Newbie Alert! :o
In my current project I want to connect an eight gang relay (the common type with blue Songle relays).
If I'm reading my meter correctly they draw 1.6 ma when active. There will be times when all 8 relays are being powered at the same time. Is this within the rating on my Arduino Uno?
John
I am surprised that the current needed by each is so low. Are you sure that your measurements are correct ? How and where are you measuring this current and how are the relays connected to the Arduino ?
Welcome to the group.
These types of relay boards should use an external power supply for the coil.
Show us a good schematic of your circuit.
Show us a good image of your wiring.
Give links to components.
Posting images:
https://forum.arduino.cc/index.php?topic=519037.0
Thanks UKHelibob and Larryd,
Apologies for my badly written question and the incorrect m.a. reading. It looks like 68 ma on each coil. The relay bank VCC is being fed by the 5v on the Arduino board.
So, what I was meaning to ask was - Is the 5v supply meaty enough to power all eight coils at the same time.
Also, is there a maximum recommended time for the coils to receive power.
John
Is the 5v supply meaty enough to power all eight coils at the same time.
No. Use an external power supply as suggested in reply #2
A good place to start is with the data sheet. Those relays come in several coil voltages and my read for a 5.0 volt coil is 89.3 mA for the standard version.
This is why trying to use an Arduino to drive even a single coil is not a good idea. Since you plan to use 8 Relays I would just think about buying an 8 relay board along these lines, just as an example. Just choose one that has any features you may want and as was covered power it with an external supply. Many experimenters just use the 12 volt version and power it with an external 12 VDC source like an inexpensive wall wart.
Ron
The link in post #6 does not work
Only takes a few mA to make the opto isolator's LED drive it's photo transistor into full conduction. However, it takes an average 72mA to energize the relay coil and switch the contacts. That's why a separate power supply of at least 90mA per relay is needed, 720mA in this case.
UKHeliBob:
The link in post #6 does not work
Uh Oh, it seems to work for me. Weird but here is where it should go:
I just copied and pasted that in my browser and it worked same as when I click the link as I posted it. Sorry about that.
Ron
“ along these lines, “
This link does not work.
Thank you again for all your very helpful and informative replies. I've learnt a hell of a lot from this thread.
John
larryd:
“ along these lines, “This link does not work.
Fixed it and my bad because when I use a link I generally check it after I post. Links to nowhere are not very useful. A little late but for future generations. 
Thanks again for pointing it out.
Ron
baxwalker:
So, what I was meaning to ask was - Is the 5v supply meaty enough to power all eight coils at the same time.
There's the point!
The "5V" terminal on the Arduino board is not by any means, a "supply". 
It is where you connect a regulated 5 V supply that is also used to power other things requiring 5 V.
