Re: [Paddlewise] LED's, was Strobe Question

John Kirk-Anderson wrote:

> With LED's having a massive advantage in operating times and durability, is
> there anyone in Paddlewise-land who would know how to adapt an Underwater
> Kinetics Mini Q-40 to use LED's? Is it as simple as making one fit, and if
> that is the case, why do some LED units have a small circuit board? Warning,
> my electronic knowledge is such that I have to check twice that I have put
> the batteries in the correct way!


Long before you could buy an LED conversion kit for a Maglite, I looked at 
making one.  I'm sure there are details I've missed, but:

LED's operate at a range of voltages, but most require over 3V - especially the 
very bright "white" LEDs.  Since a 2AA device only puts out 2.4V (on 
rechargeable batteries), you need a step-up circuit to generate 3V or so.  The 
conversion kit for my PT headlamp has this.  The result is a loss of power in 
the circuit so the life of the batteries is a little less than what a 3AA or 
3AAA could manage, all other things being equal.  If you want to use such a 
circuit, you can either modify an existing conversion kit or use the web to find 
instructions to build one - e.g.: 
<http://www.resurgentsoftware.com/perfect_led_light.html>.  There are also 
step-down circuits to allow a 4AA flashlight to run a 3.xV LED.

If you have a 3.6V source (lithium cell, 3AA or 3AAA  = 3.6V, nominally) you 
could directly power a 3.6V LED.  Some makers will add a circuit to limit the 
power to the LED to conserve battery power - for example, by flashing the LED at 
a rate that is fast enough to not be observed by a person.  These also allow 
multiple brightness levels as an option.  A resistor can be used to drop the 
voltage from 3.6 to whatever the LED requires.  You can get the specs for 
various LEDs from the web.

The flashlight you're interested in is 4AA = 4.8V rechargeable or 6V alkaline. 
You could remove one battery and replace it with a homemade plug (spacer) that 
has caps and a wire to conduct the electricity and then have a 3AA power source. 
   Another option is to use 3N alkaline batteries (4.5V) on one side and a plug 
on the other (3N is almost as long as 2AA in series - you'll need a short 
spacer).  Or you can change the flashlight (this is getting drastic) to run two 
sets of 3N in parallel rather than series - this will still give 4.5V with twice 
the life of one set of 3N.

At this point, you need to use a resistor to limit the voltage - you can put it 
in the plug/spacer.  15 ohm for alkaline or about 10 ohm for rechargeable.

There are lots of web sites for doing these conversions.  Here's a good one:
<http://www.otherpower.com/otherpower_lighting_flashlites.html>

BTW - there is an LED version of the Mini Q40 flashlight.  Perhaps they sell a 
conversion kit or new light head.

Mike
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