relay connections, is this right?

I know I asked this before but my memory sucks.

Is this right?

Should the GND of the power supply always be connected to the device which it powers and have just the positive connection be controlled by a relay like this?

nope.

that relay requires 12v dc on the coil.

you show the power passing through the ardiuino, that is not correct.even if the rely was a 5v one

How is the power passing through the arduino? I don't understand.
Oh and for the record the Device needs 12V and the PSU outputs 12V.

psu is not connected to the arduinoi

you are correct, since power is not connected nothing would get fried.

you have 5volt to ground
and ground in Vcc

if you had power connected to the arduino, you don't, then you would have power connected wrong.

if you do choose to put 12v on the 5v pin, you can get new nano for 2 bux. great price.

this might work.

based on this link

A couple problems:

  1. You have the ground from the arduino connected to the vcc of the relay board, and
    you have the +5v from the arduino connected to the ground of the relay board.

  2. You don’t indicate any power to drive the arduino board.

  3. based on the label on the relay, it does appear that it needs 12v to activate its coil.

The PSU as you have it drawn does not connect to the relay coil, only to the relay contacts, and then the device.

You probably want a relay board that will run from 5v, rather than needing 12v.

[quote author=jack wp link=msg=2403682 date=1442707300]

  1. You have the ground from the arduino connected to the vcc of the relay board, and
    you have the +5v from the arduino connected to the ground of the relay board.[/quote]
    My mistake when drawing the illustration.
  1. You don't indicate any power to drive the arduino board.

USB

  1. based on the label on the relay, it does appear that it needs 12v to activate its coil.

Mine is an Arduino Relay Shield, it wants 5v. Dont know about the model in the pic I found for illustration.

The PSU as you have it drawn does not connect to the relay coil, only to the relay contacts, and then the device.

What do you mean?

There is no need for the "device" to be connected to the relay coil. The device switching circuit is fine. It is only the Arduino to really board that is wrong. However a schematic would have been much better that what you posted.

Switch the red and black wires to the Arduino, then you are good to go, assuming you do have the 5v relay and not the 12v pictured. Slay make sure your device isn't pulling more than 10 amps.

I just checked, mine says 05VDC. Also tested in on a led, seems to work. I'm surprised the one in the pic is for 12V, they eBay page said its an Arduino relay.

My device is pulling 3 Amps.

ghosttrain:
I'm surprised the one in the pic is for 12V, they eBay page said its an Arduino relay.

That is why posting your wiring like you did is useless. Please use a schematic, draw it on paper and post a picture of it, that is all you need to do.

ghosttrain:
I just checked, mine says 05VDC. Also tested in on a led, seems to work. I'm surprised the one in the pic is for 12V, they eBay page said its an Arduino relay.

My device is pulling 3 Amps.

????
you connected an LED and it is pulling 3 amps ?
"arduino relay" ???? no such thing
you can google arduino panties and find 127,000 hits.
they can play music, light lights. all manner of things.
one pair was used as a GPS/compass/wind sock on an arctic expedition.
they hung it from a ski pole. held up, you could see which way the wind was blowing.
there is absolutely no official Arduino anything, unless you buy it from the Arduino store.

on e-bay, they put arduino in front of anything, arduino wire returns over 1,300 hits on ebay.

anything and everything that is connected to the relay Com/NO/NC pins is completely isolated from the Arduino.

there is no need or reason to tie them together such as ground and such.