Proper Relay Module with Proper Isolation

[xmen_xwk]

I need to control around 2A to 3A AC solenoid/coil with arduino. For that I got a 5V relay module. But after reading this article. I realized I would need 2 different power supply, one for arduino and one for relay. But doing that also doesn't guarantee of proper isolation. I was wondering how would I do proper isolation ?(Not 100% obviously but better)

Now second question


The above schematics shows, using NPN transistor we are controlling the relay. But with software it will work opposite, when Signal Pin will be LOW, the relay will be ON. And relay will be OFF when signal is LOW. I want to do it correctly if its not a problem ? So to do that, I want to replace VCC with signal pin and signal pin to GND. Will that be a problem with isolation ?


Thank you

 

[KlausST]

Hi,

It seems both sides of the optocoupler use the same GND, then you don't need a optocoupler. A bjt is sufficient.

The relay should be rated for an isolating voltage (coil to contacts) more than your AC voltage.
Mind to use a snubber at the contacts of the relay to avoid EMI/EMC problems.

Klaus

 

[xmen_xwk]

The GND is for relay only. Not connected to arduino. And about snubber, will just putting on AC side will be enough ?

 

[KlausST]

Hi,

And about snubber, will just putting on AC side will be enough

usually yes.

But in detail it depens on many parameters. Like load, PCB layout, sensitivity of the circuit...

Klaus

 

[xmen_xwk]

Hi,



usually yes.

But in detail it depens on many parameters. Like load, PCB layout, sensitivity of the circuit...

Klaus

Could you please explain little more ? like how to calculate or know how load and other things matters.

Thank you

 

[KlausST]

Hi,

wether a snubber is sufficient depends on some parameters.

PCB Layout. If you have a good layout, then a snubber should work. If you have a bad PCB layout then even with a snubber you will see problems.

EMI/EMC include magnetic waves. All lines with high voltage/current pulses transmit magnetic waves.
All other lines within this magnetic wave will receive the magnetic wave and produce voltage and/or current pulses.

Klaus