cheap light dimmer

[baldbaby2000]

For those handy with a soldering iron:

In my efforts to reduce battery consumption and still have the warmth of incandescent lights I built this circuit: http://electronics-tutorials.com/device ... dimmer.htm
I went to my junk box so it didn't cost anything but the parts would be cheap. I had a 100k pot so I used that instead of the 47k and it works fine. I added a reverse polarity protection diode for the electronics and put a 2000 uF capacitor from the circuit power to ground to filter electronic noise. I only have a small heat sink on the transistor and it runs pretty cool. It seems to work well giving a range of off to virtually fully on. I have it hooked to only one light now but I think I'll parallel 4 transistors to distribute the current and have one control for all 4 cabin lights. There is some electrical noise generated (not much with only one light but noticable with all 4) so I'll add a series inductor that will hopefully clean it up.

Daniel

[Frank C]

SAY WHAT~!!??? Actually not asking for an education in electronics ... just curious. I've always had the impression that cutting the intensity by 50 percent yields much less energy savings??? Am I misguided?

[Catigale]

The optical intensity should be roughly proportional to the power, so 50% decrease in light intensity would save you roughly 50% of your battery power - speaking a bit loosely. THis presumes you are doing this with some modulation technique (quickly turning the current on and off) and not just adding a resistive load like the old car 4 speed heater fans- this wont save you any electrons of course (the power is just dissipated in the resisitors rather than the light bulb)

[baldbaby2000]

The optical intensity should be roughly proportional to the power, so 50% decrease in light intensity ...THis presumes you are doing this with some modulation technique (quickly turning the current on and off) and not just adding a resistive load like the old car 4 speed heater fans- this wont save you any electrons of course (the power is just dissipated in the resisitors rather than the light bulb)

Yes, that's right. The 555 timer circuit does a pulse width modulation so the switch (transistor in this case) is turning on and off about 300 times per second. You control the brightness by the percentage of time the switch is on (duty cycle). The circuit is efficient (doesn't get very hot) because the switch is either completely on or completely off therefore dissipating very little heat. The downside to these is the potential for electrical noise creeping into other equipment like a CD player due to the fast switching. This may be an issue if I want to control more than one light so I may have to add an inductor to filter it. I built this because I wasn't sure about the West Marine ones. They seemed kind of expensive, I wasn't sure how well they would work and some seemed to be simple reostat that get hot. You can probably build this circuit for less than $10.

[Actually a simple reostat (series variable resistor) will still save some (but not as much) power because the overall current will still be decreased as you increase the resistance.]

[DLT]

Yes, that's right. The 555 timer circuit does a pulse width modulation

Yeah, back in college, I designed a robot speed and direction control around two 555 timers, one for each of two drive wheels. I could control speed and direction based on how I pulsed each motor.

The circuit is rather efficient, but its not completely efficient. For one, you are powering the added circuit. Also, you do have to account for inrush, and heating the filment... But, all that's pretty negligible in the big picture though... If you cut light by 50%, you're probably saving 40% or more power overall...

As for a filter, a proper filter may require a inline inductor and a capacitor across the power leads. The battery is basically a capacitor, but its in the wrong position, as the capacitor needs to be between the inductor and the 555. The inductor wants to keep current constant, so your other stuff doesn't see the noise. The capacitor wants to keep voltage constant, and with therefore supply the inrush current required by the timer.

[baldbaby2000]

The battery is basically a capacitor, but its in the wrong position, as the capacitor needs to be between the inductor and the 555. The inductor wants to keep current constant, so your other stuff doesn't see the noise. The capacitor wants to keep voltage constant, and with therefore supply the inrush current required by the timer.

I added a 2000 uF capacitor on the power leads both for noise filtering to other equipment and noise filtering to the 555 circuit itself. Light dimmers for AC applications generally only use an inductor and that seems to work fairly well but in a low voltage application such as this the higher current draw probably produces more noise.

I think the main inefficiency is that when you dim the bulb the ratio of visible light to infrared (not that useful) power decreases but it gives a romantic glow and makes the Admiral happy!

[LOUIS B HOLUB]

....optical intensity, capacitors, modulations, inductor, disipating resistors, reo stat, pulse width,

When I plug it in, it better work. (because, I 'aint gonna ask why)

[ronacarme]

Or for a DIY project to give the incandescentlike color at lower wattage, lconsider "warm white" LEDs. Ron

[Catigale]

Plutonium 235 has a nice glow just below critical mass - doesnt make any of those nasty greenhouses gasses either.

Just glop it on underneath and enjoy the fireworks.

Walmart carries it in the 'Astronomy' section



(I think Sloop is rubbing off on me...)

[Joe 26M Time Warp]

Or for a DIY project to give the incandescentlike color at lower wattage, lconsider "warm white" LEDs. Ron

Right!
My long term plan is to use both white & red LEDs for all kinds of interior lighting. Although dimmer circuits could be incorporated at some point, what I was planning is selector switches with several levels of brightness that turn on more LEDs.
To add just enough of an "eclectic Mac Mod" I was thinking of controlling most if not all interior lights wired with three way switches.