Led limiting resistor

[rsocor01]

What is the purpose of R2? I don't quite understand what you are trying to do. Are you trying to measure the current in the heater? Or, are you trying to switch it on/off?

[igeorge]

r2 is to turn on the opto.
all i need is to sense if the heater is burned out when the switch is closed.
I do nt measure current
thanks

[rsocor01]

r2 is to turn on the opto.
all i need is to sense if the heater is burned out when the switch is closed.
I do nt measure current
thanks

What about using a relay to detect if the heater is burned out?

[HankMcSpank]

Hello,
I have a line where the current varies from 1 to 5 amps.
I would like to insert a resistor which will turn on an optocoupler rated at 1.5 volts , 10 mA
The issue here is that at 5 amps i need a 0.24ohms resistor , and at 1 amp i need a 1.2 ohm resistor.
Assuming that i use the 1.2 ohms resistor, at 5 amps will generate 6 volts and fry my opto.
I need help to solve this issue, which i do not know how to do it
Regards
Ion

iF you place a 450R resistor in series with the opto, that'll ensure the voltage doesn't exceed 1.5V/10mA at the opto for 5A through the element ....of course the opto will only then 'get' 300mV if the element current drops to 1A....but without knowing more about the opto blah blah

[mister_e]

Why not using a Current transformer?

[igeorge]

I think Mister_e solution it is something which i will consider, but i have to solve the conversion of 10 mv ac/60 hz to a decent DC voltage so i can use it with a comparator.
As i said, analog it is a mystery for me.
Regards
Ion

[Demon]

I don't understand why the need for complicated design.

Wouldn't an appropriately rated relay do the job just as well (isolate both sides), be easy to install and be able to withstand a lot more?