# Closing a circuit with a capacitor

• daniel_i_l
In summary, the individual is looking for a way to activate their electromagnet for two seconds as soon as the power is turned on, and believes this can be achieved by connecting the electromagnet, a capacitor, and a resistor in series. However, it is suggested that this may not be the best solution as the current will gradually decrease as the capacitor charges, and there would need to be a safe way to discharge the capacitor after power is turned off. Instead, a better solution would be to use a normally-closed, timed-open relay.

#### daniel_i_l

Gold Member
I have an electromagnet that I want to be activated for two seconds as soon as I turn the power on. I think that this can be done by connecting the electromagnet to the power source in a series with a capacitor and a resistor. As soon as the power is turned on the EM would work until the capacitor gets charged up and cuts off the circuit. Is that true? If so, how do I calculate the sizes of the resistor and capacitor that I need?
Thanks.

I don't think the capacitor idea is a good solution to your problem because the current will gradually decrease as the capacitor charges. I'm assuming you would prefer to have the electromagnet have it's full power for the duration of the time interval. Also, you would need to have a safe way to discharge the capacitor after power is removed. A better solution would be to use a normally-closed, timed-open, relay.

Yes, it is true that using a capacitor in series with the electromagnet and power source can create a timed activation for the electromagnet. This is because when the power is turned on, the capacitor will initially act as a short circuit, allowing current to flow through and activate the electromagnet. However, as the capacitor charges up, it will eventually reach its maximum capacity and act as an open circuit, cutting off the flow of current and deactivating the electromagnet.

To calculate the sizes of the resistor and capacitor needed for this circuit, you will need to consider the desired time duration of the electromagnet's activation, the voltage and current ratings of the power source, and the resistance of the electromagnet. Using the formula for the time constant of a RC circuit (T = RC), you can determine the appropriate values for the resistor and capacitor to achieve your desired time duration. It is also important to choose components that can handle the voltage and current levels of the circuit to ensure safe and reliable operation.

I would recommend consulting with an expert in electronics or using online calculators to determine the exact values for your specific circuit. Additionally, it is important to carefully test and adjust the circuit to ensure it is functioning as intended before implementing it in any practical application.

## 1. What is a capacitor and how does it work?

A capacitor is an electronic component that stores electrical energy in the form of an electric field. It consists of two conductive plates separated by an insulating material called a dielectric. When a voltage is applied to the capacitor, electrons accumulate on one plate and are removed from the other, creating an electric field between the two plates. This electric field stores the electrical energy.

## 2. How do you close a circuit with a capacitor?

To close a circuit with a capacitor, you need to connect the two leads of the capacitor to the circuit in such a way that the capacitor is in parallel with the other components. This means that the positive lead of the capacitor should be connected to the positive side of the circuit, and the negative lead should be connected to the negative side. This allows the capacitor to store and release electrical energy as needed.

## 3. What happens when you close a circuit with a capacitor?

When you close a circuit with a capacitor, the capacitor will begin to charge. As the voltage across the capacitor increases, the electric field between the plates becomes stronger, causing the capacitor to store more energy. Once the capacitor is fully charged, it will stop allowing current to flow and act as an open circuit. When the circuit is opened again, the capacitor will discharge its stored energy, releasing it back into the circuit.

## 4. How does closing a circuit with a capacitor affect the overall circuit?

Closing a circuit with a capacitor can have various effects on the overall circuit, depending on the circuit's components. In general, adding a capacitor to a circuit can help stabilize the voltage, filter out unwanted signals, or provide a temporary energy source. It can also affect the circuit's frequency response, phase shift, and impedance.

## 5. Can you close a circuit with a capacitor in any configuration?

No, a capacitor must be connected in the correct configuration to function properly in a circuit. As mentioned earlier, the capacitor should be connected in parallel with the other components, with the positive lead connected to the positive side of the circuit and the negative lead connected to the negative side. Additionally, the capacitor's capacitance value and voltage rating should be suitable for the circuit's requirements.