I occasionally have to change Consumer Units / Fuse Boards, and this necessitates disconnection of the mains electricity supply to a property. Therefore, to illuminate the job, I have many LED torches / flashlights, including head torches, and many of them are remarkably bright with very useful beams. However, none of them really provides enough light to illuminate the whole area, as a mains-powered lamp would. I realise that one can buy rechargeable lamps with integrated batteries, but if they go flat half-way through the job, you're stuck. Changing batteries in normal torches is also inconvenient.

Step 1:

Since I had an old, non-working, 18V Hitachi cordless drill, with a working fast-charger and good batteries, I decided to turn it into an extra-bright flashlight / torch. The great advantage of this system is that you simply pop out the discharged battery pack and clip in a fully-charged pack, gun magazine-style. The Hitachi Li-Ion batteries are light and reliable, and also fit my other cordless tools. However, this idea should work with any make or type of cordless tool, as long as the battery voltage is higher than that of the LED used. Even lower-voltage packs could be used with a simple voltage boost converter to increase the voltage of the battery pack to that required by the chosen LED. I had some 12V 10W LEDs, so I used one of those.

I simply removed the 'guts' of the drill and replaced them with the LED mounted on a finned heatsink, plus an on/off switch and voltage regulator / brightness control. Because my batteries are 18V, and the LED I used requires a maximum of 12V, some form of voltage regulator was needed, so I decided to make it adjustable, thus providing a method of adjusting the light output. Because I have loads in-stock, I used an LM317T linear regulator with a six-way rotary switch and some fixed resistors to adjust the voltage. I mounted the regulator on the opposite end of the heatsink from the LED with a small machine screw. No isolation was required because the LED is insulated from its heatsink base. The circuit is very simple, as are the resistors required, and is to be found at: reuk.co.uk/LM317-Voltage-Calculator.htm I could just as easily have used a potentiometer / variable resistor to adjust the regulator output, but the 'first law of hobbies is to use what you have available for free.'

During testing, I tried various drive voltages, and liked the progression from the threshold at 7V to maximum output in 1V steps. The lowest 7V setting gives a low but useable output which will last for many hours, and 12V gives maximum output, equivalent to about that of a 100W halogen lamp, and will last for about 45 minutes. I used 240R for R1 and this table shows voltage, R2 value, LED current, and approximate battery life on a full charge with the 1,500mAh packs I use:-

7V - 1,100Ω - 66mA - 23 hours

8V - 1,300Ω - 110mA - 14 hours

9V - 1,500Ω - 500mA - 3 hours

10V - 1,700Ω - 1,350mA - 1.1 hours

11V - 1,900Ω - 2,250mA - 0.7 hours

12V - 2,100Ω - 2,500mA - 0.6 hours

Although advertised as a 9 to 12V LED, the maximum rated current of 1050mA is reached at about 10V, so anything in excess of this is over-running the nine LED chips contained in the package. Most of the extra current is converted to heat and wasted. Therefore, I tend not to use the 11V and 12V settings for more than a few minutes. In practice, it is seldom necessary to use maximum output anyway.

Initially, the light output was very bright and very wide, but there was no defined beam, so I decided to fit a lens to the front. The glass 50mm plano-convex lens / collimator I found on eBay, which also protects the front of the LED, fits perfectly into the front aperture of the Hitach housing, and is held in place with a 'circlip' of 5mm diameter PVC flex. This gives a greatly improved beam, and the weight of the glass lens improves the balance of the tool. (Removing the chuck had made it rather tail-heavy.)

Should the battery ever go flat during a job, I simply swap it for a fully-charged pack, just like you do with normal cordless tools. The heat-sink gets slightly warm, since the regulator drops 6V at 2,000mA at maximum output, which is 12W, but the original ventilation holes in the case keep it cooled by convection. The major advantage of using the original drill battery pack is that the fast charger charges the packs in less time than it takes to flatten them without over-charging and the built-in protection circuit means they cannot be over-discharged.

This is the best battery-powered torch / flashight I have ever used, without any of the the complexity of constructing custom housings with fans and home-made battery-packs. The convenience of using a ready-made robust case and cartridge battery charging system, interchangeable with my other cordless power tools, is great, and the 30 minute charging time is a bonus. Whether hand-held, standing on its base or lying at some other angle, there is always more than sufficient light 'on the job.' I have also found it to be a far superior replacement for the old 6V lead-acid powered halogen so-called '1 million candlepower' spotlights for outdoor use.

Since the initial construction, I have made some improvements:-

I replaced the wasteful linear LM317T with a cheap switch-mode voltage regulator, costing only about £1, including free delivery: www.banggood.com/Mini-DC-DC-Converter-Step-Down-Module-Adjustable-Power-Supply-p-920327.html) (A really useful little 1A+ buck regulator on a 15mm x 20mm PCB.) This required the voltage adjustment resistors to be changed, but the increased efficiency of this regulator has extended the run-time on one battery pack by about 30%.

Since the higher voltages were rather over-driving the LED, I have now limited the maximum voltage to 10.5V, hopefully ensuring a long and efficient life, whilst still being the brightest and most useful battery torch / flashlight I have ever used. Everyone that has seen this in action is waiting for one of their cordless tools to 'die' so that they can have one, too.....

I would still prefer a larger diameter, flatter profile, brightness adjustment knob, when I can find a suitable part, since it would be more in-keeping with the drill housing and easier to adjust whilst wearing gloves.

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