Does this halogen lightbulb have positive and negative as it only have plastic where the negative would usually get soldered? It’s a 12v lightbulb and want to use it as a step down converter for a battery charger like this … This what I’m tryna do
The bulbs like this but 12v https://www.walmart.com/ip/Candle-Warmers-Replacement-Halogen-Light-Bulb/38480205
Get a buck converter or reg. These are designed for this exact purpose 
Ya I know just a 12v lightbulb works as well and is handy
It looks like the two terminals are on the bottom of the bulb.
If charging the battery as normally done above I’m confused as he says adding more bulbs will increase the charge time. The drawing has the bulb in series and that would add more resistance with more bulbs and reduce current. Putting them in parallel would reduce resistance but only for the pathways going to a bulb and more power would be diverted from going to the battery charging no?
And why a 12v bulb and it could be any. Don’t get it.
Cause the car battery I’m charging is 12v and the light steps the current down to 12v from the 19v laptop charger and from the bulb to battery is 12v or less
i think the bulb is a resistor in series and it drops the voltage to the battery and you could use any bulb and the lower the bulb resistance the higher the voltage will be going to the battery. the stated wattage on bulb divided by the stated voltage giving a watts per volt, which could be equated to a resistance number, the higher the wattage per volt the lower the resistance and the higher the voltage to the battery out of the charger. A 100 watt 12 volt bulb being 10 times higher wattage output and lower resistance than a 100 watt 120 volt bulb. If wattage per volt is parallel with resistance, which I think it would be.