Calculating current, voltage drop & resistance

[SummersLCFC]

Hi i built a circuit for a project and I am having some trouble working out important factors of the circuit. My circuit is powered by a 12V power supply, its wired in series, it contains 85 LED's that are connected with a 1kΩ resistor across 3 off the LED's. This is then connected to a PIR sensor and a 12V relay because the PIR is n/c contact.

I need some help on working out the current, the voltage drop and the total resistance of the circuit.

Thanks tom

 

[NascentOxygen]

So from the 12V battery you have a 1kΩ resistor in series with 3 series LEDs, then this current returns to the other terminal of the battery? Is that the arrangement? Can you measure the voltage across just one LED when it conducts, here in this circuit?

 

[SummersLCFC]

There are 85 LED's in the circuit, so it starts with 3 LED's connected up with 1 resistor across them, then another 3 LED's and so on, so that makes 29.

 

[NascentOxygen]

Perhaps I should ask the important question first: is it working well as you planned?

 

[alphysicist]

First of all, it's great that you are building a circuit for a project and seeking help to understand important factors such as current, voltage drop, and resistance. These are crucial components in any electrical circuit and understanding them will help you troubleshoot and optimize your circuit.

To calculate the current in your circuit, you can use Ohm's Law, which states that current (I) is equal to the voltage (V) divided by the resistance (R). In this case, since your circuit is wired in series, the current will be the same throughout the circuit. Therefore, the current can be calculated by dividing the voltage of your power supply (12V) by the total resistance of the circuit. This includes the 1kΩ resistor and the resistance of the 85 LEDs. To calculate the resistance of the LEDs, you will need to know their individual resistance values and then add them together.

Once you have calculated the current, you can use Ohm's Law again to calculate the voltage drop across the 1kΩ resistor. This can be done by multiplying the current by the resistance of the resistor. This will give you the voltage drop across the resistor, which can then be subtracted from the power supply voltage to determine the voltage drop across the LEDs.

Finally, to calculate the total resistance of your circuit, you will need to add the resistance of the 1kΩ resistor to the resistance of the 85 LEDs. This will give you the total resistance that the power supply is pushing against.

I hope this helps you understand how to calculate the current, voltage drop, and resistance in your circuit. Keep in mind that these calculations are theoretical and may differ slightly from the actual values due to factors such as temperature and tolerance of components. It is always a good idea to double-check your calculations and measure the actual values in your circuit to ensure accuracy. Good luck with your project!