"HK" wrote in message
news
I'm trying to help my daughter with a school project and while I know my
way around house wiring, I'm a relative newbie when it comes to low
voltage.

Let's say I have a 6 volt DC power supply (4 "C" batteries). If I want to
drive a small motor and some lights, I just find 6 volt motors and lights
and wire them in parallel or series.



In parallel you are dividing the current. In series you are dividing the
voltage.

Why is it that I can't light up a 12v light with a 6 volt power supply? I
always test my batteries using a multi-meter and as the battery ages, the
voltage drops. With low voltage, the device (flashlight, etc.) still
works but the light is weak. So, wouldn't a 12v light just be weak if I
use a 6v power supply?

Is there some kind of voltage threshold at which a device won't work?

Like I said, basic question.



There is no threshold for the incandescent lamp, after all its an analog
device and light output is varied from zero to 100% continuous with respect
to varying the voltage. You don't see it because you haven't enough current
to heat the filament up - see if you could see it in the dark. I'm sure if
you have a 6V car or motorcycle battery instead of the C cells, the 12v lamp
would light up.