# How to wire circuit DC Motor with LED

I'm trying to learn a bit more about forward voltage and Ohm's law but I'm not sure how to wire this circuit.

I have:

• One 4.5 DC motor (Operating Volts: 1.5- 4.5V, Nominal Volts: 4.5V, Current (no load): 0.25A)

• Three 5mm LEDs (IF Typical (mA)20, IF Max Continuous (mA)50, VF Typical (V)2.1) -

• One 3 - 12VDC Switchmode Plugpack (Output voltage: 3, 4.5, 5, 6, 7.5, 9, Output current: 1000mA (max))

Do I use the power at 4.5V and run the motor and the LEDs in parallel?

Do I need resistors on the LEDs?

• IF Max Continuous (mA)50, LED current should be limited to this value. You may consider ignoring DC Motor until you are able to appreciate ohms law using LED, supply and resistors. Jul 13, 2015 at 3:40
• @Umar, but if I wire the motor and the LEDs in parallel, surely I don't need to cut the amperage down from 1A to 50mA? That was my question. Jul 13, 2015 at 3:51
• Yes and yes. One resistor for each LED : none for the motor.
– user16324
Jul 13, 2015 at 12:56

You can connect DC Motor and LED in parallel with the resistor in series with LED. LED can draw current about 24 mA (4.5 V - 2.1 V)/ (100 Ohms). If resistor is not placed in series with it, The LED will eventually get over heated and gets destroyed. use a fly back diode in parallel with motor if it is unidirectional. If Power is set to 4.5 V, then using a 100 ohm resistor with LED is recommended. simulate this circuit – Schematic created using CircuitLab

LED do not have a datasheet, so assuming typical Vf for calculation.

You should wire things like this: simulate this circuit – Schematic created using CircuitLab

You require a current limiting resistor in series with each LED, to limit the current in that LED to 20 mA. The motor will draw whatever current it requires - no need for a current limiting resistor for it, as long as you don't feed it more than its rated voltage.