# power supply unit for Arduino/solenoid project

I'm trying to find an off the shelf plug in ac/dc power supply unit to work with my project. I want to power an Arduino Duemilanove and six 12v 1A solenoids. Here's the solenoids -> http://www.rapidonline.com/productinfo.aspx?&tier1=Electronic+Components&tier2=Relays+%26+Solenoids&tier3=Solenoids&tier4=PCB+miniature+solenoids&moduleno=29536&catref=60-3210

But I don't know how to work out the right one. Cheers

1. Figure out what voltages you need. You say the solenoid needs 12V, then you need to check the Arduino Duemilanove. Will it work with 12V, or does it require a different voltage.

2. Figure out the maximum power you will need. 12V * 1A = 12W, seems high for a small solenoid, but I don't have a lot of experience with them. Sum this for all the components you will be running simultaneously.

3. Select a power supply that provides the required voltage(s), plus at least the maximum current you need. You should probably pick something that provides a bit more than what you need, because running a component at 100% is generally a bad practice.

• I'm not too sure about how much power the solenoids draw, the datasheet says they are 12v 1.5W? I suppose the Arduino will depend on what parts of the board are in use, I looked at the Arduino website and it says it draws in the region of mA and at a max of 1A if your using all the ports. So I'm guessing I need an amp for each solenoid and an amp for the Arduino (assuming thats not over kill) So it's 7Amps could I use the nearest value PSU? if I give it 6A will it struggle? or would 9A cook it?
– Jim
Commented Jan 14, 2010 at 21:11
• sorry dude, I should say thanks for the response first!
– Jim
Commented Jan 14, 2010 at 21:15
• hang on, I think I see what you mean now. so if they're 12v 1.5w they draw 0.125A so 6 solenoids is 0.75 amp plus the 1 amp for the Arduino. So do I need around 12v 2Amp DC power supply?
– Jim
Commented Jan 14, 2010 at 21:54
• you should not consider the arduino to be the whole 1A even if you are using every pin. That will all depend on the loads of arduino. The rating given on the site is considering the loads and I think the loads are your solenoids. The boards itself just draws 0.2mA I think Commented Apr 2, 2010 at 3:21

It might be a good idea to use two power supplies, otherwise transients from the solenoids will affect the Arduino's operation. A single power supply could be used, but you need to design it carefully.

• I'm planning on using some npn transistors on the Arduinos outputs and protective diodes over the solenoids. Is that the kinda thing you mean?
– Jim
Commented Jan 14, 2010 at 21:13
• There is a lot more to it than that. The solenoids will take a lot of current - you need to look into power and ground distribution to ensure that it doesn't affect the MCU. Commented Jan 14, 2010 at 22:16
• thanks, I may yet end up posting the circuit once i've got it on the breadboard. I don't want to knacker the MCU
– Jim
Commented Jan 14, 2010 at 23:17