Ultracaps, Is this it?

[SnowDrifter]

*cracks knuckles*

[alaskanzx5]

*cracks knuckles*

that's a good answer.

everyone keep an eye out for a nice capacitor write up from snow.

[SnowDrifter]

So first and foremost: Why caps? What do caps do that batteries don't? The idea behind this is simple, but the devil's in the details.

The basics: Unlike a battery, which stores the potential to create electricity via a chemical reaction, a capacitor stores energy in a difference of electrons. Think of it like a static shock. The idea is very similar. Two main things happen here: There is no "resting voltage" of a capacitor like what you see in a battery. The voltage your give it is the voltage it will be at. Second is they have an extremely low internal resistance. Basic review on ohms law says that voltage, or in our case voltage drop is a function of resistance and amperage. Reduce the resistance and you reduce the voltage drop.

Super-capacitors are also typically lighter than batteries because of their aluminum vs. lead construction.

However, caps aren't the end-all. Their main drawback is lack of capacity. You may have seen this before: Farads. Think of a farad as 1 amp-second-volt. You could apply a 1 amp drain to a 1 farad capacitor and it would drain at a rate of 1 volt per second. Now suppose you had a 500 farad capacitor bank: You could apply a 250 amp load to the bank and it would drop at a rate of 500f/250a = 0.5v per second. They just don't have the sustained draw that batteries do, and to get the equivalent storage of a battery bank would require a LOT of caps and a LOT of money.

I'll only suggest capacitors if you have enough alternator power to supply at least 50% of your system's draw. And at that, I like to see between 100 and 200 farads for every 1000 watts of amplifier power. The ideal situation would look like this: Occasional dips at or below battery voltage. The alternator's output is exceeded sometimes, but it has enough power at other times to bring the voltage back up. All they really do is act like a buffer - they will "average" your voltage. Now if you drop to 11.9v and stay there when bumping, you'll need more batteries, alternator, or both. The only thing a capacitor will do is slow how fast you drop to that voltage.

In terms of safety, you've heard that story of someone's uncle's friend having a capacitor blow up on them.... There are two things that will pop a capacitor: Over voltage, and reverse polarity. There are ways to prevent both. And it's not as simple as you may think

The big soda-can sized capacitors we use for car audio are generally rated at 2.5 or 2.7v. That being said, most people choose to go with a bank of 6 or 7 of these in series. As a matter of personal preference (I'll explain why in a bit) I like to have a bit of leadway. Suppose your alternator normally charges at 14.6v. But on a really really cold day, it may charge at 15.3 until your engine warms up. You need to plan on having a bank that can handle at 15.3v. Lots of folks like to charge at higher voltages than what *should* be charged at. Ideally you would only need to have your alternator set between 13.8 and 14.4v. But I know we all like to push limits here. You can't do this with capacitors. If your bank is rated to 15.4v, you do NOT under any circumstances allow it to be charged higher than 15.4. Not 15.5, not 15.42, but 15.4.

Remember when I said I like to have a bit of leadway on the bank? That's because capacitors are built to a 10% tolerance. Some may have a bit more capacity and as such, charge up slower than the others. Some may have a bit less and as such, charge faster. If you have a weak cap, or several in your bank, and you charge to your absolute maximum bank voltage, you can actually overcharge these. I'll use myself as an example: My own bank consists of 7 pairs of caps in series for a max bank voltage of 18.9v. But I only ever take it up to 16.6. Keep in mind I run 14v not 12v

In an effort to keep the capacitors reading roughly the same voltage, you need some sort of balancing circuit. This will equalize the voltage between the various capacitors, reducing the chance of one of them encountering an overcharge condition. The easiest way of doing this is to use resistors. 1 resistor across the positive and negative of each individual cap in your bank. Idea behind this being that capacitors of a higher voltage will be discharged by the resistors at a higher rate than capacitors of a lower voltage. This is the method I use and it works very well. It's simple too Only drawback is there is a slight parasitic draw with this approach, but it doesn't become an issue for me unless my car sits for 5 days or longer.

Rule of thumb for these resistors: Take the specified leakage current of your capacitors and multiply that value by 10. Ex: If my caps are spec'd out at 5.4ma leakage current (basically self discharge) I'll want to pair them with a resistor that will draw 54ma. Ohms law for calculating resistance is that R=E/I, where R is resistance, E is voltage, and I is current in amps. In my case: Each capacitor has a theoretical voltage of 16.6v/7caps = 2.37 volts per cap. I say theoretical because that assumes they are all perfectly balanced. Now knowing my capacitor's voltage and calculated current, I can plug that into my equation to find the resistance. Remember that the conversion from milliamps to amps is to divide by 1000

R = E/I, E = 2.35v, I = .054a

R = 2.35v/.054a

R = 43.5 ohms.

I can round this to 50 ohms. So each capacitor would need it's own 50 ohm resistor to keep the whole bank balanced. Make sure you buy 1% tolerance resistors, not 10% ones like you'd find at radioshack. That tolerance can actually mess up what we are trying to accomplish. A good resource for these is mouser.com

Final thing: You can't just hook a bank up to your car and be done with it. It needs to be charged first, and charging a bank from 0v is a bit like trying to charge a short circuit. It will behave that way if you tried to hook it up to your car. SPARK. Easiest way I've found is to go to the auto parts store and grab a light from a turn signal or something. Wire the turn signal to some wire, put one end on the positive of your battery, and the other end on the positive on your cap bank. Then wire the negative of your cap bank to the negative of your battery. No need for a bulb inline here, just a plain wire.

Let it sit overnight or so, or until your bank voltage is at least 12v. Then wire it up and go! Of note: A lot of people will get hung up on where to wire their capacitor for best performance. To be honest with you: These are big enough, just treat these as a battery and wire accordingly. Only exception is there's no need to fuse a cap bank. Unless you are building a massive bank, the time it would take a fuse to blow would exceed the discharge time of the bank.

[SnowDrifter]

And if you have any more questions or need specifics/clarification I'm happy to answer

[SLAYER1805]

I've been interested in using caps for my legit build when it happens to keep the weight down in my grandpa car since it's gonna be slammed on coils and wanna keep the ass end from scraping as much as possible

But this is me right now lol

[SnowDrifter]

Hahahahah!!

Oh and folks: I know a lot of us on here are on the younger side. I know some people have trouble approaching someone older and asking stuff. I'm 19, around the same age as many of you on here, so don't be shy. Seriously, any questions, ask away! I'd rather clarify something now than have you get frustrated or blow something up later. Caps are a different ballgame, yes. Lots of new things to learn and consider, but they can be lots of fun when you "nail it"

[Bump4life]

very good write up snow drifter.

only thing im gunna disagree with is when you round up to 50 ohms. with the blue 2.7 volt caps you want a lower value resistor. Im at work right now so i dont have all my calculations in front of me but, with the 50ohm resistors, they didnt seem to balance the circuits fast enough. at least from my testing. this was on the old black caps. but with my new calcs, i found the optimal to be a 27 ohm resistor. ill double check that number when i can, but i spoke with the engineer at maxwell and he double checked everything for me and said I was spot on. also gave me some cool ideas.

stay tuned though, im leavbing batteries in the past and running nothing but caps. we will see how it works.

ill come back with more info as soon as I have it.

[SnowDrifter]

I'm used 50 ohms for mine and they all read within +/- .01v of each other. Also as per maxwell's recommendation. Playing around with 200 ohms right now. I have the newer blue ones

I'll also say this: The lower the voltage of each individual capacitor, the more headroom it has, the less aggressive balancing circuit you need. Something to keep in mind

[alaskanzx5]

And that of some great info. Its to bad caps are to expensive

[TheMonolith2001]

Holy shit, I love this. Seriously hit me with wall after wall of tech info. I love reading this stuff and soaking it up. I feel like I go over people's heads sometimes so I love being taught things. I have had quite a bit to drink to be honest so I will give all this a thorough read tomorrow and get back with you. I want to install some type of capactor system in my Jeep and I am trying to decide what is right for me and my setup. It may appear I am just jumping into this but I have been researching capacitors for quite awhile now. I should be able to understand most words you use