Hi James
You are right there. I think the make and break time for these relays is 10ms. It is anybody’s guess what it would be at 3.3V. I don’t anybody realises any other repercussions this slower operation will have on other things. Like switching larger currents with the longer arcing time. Anything like this might drastically reduce the life of the device.
I don’t have any of this type relay in the 5V range and if I did they would probably be Omron. I could measure the operate time at the lower voltage if I had one. I think I have a couple of this style (Omron)
at 12V and if I get the time and motivation I might see what the difference is at 66% of nominal. I think that once operated they will hold at the lower voltage but I would not use them to operate at this voltage. I hav a feeling that operate time could extend out past 20 or even 50mS. Whatever it is it would not be good.
To be honest I have had quite a lot to say in the past about operating these relays way outside specification but no one seems to take any notice. Even Core who continually market these things as 3.3V units. Some units which use low side switching or an opto transistor switch can have 3.3V logic and are able to have a 5V relay supply. That is all good. BUT if your schematic is correct that design is CRAP. I think I saw somewhere that these units need to have VCC the same as the logic voltage to work. That appears to be so.
As I am getting a bit fed up talking about this subject I think I will pull the pin on it with one last bit of advice
Use at 3.3V relay supply at your own risk and don’t complain if experiencing problems later.
Cheers Bob
