Turning Capacitors into Batteries.

[Ronald_raygun]

OK, before people start jumping on this thread and saying that capacitors aren't allowed in FIRST, allow me to tell you that YOU ARE RIGHT. Capacitors are not allowed on FIRST robots.

If you search www.hackaday.com with the term "supercap" you find a post about a capacitor turned into a battery.

How can I do this? I'm trying to recreate it myself and am having trouble doing so.

I know there is obviouisly the capacitor involved, along with some sort of voltage regulator. But aside from those I'm stuck.

[NeedMoreEngines]

I...I guess you could do this if you really wanted to.

you'd have to find some way to access and regulate all the energy that is stored in the capacitor. it's gotta be too dangerous though, because all the current stored in a capacitor is just SHAZAM...you could get fried.

but why would you want to do this? come on man, we got like 5.54 weeks to build this thing...stay focused.

[Kevin Sevcik]

Ummm.. That's pretty much it, you're done. The capacitor would provide some (presumably large) voltage. The regulator would knock it down to a constant voltage. The only other thing you'd need is a DC power supply to charge up the capacitor to whatever voltage is safe or it's rated for.

The regulator should probably be a switching regulator. A Linear regulator is just going to dump all the extra voltage as heat and waste it. Of course linear regulators are cheap and easy, so you could use one as a proof of concept.

As for dangerous.... The cap is only dangerous if you short it. As long as the thing's hooked up properly it's plenty safe. Just treat it like you would our motorcycle battteries. They're just as or more deadly if you drop a wrench across the terminals. Saying it has a lot of current capacity so it's dangerous is like saying your bathroom faucet might drown you because it's hooked up to a gigantic reservoir somewhere. It's only going to happen if the faucet on your end is big enough and opened enough to drown you.

[EricVanWyk]

Instead of using a linear regulator, I would recommend using a buck/boost regulator. These switching regulators can achieve efficiencies of up to 96% (and theoretically they could be perfect if all the parasitic impedances vanished). What is even cooler is that it allows the super-cap to operate across a range of voltages that can be LOWER than your desired output voltage.

Basically, this would take energy from the super-cap and push it into a normal capacitor. The regulating chip would monitor the secondary cap's voltage and squirt just enough current to it through an inductor to keep it at the correct voltage. The inductor smooths things out so that even though you are giving it pulses of current, the voltage is relatively smooth.

I didn't get into enough detail to really understand the circuit, so take a look at the following link if you are interested.

http://en.wikipedia.org/wiki/Buck-boost_converter


For construction, picking a part really depends on your input voltage, output voltage, and current. TI, Linear and National all make really nice buck/boost regulators. Personally, my favorite is the TPS63000.

Also, if you _know_ that your supercap will always have more voltage than you need, use a buck regulator. If you know it will always have less voltage, use a boost regulator.

[Al Skierkiewicz]

Electronics people have been using capacitors as batteries for many years. For instance, low current devices can be powered by a large capacitor for a really long time. It was quite common for VCRs to have a large capacitor in the clock circuit or tuner memory so that people would not have a hard time resetting the VCR after a power failure. The interesting thing was that a 1 farad cap at 5 volts was only about the size of a stack of dimes, smaller than a small NiCad pack and no hazardous materials.

[Al Skierkiewicz]

As I was looking for some caps for a project at work, I saw that Digikey has a whole section on these caps from a variety of menufacturers with listed mAHr. ratings.