Resister value calulation

M

Mr KAR

New Member

• Oct 20, 2009

• #1

Hi in my design i am using 24 volt 8 amps relay.I that circuit to check the relay status iplan to add one led. I want to know that value of that rsister and how to calculate.

Can anyone help to solve this issue.

 

birdman0_o

Active Member

• Oct 20, 2009

• #2

[24V - (2 to 3 V)]/20mA = Resistor.
Where do you plan on putting the led, will it be a basic on/off indicator?

 

M

Mr KAR

New Member

• Oct 20, 2009

• #3

thanks i want to check relay is active or not so that i plan to add led.

yes basic on/off indicator

 

birdman0_o

Active Member

• Oct 20, 2009

• #4

Yea what I said will work. Just put it in parallel with the other circuitry the relay is turning on.

 

M

Mr KAR

New Member

• Oct 20, 2009

• #5

Thanks. I choose Forward volt 2.3v. So your Calculation shows 1.1k.

 

birdman0_o

Active Member

• Oct 20, 2009

• #6

The foward voltage will depend on your specific led, you can find it in the datasheet. 1.1K sounds right for the value you have chosen.

 

M

Mr KAR

New Member

• Oct 20, 2009

• #7

ya thanks in my datasheet shows forward voltage 2.3.

Thanks for youe help

 

crutschow

Well-Known Member

Most Helpful Member

• Oct 20, 2009

• #8

birdman0_o said:

Yea what I said will work. Just put it in parallel with the other circuitry the relay is turning on.

Click to expand...

If you put the LED and resistor across the relay coil instead of the contact load, you can have any value of voltage or type (AC or DC) on the relay contacts without it affecting the LED circuit operation.

 

birdman0_o

Active Member

• Oct 20, 2009

• #9

I can't picture this Carl, do you have a schematic handy?

 

M

Mr KAR

New Member

• Oct 20, 2009

• #10

Relay contact rating is 8A @ 250VAC/30VDC(NO):8A @ 250VAC; 4A @ 30VDC(NC)

I don't have any schematic.