Connecting Lamps Or Leds - tams elektronik WRM-4 Manual

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4.4. Connecting lamps or LEDs

Lamps are not polarised, thus the assignment of the two connections to the outputs of the
WRM-4 (A1a to A4b) and to the return conductor for the outputs (RL) is optional.
With LEDs you have to observe the polarity, otherwise they do not light. Connect the cathodes
(-) to the outputs of the WRM-4 (A1a bis A4b) and the anodes (+) to the return conductor for
the outputs (RL). With standard LEDs the longer connecting pin is the anode (+).
Attention:
!
When using LEDs you always have to connect them via a series resistor as the LED will be
damaged when put into operation or its duration of life will be reduced considerably.
The necessary value of the series resistor depends on the voltage supply to be available, the
forward voltage of the LED (which depends on the colour) and the current.
Calculating the series resistor:
necessary R [Ohm] = ( U
V
U = operating voltage
B
U = forward voltage of the LED
F
I = current with max. luminosity
F
For red and green LEDs you can take 2 V as a basis for the forward voltage. The luminosity
depends on the current draw, with standard LEDs the difference between 10 and 20 mA is not
visable.
Connection to a.c. voltage
Note: The operating voltage of an a.c. transformer is approx.
1,4 fold the nominal voltage given.
Necessary series resistor with
current draw
Nominal
10 mA
voltage
12 V ~ 1,5 k
14V ~ 1,8 k
16 V ~ 2,2 k
18 V ~ 2,2 k
[V] – U [V] ) / (I [mA] x 0,001)
B F F
Connection to d.c. voltage
Note: With d.c. Power packs the operating voltage
corresponds to the nominal voltage given.
Nominal
20 mA
voltage
820  16 V =
820  18 V =
1 k 20 V =
1,2 k 22 V =
Necessary series resistor with
current draw
10 mA 20 mA
1,5 k 820 
1,5 k 820 
1,8 k 1 k
2,2 k 1 k
Connecting the WRM-4 | 17
WRM-4