I am looking for a very low current switching relay to be triggered from Arduino so 5V triggering voltage.
Less than 5mA triggering current is ideally what I am looking for.
The load side will be 24V DC at 10A, but down to 2A would still be suitable.
Its pretty common to find a 5v trigger voltage for a relay. Unfortunately we don’t carry any 24V relays though! I’m not sure where you would find one but they are certainly available.
You carry quite a few relay boards Stephen.
Most of them capable of switching 24v and 10a. I don’t know what current is required to operate the solenoid, but it can’t be too high (tens of ma?) to run of an arduino or RPI.
Spot on Robin! We just don’t tend to advertise the top-end as it can often send the wrong messaging to people getting started with electronics.
Is a MOSFET out of the question? A decent N-Channel MOSFET will turn on with uA of power and can drive loads in the 10+Amps zone easily. Consider this one, which can switch 60V30A.
There are a handful of reasons why you’d use a relay over a MOSFET, for example, the most common being isolated circuits. Though that’s not often a concern for most projects.
Having already suffered some major delays to my project due to electrical noise from the 24V side of the system, I’d be wary of using a MOSFET because you mention a relay isolating circuits. Also, I have not used a MOSFET before.
Can you provide a link to an article explaining differences between relays and MOSFETs? I ask because my web searching for various topics has resulted in wildly differing advice, standard practices, etc and it would be good to get a quality article to start with.
If the 24V side of the circuit has a lot of noise (such as back-EMF from motors, etc) then there are lots of ways to improve the design. To eliminate back-EMF a flyback diode could be used with a forward pulse current rating equal or greater than the motor draws at full load. The humble 1N4001 diode can handle a burst of 35V @ 30A, which ought to be sufficient in this scenario.
If there are high-frequency signals from oscillators/other stuff then use a 0.1uF ceramic capacitor between 24V and GND, it’ll act like a short circuit for high-frequency signals. It’s good practice to use one nearby anything that is sensitive (MCUs, linear regulators, etc).
With ALL that said, this should work just fine for your project if you’d prefer a plain-old relay.
+1 million for decoupling capacitors! It is amazing how much difference a capacitor from your DC supply rail to ground will make.
We are currently using the bog std 5V relay module you linked to.
We ended up working around the problem by grounding out the shielded 5 metre PT100 temp probes in the system to the arduino. This seemed to ground the interference and the temp probes were reliable when the 24V devices turning on.
The 24V devices are an automated 24V DC ball valve and 24V liquid pump. Even with the circuits completely disconnected (eg: no relays, etc), manually firing any of the 24V devices caused interference with the 9V arduino circuits with PT100 temp probes attached.
I view the grounded shielded temp probes as a work-around, as whatever is producing all that interference is still doing it. And I think you are right about the fly-back diodes being a possible solution.
But for now, my client is happy to move ahead with his working system.
Thanks for everyone’s help