Originally Posted by rjvh

hi i need to sense a current in a AC aplication so that i have a indication that current is flowing (switched on)

alsio i need to give that signal to an imput of a plc (for monitoring)

i have this idea and it works but is not perfect for all situations (see schematic)

if the current is lower than 1 Amp i will use the 1N4007

if the current is lower than 3 amp i will use the 1N5408

but i have to monitor a 11 KW pump that consumes +/-24 Amp

diodes are getting a bit expensive in this case

is there an other solution to tackel this problem?

Thanks

Robert-Jan

Originally Posted by Optikon

Your circuit will not work..

it does it's on my work bench

1) the circuit as-is will blow up very quickly. There is nothing to current limit all those diodes in there. Dont do it!

could be duration test is not performed yet, and your right there is no current limiting component in this schematic the apliance conected in serie is that

2) when you say sense if current is flowing, I take that to mean you are sensing whether or not current is flowing elsewhere.. your circuit will force current to flow (it is a load in its own right) so it will *always* tell you there is current flowing - not very useful and fundamentally flawed.

not agreeing with you on this point if there is no load between the L1 and N than the circuit is not closed so where does the current go?
test on the bench with this circuit shows also that if the aplaince is switched off the indication is also swiched off

3) If by L1 & N you are refering to mains line voltage.. these things are dangerous. do not tinker with it. Use a compeltely isolated solution like you tried to do with opto's or take the other posters suggestion and use a hall effect device. Galvanic isolation must be maintained. A current transformer is another option for you.

Point taken but i do have expertise and experiance with these things (but your advise is the same as i tell people) you can't be warned enough about it

to be onest the hall effect device i didn't think of it as i never seen them sold here in Cambodia it's one of the problems where i walk in constantly (avalibility of for the rest of the world common components)

expensive? HA! if you think $0.1 diodes are expensive then you won't like the $3 hall effect device

i dont think $0.1 dollar diodes are expensive it gets different if you need diodes that have to handle 24 Amp (again not availible here so i have to go source them elsewhere).

Originally Posted by Ubergeek63

which is why the first reply to your question was me pointing you to them

Originally Posted by Ubergeek63

sorry I like to supply the link to their product page so you can see how much it costs and can get the link to the data sheet from there.

The one I linked to is the less expensive "little brother" of the ACS75x family