Powering a 12VDC Solenoid and 120VAC Pump

Hey All,

I am working on a project for my aquarium. I am away from home at school most of the year, so I want a way to easily change some water in the tank without being around. Essentially, I want a solenoid valve to drain water out of the tank until the water drops below the level of a float switch, then have the valve close and a pump start until water level raises to another float switch. The switches are simple digital inputs, but the other two pieces are a bit more complicated. I was hoping you all could look at my schematics and make suggestions if possible.

Solenoid- I’m using a 12VDC, 150mA solenoid, so I have basically copied my schematic from http://www.arduino.cc/playground/uploads/Learning/solenoid_driver.pdf. The only question I have is the difference between a 1k and 2.2k resistor? Is there any difference? I chose 1k for now, because that is what I have.

Pump- The pump is a small 10W guy. I am however very uncertain how I want to control this.
i.)For starters, I’m not 100% if I should be choosing a SSR over electromechanical. I like the SSR, because they don’t require a transistor, but is there any other reason I should choose one over the other?
ii.) If I do go with an SSR, is the Panasonic AQG12105 (http://www.mouser.com/ProductDetail/Panasonic-Electric-Works/AQG12105/?qs=sGAEpiMZZMuYaq4aOfOV%2bDt0xZYR48dC) going to be okay? The 5VDC control voltage is good, and 1A and load voltage range is acceptable, but they do not list a control current. I know most SSR are in the range of 10mA, so can I assume this one is okay? I picked it mainly because of cost. Does anyone have any suggestions for alternative relays?
iii.) My setup with switch the relay maybe twice a week for a few years. Do I need to be concerned about failure? Worst case is it fails closed and the pump stays running flooding my floor. Is having two relays in series going crazy?

Outside these questions, I would love to hear some other feedback and suggestions.
Thanks in advance for you help and comments!

Water Change Schematics.pdf (187 KB)

TrimmerJ55: The only question I have is the difference between a 1k and 2.2k resistor? Is there any difference? I chose 1k for now, because that is what I have.

Here's a really nice tutorial about using transistors as switches:


It gives a lot of detail, including how to calculate a suitable base resistor to get the most efficient switching.

Thanks for the input.

Does anyone have any suggestions for the relay. I’m a little concerned I’m gonna buy the wrong relay.


The AQG12105 SSR should be fine, provided that the load current of the pump is between 20mA and 1A. As it's a 120V 10W pump, it should draw around 80mA. The datasheet gives the SSR input resistance as 0.3K, so it will only draw about 16mA from the Arduino output pin, probably less than that because of the turn on voltage of the LED in the optocoupler.

Awesome, Thanks.

I just came up with one other question. Im using a 12V, 1A power supply for my Arduino. I have been searching if it would be okay to use the Vin pin to power my solenoid. I have read some mixed opinions on this. Some say as long as the amperage is less than 1A, it should be fin (limit of the diode). Can you all confirm this?

Or would it just be better to make a "Y" connection on the power supply so there is a + and - going to arduino (through power jack) and having another + solenoid (I assume - isnt needed because its the same ground as arduino)?


If the solenoid only takes 150mA, driving it from Vin is OK.

I actually was incorrect about the solenoid. The solenoid draws 500mA. Can the Vin pin still handle this?


For 500mA I think the Y-cable is the better option.


Thanks again for all the help. So I have been rethinking which SSR to use. My issue I can get all the other components locally, but not the relay. I dont want to spend $5 on shipping for a $6 part. So I have been looking at ebay. I did find a Crouzet GA8-6D05 for a good price shipped. This SSR is rated for 240v, but the data sheet had a Line Voltage range from 24V to 280VAC. Given the nominal voltage is much higher than my 120VAC, will I have any issues? Im new to SSRs, so I'm not sure that even though its within the given range, if they maybe function better near the nominal voltage, or if there is nothing to worry about at all.

Thanks, JT

Yes, that SSR looks a good choice to me. Using a 240V SSR on 120V is nothing to worry about.