Relay power from Arduino

I have just bought a bank of 4 opto-isolated relays similar to http://bit.ly/nDQcfu(except 5v coils) to switch a load via my Arduino Uno, and wanted to know if its OK to power the drivers and relays (not the switching signal) from the 5v Arduino regulated supply? I have the option of isolating the driver side via a link, to use an external supply, but would prefer to use the board's 5v if possible.

I have found the data sheet for the relays - http://bit.ly/oJJnny, and the coils are rated at 90mA 5v each, so if all 4 were energised, the total current drawn could be 360mA.

However I can't find out how much capacity is available from the Arduino 5v supply.

If powered by USB you are limited to 500mA. http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1237451844

sptrks: If powered by USB you are limited to 500mA. http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1237451844

I wont be using USB power except for programming, I have a separate power supply for the board.

If you read that forum post you will see the maximum rated current vs the actual which is significantly lower due to dissipation.

if its OK to power the drivers and relays (not the switching signal) from the 5v Arduino regulated supply?

The link you sent says these are 12V relays so no it would not work from the 5V regulated supply.

I have found the data sheet for the relays

Yes but that has data for lots of different relays only one of which is 5V, another is 12V that is the one your board uses.

However I can’t find out how much capacity is available from the Arduino 5v supply.

It is limited by heat and depends on your input voltage. see these links:-
http://www.thebox.myzen.co.uk/Tutorial/Power.html
http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html

Grumpy_Mike:

if its OK to power the drivers and relays (not the switching signal) from the 5v Arduino regulated supply?

The link you sent says these are 12V relays so no it would not work from the 5V regulated supply.

I have found the data sheet for the relays

Yes but that has data for lots of different relays only one of which is 5V, another is 12V that is the one your board uses.

However I can't find out how much capacity is available from the Arduino 5v supply.

It is limited by heat and depends on your input voltage. see these links:- http://www.thebox.myzen.co.uk/Tutorial/Power.html http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html

Thanks Mike, I added 'except 5v coils' just before you posted. I hadn't noticed that the Ebay example was 12v, and assumed that they were all 5v :blush:

Just wondering why go for opto-isolated relays and then run them from the same power supply?