Danny left a comment about powering a 12V, 3 Amp LED light with super capacitors. He asked for my thoughts on this. I’ve made higher power Joule Thiefs and I’ve tried to power several things with super capacitors and although my experience with this isn’t as extensive as my experience with JTs, I think I should be able to give some words of wisdom.
First off, 12V and 3A is 35W according to Danny, and that’s a whole lot of power. I have charged the Maxell 2600 farad Boost Caps with a 2 Amp supply and it takes a few tens of minutes at 2A. If the current drain is 3A, it probably won’t last even that long. Also, if the supply uses 350 farad caps at 6 dollars (U.S.) each, it will take 7.5 of those to make a 2600 F capacitor. That’s about $45.00, so if you can get the Maxell 2600 F caps for less than $45 each, then you can save a lot of money and space (each 2600F cap is about the size of a 12 ounce soda can, not counting the studs on the ends). I bought some used ones a year or so ago for ten dollars each but they are going for more than that now. You can buy the 3000F caps new, but the prices are much higher.
If you connect five of the 2600F 2.5V caps in series, you have a 520 F equivalent at 12.5V. This will give you less run time but you will need no other electronics – no Dc to DC converter, Joule Thief, etc.
As you might have suspected, it will take ten or twenty of these capacitors to make a large and heavy power supply that has enough capacity to run your light for a reasonable length of time. This is going to cost hundreds of dollars, so it would probably be more economical to buy a 12V sealed lead acid ‘motorcycle’ battery instead for a few tens of dollars.
I would have thought the volt v current discharge characteristics of a capacitor make it very unsuitable for a power LEDs unless there is an active power supply to keep some current flowing / regulated as the voltage drops, unless of course a flash is all that is required.
That’s what I thought until I bought a few of the Maxwell 2600 farad capacitors. Let’s say you have a 2200 uF and a 390 uF capacitor in parallel. You charge them up to several volts and you connect a LED and resistor to it. The LED glows brightly for a few seconds and then it starts to slowly dim.
The Maxwell 2600 Farad capacitor has a million times more capacitance than the above, so if you draw the same amount of current it should take a million times longer to dim. Probably about a month or so, depending on what you use to convert the 2.5V to the LED forward voltage. If you use a video camera and take a frame every hour and speed it up to 30 frames per second, then the 2600F capacitor’s discharge would be visible. But like the hour hand of a clock, the 2600 farad discharges so slow that we don’t notice it at our normal speed. It just acts sort of like a battery.