Idea for light

[aardvarcus]

Hello all, I have never made a "real" flashlight before and have been been thinking about making my own to replace the "wal-mart" brand type lights I own. I am limited on funds, so i can not afford to buy a nice light. Here is my idea- A moderate bank of led's on resistors for the light, and capacitors to store the power. I would use a large bank of cap's to store enough power to run the thing. I would have a wall charger to quickly recharge the caps to full power, so i could use it, charge it for a little bit, and go right back to using it.

Questions-
-Will this work? Is using banks of capacitors reasonable?
-Are there any special components i need to use when hooking the capacitor to the led's? (besides the appropriate resistor).
-What things do you look for when buying led's? I know you wan the light not to spread out very much or it will be way to dim.

 

[aardvarcus]

Update- I have drawn a simple schematic of what i had in mind.
Expected Capacitance=10-20F
Expected Resistance=500ohm
Expected Led's=White 3.3v, 20ma, 12degree angle.

I would mount it all in a pvc pipe and would use a power supply or car lighter to recharge the caps.

 

[jeffosborne]

Capacitors have come a long way, the max capacitors I have seen for memory backup applications are large capacity and small in size. I think your LED's should be in series, say 3 in series, so the drop from 12v across your resistor to 3.5v is not so great. Less watts lost on the dropping resistor, and more efficient for your battery, er, I mean capacitors. Do you have any particular capacitors in mind? Cheers, Jeff O.

 

[TigerhawkT3]

Sorry to rain on your parade, but buying enough capacitors (and a driver to handle them) for a reasonable light would definitely not be cheap. Supercaps the size of a C cell are about $20-30 each, with a minimum order of $75. Cheap capacitors probably wouldn't hold enough power to run the light for a reasonable amount of time.

For a cheap, long-running, efficient light, I'd recommend something like this.

 

[ktronik]

Well I have make some thing like that... a super cap based light that gets recharged from my dyno hub...but I am always re-charging the caps as I ride...

Dyno-Batt: A portable power supply system for dyno hubs

but what TigerhawkT3 said is right... super caps are not batterys just yet...

even with 4 series wired 55F super caps (fully charged) I get only 2.5min @ 350ma before the driver shuts down... & that is using the 'step down' driver to do the work converting down from 10v... with resistors you would have no hope...

Unless you are doing it for the fun of it...or run one 5mm LED... you will pay way to much for almost zero runtime...hey give it a year & try then...

best

Ktronik

 

[aardvarcus]

Hmm- Using 8*2.2F Caps (12V) pulling 12v @ 20mA per series run of 1 resistor and 3 led's, Ohms law, R=(V/I)=600ohm. For three runs, 600 ohm's each in parallel (9led's=1,170,000mcd) R=200ohm. Time Constant of RC circuit=58.67 minutes until 33% of charge is gone so approx 30 minutes till half of charge is gone.

8*2.2F caps= $20
10Led's = $10
Assorted parts = $5 ( ive got lots of junk laying around)

Is this going to be bright enough? Did i screw up my calculations?

Edit= angle on those led's is 10-12 degrees.

How inexpensively can i buy decent AA/AAA rechargeables. (decent, not top of line, and not trash, i already own charger)

 

[Long John]

These days, the caps are not ready for your idea, specially in terms of low-costs and long time draining.
For $20 you can get "AW"'s charger and a RCR123 cell which would be much more satisfactory.
You can drive one SSC or Cree in DD, so the costs would be down.

Best regards

____
Tom

 

[ktronik]

Hmm- Using 8*2.2F Caps (12V) pulling 12v @ 20mA per series run of 1 resistor and 3 led's, Ohms law, R=(V/I)=600ohm. For three runs, 600 ohm's each in parallel (9led's=1,170,000mcd) R=200ohm. Time Constant of RC circuit=58.67 minutes until 33% of charge is gone so approx 30 minutes till half of charge is gone.

8*2.2F caps= $20
10Led's = $10
Assorted parts = $5 ( ive got lots of junk laying around)

Is this going to be bright enough? Did i screw up my calculations?

Edit= angle on those led's is 10-12 degrees.

How inexpensively can i buy decent AA/AAA rechargeables. (decent, not top of line, and not trash, i already own charger)

you know that 8*(series) 2.2F = 275mF (12v) right??

Since the capacitance of any capacitor is inversely proportional to the distance between the plates.

 

[TorchBoy]

The way capacitors discharge really isn't suitable at all. You want something that provides a level voltage, not one that plumets at the start. If you used capacitors you'd need a buck driver, and run all your LEDs in parallel.

Since you're on a budget... have you browsed DX?