second headlamps and electrical questions...

[snowbeard]

Hi All,

found a small (5"?) dirtbike headlight in the recycling dumpster, so I figured I'd recycle it. it's a 6V, so I expect I need to do something to reduce the power if I want to use it on my bike somehow...

2 questions: 1) how would I reduce the voltage to it without creating a drain?

2)wasn't there a brown aux wire unused in the wiring harness? I couldn't find it in my headlight bucket when I looked...? would that be a good idea to wire thru a switch for it?

thanks!!
'beard

[jonr]

Snowbeard,

I'm assuming that the headlight is around 50W or so. If that's the case, it's pulling 3.1 amps or so. There are more savvy electrical people on the forum, so this suggestion is just a basic solution to your problem. If you need to drop 12V to 6V, you need an inline resistor that has a high enough wattage rating to handle your load (assuming 50W or so). Using Ohm's law, you need a 1.935 Ohm resistor that can handle some wattage. The closest resistor to that size is 2.2 Ohms. Yes, you're going to dump 6 volts via some heat discharge, but it's really uncomplicated that way.

I'm guessing if you want a voltage drop of 6 volts with no loss, then you're going to need something more sophisticated (me not know how to do!).

Best,
jon

[snowbeard]

that's a start! I just want to make sure not to overdraw my system and cause a failure somewhere...

[jonr]

Snowbeard, it's important to know exactly how many watts that recycled headlight is pulling. The wattage makes a difference in how the resistance is calculated.

Jon

[Ghostgs1]

Hi beard, Be sure to put the resister in a well vented area, out of touching distance. It will be very warm, ie burns. Ray

[bwringer]

Personally, I'd look pretty hard for a 12V bulb before dinking around with resistors.

[GSstiny]

that aux wire is in that headlight bucket rats nest somewhere. It shouldnt be too hard to run it back out to the dash area to a switch.

[snowbeard]

ok, so I finally looked at the lamp at home, its a 6V 15W off some little old dirtbike. it's about four inches and yellow.

so what would be a way to just limit what can get to the light without having to dump wattage in the way of heat?

what if I had two 6V lamps on the same circuit??

shoulda paid more attention in physics

[Boondocks]

Put it back in the dumpster.

[koolaid_kid]

I suggest finding a 12v lamp that fits in your fixture.
If you get a resistor, you would need a power resistor. It dissipates power (wattage or amperage). It gets quite warm, as mentioned before. It is also a bit expensive, not mentioned before. They are normally gold in color, and quite large (including heat dissipation fins) compared to a non-power resistor.
IMHO, I suggest taking another path to your goal.

[snowbeard]

oh, I see. all y'all really had to say was "its not cheap" and I woulda got it...!#-o

[jonr]

Snowbeard,

If it is a 15W lamp, then it pulls about 2.5 amps (6V x 2.5A = 15W). Yes you could dump the voltage through another light or though a resistor, but either is going to produce heat as waste.

Is your original headlamp not functioning or present? If not, why hassle with it? I know it was a find, but I might save it for a rainy day or something.

jon

[tpeeples]

Use Voltage Regulator

Or you could use a Voltage Regulator taking 12 Volt to 6 Volt. Of course the circuit would need to be built, heat-sinked and isolated (little bit of electrical tape never hurt anyone!).

The link below would be able to handle the 2.5 Amps ( 6 Volt * 2.5 Amps = 15 Watts).

http://www.national.com/pf/LM/LM350.html