Stepdown Transformer for my Project

I want to run an Arduino with a shield (currently being developed) and a 8 Relay board to switch Mains Power on and off to 8 Single Mains sockets.

I'm looking for a power unit that can run the Arduino as well as the Relay board.

The one I have seen is a 230v to 2 x 6v 1.8VA

Here is a link to the Relay Board:

http://www.ebay.co.uk/itm/131297384530?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Here is a link to the transformer I am thinking of using:

http://www.ebay.co.uk/itm/Encapsulated-Mains-Insulated-PCB-Power-Transformers-230-6-9-12-15-18-24-VAC-V-AC-/180843068279?var=&hash=item2a1b163b77

Is this a good idea and do I need a 1.8va and is 6v sufficient for the Arduino as the relay board only needs 5v.

Thanks
Graham

You need to know the current required by the relays, worst case. 1.8 VA is not much power.

Hi, thanks for replying.

I've heard that you can only run about 4 using the power from the Arduino.

I have had a look at some other boards that use the same relays and found this:

5V 4-Channel Relay interface board, and each one needs 15-20mA Driver Current

The next power unit up is a 10VA one. Am I right in saying if it doesn't need the current it wont draw it? As I don't want to burn anything out by using something with too much current!

Thanks

Graham

Circuits draw the only current they require, so there is no danger of burning something out by "supplying too much current". But devices won't run properly or at all if the available current is less than the required current.

The available current from a 1.8 VA transformer is roughly 1.8VA /5V or somewhat less than .36 A (360 mA). That is enough to run the Arduino and a few relays at 20 mA each.

However, the transformer you LINKED is rated at 0.6 VA, or 100 mA.

You also need a rectifier, filter and 5V regulator between the transformer and the rest of the circuit. It would be better to use a 5V regulated wall wart or other prepackaged line power source.

I did look at regulated packages but they was rated at milliamp.

I have considered your suggestion about a wall ready PSU as I could strip them down and use one for the Arduino and another for the Relay unit.

Graham