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Low Voltage LED Lighting
My kitchen has had halogen lighting for 20 years, from back when it was a slightly more efficient choice than incandescent lighting and had a pleasing, cooler (bluer, meaning the filament runs hotter) color temperature.
Progress has moved on and while fluorescent lights still have a lead in maximum luminous efficacy (lm/w), for example the GE Ecolux Watt-Miser puts out 111 lm/W, they’re less versatile than LEDs and installation is a hassle while low voltage LEDs are easy to install and look cool.
System Design
The goal of this project was to add dimmable, pleasing light to the kitchen that I found aesthetically interesting. I wanted a decent color rendering index (CRI), ease of installation, and at reasonable cost. I’ve always liked the look of cable lighting and the flexibility of the individual, adjustable luminaires.
I couldn’t find much information on how variable output LEDs work and what can be used to drive them. I have a pretty good collection of high quality power supplies, which I wanted to take advantage of, but wasn’t sure if I’d be able to effectively dim the bulbs from the documentation I found. So I did some tests.
Test Configuration
I bought a few different 12V, Dimmable LEDs and set up a test configuration to verify operation and output with variable voltage and variable current. The one bit of data I had was that using standard commercial controllers, the lowest output is typically stated to be around 70% of maximum output: that is the dimming range is pretty limited with standard (PWM/Transformer) controllers. The results I found were much more encouraging, but revealed some quirks.
I used a laboratory-grade HP power supply with voltage and current control to drive the LEDs, decent multimeters to measure voltage and current, and an inexpensive luminance meter to measure LED output.
I measured 3 different LEDs I selected based on price and expected compatibility with the aesthetics of the project and because they looked like they’d have different internal drivers and covered a range of rated wattage.
Test Results
These bulbs have internal LED controllers that do some sort of current regulation for the diodes that results in a weird voltage/current/output response. Each bulb has a different turn-on voltage, then responds fairly predictably to increasing input voltage with increasing output, reaches the controller stabilizing voltage and runs very inefficiently until voltage gets over the rated voltage and then becomes increasingly efficient until, presumably, at some point the controller burns out. I find that the bulbs all run more efficiently at 14V than at the rated 12V.
As a side note, to perform the data analysis, I used the excellent xongrid
plugin for excel to perform Kriging interpolation (AKA Gaussian process regression) to fit the data sets to the graphing function’s capabilities. The graphs are generated with M-Chart and the table with TablePress.
Watts v. Volts
This chart shows the wattage consumed by each of the three LEDs as a function of input voltage, clearly demonstrating both that the power consumption function is non-linear and that power consumption in watts improves when driven over the rated 12V. Watts are calculated as the product of the measured Volts * Amps. Because of the current inversion that happens as the controllers come fully on-line, these LEDs can’t be properly controlled near full brightness with a current-controlled power supply, though it works well to provide continuous and fairly linear dimming at low outputs, once the voltage/current function changes slope, the current limiting controller in the power supply freaks out.
Lux v. Volts
This chart shows the lux output by each of the three LEDs as a function of input voltage, revealing the effect of the internal LED driver coming on line and regulating output, which complicates controlling brightness but protects the LEDs. The 5W LEDs have a fairly gentle response slope and start a very low voltage (2V) so are a good choice for a linear power supply. The 4W LEDs don’t begin to light up until just over 6V, and so are a good match for low-cost switch mode supplies that don’t go to zero.
Lux/W v. Volts
This chart shows the luminous efficiency (Lux/Watt, Lumen measurement is quite complicated) by each of the three LEDs as a function of input voltage, showing that overdriving the LEDs past the rated 12V can significantly improve efficiency. There’s some risk it will overheat the controller at some point and result in failure. I’ll update this post if my system starts to fry LEDs, but my guess is that 14V, which cuts the power load by 20% over 12V operation with the 7.5W lamps I selected, will not significantly impact operational lifetime.
Update: This system has been running for 7 years now. In that time two linear power supplies have failed (they were fairly inexpensive models as such things go). The LED modules had a high infant mortality rate: 2-3 failed in the first few months, another one failed just about every 6 months for the first couple of years. I think it has been 4 years since the last one failed. This implies that longevity is primarily a function of build quality, which varies.
Total System Efficiency
The emitter efficiency is relatively objective, but the total system efficiency includes the power supply. I used a Daiwa SS-330W switching power supply I happened to have in stock to drive the system, which cost less than a dimmable transformer and matching controller, and should be significantly higher quality. The Daiwa doesn’t seem to be easily available any more, but something like this would work well for up to 5A total load and something like this would handle as many as 40 7.5W LEDs on a single control, though the minimum 9V output has to be matched to LEDs to get satisfactory dimming. It is important not to oversize the power supply too much as switch mode supplies are only really efficient as you get close to their rated output. An oversized switchmode power supply can be extremely inefficient.
With the Daiwa, driving 13 7.5W LEDs, I measured 8.46A at 11.94V output or 101 Watts to brightly illuminate the entire kitchen, and providing far more light than 400W of total halogen lights. I measured the input into the power supply at 0.940A at 121.3V or 114 Watts. That means the power supply is 88.6% efficient at 12V, which is more or less as expected for a variable output supply.
Increasing the output voltage to 14.63 Volts lowered the output current to 5.35A or 78 Watts without lowering the brightness at the installation; I measured at 168 lux at both 12.0V at 14.6V. The input current at 14.63V dropped to 0.755A or 91.6 Watts, meaning the power supply is slightly less efficient at lower output currents (as is usually the case).
- Overdriving the 12V rated LEDs to 14.63V improves plug efficiency by 20%.
At the low end, the SS-330W’s minimum output is 4.88V, which yields 12 lux at the counter or a 14x dimming ratio to 7% of maximum illumination, a far better range than is reported for standard dimmer/transformer combinations.
Parts
- 7.5W LED modules from JackyLED
- Daiwa power supply (alternate version)
- 16 gauge speaker cable
- MR-16 cable lamp mounts
- Digital light meter
Raw Data:
(MS Excel file, you will need the xongrid
plugin to update the data as rendered in the graphs)
Basra Snow Storm
I was feeling a little left out, reading posts by people digging out of snow storms and here I am in Basra where it gets down to 10C at night sometimes and usually hits the mid 20’s during the day. Rough. But the weather here came through with our own sort of snow storm.
Starting to look like a brown-out!
Obligatory shot of the yard furniture getting covered.
Kitty’s head is starting to show some accumulation.
With all this blowing through you can barely see a few hundred meters!
It’s really starting to accumulate. Where’s the snow blower?
It takes some special cleaning after playing out in it.
Cat Watch
Cat Watch
The twins resting after a busy day.
Lizard Visit
A New animal visitor came by today.
Power Adventures In Iraq
Plugging things in here is always an adventure. Most of the outlets are the horrible giant British style so they have interlocked grounds, but most appliances are European style, so plugging things in means either using something to jam open the ground interlock, breaking the interlock tabs with force, or dispensing with the plug entirely and just stuffing bare wires in the holes.
When using the latter method, it turns out the British plugs are actually kind of useful because toggling the ground tab with a screwdriver uses the interlocks to bind the wires in place. You just hope the ground pin is wired to ground, not hot. Usually it just isn’t wired to anything.
Most appliances and power strips here come from China and are the sort of manufacture China was famous in the US for about 30 years ago: taking something out of the package usually breaks it. The wires inside are so thin it is amazing they survive and grounds are never, ever actually connected. I have cables that on the inside have a ground insulator but no ground conductor inside the insulator. Awesome!
But we just rewired the new villa and even though the ground isn’t wired (of course), the outlets are new and seem like they’re decent quality. And we even got British style plugs to dispense with the highly problematic and very melt-prone plug adapters. All seemed good until….
Uh oh. Maybe it just needed to create a little vent….
Nope. Melt down. Good thing these have a built-in fuse… (which is still fine, though encrusted in melted plastic).
Regional Energy Drink
I’ve run across this energy drink in dramatic packaging. Energy drinks aren’t really my thing, but I thought I’d try it: slightly orange tasting fizzy water, mildly sweet with that slightly weird energy drink taste. But the bottle is fun:
It is made in Austria and seems to be distributed more to the East than the West, at least as far as my travels have indicated. I have seen it in a lot of Middle-Eastern markets, but not in many European ones.
The lid release mechanism is kind of thematically clever.
I suspect this would be a particularly problematic beverage to forget in your carry-on luggage.
Speaker Build
In December of 2002 (really, 2002, 12 years ago (OMG, >20 years ago)), I decided that the crappy former Sony self-amplified speakers with blown amplifiers that I had wired into my stereo as surround speakers really didn’t sound very good as they were, by then, 7 years old and the holes in the plastic housing where the adjustment knobs once protruded were covered by aging gaffers tape.
At least it was stylish black tape.
I saw on ebay a set of “Boston Acoustics” woofers and tweeters back in the time when ebay prices could be surprisingly good. Boston Acoustics was a well-respected company at the time making fairly decent speakers. 36 woofers and 24 tweeters for $131 including shipping. About 100 lbs of drivers. And thus began the execution of a fun little project.
Design Phase: 2003-2011
I didn’t have enough data to design speaker enclosures around them, but about a year later (in 2003), I found this site, which had a process for calculating standard speaker properties with instruments I have (frequency generator, oscilloscope, etc.) I used the weighted diaphragm method.
WOOFER: PN 304-1150001-00 22 JUL 2000 80MM CONE DIA = 8CM FS = 58HZ RE = 3.04 OHMS QMS = 1.629 QES = 0.26 QTS = 0.224 CMS = 0.001222 VAS = 4.322 (LITERS) 264 CUBIC INCHES EBP = 177.8 NOMINAL COIL RESISTANCE @ 385HZ (MID LINEAR BAND) 3.19 OHMS NOMINAL COIL INDUCTANCE (@ 1KHZ) 0.448 MHENRY
TWEETER: PN 304-050001-00 16 OCT 2000 35MM CONE DIA FS = 269HZ RE = 3.29 OHMS QMS = 5.66 QES = 1.838 QTS = 1.387 CMS = 0.0006 VAS = 0.0778 (LITERS) EBP = 86.7 NOMINAL COIL RESISTANCE @ 930HZ (MID LINEAR BAND) 3.471 OHMS NOMINAL COIL INDUCTANCE (@ 1KHZ) 0.153 MHENRY
Awesome. I could specify a cross over and begin designing a cabinet. A few years went by…
In January of 2009 I found a good crossover at AllElectronics. It was a half decent match and since it was designed for 8 ohm woofers, I could put two of my 4 ohm drivers in series and get to about the right impedance for better power handling (less risk of clipping at higher volumes and lower distortion as the driver travel is cut in half, split between the two).
https://web.archive.org/web/20120904083243/http://www.allelectronics.com:80/make-a-store/item/XVR-21/2-WAY-CROSSOVER-INFINITY/1.html CROSS OVER FREQUENCY 3800HZ CROSSOVER LOW-PASS: 18DB, 8 OHM HIGH-PASS: 18DB, 4 OHM
Eventually I got around to calculating the enclosure parameters. I’m not sure when I did that, but sometime between 2009 and 2011. I found a site with a nice script for calculating a vented enclosure with dual woofers, just like I wanted and got the following parameters:
TARGET VOLUME 1.78 LITERS = 108 CUBIC INCHES DRIVER VOLUME (80MM) = 26.25 CUBIC INCHES = 0.43 LITERS CROSS OVER VOLUME = 2.93 CUBIC INCHES = 0.05 LITERS SUM = 0.91 LITERS 1" PVC PORT TUBE: OD = 2.68CM, ID = 2.1CM = 3.46 CM^2 PORT LENGTH = 10.48CM = 4.126" WIDTH = 12.613 = 4.829" HEIGHT = 20.408 = 7.82" DEPTH = 7.795 = 3"
In 2011 I got around to designing the enclosure in CAD:
There was no way to fit the crossover inside the enclosure as the drivers have massive, magnetically shielded drivers, so they got mounted on the outside. The speakers were designed for inside mounting (as opposed to flange mounting) so I opted to radius the opening to provide some horn-loading.
I also, over the course of the project, bought some necessary tools to be prepared for eventually doing the work: a nice Hitachi plunge router and a set of cheap router bits to form the radii and hole saws of the right size for the drivers and PVC port tubes.
Build Phase (2014)
This fall, Oct 9 2014, everything was ready and the time was right. The drivers had aged just the appropriate 14 years since manufacture and were in the peak of their flavor.
I started by cutting down some PVC tubes to make the speaker ports and converting some PVC caps into the tweeter enclosure. My first experiment with recycled shelf wood for the tweeter mounting plate failed: the walls got a bit thin and it was clear that decent plywood would make life easier. I used the shelf wood for the rest of the speaker: it was salvaged from my building, which was built in the 1930s and is probably almost 100 years old. The plywood came with the building as well, but was from the woodworker who owned it before me.
I got to use my router after so many years of contemplation to shape the faceplates, fabricated from some fairly nice A-grade plywood I had lying around.
Once I got the boxes glued up, I installed the wiring and soldered the drivers in. The wood parts were glued together with waterproof glue while the tweeters and plastic parts were installed with two component clear epoxy. The low frequency drivers had screw mounting holes, so I used those in case I have to replace them, you know, from cranking the tunage.
I lightly sanded the wood to preserve the salvage wood character (actually no power sander and after 12 years, I wasn’t going to sand my way to clean wood by hand) then treated them with some polyurethane I found left behind by the woodworker that owned the building before I did. So that was at least 18 years old. At least.
I supported the speakers over the edge of the table to align the drivers in the holes from below.
The finished assembly looked more or less like I predicted:
Testing
The speakers sound objectively quite nice, but I was curious about the frequency response. To test them I used the pink noise generator in Audacity to generate 5.1 6 channel pink noise files which I copied over to the HTPC to play back through my amp. This introduces the amp’s frequency response, which is unlikely to be particularly good, and room characteristics, which are certainly not anechoic.
Then I recorded the results per speaker on a 24/96 Tascam DR-2d recorder, which also introduces some frequency response issues, and imported the audio files back into Audacity (and the original pink noise file), plotted the spectrum with 65536 poles, and exported the text files into excel for analysis.
Audacity’s pink noise looks like this:
It’s pretty good – a bit off plan below 10 Hz and the random noise gets a bit wider as the frequency increases, but it is pretty much what it should be.
First, I tested one of my vintage ADS L980 studio monitors. I bought my L980s in high school in about 1984 and have used them ever since. In college I blew a few drivers (you know, cranking tunage) but they were all replaced with OEM drivers at the Tweeter store (New England memories). They haven’t been used very hard since, but the testing process uncovered damage to one of my tweeters, which I fixed before proceeding.
The ADS L980 has very solid response in the low frequency end with a nicely manufactured 12″ woofer and good high end with their fancy woven tweeter. A 3 way speaker, there are inevitably some complexities to the frequency response.
I also tested my Klipsch KSC-C1 Center Channel speaker (purchased in 2002 on ebay for $44.10) to see what that looked like:
It isn’t too bad, but clearly weaker in the low frequency, despite moderate sized dual woofers and with a bit of a spike in the high frequency that maybe is designed in for TV and is perhaps just an artifact of the horn loaded tweeter. It is a two way design and so has a fairly smooth frequency response in the mid-range, which is good for the voice program that a center speaker mostly carries.
And how about those new ones?
Well… not great, a little more variability than one would hope, and (of course) weak below about 100Hz. I’m a little surprised the tweeters aren’t a little stronger over about 15kHz, though while that might have stood out to me in 1984, it doesn’t now. Overall the response is quite good for relatively inexpensive drivers, the low frequency response, in particular, is far better than I expected given the small drivers. The high frequency is a bit spiky, but quite acceptable sounding.
And they sound far, far better than the poor hacked apart Sony speakers they replaced.
Raw Data
The drawings I fabricated from and the raw data from my tests are in the files linked below:
Cactus Farmer
Just a few years back, when I was in 3rd or 4th Grade, my brother and I went to visit David and Jesse Lenat at their Cactus Farm. While we were exploring the green houses, their dad, Richard, gave my brother and I each a cactus to take home.
Mine lived in a small pot near a window through the rest of grade school and high school and then my mom cared for it through college. It grew into a little cluster of pencil thin, green, spiky pads over the years.
After I graduated, moved to California and got an apartment in SF; I was home for Christmas one year and took one of the pads wrapped in tissue to California. It grew well there and now produces big, bright yellow flowers every year.
This Christmas, I stuffed two tiny buds into glass bottles and brought them to Iraq and planted in the yard with one of the cat’s help (paw in the background).