degarb
Flashlight Enthusiast
I have a headlamp with two heads in series that I built from local parts (rebel 80 and xrc). It is run from 8.4 volts built of a one pound 6V agm (~10 AA NiMH at $14 but is easier/more practical to charge than 10 AA's) in series with two AA cells. The built in resistor (unknown value to me) allows up to 500 milliamps at 8.4 volts, but I also control the current with a $4 Shack 3 watt pot/variable resistor. Typically, I might drive at 400 milliamps, or down to 80 milliamps when I only need 60 lumens.
I got a little yerning to attempt a three head headlamp that would be run from a 2 lb. 12volt/5ah agm.
Is my logic correct that with 3 heads-each with some resistance of their own- I would still be good with this 3 watt pot, since actual voltage on the resistor would be only wattage it needs to burn off. So voltage - Vf (total for all lights) times current = needed resistor wattage. So, say Vf average was 3 volts for each led, I would need to regulate only 3 volts of a 12 volt battery, so maximum current could be up to 1 amp with a 3 watt resistor.
Am I not correct? What is maximum current a naked cree will draw at 4 volts? Can you buy a 6 watt variable pot locally? Also, I don't see good small resistors being sold at Radio Shack.
I haven't decided if I would use netural rebels from futureelectronics or a dx cree drop-in. Color rendering is important and a tight and wide beam pattern. (F.E. probably better color and DX probably better beam pattern?) If I decided on a controller, would a standard controller work, since I wouldn't be pumping 12 volts to one head, but average of 4 volts to each. (I am not convinced that a controller is way to go, since the pwm thread concluded a pot is more efficient, and my only controller experience is with my 2 aa controlled lights that eat batteries and are unreliable. Also, I haven't seen a controller you can actually control. On a pot, you have a knob. Quickly clicking on/off isn't something I can see as practical.)
Of course, if money no object, I could use 1 to 3 mce dropins. Downside would be cost, a serious need for well though out second resistor, color control, and beam pattern/ throw.
I got a little yerning to attempt a three head headlamp that would be run from a 2 lb. 12volt/5ah agm.
Is my logic correct that with 3 heads-each with some resistance of their own- I would still be good with this 3 watt pot, since actual voltage on the resistor would be only wattage it needs to burn off. So voltage - Vf (total for all lights) times current = needed resistor wattage. So, say Vf average was 3 volts for each led, I would need to regulate only 3 volts of a 12 volt battery, so maximum current could be up to 1 amp with a 3 watt resistor.
Am I not correct? What is maximum current a naked cree will draw at 4 volts? Can you buy a 6 watt variable pot locally? Also, I don't see good small resistors being sold at Radio Shack.
I haven't decided if I would use netural rebels from futureelectronics or a dx cree drop-in. Color rendering is important and a tight and wide beam pattern. (F.E. probably better color and DX probably better beam pattern?) If I decided on a controller, would a standard controller work, since I wouldn't be pumping 12 volts to one head, but average of 4 volts to each. (I am not convinced that a controller is way to go, since the pwm thread concluded a pot is more efficient, and my only controller experience is with my 2 aa controlled lights that eat batteries and are unreliable. Also, I haven't seen a controller you can actually control. On a pot, you have a knob. Quickly clicking on/off isn't something I can see as practical.)
Of course, if money no object, I could use 1 to 3 mce dropins. Downside would be cost, a serious need for well though out second resistor, color control, and beam pattern/ throw.
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