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.

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.

Light bulbs work at may voltages. For example, a 120 volt
incandescant bulb will work at 60 volts AND last for maybe 100 years
continuous. As voltage drops, bulb life expectancy increases
exponentially (about a factor of 12). As voltage drops, bulb
intensity also decreases exponentially. Sure, the 12 volt bulb will
work at 6 volts. But its light output will be massively diminished
and its efficiency is decreases (less light per amp of electricity).

So yes, a 12 volt lamp will work on 6 volts (if power supply can
provide sufficient current). Just not work very well.

On Feb 14, 10:21 am, "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 or series.

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?

"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.

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.
It is an interesting question actually.
A 15w 12v bulb, when wired to a 6v battery draws .6a. Apparently your
batteries can't produce .6a, so the bulb doesn't light up. Wouldn't be very
bright anyhow.

On Feb 14, 10:03 am, "Toller" wrote:
"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.

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.

It is an interesting question actually.
A 15w 12v bulb, when wired to a 6v battery draws .6a. Apparently your
batteries can't produce .6a, so the bulb doesn't light up. Wouldn't be very
bright anyhow.


You're on the right track. The bulb filament glows from the amount of
current through it. Too much current and the bulb is overbright or
blows. Not enough current and the bulb glows weak or not at all.
Current is a function of voltage divided by resistance. Higher
voltage bulbs have higher resistance filaments. Therefore 6v divided
by higher resistance equals less current and less glow.

Bob

On Feb 14, 10:23 am, "Bob" wrote:
On Feb 14, 10:03 am, "Toller" wrote:



"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.

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.

It is an interesting question actually.
A 15w 12v bulb, when wired to a 6v battery draws .6a. Apparently your
batteries can't produce .6a, so the bulb doesn't light up. Wouldn't be very
bright anyhow.

You're on the right track. The bulb filament glows from the amount of
current through it. Too much current and the bulb is overbright or
blows. Not enough current and the bulb glows weak or not at all.
Current is a function of voltage divided by resistance. Higher
voltage bulbs have higher resistance filaments. Therefore 6v divided
by higher resistance equals less current and less glow.

And, to follow up, OP could take the bulb and his VOM and measure the
resistance across the filament and see what it is to see what the
current draw should be...or maybe the bulb isn't good, even?

Or, of course, take enough batteries in series to make 12V ...

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.

w_tom wrote:
Light bulbs work at may voltages. For example, a 120 volt
incandescant bulb will work at 60 volts AND last for maybe 100 years
continuous. As voltage drops, bulb life expectancy increases
exponentially (about a factor of 12). As voltage drops, bulb
intensity also decreases exponentially. Sure, the 12 volt bulb will
work at 6 volts. But its light output will be massively diminished
and its efficiency is decreases (less light per amp of electricity).

So yes, a 12 volt lamp will work on 6 volts (if power supply can
provide sufficient current). Just not work very well.

NO, it will not. There will be insufficient heat in the element to provide
any light or even a glow with a 12V bulb at 6V DC. A 12VDC bulb will begin
to dim substantially at 9 VDC and may not even be visible in the light of a
room.

Do not profess knowledge you do not have.


On Feb 14, 10:21 am, "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 or series.

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?

In article .com, "dpb" wrote:

Or, of course, take enough batteries in series to make 12V ...

Since power increases in proportion to voltage, but increases in proportion to
current *squared*, don't you suppose he's better off to put the batteries in
parallel to increase the current?

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

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

"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.

In article W6HAh.3741$Aa5.925@trnddc01, "Pop`" wrote:
w_tom wrote:
Light bulbs work at may voltages. For example, a 120 volt
incandescant bulb will work at 60 volts AND last for maybe 100 years
continuous. As voltage drops, bulb life expectancy increases
exponentially (about a factor of 12). As voltage drops, bulb
intensity also decreases exponentially. Sure, the 12 volt bulb will
work at 6 volts. But its light output will be massively diminished
and its efficiency is decreases (less light per amp of electricity).

So yes, a 12 volt lamp will work on 6 volts (if power supply can
provide sufficient current). Just not work very well.

NO, it will not. There will be insufficient heat in the element to provide
any light or even a glow with a 12V bulb at 6V DC. A 12VDC bulb will begin
to dim substantially at 9 VDC and may not even be visible in the light of a
room.

I guess you didn't understand the part where he said "if power supply can
provide sufficient current."

Do not profess knowledge you do not have.

That's good advice, Poop. Maybe you should take it, too.

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

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

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.

On Feb 14, 10:57 am, (Doug Miller) wrote:
In article .com, "dpb" wrote:
Or, of course, take enough batteries in series to make 12V ...

Since power increases in proportion to voltage, but increases in proportion to
current *squared*, don't you suppose he's better off to put the batteries in
parallel to increase the current?
....

But, since by the same token, I=V/R and R is what he's given w/ the
particular bulb, P ~ V^2/R so same can be said of voltage...

I was only commenting wrt to the fact OP has a 12V-rated bulb and is/
was 'spearmint-ing so was only one of many alternatives to try and
observe what happens, certainly not the only one..."Best" in any sense
wasn't at all a part of the suggestion.

HK inspired greatness with:

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.


You do know that LED's must be wired in series with a resistor to make
them glow, right?

On Feb 14, 11:04 am, "HK" wrote:
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.

Nothing wrong with that as long as they are in series.


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?

No. a good mix of math and science.



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?

Go back to Ohms law. 2X resistance = 1/2 current


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.

Aahhh... Remember that we've been talking incandescent light bulbs.
A LED is a diode and not a bulb even though it gives off light.
Although the same principles apply since LED's use a dropping resistor
to limit current, similar to items in parallel.



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

Google or your local library.

On Feb 14, 11:32 am, "Bob" wrote:

Although the same principles apply since LED's use a dropping resistor
to limit current, similar to items in parallel.

OOPS. I meant series. Now I'm getting tongue tied.

Chop Suey wrote:

You do know that LED's must be wired in series with a resistor to make
them glow, right?

I agree that is the proper way to do it.

However, they work just fine by themselves if the voltage supply is low
enough, or if you parallel enough LEDs together.

Chris

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

http://www.lindsaybks.com/bks9/ething/index.html

On Wed, 14 Feb 2007 11:28:38 -0600, Chop Suey
wrote:

HK inspired greatness with:

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.


You do know that LED's must be wired in series with a resistor to make
them glow, right?


Actually, they don't. They have to be wired in series with a resistor
to keep them from eating your battery whole, but as long as you have
enough voltage, they'll light.

You can make the worlds smallest flashlight by just taping
the leads of an LED to either side of a watch battery.

In article , "HK" wrote:
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.

So what's the problem? Connect them in series.

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?

Too much cumulative resistance at some point, anyway -- not necessarily all
the way at the end.

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?

Browse around at the web site for Edmund Scientific
//http://scientificsonline.com/
Lots of good stuff there.

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

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

On Wed, 14 Feb 2007 10:21:27 -0500, "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 or series.

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?


It should light, but dimly and more yellowish.

Try measuring the 6V supply WITH that light connected. You may find
that it's loading your C cells so much it's getting a lot less than
6V.

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

Like I said, basic question.

--
Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

On 14 Feb 2007 07:31:31 -0800, "w_tom" wrote:

Light bulbs work at may voltages. For example, a 120 volt
incandescant bulb will work at 60 volts AND last for maybe 100 years
continuous. As voltage drops, bulb life expectancy increases
exponentially (about a factor of 12). As voltage drops, bulb
intensity also decreases exponentially. Sure, the 12 volt bulb will
work at 6 volts. But its light output will be massively diminished
and its efficiency is decreases (less light per amp of electricity).


The filament won't be as hot, which leads to a change in color (it
won't be as white).

So yes, a 12 volt lamp will work on 6 volts (if power supply can
provide sufficient current). Just not work very well.


Maybe that 12V bulb is a car headlight, which is severely overloading
the power supply.

On Feb 14, 10:21 am, "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 or series.

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?
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

On 14 Feb 2007 08:42:08 -0800, "dpb" wrote:

On Feb 14, 10:23 am, "Bob" wrote:
On Feb 14, 10:03 am, "Toller" wrote:



"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.

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.

It is an interesting question actually.
A 15w 12v bulb, when wired to a 6v battery draws .6a. Apparently your
batteries can't produce .6a, so the bulb doesn't light up. Wouldn't be very
bright anyhow.

You're on the right track. The bulb filament glows from the amount of
current through it. Too much current and the bulb is overbright or
blows. Not enough current and the bulb glows weak or not at all.
Current is a function of voltage divided by resistance. Higher
voltage bulbs have higher resistance filaments. Therefore 6v divided
by higher resistance equals less current and less glow.

And, to follow up, OP could take the bulb and his VOM and measure the
resistance across the filament and see what it is to see what the
current draw should be...or maybe the bulb isn't good, even?

Or, of course, take enough batteries in series to make 12V ...

That won't increase the current capability. It may still be
insufficient for that bulb.

What is the current capacity for new C cells?
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

On Feb 14, 11:04 am, "HK" wrote:

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


Here's one you might enjoy, or at least get sone ideas from.
http://blogs.gotdotnet.com/mhop/arch...as-lights.aspx

On Wed, 14 Feb 2007 12:04:23 -0500, "HK" wrote:

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?


I knew that stuff by fourth grade, but then I wasn't aliterate (can
read but won't).

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?


Cumulative resistance in the circuit. Which end, is irrelevant.

In a series circuit, current is the same through all devices. Voltage
is divided according to resistance. If all lights are the same, it
will be divided equally.

With a 12V supply and 2 (identical) lights in series, each light will
be operating on 6V. Current for this circuit will be the same as one
light on 6V.

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?


How about using both series and parallel lighting circuits?

When I was in 3rd or 4th grade, a relative gave me a book of simple
experiments. The section on electricity used both series and parallel.

BTW, I remember how hard it was to find the "#6 dry cells" that book
called for. Most people hadn't heard of such things. These are large
round 1.5v cells, bigger than the ones they make lantern batteries out
of.



"Doug Miller" wrote in message
t...
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.

--
Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

On Wed, 14 Feb 2007 08:58:53 -0800, "Jack" wrote:


"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.


An incandescent lamp gives off light because the filament is hot. The
frequencies given off depend on the temperature of the filament. To
see light, you need enough current to heat the filament enough that
it's temperature corresponds to frequencies in the visible range.

If you get light from a lower voltage/current, the light will be
redder (or yellower). These colors correspond to the low end of the
visible spectrum. At full voltage you get more blue (high end
frequency).
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy

On Feb 14, 10:21 am, "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 or series.

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.

I haven't read the rest of the responses yet, so I'll just say some
dumb stuff until somebody explains to me I'm an idiot.

First: heat is related to wattage through bulb. wattage is
proportional to voltage squared, so at half voltage you get one
quarter the wattage therefore one quarter the heat produced, all else
being equal (which it never is).
Temp vs. heat.... umm, i think that's more or less linear, so half the
voltage means one quarter the wattage means one quarter the heat means
one quarter the rise in temp over room temp.
Now the fun.... the radiated energy vs temp follows the black body
equation, which relates the energy at each wavelength to the
temperature and is best explained by your looking here http://
hyperphysics.phy-astr.gsu.edu/hbase/bbrc.html#c1 rather than me
trying to reproduce it in words. You see that the intensity,
particularly at visual light, falls off real quick as the temp falls
off.

On Wed, 14 Feb 2007 10:21:27 -0500, "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 or series.

Parallel. If you put 6 volt items in series, the required voltages
are the sum of the individual voltages. Just like xmas tree lights
that only need a couple volts, but times 50 and you get 110 volts and
they plug into the wall directly. If you tried to use a 2.5 volt
power supply with 50 xmas tree bulbs in a row, you'd get no light.
Same with nmotors.

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.

mY aNswer is going to conflict a little, maybe, with the first two,
but not directly.

When a battery is running low, it still has most of the voltage it did
when new. It was surprising to me, but the chem teacher did the
arithmetic in front of us, and he didn't make any errors.

So when a battery is 80% dischagred it still has 80% of the original
voltage. It might even have been that when 90% discharged it had 90%
of the orignal voltage. So by the time a 12 volt battery is down to
6 volts, it must be 98+ discharged, and it's not going to have enoug
output to actually make light from a 12 volt bulb. Frankly, I don't
even think amperage is the problem, and I don't think a 12 volt large
size car battery could light a 12 volt bulb when it is so discharged
it puts out 6 volts, though I don't remember ever having a 12 volt
battery that was so low.** Or if output ampterage is still linited,
assume 100 such batteries in parallel, but still with only 6 volts.

Even a brand new 6 volt battery, even a big one like a 6 volt car
battery (still used for golf-carts??) I don't think could light a 12
volt bulb.


**Well actually now I do. It's a gelcell I bouught for testing
indoors, and it is down to about 5.5 volts, maybe partly because when
it was 7, I connected a battery charger backwards! and drove it even
lower. So in the next day or two I'll try to try it with a 6 volt
bulb.

Should they be learning to hook up
basic circuits without learning Ohm's Law and the concepts of voltage,
current and resistance?


Sure, why not? Ohm's Law or not, its still a good exposure to basic
circuits.


Is Grade 6 too early to teach Ohm's Law?

My friend graduated from MIT at sixteen. I'll bet he was doing Laplace
Transform for circuit analysis and wave equations when he was at the grade 6
age.

"Doug Miller" wrote in message
...
In article W6HAh.3741$Aa5.925@trnddc01, "Pop`"
wrote:
w_tom wrote:
Light bulbs work at may voltages. For example, a 120 volt
incandescant bulb will work at 60 volts AND last for maybe 100 years
continuous. As voltage drops, bulb life expectancy increases
exponentially (about a factor of 12). As voltage drops, bulb
intensity also decreases exponentially. Sure, the 12 volt bulb will
work at 6 volts. But its light output will be massively diminished
and its efficiency is decreases (less light per amp of electricity).

So yes, a 12 volt lamp will work on 6 volts (if power supply can
provide sufficient current). Just not work very well.

NO, it will not. There will be insufficient heat in the element to
provide
any light or even a glow with a 12V bulb at 6V DC. A 12VDC bulb will
begin
to dim substantially at 9 VDC and may not even be visible in the light of
a
room.

I guess you didn't understand the part where he said "if power supply can
provide sufficient current."


If the voltage is insufficient, no power supply, no matter what current it
can deliver, will light the bulb.


Do not profess knowledge you do not have.

That's good advice, Poop. Maybe you should take it, too.

You say?

Bob

"HK" wrote in message
.. .
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.

That's one way to do it.


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?

So teach her ohm's law.


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?

There is no "far end" of a circuit unless you have long small
wires creating resistance.

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.

"3v LED" suggests LEDs with built in resisters. Remember LEDs
are polarized - if you connect them backwards, they won't light.
2 3v LEDs in series should work fine off of 6V. Do that twice for
4 bulbs.


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

A crystal radio?
http://sci-toys.com/scitoys/scitoys/...ade_radio.html

Bob

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

Jacobs ladder. Then when the class is over you can make it into a
super deluxe Taser.

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.

It will light but just barely. Remove one cell from a two cell
flashlight and you'll see.

"Bob F" wrote in message
"3v LED" suggests LEDs with built in resisters. Remember LEDs
are polarized - if you connect them backwards, they won't light.
2 3v LEDs in series should work fine off of 6V. Do that twice for
4 bulbs.

Oops - I missed the 2 C batteries. Just parallel the 4 LEDs to the 2 cell
in series.

In article , "Bob F" wrote:

If the voltage is insufficient, no power supply, no matter what current it
can deliver, will light the bulb.

Oh, really? Let's see the explanation of that.

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

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

On Feb 14, 10:21 am, "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 or series.

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.

Lots of factors are at play here. Changing the supply voltage will
change the filament temperature, and hence the filament resistance.
So cutting the voltage in half will not cut the current in half.

I made a spreadsheet which accounts for the changes in temperature and
resistance, and here's what I found:

A 100W, 12V lamp, when run at 6V, will require 5 or 6 Amps and run at
30 to 35 Watts. The filament temperature will be in the range
1800-2100 C, and will definately be visible. BUT you're 6V supply
must be capable of 6 amps, which your battery of "C" cells is NOT.

A 10W, 12V lamp will need almost 0.5 to 0.6 A at 6V, and run at 3 to
3.5 Watts. I'm not sure if C cells are capable of this or not.

A 1W, 12V lamp will need only about 50-60 mA, and your C cells will be
sufficient to power it.

Hope this helps.

Mark

On Wed, 14 Feb 2007 22:57:58 GMT, (Doug Miller)
wrote:

In article , "Bob F" wrote:

If the voltage is insufficient, no power supply, no matter what current it
can deliver, will light the bulb.

Oh, really? Let's see the explanation of that.

He's correct. It's simple electricity 101.

On Feb 14, 6:07 pm, "Redbelly" wrote:
On Feb 14, 10:21 am, "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 or series.

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.

Lots of factors are at play here. Changing the supply voltage will
change the filament temperature, and hence the filament resistance.
So cutting the voltage in half will not cut the current in half.

I made a spreadsheet which accounts for the changes in temperature and
resistance, and here's what I found:

A 100W, 12V lamp, when run at 6V, will require 5 or 6 Amps and run at
30 to 35 Watts. The filament temperature will be in the range
1800-2100 C, and will definately be visible. BUT you're 6V supply
must be capable of 6 amps, which your battery of "C" cells is NOT.

A 10W, 12V lamp will need almost 0.5 to 0.6 A at 6V, and run at 3 to
3.5 Watts. I'm not sure if C cells are capable of this or not.

A 1W, 12V lamp will need only about 50-60 mA, and your C cells will be
sufficient to power it.

Hope this helps.

Mark

p.s.: I'm assuming these are filament lamps, not LED's or other.

As a test of your existing setup:

1. What is the wattage of the filament you tried?

2. What happens to the voltage across the filament when you try to
power it with the C batteries? If it drops way below 6V, then it
requires a lot more current than the batteries can provide. You'll
need a voltmeter for this, of course.

Regards,

Mark

In article , wrote:
On Wed, 14 Feb 2007 22:57:58 GMT, (Doug Miller)
wrote:

In article , "Bob F"
wrote:

If the voltage is insufficient, no power supply, no matter what current it
can deliver, will light the bulb.

Oh, really? Let's see the explanation of that.

He's correct. It's simple electricity 101.

OK, fine -- explain it.

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

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

If the voltage is insufficient, no power supply, no matter what current it
can deliver, will light the bulb.

Oh, really? Let's see the explanation of that.

He's correct. It's simple electricity 101.

OK, fine -- explain it.

A power supplies current draw depends on what the load is
and what the voltage is.

The current draw is not determined by the rating of the supply.

On Feb 14, 6:25 pm, wrote:
If the voltage is insufficient, no power supply, no matter what current it
can deliver, will light the bulb.

Oh, really? Let's see the explanation of that.

He's correct. It's simple electricity 101.

OK, fine -- explain it.

A power supplies current draw depends on what the load is
and what the voltage is.

The current draw is not determined by the rating of the supply.

FYI, that's only true if the required current is less than the rating
of the supply.

If the required current is more than the supply's rating, then actual
current IS determined by the supply.

Mark