Provide me the schematic (circuit) for discharging almost any capacitor ? thanks

[danishdeshmuk]

Kindly, provide me the schematic (circuit) for discharging almost any type & almost any value Capacitor ?

thanks

 

[alexan_e]

a simple resistor could do the job, why do you need a special circuit?

 

[tsvetelin_velkov]

Yes, right value resistor will do the job. How to find the right value ?

Well this depends on what do you want to achieve. A simple LED with bias resistor calculated for your supply voltage will be also OK in most cases and will give a visible indication that the circuit is discharged.

I calculate it like that R = ( Uvdd - Uled ) / Iled where :

R is the resistor value in Ohms
Uvdd is the supply voltage in Volts
Uled is the led voltage at current Iled, first in Volts, second in Amps
Iled is the nominal current of the LED, most 3mm and 5mm leds are rated at 20 mA or 0.02 A

Hope this helps!

 

[danishdeshmuk]

So, what type of LED & what value Resistor would be required to discharge the 500 uF , 50 V Capacitor ?

What is the value of Vled at Iled ? How to find Vled & Iled ?

Can you show me the calculation ?

thanks

 

[tsvetelin_velkov]

So this is :

take any red led, Vled voltage is about 1.2V, for a 5mm led assume 20mA current :

R = ( 50 - 2 ) / 0.02 = 2400 Ohm or 2.4 kOhm

Hope that helps

Edited : Vled changed from 1.2V to 2.0V. The capacitor energy is huge so the discharge will be slow, however you can combine this circuit by adding in parallel a resistor with lower value. Than the led will just give you indication when the discharge is ready

Keep in mind the power dissipation of your discharge circuit, you don't want some parts to get burned.

 

[alexan_e]

I would do the calculation for a Vf close to 2v, 1.2v seems very low for a led, I only know of infrared leds that have such low Vf..

There is a nice tutorial about leds Light Emitting Diodes (LEDs)

note the only advantage of the led will be that it provides a visual indication of the capacitor voltage, you can use a simple resistor to achieve the discharge and in that case there will be no current limitation like when using the led (since a led can only work up to about 20mA).

Alex

 

[tsvetelin_velkov]

alexan_e,

you are right, led voltage should be about 2V for red led.

See this table here Light-emitting diode - Wikipedia, the free encyclopedia

I will edit the previous post

 

[danishdeshmuk]

So this is :

take any red led, Vled voltage is about 1.2V, for a 5mm led assume 20mA current :

R = ( 50 - 2 ) / 0.02 = 2400 Ohm or 2.4 kOhm

Hope that helps

Edited : Vled changed from 1.2V to 2.0V. The capacitor energy is huge so the discharge will be slow, however you can combine this circuit by adding in parallel a resistor with lower value. Than the led will just give you indication when the discharge is ready

Keep in mind the power dissipation of your discharge circuit, you don't want some parts to get burned.

Of what value a resistor would be add in parallel to the first resistor ? How to calculate the resistance of that lower value resistor ?

 

[alexan_e]

the second resistor will not be connected in parallel with the led resistor because this will damage the led from high current, you should connect it between the two connections of the capacitor.

The value of that resistor depends on the capacitor voltage and the discharge current you want

for example with 50v if you want to discharge at a rate of 0.2A then the resistor you need is 50v/0.2A=250 ohm , the power consumed on the resistor is (V*V)/R , in this case 2500/250=10W.
Note that the above calculations are made for the initial full voltage, as the capacitor discharges and the voltage drops so will the numbers of the calculation (less current and less power on the resistor).

Alex

 

[danishdeshmuk]

a simple resistor could do the job, why do you need a special circuit?

ok if a simple resistor could do the job then how to calculate its value
for e.g: if a cap has a value of 4700 uF & 50 V then what value of a capacitor is connected across it to discharge it & how much time would it take to discharge ?

Also, how to connect the resistor across the capacitor ?

thanks

 

[alexan_e]

For the capacitor discharge calculation use this Capacitor Discharging

 

[tsvetelin_velkov]

try this link : Resistance, Capacitance, Voltage, And Time Calculator

for your case ( 4700uF / 50V and 100Ohm / 25W ) it is about 2 seconds until voltage drop to zero , I would prefer to have a longer discharge time, i.e. 10 seconds, but also lower quiescent current ...

 

[Raza]

Hi Danish,
You asked for any type of capacitor and any value but you did not define the real requirement " THE WORKING VOLTAGE ". And the resistor wattage will be changed for high value/high working voltage.