor, I assume, is so sort of "even out" the V_out? The only resistor that I would deem necessary in your given setup is R4. R5 just drops voltage across it. That's all it does. Same with R7. I would Ditch R5 and R6, including the entire branch that R6 lies on.

Let me ask you this, why are they there? Is it just part of trial and error?

16. Feb 20, 2016

### rbelli1

Are you looking to get 12V out of a 2V input? If so then you need a lot more than passive components.

BoB

17. Feb 21, 2016

### mike younes

hey bob. im trying to design a bank that will output a voltage of 12v so i can use it to recharge a laptop.
to simulate this bank, im trying to use an input of 2V since the 2 volts are divided over the first 2 resistors to give me back 1 single volt on the 2nd resistor.
is this a correct way to proceed?

18. Feb 21, 2016

### mike younes

test

19. Feb 21, 2016

### BiGyElLoWhAt

That would work. You need really high capacitance. Really high. Otherwise it'll just discharge at once.

20. Feb 21, 2016

### rbelli1

To get energy out of a capacitor you need to put it in there in the first place. If you have no switches and your source is 2V you can get the capacitors charged to at most 2V.

BoB