Post by thread:12 V halogen lamp dimmer/motion sensor triggered s

Hi all, I'm looking for ideas on how to make a lamp driver/dimmer based on the 12CE518 chip. Its going to drive 4 (for now, maybe more later) 12V 20 Watt halogen lamps that can be triggered on by motion sensors, stay on for a programmable amount of time and then turn themselves off. I need to be able to control the brightness of the lamps as well. The reason I want to use the CE chip is so that I can retain brightness and the turn-off delay information. Now I guess the traditional way would be to stick a 12V high amperage transformer and drive a MOSFET by 12CE518 to control the brightness and on/off operation. But I dont want to keep the transformer running at all times. BTW, what is uaully the no load mains current draw of like a 35A 12V transformer? The other thing I can do is to turn on/off the transformer as well and supply the MCU power from another source. I have a couple of 120VAC devices that need to be turned on at the same time as well which donot require the dimmer function and I think the easiest way to do that would be to stick a relay in there. The same relay can drive the transformer. Anyone has any ideas to approach this from a different angle? Maybe a way to not use the transformer at all. What about ideas for a cheap power supply for the 12CE519 that runs off 120VAC. Shahid.

>I'm looking for ideas on how to make a lamp driver/dimmer based on the >12CE518 chip. Its going to drive 4 (for now, maybe more later) 12V 20 Watt >halogen lamps that can be triggered on by motion sensors, stay on for a >programmable amount of time and then turn themselves off. A reasonable request... > I need to be able to control the brightness of the lamps as well. However, having been in the Theatre lighting / Electrics industry for a few years I would advise AGAINST dimming Low volt' Halogens. Why ???? - unless a halogen lamp is run at its (normal) - preferred operating temperature, you WILL find that the life of the globe / lamp is reduced by quite a dramatic amount, these lamps seem ( from Practical experience ) to prefer full voltage - to achieve maximum lifetime operation within design parameters. It seems that running them "undervolt" causes them to fail to reach the correct "burn-off" temperature internally. (The full technical reason was discussed in the Theatre technical forums a couple or three years ago) - I admit I can longer drag up the original replies and etc, but remember thinking at the time that the comments made mirrored our own experiences with these lamps. We found that a "cool down" cycle was also very important to long lamp life, although in our moving lights we did lose a few globes - due to hot filament breakage, this is why you may notice a lot of Theatre / FX lighting systems that use a Halogen source, move a mirror or some other part of the optical path - rather than the complete luminaire. I know this has not really answered your question Shahid, but thought that you might like to be made aware of this potential problem. Glenville T. Sawyer Outback Communications, South Australia. "Solutions through Silicon". Software, Hardware Communications and Theatrical Special Effects.

Shahid Sheikh wrote: <snip> > Now I guess the traditional way would be to stick a 12V high amperage > transformer and drive a MOSFET by 12CE518 to control the brightness and > on/off operation. But I dont want to keep the transformer running at all > times. BTW, what is uaully the no load mains current draw of like a 35A 12V > transformer? My understanding is that if no current is being drawn from the secondary of a tr ansformer, then the only power consuption is the resistance in the windings of the primary plus some negligable amount for hysteresis. If I am wrong on this, I would surely like to know. Michael ************************************************************************* When the way of the Tao is forgotten, kindness and ethics must be taught. Men must learn to pretend to be wise and good. -- Lao Tzu *************************************************************************

Not quite. A transformer with no load that is running efficiently and not saturating or loosing flux to the big wide world stores energy in itself that is almost equal and almost 180 degrees out of phase as the energizing signal which means that when there is no load on the secondary, there is almost no current being drawn at the prinary. If the transformer was 100% efficient, there would be no current drawn at all and it would look like a totally open circuit. The impedance at the secondary compared with that of the primary is found by squaring the turns ratio. Thank your lucky stars that it isn't just the resistance of the wire. Some of those primaries would truly make things smoke if they were connected to 117 or 240 volts DC. Cheers, Martin McCormick WB5AGZ Stillwater, OK OSU Center for Computing and Information Services Data Communications Group "Michael J. Ghormley" writes: {Quote hidden}>My understanding is that if no current is being drawn from the secondary of a >transformer, >then the only power consuption is the resistance in the windings of the primar >y plus some >negligable amount for hysteresis. If I am wrong on this, I would surely like >to know. > >Michael > >************************************************************************* >When the way of the Tao is forgotten, kindness and ethics must be taught. >Men must learn to pretend to be wise and good. -- Lao Tzu >*************************************************************************

Martin McCormick wrote: > Not quite. A transformer with no load that is running > efficiently and not saturating or loosing flux to the big wide world > stores energy in itself that is almost equal and almost 180 degrees > out of phase as the energizing signal which means that when there is > no load on the secondary, there is almost no current being drawn at > the prinary. If the transformer was 100% efficient, there would be no > current drawn at all and it would look like a totally open circuit. > The impedance at the secondary compared with that of the primary is > found by squaring the turns ratio. > > Thank your lucky stars that it isn't just the resistance of > the wire. Some of those primaries would truly make things smoke if > they were connected to 117 or 240 volts DC. I think that we're on the same page here. I agree with everything that you say. My original statement is that _what power is being consumed_ is due to the resistance in the wire. I wasn't saying that the primary is a short. Most transformers (especially cheap ones) w ith no secondary load are warm (or downright hot) to the touch. This heat is from some amount of current running through the resistance in the primary windings, yes? Michael ************************************************************************* When the way of the Tao is forgotten, kindness and ethics must be taught. Men must learn to pretend to be wise and good. -- Lao Tzu *************************************************************************

At 01:08 PM 14/12/98 -0800, you wrote: >Martin McCormick wrote: > >> Not quite. A transformer with no load that is running >> efficiently and not saturating or loosing flux to the big wide world >> stores energy in itself that is almost equal and almost 180 degrees >> out of phase as the energizing signal which means that when there is >> no load on the secondary, there is almost no current being drawn at >> the prinary. If the transformer was 100% efficient, there would be no >> current drawn at all and it would look like a totally open circuit. >> The impedance at the secondary compared with that of the primary is >> found by squaring the turns ratio. >> >> Thank your lucky stars that it isn't just the resistance of >> the wire. Some of those primaries would truly make things smoke if >> they were connected to 117 or 240 volts DC. > >I think that we're on the same page here. I agree with everything that you say. My original >statement is that _what power is being consumed_ is due to the resistance in the wire. I wasn't >saying that the primary is a short. Most transformers (especially cheap ones) with no secondary >load are warm (or downright hot) to the touch. This heat is from some amount of current running >through the resistance in the primary windings, yes? > >Michael Nope, you have it wrong there. The current is limited by the inductance of the transformer, if you run DC through them the resistance is very low and would limit the current to about 10A primary, this is on a hammond 48VA transformer. The wire is sized to carry about 1/2A. The heat actually is caused by a LACK of iron in the core. The more iron you put in the more current you can put through the transformer. Most transformers these days appear to operate on the edge of the design limits. Barry

Barry Cooper wrote: > Nope, you have it wrong there. The current is limited by the inductance > of the transformer, if you run DC through them the resistance is very low > and would limit the current to about 10A primary, this is on a hammond 48VA > transformer. The wire is sized to carry about 1/2A. The heat actually is > caused by a LACK of iron in the core. The more iron you put in the more > current you can put through the transformer. Most transformers these days > appear to operate on the edge of the design limits. Barry, I didn't say that the current is limited by the resistance. I re-read my post a nd cannot see how you made that conclusion. I was agreeing with you about inductan ce, AC, etc. What I am saying is that the power that *is* consumed by a transformer 's primary when the secondary is open is caused mainly by the resistance in the wir e. Do we argree on that? Or am I still off base? The LACK of iron in the core? Are you implying that an air core would be hotter than an iron core? :) But back to the bottom line...we are far afield of the request by the original poster. What I am suggesting is that the original poster does not need to cut off the primary windings to conserve power. Michael ************************************************************************* When the way of the Tao is forgotten, kindness and ethics must be taught. Men must learn to pretend to be wise and good. -- Lao Tzu *************************************************************************

"Michael J. Ghormley" wrote: > Barry Cooper wrote: > > > Nope, you have it wrong there. The current is limited by the inductance > > of the transformer, if you run DC through them the resistance is very low > > and would limit the current to about 10A primary, this is on a hammond 48VA > > transformer. The wire is sized to carry about 1/2A. The heat actually is > > caused by a LACK of iron in the core. The more iron you put in the more > > current you can put through the transformer. Most transformers these days > > appear to operate on the edge of the design limits. > > Barry, > > I didn't say that the current is limited by the resistance. I re-read my post and > cannot see how you made that conclusion. I was agreeing with you about induct ance, > AC, etc. What I am saying is that the power that *is* consumed by a transform er's > primary when the secondary is open is caused mainly by the resistance in the w ire. > Do we argree on that? Or am I still off base? > For a fixed input voltage / frequency transformer with a ferromagnetic core ther e is a fixed power loss due to the core's properties. This core loss is set by transfor mer's designer. A transformer with an undersized core will dissipate more power than o ne with a properly sized core. The current into an idle 60 Hz power transformer should be small enough that the power loss due to the winding resistance should be insignificant. > > The LACK of iron in the core? Are you implying that an air core would be hott er > than an iron core? :) An air core transformer would be many times larger than an iron core transformer . It would run cooler when idle but would dissipate much more power than an iron core transformer when at full power. --------------------------------------------------------------------- | Dr. Kevin Dale Kirmse, PhD EE | Portable System Design, High Speed Serial Links | FPGA Design, Video Hardware | | King of Prussia, PA 19406 | spam_OUTkirmseTakeThisOuTnetaxs.com ---------------------------------------------------------------------

|In fact, cheap mass produced transformers, such as ones meant for Halogen |lighting are absolutely lousy when used open circuit, drawing as much as |4% of the rated power in losses. A 400W one could easily consume 20W |idling. This does not look like much, but you don't want it in 1000 copies |in a hotel, or attached to a UPS backed circuit. What is the relationship between transformer loading and core saturation? I was working awhile ago on a PIC-controlled inverter and found it difficult to interpret what was going on. Will adding a load to a transformer cause it to saturate less quickly (since the energy going into the transformer has someplace to go besides the core) or more quickly (since more energy will be drawn into the tran- sformer). What are the best ways to avoid saturation? Also, on the original halogen lamp subject: is it better to cycle halogen lamps full on/full off, or to go between full on/minimally on (i.e. as hot as possible without glowing) to reduce the rate at which the glass cools off? Are there any real statistics on how to best operate them? Attachment converted: wonderland:WINMAIL.DAT (????/----) (00025407)