I need a simple way of dimming 12V Halogens

[[email protected]]

I work with a preformance arts company doing shows in the scottish
highlands and due to the massive amount of rain fall we need to use
water-prof lighting.

We have been using 12v hallogens with some success but I cant find any
pre-built 12v dimmers. I have found several that use 240v dimmers and
then drop the voltage down to 12v but none so far that start with a 12v
input.

My limited understanding of switch mode power suplys makes them seem
like the logical solution but I dont know enough to pick the right
chip.

I have found some that require only couple of external componets and
only a small heat sink.

If someone could point me in the right direction it would save me a
great deal of heart ache.

Thank you for your time.
Nik

 

[martin.shoebridge]

I work with a preformance arts company doing shows in the scottish
highlands and due to the massive amount of rain fall we need to use
water-prof lighting.

We have been using 12v hallogens with some success but I cant find any
pre-built 12v dimmers. I have found several that use 240v dimmers and
then drop the voltage down to 12v but none so far that start with a 12v
input.

SNIP
Take a look at model plane/car speed controllers for electric motors....
They are pwm devices and can supply several amps. Some go into the tens of
amps.

 

[Father Haskell]

I work with a preformance arts company doing shows in the scottish
highlands and due to the massive amount of rain fall we need to use
water-prof lighting.

We have been using 12v hallogens with some success but I cant find any
pre-built 12v dimmers. I have found several that use 240v dimmers and
then drop the voltage down to 12v but none so far that start with a 12v
input.

Can't you get the same effect by just turning off selected lamps
out of each bank?

 

[martin griffith]

On 4 Jan 2007 12:34:44 -0800, in sci.electronics.design

I work with a preformance arts company doing shows in the scottish
highlands and due to the massive amount of rain fall we need to use
water-prof lighting.

We have been using 12v hallogens with some success but I cant find any
pre-built 12v dimmers. I have found several that use 240v dimmers and
then drop the voltage down to 12v but none so far that start with a 12v
input.

My limited understanding of switch mode power suplys makes them seem
like the logical solution but I dont know enough to pick the right
chip.

I have found some that require only couple of external componets and
only a small heat sink.

If someone could point me in the right direction it would save me a
great deal of heart ache.

Thank you for your time.
Nik

First, get a professional to help you, mucking around with mains is
dangerous, and get a budget from the boss

2) I assume you are using 230/240V ac in, the easiest way would be to
use 230V dimmers, directly into a 12V out transformers, close to the
dimmer pack. Then cable up to the 12v lamps. Choose a nice XLR that
wont annoy the sound guys when they plug your connector into their
stuff. I'm not in the biz anymore, but there probably is a "standard"

3) If you agree with point 2), you will need thicker cables

4) Many people here have studied for days, even weeks to become
professional engineers, you wont do this overnight (safely anyway)

5) check your insurance policies


martin

 

[default]

I work with a preformance arts company doing shows in the scottish
highlands and due to the massive amount of rain fall we need to use
water-prof lighting.

We have been using 12v hallogens with some success but I cant find any
pre-built 12v dimmers. I have found several that use 240v dimmers and
then drop the voltage down to 12v but none so far that start with a 12v
input.

My limited understanding of switch mode power suplys makes them seem
like the logical solution but I dont know enough to pick the right
chip.

I have found some that require only couple of external componets and
only a small heat sink.

If someone could point me in the right direction it would save me a
great deal of heart ache.

Thank you for your time.
Nik

This post should be to the basic electronics
group............................

Search for <12v DC dimmer> Lot of circuits, or kits. A simple mosfet
dimmer with the right mosfet(s) can control many amps.

 

[John B]

I work with a preformance arts company doing shows in the scottish
highlands and due to the massive amount of rain fall we need to use
water-prof lighting.

We have been using 12v hallogens with some success but I cant find any
pre-built 12v dimmers. I have found several that use 240v dimmers and
then drop the voltage down to 12v but none so far that start with a
12v input.

My limited understanding of switch mode power suplys makes them seem
like the logical solution but I dont know enough to pick the right
chip.

I have found some that require only couple of external componets and
only a small heat sink.

If someone could point me in the right direction it would save me a
great deal of heart ache.

Thank you for your time.
Nik

Hi Nik,

You might get some help from 'rec.arts.theatre.stagecraft'. Otherwise
email me off list.

 

[Homer J Simpson]

I work with a performance arts company doing shows in the Scottish
highlands and due to the massive amount of rain fall we need to use
water-proof lighting. ....
My limited understanding of switch mode power supplies makes them seem
like the logical solution but I don't know enough to pick the right
chip.

....

Probably not the way to go. What is the total wattage at 12V?

I'd be inclined to step down to 15 VAC and use remote control dimmers to
feed the lamps from there.

Look in your local library for a copy of the GE SCR manual or a GE hobby
manual - old but if you can find one it will have useful ideas you can use.






--

 

[[email protected]]

I recommend checking what Solar Converters has to offer.
It may be worth a phone call. http://www.solarconverters.com

 

[Phil Allison]

** Groper alert:

I work with a preformance arts company doing shows in the scottish
highlands and due to the massive amount of rain fall we need to use
water-prof lighting.

We have been using 12v hallogens with some success but I cant find any
pre-built 12v dimmers. I have found several that use 240v dimmers and
then drop the voltage down to 12v but none so far that start with a 12v
input.

** Are you using 12 volt batteries or AC power ?

My limited understanding of switch mode power suplys makes them seem
like the logical solution but I dont know enough to pick the right
chip.

** It is generally not practical to *directly dim* 12 volt lights used in
stage performances. Any dimming is done at the much higher AC supply
voltage level.

The problem is excessive "voltage drop" in the cables feeding the lights. A
voltage drop ( due to cable resistance and dimmer losses) of 5 to 10 volts
in a 230 volt system has very little consequence, but in a 12 volt system
it would be a disaster.

This is why you always see 12 volt halogen lamps sited very close to their
step down transformers.




........ Phil

 

[Al]

I work with a preformance arts company doing shows in the scottish
highlands and due to the massive amount of rain fall we need to use
water-prof lighting.

We have been using 12v hallogens with some success but I cant find any
pre-built 12v dimmers. I have found several that use 240v dimmers and
then drop the voltage down to 12v but none so far that start with a 12v
input.

My limited understanding of switch mode power suplys makes them seem
like the logical solution but I dont know enough to pick the right
chip.

I have found some that require only couple of external componets and
only a small heat sink.

If someone could point me in the right direction it would save me a
great deal of heart ache.

Thank you for your time.
Nik

Remember that halogen lamps work on an iodine-tungsten cycle. If you
drop the voltage, hence reducing the power, you will interrupt the cycle
and damage the bulbs. What does this mean? Probably a much shorter life
for the bulbs.

If you can live with that, and you use AC, use a variac to control the
AC to a transformer that drops the voltage to the 12AC that the lights
use. So, if you drop the voltage to the transformer in half, than the
voltage to the lights will drop to 6V. Will this mean a decrease in half
of the illumination? Dunno, you have to experiment.

You will need some hefty transformers and variacs. It, of course,
depends on the number of lights you want to control.

Al

 

[John B]

On 05/01/2007 Al wrote:

..
..
..

Remember that halogen lamps work on an iodine-tungsten cycle. If you
drop the voltage, hence reducing the power, you will interrupt the
cycle and damage the bulbs. What does this mean? Probably a much
shorter life for the bulbs.

This is helpful to understand the problem:

http://americanhistory.si.edu/lighting/webnotes/webnote7.htm

If you can live with that, and you use AC, use a variac to control
the AC to a transformer that drops the voltage to the 12AC that the
lights use. So, if you drop the voltage to the transformer in half,
than the voltage to the lights will drop to 6V. Will this mean a
decrease in half of the illumination? Dunno, you have to experiment.

You will need some hefty transformers and variacs. It, of course,
depends on the number of lights you want to control.

Al

In our Scottish climate, it would probably be better to use 110VAC
distribution and local dimmer boxes with DMX interfaces. Use a bridge
rectifier and a power FET for each luminaire. Assuming 50W lamps you'll
need 8A components to allow some headroom. Because of the losses in the
semiconductors you need to start at around 15VAC. To minimise filament
rattle each dimmer channel should switch on at the zero crossing and
turn off in mid-phase.

There's a good starting point for home brew stuff here:

http://www.hoelscher-hi.de/hendrik/english/dimmer.htm

but I think the software only supports triacs which fire in mid-cycle.


If you want to buy then have a look here:

http://www.anytronics.com/