Control/Dimming Low cost PC-controlled 12V dimmer?

[ralfha]

I have an application where I need to control 280 12V 20W halogen lamps individually from a PC. The key constraint is I need to keep the hardware scalable to that large number of lamps at low cost (max $50 per circuit.)

Can anybody suggest low cost 12V dimmers (rated at 2A or more) that would fit the bill? I don't have hard requirements on the control interface; it could be DMX, other PC-based interface, or even 0-10V.

Thanks,
Ralf

 

[JD]

I just want to be sure of the math here... 280 12V 20W halogen lamps individually? That would require 280 circuits. At $50 per, that comes to $14,000 which would not be what I would call low cost! The cheapest way would be to use low cost DMX 120v dimmers with transformers. Transformers can be funny as they are inductors, but when loaded with an incandescent lamp, they will usually work. Using a 4 channel Optima DMX dimmer (about $70) and Home Depot type transformers, your cost would be under $30 per channel. No guarantees! Check with the manufacturer about the transformers though..

 

[ralfha]

Thanks for the reply. I agree that 14K is not a small cap on the investment but I have come to grips with the fact that given the number of circuits this will not be inexpensive.

I would prefer dimming at the 12V level. (I am hoping i can get economies of scale/size by sharing transformers, plus the purely resistive load should indeed behave better). But I will look into the line voltage route you suggest as well.

(If there are other folks who know of 12V dimers I'll appreciate any pointers.)

 

[JD]

Considering the scale of the project, you may want to consult with an qualified electronics fabricator. The dimmers I referred to may only require minor modifications to run off of 12 volts. Hypothetically, the only part inside the dimmer packs that needs 120 volts is the power transformer which supplies the low voltage electronics. It also provides electrical isolation from the electronics. As long as the electronics are powered up, you could pretty much plug the power cord into the output of a large 12 volt transformer. The triacs inside don't really care what voltage they are switching, up to the breakdown voltage of the device. They are also optically isolated from the control electronics by a photo-coupler. As you are downverting the voltage, this will not be a factor. The only possible problem may be that at some setting there is not enough current to fire the gate of the triac, but considering the costs involved, a prototype may be warranted. If it were to work, your cost per channel would be down to $17 per channel. Once again, only a qualified shop should attempt this. As the packs would be modified, they would loose their warranty. I would assume that the UL rating would also be null and void (If the Optima packs had one to begin with), although at 12 volts, the unit would no longer be in the same class as 120 volt equipment. As I said before, "Hypothetically."

 

[cutlunch]

If you need to do this I would suggest looking at PWM (Pulse Width Modulation) controllers. You can often get them as kitsets for things like driving low voltage DC motors but they also work for lights if you get the right wattage rating.

They normally have a pot to control the speed but you could probably get a PC - Analouge interface made to provide the control voltage.

Here's a link to a Velleman kit for the dimmer / motor control type of thing I am thinking of to do the dimming part.
Velleman Components n.v.

I think you will find it will be cheaper to have something custom made for you. To try and make it up from a lot of bits it will start to look like Frankestein's monster.

What is the power source you will be using AC from the mains supply or battery, If it is AC then you will need transformers for the 12 Volts anyway. I actually like the "use a dimmer" idea. Is this a fixed installation or will it moved from space to space.

You say you need 280 individual channels but if you actually gone through your lighting plot to see which lights are always on together? Depending on what you are doing it would be rare not to have at least a couple of lights paired up.

Can you give any more details on what you are doing? As this would give some more design ideas to work with. Such as will the control boards be all in one place or will they need to be spread around the space.

If you don't have background in building electronic projects from scratch you will need to get help from someone with the experience.

I have just come across this dimmer system that runs from 12 - 36 volts and will dim 12 volts. It has 4 channels and uses DMX control. You would only need 70 of them !!! I don't know the price.
ARTDC Dimmer

I know there are more 12 Volt dimmers out there but my browser keeps freezing up so I'll post this before I loose it.

 

[ralfha]

Thanks cutlunch. The ART dimmer seems like overkill for what I am trying to do (given the serious power handling I am sure it is pricey, and I don't look forward to stacking 140 of those relatively big boxes.)

The velleman kit is more my speed (I knew they had line voltage dimer kits but didn't know about this DC one.) I found it for sale at $20.95 a piece, I could pair that with a Doug Fleenor 96 output 0-10V D-A which works out to about $12.5 per circuit for a total of $ 33.45 per circuit (excluding power supply.) Not bad, though I would have to spend a few days assembling the 280 Velleman kits

Since you ask, what I an trying to do is to set up what you might call "need-based lighting" in the living room of a home under construction. Today's homes spend untold amounts of energy lighting entire rooms to full power when only certain areas of the room need full lighting at any given time (typically where people gather.) So this large living room has 280 very small (1" diameter) 20W halogen spotlights built into the ceiling arranged in a 20 x 14 matrix (the lights are 2 feet apart.) By dimming each of them separately under PC control, the homewoner will be able to vary the lighting of the room in practically infinite patterns based on what's going on the room. One relative static application of this is changing the light patterns occasionally when furniture gets moved around. More dynamic applications would be lighting up areas of the room where there are currently people while keeping the other ones at a background level (this could be done manually via a touch screen, or automated via some kind of presence sensor, e.g. infrared, sonar, or floor weight.) The brighter light would essentially "follow" people around the room (something that theaters have been doing forever). Then there are other gimmicks that you get free like having scrolling vanity signs across the ceiling of the room.

That said, it will be a long time before mainstream homes have a chance to get lit up this way but as the technology comes down the price curve there is no reason this couldn't happen. This is just an early experiment.

Best,
Ralf