Looking to power a mini halogen bulb to do film capture. It would be great
if I could power it off the movie projector itself without having to get an
additional power supply. The socket for the projector reads slightly over
24v. However, the lamps it uses are 21v. Someone has stated that load is a
factor. Does that mean that the voltage needs to be higher than the bulb
rating or not necessarily?

What I wonder is if this 24v bulb should work off the 24v socket on the
projector?

http://www.1000bulbs.com/product.php?product=685

Thanks

HiC wrote:

Looking to power a mini halogen bulb to do film capture. It would be great
if I could power it off the movie projector itself without having to get an
additional power supply. The socket for the projector reads slightly over
24v. However, the lamps it uses are 21v. Someone has stated that load is a
factor. Does that mean that the voltage needs to be higher than the bulb
rating or not necessarily?

What I wonder is if this 24v bulb should work off the 24v socket on the
projector?

I'd be more concerned about overloading the transformer in the projector
myself.

Graham

On Sun, 15 Oct 2006 12:22:14 +0100, Eeyore
wrote:



HiC wrote:

Looking to power a mini halogen bulb to do film capture. It would be great
if I could power it off the movie projector itself without having to get an
additional power supply. The socket for the projector reads slightly over
24v. However, the lamps it uses are 21v. Someone has stated that load is a
factor. Does that mean that the voltage needs to be higher than the bulb
rating or not necessarily?

What I wonder is if this 24v bulb should work off the 24v socket on the
projector?

I'd be more concerned about overloading the transformer in the projector
myself.

Graham

He seems to be implying that the 24 volts is measured output and 21
volts is the proper bulb for the projector - so the voltage under load
is expected to be lower. In that case using a 24 volt lamp to replace
a 21 volt one will be less strain on the transformer.

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On Sun, 15 Oct 2006 08:37:01 GMT, "HiC" wrote:

Looking to power a mini halogen bulb to do film capture. It would be great
if I could power it off the movie projector itself without having to get an
additional power supply. The socket for the projector reads slightly over
24v. However, the lamps it uses are 21v. Someone has stated that load is a
factor. Does that mean that the voltage needs to be higher than the bulb
rating or not necessarily?

The actual no load voltage will almost always be higher than the
under-load voltage - unless the power supply is regulated (most movie
projectors aren't regulated unless you have a theater projector)

Voltage ratings on incandescent bulbs have to be taken with some
skepticism. They are usually intended to be "nominal" ratings.

For instance, a 12 Volt bulb intended for auto use will spend most of
its life working at 13.8 or higher and the people that make the bulbs
know that and take it into account.

Likewise projectors. The 21 volt bulb may be intended to run at 21
volts or 24 volts - unless you see the manufacturers curves regarding
ambient temperature, color temperature of the light, voltage and life
expectancy you're just "whistling in the dark."

Sometimes a lower voltage bulb is used at a higher voltage - it
shortens the life, but puts out more light and puts out higher color
temperature light - so color renditioning may be better.

Likewise, under load, your 24 volts will almost certainly be lower
than 24V.

What I wonder is if this 24v bulb should work off the 24v socket on the
projector?

http://www.1000bulbs.com/product.php?product=685

Thanks

Get a 24 V lamp and try it. If you can't live with the color (should
be "warmer" -less blue) be happy and expect the lamp to last longer
than a 21 V lamp in the same application .



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default wrote:
On Sun, 15 Oct 2006 08:37:01 GMT, "HiC" wrote:

Looking to power a mini halogen bulb to do film capture. It would be great
if I could power it off the movie projector itself without having to get an
additional power supply. The socket for the projector reads slightly over
24v. However, the lamps it uses are 21v. Someone has stated that load is a
factor. Does that mean that the voltage needs to be higher than the bulb
rating or not necessarily?

The actual no load voltage will almost always be higher than the
under-load voltage - unless the power supply is regulated (most movie
projectors aren't regulated unless you have a theater projector)

Voltage ratings on incandescent bulbs have to be taken with some
skepticism. They are usually intended to be "nominal" ratings.

For instance, a 12 Volt bulb intended for auto use will spend most of
its life working at 13.8 or higher and the people that make the bulbs
know that and take it into account.

Likewise projectors. The 21 volt bulb may be intended to run at 21
volts or 24 volts - unless you see the manufacturers curves regarding
ambient temperature, color temperature of the light, voltage and life
expectancy you're just "whistling in the dark."

Sometimes a lower voltage bulb is used at a higher voltage - it
shortens the life, but puts out more light and puts out higher color
temperature light - so color renditioning may be better.

Likewise, under load, your 24 volts will almost certainly be lower
than 24V.

What I wonder is if this 24v bulb should work off the 24v socket on the
projector?

http://www.1000bulbs.com/product.php?product=685

Thanks

Get a 24 V lamp and try it. If you can't live with the color (should
be "warmer" -less blue) be happy and expect the lamp to last longer
than a 21 V lamp in the same application .

A 24v bulb is likely to be a 28-29v bulb in reality, running this on
21v will give a very poor result. OP needs to tell us if the 24v
reading is under load or not. If its with no load, OP needs a 21v bulb,
anything else will just be crap. Depending on the type of psu, it may
be possible to change the output voltage to suit other bulbs
voltage-wise. Whether they will have the right optical situatoin is
another matter.


NT

wrote:

A 24v bulb is likely to be a 28-29v bulb in reality

So how come you can buy 28V bulbs too ?

Graham

On Sun, 15 Oct 2006 16:27:06 +0100, in sci.electronics.design Eeyore
wrote:



wrote:

A 24v bulb is likely to be a 28-29v bulb in reality

So how come you can buy 28V bulbs too ?

Graham

Thats for when you have a 35V supply :-)


martin

You are supposed to underpower the light bulb. Why do you think normal
house light bulbs are 120v when you only have 110v at the outlet. It
increases the life of the light bulb.

On Oct 15, 9:35 am, martin griffith
wrote:
On Sun, 15 Oct 2006 16:27:06 +0100, in sci.electronics.design Eeyore

wrote:

wrote:

A 24v bulb is likely to be a 28-29v bulb in reality

So how come you can buy 28V bulbs too ?

GrahamThats for when you have a 35V supply :-)

martin

On 15 Oct 2006 07:43:59 -0700, wrote:

A 24v bulb is likely to be a 28-29v bulb in reality, running this on
21v will give a very poor result. OP needs to tell us if the 24v
reading is under load or not. If its with no load, OP needs a 21v bulb,
anything else will just be crap. Depending on the type of psu, it may
be possible to change the output voltage to suit other bulbs
voltage-wise. Whether they will have the right optical situatoin is
another matter.


NT

Then one is "second guessing" the lamp specifications, the
manufacturer specifications, and the ops application.

To make a really good "informed judgment" one would have to know how
the manufacturer originally intended the lamp to work - perhaps they
were sacrificing some life to add better color rendition.

Anyhow the op may be transferring film to video or digital.

He states: "Looking to power a mini halogen bulb to do film capture."

That could easily mean transferring film to digital (or tape). If it
is done via computer he could just as easily adjust the white level /
color temp, as fiddle with the hardware.

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default wrote:
On 15 Oct 2006 07:43:59 -0700, wrote:

A 24v bulb is likely to be a 28-29v bulb in reality, running this on
21v will give a very poor result. OP needs to tell us if the 24v
reading is under load or not. If its with no load, OP needs a 21v bulb,
anything else will just be crap. Depending on the type of psu, it may
be possible to change the output voltage to suit other bulbs
voltage-wise. Whether they will have the right optical situatoin is
another matter.


NT

Then one is "second guessing" the lamp specifications, the
manufacturer specifications, and the ops application.

Not really. The vast majority of 24v bulbs are for road use, where
nominally 24v systems are IRL approx 28-29v. The lamps are designed to
run on those systems.

I suppose the OP could underpower the bulb as you say, but its not the
best option. It should work, but 21v on a 28v bulb will give lousy
results.


NT

On 15 Oct 2006 15:45:18 -0700, wrote:

default wrote:
On 15 Oct 2006 07:43:59 -0700, wrote:

A 24v bulb is likely to be a 28-29v bulb in reality, running this on
21v will give a very poor result. OP needs to tell us if the 24v
reading is under load or not. If its with no load, OP needs a 21v bulb,
anything else will just be crap. Depending on the type of psu, it may
be possible to change the output voltage to suit other bulbs
voltage-wise. Whether they will have the right optical situatoin is
another matter.


NT

Then one is "second guessing" the lamp specifications, the
manufacturer specifications, and the ops application.

Not really. The vast majority of 24v bulbs are for road use, where
nominally 24v systems are IRL approx 28-29v. The lamps are designed to
run on those systems.

I suppose the OP could underpower the bulb as you say, but its not the
best option. It should work, but 21v on a 28v bulb will give lousy
results.



Here in the states, most cars use 12 volts. I've seen some indication
that 42 volts may be in the offing in future cars. There are still a
few 6 volt systems around in vehicles.

We do have some 24 VAC equipment; it is a popular "control" voltage
for relays, valves, HVAC control circuits, etc.. and some lighting . .
.. like "landscape","accent" and pathway lights.

He's talking about reducing the power used dramatically - so he will
have close to 24 volts under load - assuming I'm following all this
correctly.


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"default" wrote in message
...

Anyhow the op may be transferring film to video or digital.

He states: "Looking to power a mini halogen bulb to do film capture."

That could easily mean transferring film to digital (or tape). If it
is done via computer he could just as easily adjust the white level /
color temp, as fiddle with the hardware.

Actually there's a specific reason to use a lower wattage mini-bulb. I need
a less powerful lamp to project a useable image through a diffuser and
condenser lens and bounce it into the camera with a front surface mirror.
Normal projector lamps are too bright.

HiC wrote:

Actually there's a specific reason to use a lower wattage mini-bulb. I need
a less powerful lamp to project a useable image through a diffuser and
condenser lens and bounce it into the camera with a front surface mirror.
Normal projector lamps are too bright.

How about a neutral grey filter?

I was origianlly going to write a warning about testing the new bulb
arrangement before using it on unreplaceable film, to check for melting
or scorching of the film. However, if you are going to a lower power
bulb, and it survives, you shouldn't have that problem.

Another worry: Are you planning to stop the film at each frame to
capture the image? If so, beware of overheating the film. In normal
use, each frame of the film spends a short time stopped for
projection(1/24 second, is that right?) and is only illuminated for a
portion of that time.