Nuts and Volts - November 2007

Holiday Lights

■ CONTROLLER SCHEMATIC 2

approximately 20 amps drawn from the AC input. The wiring should be sized accordingly, preferably with 14 AWG or larger conductors. The incoming AC cable and standard grounded plug were salvaged from a heavy duty outdoor extension cord, which should be made long enough to reach a sheltered ( preferably CGFI protected) outlet in your home or in a raintight enclosure outdoors.

In practice, the light show draws a lot less average current, so for piece of mind, the wiring, PCB traces, and fusing scheme were designed for the worst case loading. Depending upon the application, different light strings can be installed and typically several strings may be daisy-chained together on each channel. Recently-introduced LED strings draw a lot less power, mini-lights more, and the older strings of C7-1/2 (5W

bulbs) or C9-1/4 (7W bulbs) draw the most. Figure 7 shows the ratings for common bulbs and strings.

If all channels on a card drew one

amp each at the same time, it would pop the five amp fuse on that card. Under other uses, a single channel could support up to five amps (again, limited by the fuse), but a single channel application would be wasteful of an eight channel card!

The important point is that a correctly designed installation will allow all lights to come on safely, and each branch (I/O channel) should

Typical mini-lights are rated at 2.4V and wired in series or series/parallel. They draw different current depending on “standard,” “energy saving,” or “super bright” bulbs, as follows:

Type Super Bright Standard Energy Saving Single LED per lamp

Bulb Current 200 mA 160 mA 100 mA 20 mA

Bulb Power 480 m W 384 m W 240 m W 48 m W

Power
Per String
16.8W/35 24W/50 48W/100
13.44W/35 19.2W/50 38.4W/100
8.4W/35 12W/50 24W/100
1.68W/35 2.4W/50 4.8W/100

Note: LEDs consume only 10% (1/10th) of super bright, 12.5% (1/8th) of standard, and 20% (1/5th) of energy saving strings of mini-lights, all other things being equal.