"Turbo Charging" a flashlight

\"Turbo Charging\" a flashlight

During the past year or so I've spent some time playing around with LEDs trying to make a bright flashlight. LEDs are fine when you need a small amount of light, but I've decided what I really want is a small flashlight that is rechargeable and puts off a lot of light.

I can't justify purchasing one of the ~$100 commercially available flashlights so I've been experimenting.

I have some lithion-ion cell phone battery packs that are 7.2-8V and about 1250mAH capacity. The packs are a little taller than a D-cell and a little wider (the pack is made of 2 cells that look like big AAs). I've found I can put 1 in most 2-D cell flashlights and solder in some wires. Of course I need to change bulbs too something beefier. My first bulb experiment is using the Maglite 5-cell kryton bulb.

It puts out a LOT of light...and heat. The first flashlight I tried it in had the lens cover too close to the bulb and it started to deform after 5-10 minutes. Next, I bought a cheapo $1 flashlight where the lens cover was further away. This time the reflector started melting.

Today I bought a $5 Eveready flashlight with a thicker reflector. Don't know if it will work since it is still plastic.

Does anybody have any thoughts? These battery packs won't fit in a maglite since they don't have enough room diameter wise.
I'd like to find a "cheap" 2-D cell flashlight with a metal reflector and lens cover that can take the heat.

Thanks.

Re: \"Turbo Charging\" a flashlight

First of all, you have to be more specific with your nomenclature. Mag Light sells two different lamps for 5 cell lights. The White Star is the cheapo one that is the original one that comes with the Mag Light. It looks like the old PR flashlight bulbs. The second one is the Magnum Star; this has a cylindrical quartz tube with a biconvex lens in the tip. Both of these lamps, btw, are made by Carley lamp.

Assuming you were using the Magnum Star, called the Krypton Star by Carley, you were using a lamp rated at 6.3 V. Now the rechargeable Li ion cells you are using are rated at 7.2 to 8 volts, you stated. This means that you are using the lamp at a much higher voltage than for which it was designed. The reason for this is that the lamp was designed for alkaline cells, which tend to lose voltage linearly during use. Rechargeable lamps, however, are designed to follow the discharge pattern of the rechargeable battery, which is to remain near rated voltage until the battery is nearly discharged. You know this already. An alkaline cell flashlight will get slightly dimmer with use, giving lots of warning that the cells are becoming discharged. NiCd flashlights, however, notoriously become dim in just a few minutes, leaving you in the dark.

The problem is that even if you were to use a lamp rated at a higher voltage, say the Krypton Star designed for six alkaline batteries, rated for 7.5 V, the lamp is still held above its' expected voltage for a longer period, as the Li ion cells do not discharge linearly. This will result in a shortened lamp life.

But what does this have to do with your problem of over heating? Well, it means that your project is doomed to failure. This is because, as I demonstrated above, you are using a lamp incorrectly. The correct lamp is not available in the KSR rechargeable series of lamps, the highest voltage of which is the KSR 1.7A, designed for six NiCd batteries. This is rated for only six volts, but here is the problem; the KSR 1.7A is rated at 10.2 watts at six V. The KSA 5 lamp you were using is rated at 4.4watts at 6.3 V.
You were of course actually making more watts than rated, as voltage times amperage = watts, as the good Mr. Ohm told us.

Thus a rechargeable lamp burns even hotter than does a lamp designed for alkaline batteries. Even if you could find a rechargeable lamp rated for 8 V, it would probably melt your flashlight reflector and lens in several seconds. The hottest lamp I use is the KSR 4 1.7A. This is designed for four NiCd cells, a rated voltage of 5 V, and 8.5 watts. This will warn your hand to the point of discomfort within about 8 to 10 seconds if held near your palm. This is safe for use in Mag Lights, and I have been doing so for about 20 years, but any cheap flashlight will melt with this combination.

I suggest that you get a Carley Xenon Star lamp for your 2 cell Mag Light, and use two alkaline batteries. This set up puts out 1.9 spherical candlepower. If you want to try out the NiCd combination, I have some KSR2 1.3 Carley Krypton Star Rechargeable lamps I would be glad to send you. They are rated at 2.5V, 1.3A, 3.3W, and 3.3 Spherical Candlepower. I have not found this combination to be particularly useful, however, as the hi cap 4500 mAh batteries from Radio Shack are about $8 each, and the run time for this set up is only about 90 min. The xenon star lamp / alkaline cell set up will run about 10-12 hours. Further, the higher color temperature of the xenon star lamp makes the difference in candle power seem a lot less than it is.

Hope this helps, Walt

Re: \"Turbo Charging\" a flashlight

For a bulb I recomend looking at Lowes or Home Depot. Goto the powertool section and see if they sell replacement bulbs for the rechargeable lights that use the battery packs from powertools. Like cordless drills. You might be able to find something close to 7.2-8v.

For a reflector I think the eveready yellow flashlight is about $5-$10 and has a metal reflector. Used to anyways.

------------------
"A knifeless man is a lifeless man"
-Nordic proverb

Re: \"Turbo Charging\" a flashlight

Thanks Walt and David for your input!

The bulb I'm using must be the White Star. I did measure the current at 750mA however I didn't check to see what the voltage under load was on the lithium-ion cell. It is rated at 7.2V, but after being charged and under a light load is about 8.1V. The bulb is probably similar to a KPR112. I like the lithium-ion cell because it holds a charge a lot longer than nicads and the energy density is higher, plus I don't have to buy any new batteries.

I did move the bulb and battery pack to the new flashlight I mentioned in my original post and it worked fine without melting anything when I left it on for 15-20 minutes continuous. It is brighter than my 4 cell maglite (and much lighter). I expect run time on one charge to be a little over an hour.

I'll look for the Eveready yellow flashlight and see if it has a metal reflector.

As for a bulb I see Radio Shack has an XPR118 7.2V Xenon bulb with a 36 hour life that I would like to try.

Re: \"Turbo Charging\" a flashlight

Carley lamps sells metal reflectors too, if you where really hardcore you could order one though I understand the minimum order is $50.

ALso do a few searches on building your own dive light, that may give you some hints, use your favorite search engine.

DaveH

Re: \"Turbo Charging\" a flashlight

Hey! Who let Walt in the door? Just kidding!
Seriously, everything said above is true, heat kills plastic, heat is generated with a filament based bulb, and heat is a sign of inefficiency of the device.

I've played around with a couple Streamlights I own:
My duty light is a SL-20X, with an SL-35X bulb/reflector assembly (20 watt bulb). SUper bright, last about an hour continously, but puts out heat like crazy, though I haven't melted a lens, and the reflector is aluminum.

Another project is with a SL-20XP (polymer bodied version of the 20X) with a custom made battery pack consisting of NiMH sub-c cells (3000MAH rated) and a 35X bulb assembly. I've been talikng about doing this for months, but haven't found the time. It should work in theory, but I dont think the polymer body would take the heat over an extended period of time, nor do I think the lights innards could take the heat, as the light doesn't have the heat sink ability of an aluminum body.

--dan