Anyone familiar with relays mechanical or otherwise? I would like to be able to switch on/off up to 250W (120V) load using a microcontroller.
Will be used to control lighting to an aquarium.
Electronic – Which relay – Mechanical or Solidstate
relay
Related Solutions
The switching of the pump causes much EMI (ElectroMagnetic Interference). This can be conducted, like Wouter suggests, and then an easy way to test is indeed temporarily use a battery, so that the interference can't come in through the power supply. If it works OK on a battery you'll have to decouple the power supply better. Filters! You can use a mains EMI filter, like this one, built into the socket:
Also decouple input and output of the power supply with capacitors, and the power connections of the microcontroller and other ICs. Use 10 µF parallel with 100 nF, as close as possible to the power supply pins.
If the battery doesn't help then the EMI is radiated. Also here decoupling with capacitors should be the solution.
This will drive a relay from a micro-controller pin: -
The relays you have described are fine and putting a contact in live and neutral is fine too. Just make sure you select your final one to switch 10A and check to see it is rated for the voltage and has a good gap coil to contacts (or is specified as being suitably safe).
The transistor in the circuit has to be able to supply the relay coil current so it may need to be rated at 200mA depending which relay you choose. Voltage rating 20V or above. If you are using a "hungry" coil and it needs more than 100mA you might want to reduce the 10k to a 2k2 to make sure the transistor turns on properly.
If the relay doesn't have an in-built diode protection circuit then you'll need to add a diode to the circuit across the relay. It's normally not conducting with the anode at the collector of the transistor. 1N400x type will do.
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Best Answer
Solid-state relays are easier to use than electro-mechanical ones. They can be controlled directly by MCU outputs and you don't have to worry about things like putting diodes across coils. I've used lots of them with an ARM to control motors and valves in a complex piece of medical equipment.