I am trying to activate relays with optocoupler module i bought.
I have attached the module picture with all measurements i have done.
The Optocoupler module uses 5V to activate 12V on the other side where relays are connected.
When I apply voltage to 1+ and 1- (5V), top LED will turn on together with bottom LED.
However when i connect Omron G2R-1-E 12VDC relay, it wont activated the coil. It will activate RT424012.
In the picture, there are some measurements that i have 11,89V between GND and VCC.
But when i connect the relay Omron(R=266 Ohm), voltage between O1 and VCC drops to 7,21V. Current on coil is 25mA even without activated coil (without making sufficient field to switch the contacts). Voltage between O1 and gnd is 4,68V.
When using RT424012 with R=364 Ohm, the voltage between O1 and VCC is 8,79, O1 to GND is 4,68 and coil current with activated coil is 25mA.
Can you please suggest me what to do? Can i change some resistors to fix it?
I really dont know what else to do with it.
Thank you.
Thanks for the answer, it really seems like the problem is really low through coil current.
Whe i connect the relay straight to the PSU, it takes 55mA on 12V.
In the datasheet: http://www.everlight.com/file/ProductFile/EL817.pdf
it is said collector current 50mA so it should give me my 50mA....?
yeah, i have seen this picture, but how can i connect the transistor to my circuit?
If i am not mistaken, in my circuit Emitter pin is connected straight to GND.
So the circuit below is not possible in my case or am i mistaken?
I used PNP transistor 2N3906.
My point O8 is marked in attached picture.
I have also changed the value of the resistor between VCC and O8 to 20k but could you please explain why? Does it limit the current? Or what is the purpuse of resistor here?
Then i added 10k resistor between O8 and Base of transistor and connected collector to relay and then relay to the GND.
Result is 40mA on coil with 12V. And Coil works for both relays.
It will be quite messy setup with 12 PNPs on my 12relay bord but cheper than a new board.
I assume you don't know about CTR (Current Transfer Ratio). Transfer characteristics in the datasheet.
The board you posted has ungraded EL817 optos (no letter behind that).
This opto's CTR can be anything between 50% and 600%.
Meaning if you drive the opto LED with 7mA (510 ohm resistor), you could only switch 3.5mA (50% CTR) with the opto transistor worst case.
But 3.5mA is more than enough to drive the base of a transistor for those relay currents.
A resistor in series with the opto transistor must be used to limit relay transistor base current to about 2mA in case the CTR is more than 50%.
Leo..
