Concept Presentation
I want to power a 100 W (36 V) LED using a 2.7 V, 100 F supercapacitor. I'll put the capacitor, circuit and LED in an aluminium box, connect them to a central power source using mil surplus 2-lead wire to charge them and then wait. The idea is to use it for illuminating an area for a short time, at a low cost and relatively low weight.

So I need to design a circuit that takes the input voltage decreasing from 2.7 V and automatically boosts it to 36 V. Either that or find an existing circuit that does this on a student's budget.

Purpose
Feral hog hunting. They're an aggressive invasive species, the situation here in Sweden has gotten so bad we're now allowed to hunt them with artificial lights. This construction would allow a large area to be lit for a low cost.

Advantages

• Practical: The supercapacitor can be charged slowly using fairly thin, cheap double leads over distances in the 1 Km range. This means that several of these can be placed in advance, charged and then turned on by the hunter.
• Price: Cheap batteries burst when it gets too cold. Cheaper supercapacitors don't. Really expensive batteries also work, but the price is a problem.
• Weight: Frost resistant batteries capable of delivering that power at -20 degrees c (- 4 f) are rather heavy, meaning I can't carry as many of them with me on each walk from the watch tower.

Issues
Very low varying input voltage. The capacitor I intend to use has a maximum voltage of 2.7 V. The LED requires 36 V constant.
There are many circuits that boost DC-DC, a few that can compensate for varying input voltage but none that deal with voltage differences this great.

Question
Where should I look for information about designing a circuit that boosts DC voltage automatically to a pre set level while the input voltage drops steadily
from 2.7 V?

Which general type of circuit would you recommend?

If you point me in the right direction? I'm sure I can solve it, but I can't find a good starting point.

Any input appreciated, I will post progress repports here when I have something interesting to repport.

--------------------
Personal background and experience level
Studied an introduction course to analogue electronics at my university. Other than that I'm a self taught hobbyist with basic understanding and skills. This is part of my problem, I don't know where to start. When I know where to start I can read up on the designs, test it and finally make a PCB.

 

A 100F 2.7V super capacitor will not run a 100W LED for long at all. Maybe a second or two if that, if you are lucky. It will run at almost 40Amps minimum when fully charged. And as the charge drops, the current will go up. Then you would have high losses in the boost converter running at that low input...
To run it on super caps, you would have to have MUCH more than 100F, and preferably higher than 2.7Volts.
Even running on a 40AH 12V car battery you may get 4 hours from it.
I'd look at other than super caps or drastically lower the LED power.

 

I feel kind of stupid now. I'll look at other solutions. Thanks.

 

A 100F capacitor charged to 2.7 volts stores 2.7V * 2.7V * 100F / 2 = 364 Joules of energy, or 364 watt-seconds. This would drive a 100W LED for just over three and a half seconds, IF you could somehow take every last bit of that stored energy and deliver it to the LED. And you can't.

No can do.

 

I question your range. Can these hunters actually make a kill shot over this 1 km range?

I'd put my money into larger gauge wire and run the whole thing off 36 volts to begin with. You may want to keep the boost converter to top off any line drops.

Or even better, run this off a higher voltage with a buck converter on each LED. 100W at 36v is about 3 amps... run the system off 360 volts (probably too high but easy numbers for an example) and you only need supply .3 amps. That can use smaller gauge wire for the same drop.

Happy hunting!