Thanks everyone. Good information here.

This is a Grade 6 project and I was a little distressed to find that even
the basic concepts of electricity haven't been taught yet they are supposed
to build a basic circuit and working model.

For instance, my daughter assumed that to power two 6v lights, she needed a
12v power supply. Yikes.

Is Grade 6 too early to teach Ohm's Law? Should they be learning to hook up
basic circuits without learning Ohm's Law and the concepts of voltage,
current and resistance?

Some of this stuff is coming back to me. Am I correct in assuming that the
problem with wiring the lights in series is there is too much cumulative
resistance at the far end of the circuit to light the lights?

FYI, we're building a small airboat. There are four 3v LED lights powered
by 2 "C" batteries and a single 6v motor powered by 4 "C" batteries.

Any suggestions on a fun followup project that will help both of us learn
more electricity concepts?



"Doug Miller" wrote in message
...
In article , "HK"
wrote:
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

Yes.

or series.

No.

Why is it that I can't light up a 12v light with a 6 volt power supply?

The filament resistance is too high, and/or your 6 volt source doesn't
supply
enough current. Are you trying to light up an automobile light bulb with
four
AA batteries?

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?

It depends on the current as well as the voltage.

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

Depends on the device. For something as simple as a light bulb, I wouldn't
think so. Try an experiment: see if you can light up an ordinary 60W
incandescent light bulb (120V) from a car battery (12V).

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.