Trying to figure out which relay I need for a project I'm working on. The source is a 12V battery, and I'm looking to turn on a 12v solenoid using a relay. I want the control voltage on the rely to be 5V, so I need a 5v relay capable of switching 12V. Found this relay but I'm not sure if I'm looking at it right. Would this relay be capable of doing what I want?
What kind of relay do I need for for 12V source with a 5V control voltage
12v5vrelaysolenoid
Related Solutions
Presumably there is a regulator between the 12V supply and the arduino. As long at the 12V supply remains high enough for the regulator to function, it will keep the voltage to the arduino constant.
However, regulators aren't perfect. In particular, they can only compensate for input power variations up to some frequency. Noise above that will be passed to the output. If you think the input power might be noisy enough so that the regulator can't block it all, put a small filter on the input of the regulator. Most regulators will work OK up to a few 10s of KHz. You didn't say how much current the arduino draws, but you have plenty of voltage headroom. A 10 Ohm resistor will only drop 1V at 100mA, which still leaves plenty for the regulator to work with. That followed by a 10uF ceramic cap to ground right in front of the regulator will form a low pass filter with 1.6KHz rolloff. That should be good enough to keep the input of the regulator down to frequencies it can deal with.
Of course the best way to handle noise is to not make it in the first place. You absolutely need a diode or some kind of snubber to catch the inductive kickback when the solenoid is turned off. The main reason is to keep from frying whatever is switching the solenoid, but a secondary effect will be to decrease overall noise.
The first choice to make is whether you want to switch the input to the 12 V power supply, or switch the 12 V to the pump. If the pump spends a lot of time off, then powering down everything is probably a good idea. The 12 V supply will take some idle current, which is a waste if the 12 V isn't used for long periods of time. On the other hand, if the pump is on a lot and is turned on and off a lot, it will be easier to switch the 12 V to the pump. You could then even run the microcontroller off of the 12V, perhaps even with a linear regulator if you can keep its current down.
To switch the line power into the power supply, a plain old relay would be the simplest choice. There are plenty of relays that can be controlled from 5V that are intended to switch line power. Your supply will take well under 1 A, so there will be a wide choice of relays.
To switch the 12 V power to the pump, I'd probably use a transistor as a low side switch. Since the 12 V is already isolated from the line, you can tie the - side of the 12 V supply to the processor ground and use a direct connection. Lots of stuff can switch 1 A at 12 V. Here is a simple circuit:
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Best Answer
In the comments, efox29 found a datasheet for this relay which will help in my answer. (Thanks!)
There are two parts of a relay to look at:
Coil
Your control voltage needs to match the coil voltage. They're both 5 V here. Good.
Your control output needs to supply enough current to make the coil work. The datasheet says that this relay takes 71.4 mA of coil current. That's quite a bit, and it's definitely more than an Arduino can source. I don't know what you're planning here - you should look at driving the coil with some sort of transistor driver.
Load
The relay needs to be able to withstand the load voltage when it's off. Here, the contacts are rated to 30 VDC, and the highest voltage in your system is 12 V. Good.
The relay needs to be able to pass all of the current into your load. The link says 10 A. You didn't say anything, so I can't confirm this. If your solenoid's required current is less than 10 A, this is fine.