Relay board that works with DC solonaid ?

If you’re working entirely with DC then a transistor would work just as well and be a lot cheaper. Something like a 2N2222 would work, depending on how much current your solenoid pulls.

I see some 9v solenoids that only need 240mA so an 800mA transistor would work.

Scott

I’m not suggesting you change an existing board, I’m suggesting you just use a transistor. When working with low voltage DC you can use components directly without the need for fancy boards. It know it might be scary to work with solder but if I can do it – and I’m a CS grad, not EE – then you can too :). There are lots of examples on the web on how to use it to switch DC. And from a cost standpoint, you can’t beat it – I see you can buy one of those 2N2222 for 10 cents ($0.10).

And besides, if you fry something it probably won’t hurt anybody. It’s when you start messing around with AC 120v 15A that things get … challenging. That’s when buying a board is a good idea – somebody else has already worked to make that safe.

You can pull a lot of mA out of a 9V battery; but that’s not the issue – the issue is the load, so you’ll have to look at the solenoid and see what it draws.

What are you trying to do?

Oh I see – you want OSPi to work with this DC solenoid instead of the standard 24V AC solenoids? That’s Ray’s department, not mine. I’m not sure what it would take to get that to work.

@ChaoscripT: the valve shown in your link is clearly a latching solenoid (note that the two wires have different colors, meaning there is polarity). Latching solenoids are typically used in battery-powered controllers, and CANNOT work with 24V AC sprinkler controllers (such as OpenSprinkler or OSPi), because the electric spec and the controler mechanism are completely different. OpenSprinkler Bee is designed to work with latching solenoids:
http://rayshobby.net/?p=8527
We have an Arduino Shield version of OpenSprinkler Bee (called OSBee Sheild) that will be released shortly this week.

24V AC valves require a 24V AC power adapter and cannot work on batteires. If you must use latching solenoids, then OpenSprinkler or OSPi are not suitable. If the valve type doesn’t matter, I suggest that you get 24V AC valves, they are cheap and widely available online or at home improvement stores.

It’s possible to use OSPi with DC solenoids, but as I said, the one in the link you showed is DC Latching solenoids, and to interface with those it’ complicated. You can find DC non-latching solenoids, and you can use them with OSPi by replacing the on-board triacs with transistors or MOSFETs.

Latching solenoid only draws power when it opens or closes, and does not draw power when it remains in the same state. It’s sometimes called bistable solenoid. Applying a positive voltage opens the solenoid valve, and reversing the polarity closes the valve. The coil on the solenoid typically has very low resistance (a few ohms) so it momentarily draws a high current, often up to a few amps. You are supposed to only apply an impulse voltage instead of continuous voltage, otherwise it can quickly burn the coil or short the power supply.

There are many relay boards that will work. I used this 4 relay board from SainSmart. It’s connected to my Raspberry Pi and running my sprinkler system for 2 years. You can buy from SainSmart, I bought one off Amazon for a $6. They also offer relay boards with more or less relays, and also small signal and solid state relays – http://www.sainsmart.com/arduino-compatibles-1/relay.html

I want to re-state what I said earlier: when working with DC solenoid, be sure to check if the solenoid is latching or non-latching. Some DC valves use latching solenoids, the coil resistence is typically very low (a few ohms). These valves must be ‘pulsed’ open or close, you should never apply constant voltage more than 50 to 200 milliseconds, as that will smoke the coil. Other DC valves that are non-latching, the coil resistance is typically higher (30 to 60 ohms), and you can apply constant voltage on it to open the valve, and release voltage to close the valve.