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.
Parallel connected strings use 120V lamps, as follows:
Type
C7-1/2
C9-1/4
Bulb
Current
40 mA
60 mA
Bulb
Power
5W
7W
Amps
Per String
1.0
1.5
Power
Per String
125W/25
175W/25
■ FIGURE 7
November 2007 55