Dimming a 6V bulb by half.

[Tibur Waltson]

My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.
TIA, Tibur

 

[rob]

"Tibur Waltson" <Toush@hi.com> wrote in message news:<965893c3b7116e42b340314e85596346@news.bubbanews.com>...

My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.
TIA, Tibur
You CAN use a mosfet in a 'linear' control scheme , but it is goung to

dissapate a lot of heat and will require a large heatsink.

A simple PWM would be much better.You can then vary the bulb
brightness from off to full on with very little dissapation in the
FET. You can build a nice simple one with a lm393 a few resistors and
caps and a mosfet. (logic level mosfet for your 6V app)
Use half of the 393 as a oscillator to generate a rough sawtooth
waveform.
Use the other half as a comparator to compare a reference(from a pot)
with the
sawtooth. Output is a PW Modulated square wave which you feed to the
mosfet.
Used this design with a IRF1010e mosfet to control 100W 12v bulb.
Worked like a charm , did not even need a heatsink on the Fet. I made
one small enough to fit in the handle of my "spotlight" with a pot on
the bottom of the handle for brightness.
If you want I'll send you a schematic (email).Can't seem to get to
a.b.s from here :0(

Cheers
Rob

 

[petrus bitbyter]

"Tibur Waltson" <Toush@hi.com> schreef in bericht
news:965893c3b7116e42b340314e85596346@news.bubbanews.com...

My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.
TIA, Tibur

Tibur,

Bulbs are made to do their job at some voltage. 6V in your spot. Lowering
the voltage will reduce the brightnes but more than proportional. It will
also lower the current, but less then proportional. I wonder whether you
will have any usefull light left at 3V. The best way to dim your light is
looking for a 6V/10W or 6V/15W bulb.

petrus


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.561 / Virus Database: 353 - Release Date: 13-1-2004

 

[James]

Why dont you try adding a few diodes in series until you get your
desired brightness?

A very simple idea, but it may accomplish what your after.

James


On Thu, 15 Jan 2004 07:56:28 GMT, "Tibur Waltson" <Toush@hi.com>
wrote:

My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.
TIA, Tibur

 

[Garrett Mace]

You CAN use a mosfet in a 'linear' control scheme , but it is goung to
dissapate a lot of heat and will require a large heatsink.

A simple PWM would be much better.You can then vary the bulb
brightness from off to full on with very little dissapation in the
FET. You can build a nice simple one with a lm393 a few resistors and
caps and a mosfet. (logic level mosfet for your 6V app)
Use half of the 393 as a oscillator to generate a rough sawtooth
waveform.
Use the other half as a comparator to compare a reference(from a pot)
with the
sawtooth. Output is a PW Modulated square wave which you feed to the
mosfet.
Used this design with a IRF1010e mosfet to control 100W 12v bulb.
Worked like a charm , did not even need a heatsink on the Fet. I made
one small enough to fit in the handle of my "spotlight" with a pot on
the bottom of the handle for brightness.
If you want I'll send you a schematic (email).Can't seem to get to
a.b.s from here :0(

Cheers
Rob

PWM gets some more bonus points in this application, since the spotlight
will actually use less battery power and last longer when dimmed. Light
where you're walking, not the whole countryside, unless you need it.

 

[Tibur Waltson]

..>"Garrett Mace" <g.ryan@macetech.com> wrote in message

You CAN use a mosfet in a 'linear' control scheme , but it is goung to
dissapate a lot of heat and will require a large heatsink.

A simple PWM would be much better.You can then vary the bulb

PWM gets some more bonus points in this application, since the spotlight
will actually use less battery power and last longer when dimmed. Light
where you're walking, not the whole countryside, unless you need it.

I have a square wave PWM. If it actually save more power I will
use this to drive the mosfet. If I understand correctly the PWM acts
like turning the switch on or off quickly. Mosfets are happy either on
or off. But why do my sewing machine speed control transistor
don't become hot. They don't seem to use PWMs or do they?
Thanks
Tibur

 

[Tibur Waltson]

"petrus bitbyter" <p.kralt@hccnet.nl
"Tibur Waltson" <Toush@hi.com
My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.

Bulbs are made to do their job at some voltage. 6V in your spot. Lowering
the voltage will reduce the brightnes but more than proportional. It will
also lower the current, but less then proportional. I wonder whether you
will have any usefull light left at 3V. The best way to dim your light is
looking for a 6V/10W or 6V/15W bulb. petrus

I have a 4.7V/10W. How can I use this bulb without burning out the filament?
Thanks
Tibur

 

[Tibur Waltson]

"James" <james@unknown111.demon.co.uk> wrote in message
"Tibur Waltson" <Toush@hi.com> wrote:

My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.
TIA, Tibur

Why dont you try adding a few diodes in series until you get your
desired brightness?... but it may accomplish what your after. James

Would diodes work on DC bulbs? What
mechanisms in the diodes make the lights dim?
Thanks
Tibur

 

[petrus bitbyter]

"Garrett Mace" <g.ryan@macetech.com> schreef in bericht
news:TwKNb.27129$LW.1743@twister.rdc-kc.rr.com...

You CAN use a mosfet in a 'linear' control scheme , but it is goung to
dissapate a lot of heat and will require a large heatsink.

A simple PWM would be much better.You can then vary the bulb
brightness from off to full on with very little dissapation in the
FET. You can build a nice simple one with a lm393 a few resistors and
caps and a mosfet. (logic level mosfet for your 6V app)
Use half of the 393 as a oscillator to generate a rough sawtooth
waveform.
Use the other half as a comparator to compare a reference(from a pot)
with the
sawtooth. Output is a PW Modulated square wave which you feed to the
mosfet.
Used this design with a IRF1010e mosfet to control 100W 12v bulb.
Worked like a charm , did not even need a heatsink on the Fet. I made
one small enough to fit in the handle of my "spotlight" with a pot on
the bottom of the handle for brightness.
If you want I'll send you a schematic (email).Can't seem to get to
a.b.s from here :0(

Cheers
Rob


PWM gets some more bonus points in this application, since the spotlight
will actually use less battery power and last longer when dimmed. Light
where you're walking, not the whole countryside, unless you need it.

The bulb will not like it so you'll need some extra spares. The power
savings are also questionable. A cold buld needs much more current then a
hot one.

petrus


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.561 / Virus Database: 353 - Release Date: 13-1-2004

 

[Ian Stirling]

Tibur Waltson <Toush@hi.com> wrote:

"James" <james@unknown111.demon.co.uk> wrote in message
"Tibur Waltson" <Toush@hi.com> wrote:

My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.
TIA, Tibur

Why dont you try adding a few diodes in series until you get your
desired brightness?... but it may accomplish what your after. James

Would diodes work on DC bulbs? What
mechanisms in the diodes make the lights dim?

The better way is probably to cut a small hole in the reflector and
add a small spotlight bulb (with reflector) in it.
The newer crop of these lights have a small light along with the big one,
so practically, it may be easier to just buy one.

 

[Bob Masta]

On Fri, 16 Jan 2004 12:34:48 GMT, "petrus bitbyter"
<p.kralt@hccnet.nl> wrote:

"Garrett Mace" <g.ryan@macetech.com> schreef in bericht
news:TwKNb.27129$LW.1743@twister.rdc-kc.rr.com...

PWM gets some more bonus points in this application, since the spotlight
will actually use less battery power and last longer when dimmed. Light
where you're walking, not the whole countryside, unless you need it.



The bulb will not like it so you'll need some extra spares. The power
savings are also questionable. A cold buld needs much more current then a
hot one.

petrus

The bulb should be perfectly happy with PWM, as long as you don't
make the frequency so low that the filament cools down between
pulses. That's not likely to be an issue here, since you'd have to
slow it down so much it became a flasher. So you will indeed get
excellent power savings, inversely proportional to the duty cycle.


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

[Michael A. Terrell]

Tibur Waltson wrote:

"James" <james@unknown111.demon.co.uk> wrote in message
"Tibur Waltson" <Toush@hi.com> wrote:

My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.
TIA, Tibur

Why dont you try adding a few diodes in series until you get your
desired brightness?... but it may accomplish what your after. James

Would diodes work on DC bulbs? What
mechanisms in the diodes make the lights dim?
Thanks
Tibur

A diode only passes one half the waveform, and leaves an effective
70.7% of the voltage, less the forward drop of about .6 volts. 12.6 *
..707 = 8.9082 -.6 = 8.3082 volts.

Some series string tube TV sets were built with a diode in series
with 84 volts worth of tubes, and ran on 120 volts. if you plugged the
set into DC, the tubes would either not light, or you would blow the
filament in at least one tube.

--
We now return you to our normally scheduled programming.

Take a look at this little cutie! ;-)
http://home.earthlink.net/~mike.terrell/photos.html

Michael A. Terrell
Central Florida

 

[James]

Each diode would drop the voltage by about .6 of a volt, therefore
dimming your bulb slightly. Very simple, and effective.

James


On Fri, 16 Jan 2004 15:47:20 GMT, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

Tibur Waltson wrote:

"James" <james@unknown111.demon.co.uk> wrote in message
"Tibur Waltson" <Toush@hi.com> wrote:

My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.
TIA, Tibur

Why dont you try adding a few diodes in series until you get your
desired brightness?... but it may accomplish what your after. James

Would diodes work on DC bulbs? What
mechanisms in the diodes make the lights dim?
Thanks
Tibur

A diode only passes one half the waveform, and leaves an effective
70.7% of the voltage, less the forward drop of about .6 volts. 12.6 *
.707 = 8.9082 -.6 = 8.3082 volts.

Some series string tube TV sets were built with a diode in series
with 84 volts worth of tubes, and ran on 120 volts. if you plugged the
set into DC, the tubes would either not light, or you would blow the
filament in at least one tube.

 

[James]

The guy did say that this was d.c. so there is no waveform. They are
used here for dropping voltage slightly.

James

On Fri, 16 Jan 2004 15:47:20 GMT, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

Tibur Waltson wrote:

"James" <james@unknown111.demon.co.uk> wrote in message
"Tibur Waltson" <Toush@hi.com> wrote:

My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.
TIA, Tibur

Why dont you try adding a few diodes in series until you get your
desired brightness?... but it may accomplish what your after. James

Would diodes work on DC bulbs? What
mechanisms in the diodes make the lights dim?
Thanks
Tibur

A diode only passes one half the waveform, and leaves an effective
70.7% of the voltage, less the forward drop of about .6 volts. 12.6 *
.707 = 8.9082 -.6 = 8.3082 volts.

Some series string tube TV sets were built with a diode in series
with 84 volts worth of tubes, and ran on 120 volts. if you plugged the
set into DC, the tubes would either not light, or you would blow the
filament in at least one tube.

 

On Fri, 16 Jan 2004 15:47:20 GMT Michael A. Terrell <mike.terrell@earthlink.net> wrote:
| Tibur Waltson wrote:
|>
|> >"James" <james@unknown111.demon.co.uk> wrote in message
|> >> "Tibur Waltson" <Toush@hi.com> wrote:
|>
|> > >My spot light is too bright (500,000CD). I like to dim it down when-
|> > >ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
|> > >I'm trying to dim this in the most simplest way. How could I build one
|> > >that could dim the light by half? I have resistors, mosfet, etc.
|> > >TIA, Tibur
|> > >
|> > > Why dont you try adding a few diodes in series until you get your
|> > desired brightness?... but it may accomplish what your after. James
|>
|> Would diodes work on DC bulbs? What
|> mechanisms in the diodes make the lights dim?
|> Thanks
|> Tibur
|
| A diode only passes one half the waveform, and leaves an effective
| 70.7% of the voltage, less the forward drop of about .6 volts. 12.6 *
| .707 = 8.9082 -.6 = 8.3082 volts.

What kind of waveform do you get from a lead battery (like the OP has)?

--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------

 

[Tibur Waltson]

"Bob Masta" <StopSpam@EveryChance.org> wrote in message
"petrus bitbyter" <p.kralt@hccnet.nl> wrote:
"Garrett Mace" <g.ryan@macetech.com> schreef in bericht
PWM gets some more bonus points in this application,

The bulb will not like it so you'll need some extra spares. petrus

The bulb should be perfectly happy with PWM, as long as you don't
make the frequency so low that the filament cools down between
pulses. That's not likely to be an issue here, since you'd have to
slow it down so much it became a flasher. So you will indeed get
excellent power savings, inversely proportional to the duty cycle.

I cannot get a 12-volt PWM to work on
a 6-volt power supply. What is wrong?
Tibur

 

[Don Klipstein]

In article <ITQNb.25328$DF4.19758@amsnews02.chello.com>, petrus bitbyter
wrote:

"Garrett Mace" <g.ryan@macetech.com> schreef in bericht
news:TwKNb.27129$LW.1743@twister.rdc-kc.rr.com...
You CAN use a mosfet in a 'linear' control scheme , but it is goung to
dissapate a lot of heat and will require a large heatsink.

A simple PWM would be much better.You can then vary the bulb
brightness from off to full on with very little dissapation in the
FET. You can build a nice simple one with a lm393 a few resistors and
caps and a mosfet. (logic level mosfet for your 6V app)
Use half of the 393 as a oscillator to generate a rough sawtooth
waveform.
Use the other half as a comparator to compare a reference(from a pot)
with the
sawtooth. Output is a PW Modulated square wave which you feed to the
mosfet.
Used this design with a IRF1010e mosfet to control 100W 12v bulb.
Worked like a charm , did not even need a heatsink on the Fet. I made
one small enough to fit in the handle of my "spotlight" with a pot on
the bottom of the handle for brightness.
If you want I'll send you a schematic (email).Can't seem to get to
a.b.s from here :0(

Cheers
Rob

PWM gets some more bonus points in this application, since the spotlight
will actually use less battery power and last longer when dimmed. Light
where you're walking, not the whole countryside, unless you need it.


The bulb will not like it so you'll need some extra spares.

a) Pick a higher PWM frequency if you are worried about that

b) Surges are not as hard on lightbulbs as many people think.

Although household incandescent lightbulbs usually burn out from a
cold start, the famous surge of a cold start does not cause extra wear
so much as kill lightbulbs that are already so badly aged (and by
run time rather than starts!) that their hours are numbered.

details in http://www.misty.com/~don/bulb1.html

The power savings are also questionable. A cold buld needs much more
current then a hot one.

At equal voltage, a cold filament needs more current than a hot one.
But in a PWM scheme, the "average current" (battery drain) will vary
directly (but less than proportionately) with the duty cycle. Give a
lightbulb full voltage for 50% duty cycle (1 millisecond on, 1 millisecond
off) and the average current (and this is actual power consumption) will
be about 70% of that with the same voltage applied steadily.
(Light output will be about 30-33% of full light output from that
roughly 68-72% of full power, and that means if the lightbulb in question
is usually being dimmed then you get better energy efficiency by using a
lower wattage lightbulb than from using one that is normally being
dimmed.)

petrus

- Don Klipstein (don@misty.com)

 

[Don Klipstein]

In article <542137f534acda304a32f523b428f257@news.bubbanews.com>, Tibur
Waltson wrote:

"petrus bitbyter" <p.kralt@hccnet.nl
"Tibur Waltson" <Toush@hi.com
My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.

Bulbs are made to do their job at some voltage. 6V in your spot. Lowering
the voltage will reduce the brightnes but more than proportional. It will
also lower the current, but less then proportional. I wonder whether you
will have any usefull light left at 3V. The best way to dim your light is
looking for a 6V/10W or 6V/15W bulb. petrus

I have a 4.7V/10W. How can I use this bulb without burning out the
filament?

The effective voltage is the RMS voltage, and in a variable duty cycle
application of full voltage the RMS voltage is the peak applied voltage
times the square root of the duty cycle.
If you want PWM "effective voltage reduction", then the duty cycle
should be the square of the ratio of desired effective voltage to peak
applied voltage.

Examples:

4.7 volts desired effective voltage from 6 volts: Take the square of
(4.7/6), and that is .614, or 61.4%

4.7 volts from 6.3 volts, higher side of lead-acid "6-volts":

Square of (4.7/6.3) is .556, or 55.6% - a 3/5 duty ratio is probably close
enough to run a 4.7V bulb from "6V"

4.7 volts from 12V: Square of (4.7/12) is approx. 15.3% - a 1/6 duty
cycle should be close enough for "4-cell" flashlight bulbs to be
powered from 12-12.6V

The main "gotcha": Slight chance the PWM frequency or one of its
harmonics will excite a resonance of the filament seriously enough to make
it vibrate enough to suffer damage. Try projecting an image of it onto a
wall with a smaller magnifying lens of shorter focal length - if the ends
appear skinier than the middle region (even considering that the ends may
not be coiled while the middle is usually coiled), then try a different
frequency. Try variable frequency to see what is best and worst for
shaking up the filament. Then again, most lightbulbs last a little longer
on 60 Hz AC than on DC among the ones where a difference is measurable.

- Don Klipstein (don@misty.com)

 

[Don Klipstein]

In article <83b2ea3be6acd86894260d9ae972a720@news.bubbanews.com>, Tibur
Waltson wrote:

"James" <james@unknown111.demon.co.uk> wrote in message
"Tibur Waltson" <Toush@hi.com> wrote:

My spot light is too bright (500,000CD). I like to dim it down when-
ever I toggle a switch. It uses a 6 volt lead-battery with a 25W bulb.
I'm trying to dim this in the most simplest way. How could I build one
that could dim the light by half? I have resistors, mosfet, etc.
TIA, Tibur

Why dont you try adding a few diodes in series until you get your
desired brightness?... but it may accomplish what your after. James

Would diodes work on DC bulbs? What
mechanisms in the diodes make the lights dim?

Diodes have a voltage drop. Most rectifier diodes have a voltage drop
close to .8 volt at usual current and usual temperature, maybe .7 volt
at lower currents or where they have less "heatsinking" than "usual good
design" for the amount of current being conducted.

At lower currents .5-.7 volts is common (At microamps, many common
rectifier diodes at room temperature can drop .35-.4 volt). Schottkey
diodes are special lower voltage types and many of that type drop near .5
volt at full current. On the other hand, diodes heavily heatsunk and
conducting higher currents can drop 1-1.1 volts. Diodes conducting spiky
current waveforms tend to have a slightly higher voltage drop than ones
conducting more continuously.

- Don Klipstein (don@misty.com)

 

[Tibur Waltson]

"Tibur Waltson" <Toush@hi.com> wrote in message
"Bob Masta" <StopSpam@EveryChance.org> wrote in message
"petrus bitbyter" <p.kralt@hccnet.nl> wrote:
"Garrett Mace" <g.ryan@macetech.com> schreef in bericht
PWM gets some more bonus points in this application,

The bulb will not like it so you'll need some extra spares. petrus

The bulb should be perfectly happy with PWM,

I cannot get a 12-volt PWM to work on
a 6-volt power supply. What is wrong?

Problem solved. I just add an old 9-volt battery in series.
Thanks all.
Tibur