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TL;DL – .NET Rocks! 1373 (DC Lighting Geek Out)

Show link.NET Rocks! 1373 (DC Lighting Geek Out)

Guests: Richard Campbell and Carl Franklin

Show Notes

  • Soraa makes LED lamps that replace halogen lamps; if you’re using AC they work at 12 V. However, you have dimming problems. For typical North American electrical systems, you have 60 Hz AC operating at +/- 120 V. When you dim a lamp, you’d think it would be just a lower voltage, but it’s more complex. There are types of notches:
    • Leading edge notch — keep at 0 V and then jump at 120 V; cheaper
    • Trailing edge notch — gradually go from 0 V to 120 V and then suddenly drop; more expensive
    • A problem with leading edge notches is that you’re hitting that rectifier really hard (i.e., 0 V to 120 V instantly) as opposed to being at 120 V then dropping down. This approach limits its lifespan.
  • Converting AC to DC:
    • Put the AC sine wave that alternates between -120 V and +120 V through a bridge rectifier. The wave is now all positive — i.e., +120 V , 0 V , +120 V, 0 V, etc. Now you have a variable voltage DC signal at 60 Hz, which makes your lamps flicker, assuming they have time to cool down.
    • The next stage is a capacitor so that you hold the power when voltage drops. This smooths the wave out (+80-90 V instead of 0 V). The more technology you add to smooth out the frequency, the more expensive it is.
  • With true DC lighting, you convert the voltage at the power source, not at the lamp itself.
  • There are three components: a switch to control the lamp, the lamp itself, and the “smarts” (e.g., dimming, scene controlling).
  • Conventional dimming is in the switch, which is why sometimes the switches buzz and get hot. In scene controllers, the dimmers are located elsewhere (e.g., in a closet).
  • A vendor LumenCache provides equipment for DC lighting. Most DC lighting has been commercial because of companies wanting to control costs; therefore, not much attention has been given to the consumer space. There’s a single AC/DC converter, and then that DC power is distributed to the lamps.
  • To properly dim a DC lamp, it depends on the lamp’s type: constant current (amperage) or constant voltage.
  • Cat 5 cable is used in DC lighting: it’s inexpensive and offers some fire protection. However, the wire is very thin and can only handle so much power (i.e., 300 mA). Cat 5 works well for constant current lamps.
  • In a constant current lamp, a particular LED driver in the lamp expects 300 mA and responds to variations in voltage (i.e., between 0 V and +24 V) by varying brightness of the lamp.
  • Any Cat 5 cable can handle a single 12 W lamp.
    • For a 12 W lamp, use one cable.
    • For two 6 W lamps, daisy chain the same cable between the pair.
    • For a 24 W lamp, use two cables.
  • With LumenCache, the complexity is stored away in a closet. The switches are dumb, the lamps are dumb, and also inexpensive (e.g., $15-20).
  • Most of the size that goes into a typical recessed light fixture is metal shielding to dissipate heat. With LEDs you don’t need as much space because heat is no longer a concern.
  • LumenCache supports variable amperage lamps via switched voltage, which runs to a separate amplifier to power the lamp. There’s 14/2 (14 gauge wire, 2 leads) that runs out to the light fixture.
  • LumenCache is dealer/distributer-oriented, so Richard took the training to become a dealer, as there wasn’t one in his area.
  • There’s a power distribution module that brings in power and distributes it to the lamps. Three things get plugged into the panel besides the cables themselves – WP1 (reads the switches, sensors, etc. to control up to 96 LEDs), SV1 (switched voltage driver to deal with higher amperages), and a CCB (constant current boost driver).
  • If you have MR16s (multi-reflector halogen lamps) you can use Soraa bulbs, as they work on AC or DC. You can remove the step-down transformer that converts from 120 V AC to 12 V AC, then just use DC.
  • Cost example: 2 switches, 26 recessed lights, and controlling hardware came to about $60 per lamp ($1500 total). Soraa lamps are about $20 each.
  • To replace fluorescent tubes, KLUS Design has multiple offerings. They sell LED lighting solutions with aluminum extrusion housings, LED tape, and a diffuse housing to blur the light; you can make stuff to size. Their highest power offering is 14 W per meter, which is quite bright. You can use this for shelving, too. The result is a product with a low profile and no heat. Because these solutions work on DC, you can experiment with lighting options by simply carrying around a battery pack. They also lend themselves well to being connected to battery backup systems.
  • A relevant topic is USB power.
    • You have a communication channel that allows you to negotiate how much power you want.
    • The spec provides between 10 W (5 V at 2 A) to 100 W (20 V at 5 A); you could potentially run a tablet.
    • The new USB Type-C has bi-directional power, a small plug (2.4 mm), and huge data capacity (e.g. capable of handling DisplayPort).

Better Know a Framework

Listener E-mail

From show #946 (The DC Revolution Geek Out); most home devices should be DC, with AC for legacy appliances (e.g., ovens). The Japanese power system was made by both Germans and Americans, so there are different voltages and cycle frequencies, which is why you need a switched power supply.

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