Hi, I am given a project assignment of building a supercapacitor LED flashlight. It is very like Michael's Ultra Cap Battery - Part 8 - Flashlight conversion. But we want to use three 2.3v 300F supercapacitor series connection. I don't know the supercapacitor. Who can tell me how to charge it. Thank you very much.

1. Use a DC power adapter (12V to 6, 9 Volts) and plug it into your car battery or any 12 Volt battery. (I charge my U-Caps this way as my 12V battery bank is solar charged. Radio Shack has Power adapters (eg. cat # 273-365) and All Electronics has them for less.

2. Solar charge it. You can get 7 Volt thin film solar panels to directly charge the U-Caps.

3. An AC to DC power supply. You might have a 7-7.5V power supply (wall wart) already (used on another device) that you can borrow for this project. (A 12V power supply could be used with the car power adapter to get 7V)

4. Use a wind-up device. I added a charging jack to a wind-up flashlight for charging my U-Caps. Wind-up radios (eg. FR-300) have a jack that can be used to charge phones or U-Caps.

Hope this helps…

Hi Michael, Thank you very much. I have the below three question.
1. If I want to charge the U-Caps full in 90 seconds. my charger output current maybe ?A.

2. Should I need a voltage balance circuit parallel with every U-Caps.

3.If my load's current is 350mA and votage is 7V, How long can I use it.

Best regards,
HT

Well, all these questions require some thought. Just to size up the situation: you'll have (when finished) a 6.9V (3 x 2.3V) 100F (300F / 3) Ultra Cap flashlight running at 350mA.

1 - My flashlight (4.6V at 25F) charges in 10 seconds on my 4.5 (max 4.75V) 2.5A power adapter so, I will guess that your U-Caps will charge in 4-6 times longer. Since you asked about 90 seconds I would alter my estimate to 7V at 2A.

2 - Maybe, a simple resister (parallel for each cap) could be used to insure that you do not over voltage them. I have not used any because of 2 reasons: I have only 2 Caps in series and I do not charge them with high amperage. I, myself, would risk going without resisters on a 3 U-Cap series flashlight only because there is only 3 and you won't hook up a 10 amp power charger.

3 - This will be subjective. If I compare my flashlight (see Ultra Cap Battery - Part 8 - Flashlight Conversion for run times) with yours in Storage to Load ratio:

My flashlight 25F / 200mA load = 0.125 S/L

Yours 100F / 350mA load = 0.286 S/L

Your flashlight looks like it will last more than twice as long as mine. But, I might see better in a darker light or your flashlight might do poorly at slightly lower voltage. How dim it can get before you think that it needs recharging is your call.

Hi Michael,

Thanks for your self-giving help. I heard 5.11 tactical's flashlight UC3.400 used three 2.3V 300F U-Caps and three 1W LEDs. It can use 2 hours actually. My friend told me that its current is 5-10mA. I can hardly believe it. How could it? My sample is finished. But my current is 880mA, and Vmax-Vmin is 7-2V. But I can only use 10min. I am very sadly.

One of the first things I did before actually working the flashlight was to hook up the U-Caps to the plus & minus wires and try the light with them. I tested the light before I actually made any changes to see how long it would run. No calculation needed.

The other thing that I did was to check the current going through the light.

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I suggest that you might find some lower power LED's that fit in the same space to replace what is there now.

The other approach would be to disconnect a few of the LED's for lower power loss. Leave them in so you can re-attach them to replace a burned out LED.

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The low current rating on newer LED's is because they are O-LED's (Organic-LED's) and have very low current draw. My flashlights have the newer O-LED's. I think that you may have a bright flashlight because the LED's are "driven" (by amperage) to shine bright. Cheer up - all these flashlights were meant for regular batteries, just think how much batteries they use.

Michael, Thanks for your help.

You might consider using a dc/dc converter for your flashlight. There are many LED driver ICs out there, or the circuit Ptemp (a user here) mentioned a while back. The February 2008 issue of Nuts and Volts magazine had an article on making LED flashlights that is worth looking at, you may be able to find it at a library or at www.nutsvolts.com