Hi, I am very new when it comes to electronic devices and Arduino. I started play around with mini-projects with Arduino and I kinda need some knowledge from some PROs.
I am trying to turn on and off AC driving Aquarium Heater (50Watt) with Arduino and I could not decide with relay to choose.
I google for some answers but I got confused.
According to above schematic, Is this schematic works for AC also? There are too many relay options out there and how do I decide which relay to use? For a simple device like Aquarium Heater or a light bulb, will any relay will work?
Thank you in advance.
You will need to know how many Amp's the heater is drawing, and then find a realy that can be switched by 5 V (what Arduino digital pins put out when they are HIGH), and the realy must be able to switch 110 (or 220) Volts at the Amp ratting of your heater.
I'm using one of their 18A relays to control the floor heating element under my tile floor in the bathroom, an Arduino & 1-wire temp sensor
Just be careful of the 120v wiring and try and keep it separated as much as possible from the low voltage stuff. battery voltage is a liitle more forgiving when you accidently touch it....
For the most part I agree that solid state relays are the safest and easiest relay to use. Assuming your 50watt heater is using 120v AC then thats only about 400mA or less than half an amp. For this a simple 1A 5v reed relay from radio shack p/n 275-232 would work. For this a transistor is not needed but a diode across the coil is.
Something like that should do it if you can make sense of it. Basically a reed relay is a very simple normally open switch surrounded by a wire coil. Take the hot wire or the black wire from the ac cord and connect it to both sides of the switch part of the relay. Connect a digital pin to one side of the coil and connect the other side to ground. Also make sure you have a diode (1n4001 or similar) connected across the coil as well. Theres a better drawing of how the relay works on the back of the package. Because this relay is so simple theres really nothing wrong with running it straight from the arduino. While this will work with solid state relays this is not the case with other mechanical relays.
Above all, make sure you work safely, that nothing is wired while plugged in, and make sure that any exposed part of the AC side is protected with black electrical tape or heat shrink tubing.
Hi,
In your case, with only a 50watt heater, you only need about 0.5 amps. With the formula P=IV (power (P) = current (I) times volts(V). So you have 50 watts = current * 110 Volts. So current is less than half an amp. So you are well in the clear. You might save money looking around to get a smaller 10 Amp variety or even less (though harder to find). One special aspect of this large style of relay is that it's a zero-crossing, meaning that it will only switch the alternating current as the voltage crosses zero. This creates a nice "noise free" switch. Have you ever heard a pop on the radio when you plugged or switched on a light? Well, I'm pretty sure if you had this switching it, you wouldn't hear anything. A nice feature to splurge on if you find it is an LED light on the front so you know if its been switched or not. Nice debugging tool. Make sure it is switchable by a 5V dc signal and that the output is AC and includes 110V.