Charging a Capacitor With a Relay

This instructable is all about how to charge a High voltage (HV) rating capacitor with a relay. The electromagnet used in relay ,can be seen as a inductor . When a inductor is connected to a power supply, a magnetic field is induced across the inductor and when power is suddenly removed the collapsing magnetic field produces a huge voltage spike but in opposite direction.This voltage can be stored in a capacitor through a diode.

Step 1: Parts and Equipment

#1. Relay (6 volt 100 ohms or 12 volt 200 ohms).

#2. Diode (1N4007 or similar).

#3. Electrolytic Capacitor (200 volt, 280 uf or 400 volt, 120 uf or similar).{can be found in old flash camera or u can always buy a new one}

#4. Power Supply ( 9 volt min , 12 volt max).

#5. Switch.

#6. Soldering iron and wire.

Step 2: Relay

Relay is a just an electromagnet which pulls an iron plate (terminal ) which touches to a pad (terminal) which intern close the circuit connected to it just like a switch.A spring attached to the plate pulls it back from the electromagnet which touches another pad (terminal) which closes the other circuit or act like a ON switch , here the switch which is closed when electromagnet is off is called 'Normally Closed' or 'NC' for short...and the pad which connected to the plate, when electromagnet is on is called 'Normally open' or 'NO'......and the plate is the common terminal....

Beside this 3 pin NC, NO, COMMON.....there are two more terminals for the electromagnet....so there are a total of 5 terminals for the common single pole double through (SPDT) relay . A relay more or less just work like a transistor. it was and has been used till this date for switching high voltage with a low voltage or switching the ac voltage with the dc signal which have become the heart of the home automation system.

Here i am using a old bulky relay of rating 6 volt and 100 ohms ...it was used in the old fax machine but you can use any relay ...specifically the SPDT relay for the sake of the simplicity . The pin number 1 and 5 shown in the picture are for the electromagnet inside ...2 is the common pin.... 3 and 4 are normally closed and normally open terminals respectively

Step 3: Connections

The connection are fairly very simple ....the negative terminal of your power supply is connected to the common pin of your relay and then normally closed (NC) is connected to one side of the relay's electromagnet and other terminal of the electromagnet is connectede to the positive terminal of the battery.....remember to connect the cathode side of the diode to this terminal where positive terminal of the battery connects to the electromagnet .

Here in the circuit you can see that the capacitor and diode are connected in such a way that it gets charged by the charge generated by the inductor not by the battery.

Step 4: Working and Use

When we close the switch, the common pin of the relay is connected to normally closed pin of the relay which leads to close loop and current flows through the inductor and builds a magnetic field around it , meanwhile the relay does it work and electromagnet pulls the common terminal which disconnects it from NC terminal which leads to the sudden cutoff of the voltage of the inductor which was supplied by the battery, this leads to the collapsing magnetic field across the inductor which produces a huge voltage spike in the opposite direction which is passed by the diode because now the diode is in forward bias and hence,the capacitor get slowly charged.

The output of the capacitor can be measured by the voltmeter or multimeter ....remember to place your multimeter in the range of 200 volts to 1000 volts DC or you can try the fun way by short-circuiting the capacitor terminal with a screwdriver or any conductor. Here i am using my external 12 volt power supply to power this thing.

Caution - : After few min. of charging the capacitor ,the voltage can reach up to 300 volt dc, which is can be dangerous and must be handled safely .