Conrad 190486 Mode D'emploi page 30

The following example calculation assumes a 3-cell LiPo battery used as drive battery in a
model. If you are using a 2 or 4 cell LiPo battery or a NiCd or NiMH battery, the rated voltage
of the battery must be used as operating voltage (UB). For stationary use, calculate the
dropping resistance with the mains adapter's rated voltage.

Practical advice:
Even if the rated voltage of a 3-cell LiPo battery is 11.1 V, you should work with an
operating voltage of 12 V for calculating the dropping resistor, since the terminal
voltage for a freshly charged 11.1 V battery clearly exceeds 12 V.
Example calculation:
Assuming that the light diode used has a supply voltage of 2.6 V and a power intake of 20 mA.
In the first step of the calculation, the voltage that needs to drop at the dropping resistance must
be calculated:
12 V – 2. 6 V = 9.4 V

If you want to switch two same diodes in sequence, 2 x 2.6 V = 5.2 V must be
subtracted from the operating voltage of 12 V.
Now use Ohm's law R = U : I to calculate the dropping resistance Rv:
Rv = 9.4 V : 0.02 A = 470 Ohm
Use the formula P = U x I to also calculate the output the dropping resistor must be able to
withstand:
9.4 V x 0.02 A = 0.188 W
A resistor of 470 Ohm with an output of ¼ W (0.25 W) would therefore be sufficient.
Important!
Please observe correct polarity of the connection lines when connecting the LEDs,
since LEDs only conduct power in one direction.
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