The way that I had imagined to put a VR in the Tail Cap was to make a sort of washer sandwich. You would have the negative available from the bottom battery, then a thin 1” washer with a wire soldered to it then a thin slice of rubber then another washer of about ¾” also with another wire soldered to it. Then just attach both wires to the VR circuit that would reside in the tail cap. The wire would, of course, run through the middle of the tail cap spring. I know it’s a little hard to explain without a diagram, but if you have your MagLite handy, then just take a look at it and I think you will see what I mean. This design would allow someone with no electronics skills what so ever to install such a device.
This was my original design that I came up with close to a year ago, but so far I’ve not found a suitable VR for this application. Most chips just can’t handle the amount of amperage involved. That’s why you see so many different chips that will work for low amperage LED applications, but when it comes to incandescents it is very difficult to find a chip, that is very efficient (which is an absolute must in a battery operated device), and that can still handle that kind of amperage.
I don’t currently own a suitable 12volt bulb for this project so I can’t do a test for wattage, but I do have a 6volt 4D MagLite with the stock bulb. I just tested it at 6.25volts and pulling .75amps with brand new rechargeable alkaline batteries. I mentioned what type of batteries that I was using because with regular Alkalines, it would probably pull a bit more amperage because of a slightly less internal resistance in “normal Alkalines”. Of course this is a “running amperage” once the bulb has warmed up for like a second. As I’m sure you are well aware, when a bulb is cold and just starts up, it can pull many times this amount of power. There would definitely need to be a built in protection in the circuit for this start-up amperage draw in order to keep from blowing a chip. Also worth noting, a VR would also help to preserve bulb life if it was set to start the bulb off at a bit less than full power for the fist second instead of starting it off at full power such as is the case without a VR.
Also, unless we were to use just one particular kind of 12volt bulb, then we would get very different current draws for them anyway (well, up to the maximum that the batteries were able to put out anyway). I know for sure that there are 12volt bulbs that pull a comparatively small amount of watts and then there are those several million CP spotlights that pull something like 100 watts!
After putting a great deal of thought into this, I think a safer bet might be to try the following. Since MagLite makes a pretty standard 9Volt bulb to go in their 6D MagLites, and the bulbs are pretty commonly available, why don’t we shoot for using a 9volt bulb in a 4D 6volt MagLite? A 9volt bulb would also be very bright (although not quite as bright as a 12volt), and would be very commonly available and I’m pretty sure the MagLite 9volt bulb only pulls like 1amp of current. Could someone that has a 6D MagLite confirm this? Also try taking amperage readings using rechargeables if possible. If it does only pull like 1amp then you could, perhaps, not be forced to use rechargeables if you didn’t want to for some reason given this scenario.
I’ll just stop right here and let you guys digest what I’ve typed up so far and see what you think of it.
