Hi everyone,

I'm using a relay for the first time and I am a bit confused. I copied some schematics from the internet, and this seems right with a relay and an optocoupler.

I am most worried if the direction across the relay 5 .... 2 matters and I am not sure I have it right.

Thanks!

 

hi Ali,
Welcome to AAC.
The Diode D1 is the correct direction.
The relay coil can be connected either way on a standard relay as shown in the circuit.
E

 

hi Ali,
Welcome to AAC.
The Diode D1 is the correct direction.
E

Thanks very much for the quick answer. Is there a way I can be sure of getting this right every time more than just knowing it?

 

hi,
Are you asking about the relay coil or the suppression diode direction.?
E

 

Hi, sorry to not be clear. It's the combination of the coil and diode that I am worried about. Or perhaps the coil is bidirectional?

 

hi,
If there is no polarity coding marked near the pins on the base, ie: no + or - symbols, the coil can be connected either way.
When using a 'special' type of relay its a good idea to get the relay datasheet to check the pins.

The Cathode [ marked with a Bar ] of the suppression diode, always points to the positive supply end of the relay coil.

E

 

Brilliant. Huge thanks for your help.

 

If there is no polarity coding marked near the pins on the base, ie: no + or - symbols, the coil can be connected either way.

I've seen octal sockets marked + and - where polarity doesn't matter.
For most relays polarity doesn;t matter.

Latching relays, it does.
Relays with integral suppression diodes, it does.

In automotive relays, particularly the Bosch style, there is a "suggested" polarity. Some of these relays have an integral diode.

 

This is why it always pays to consult the app sheet, some relays not only have BEMF diode, but also LED indicator.
Max.

 

Just drive the relay with the opto and ditch the transistor.

 

Just drive the relay with the opto and ditch the transistor.

As far as I can tell the opto output is 50ma max, the relay is 70ma at 5vdc.
Max.

 

This is why it always pays to consult the app sheet, some relays not only have BEMF diode, but also LED indicator.
Max.

Don't forget the check button. It mechanically moves the contacts.

I like the Idec octal relays because the diagram is on the top of the relay.

 

I like the Idec octal relays because the diagram is on the top of the relay.

I mainly use the Omron MY4ZN etc.
They have the digram on the side and option indicators on top.
Also 4 contact sets.
Max.