Relay advice

Hi, I want to hook and control some mains (220v) from the Arduino and am looking for some information on relays.
Is there any preferable type? Solid state or no?
I've seem to remember reading somewhere relays tturning on and off can interfere with electronics. Is this correct? I don't want it to affect sensors I am using.
I'm looking for a good "Relays 101" to read if you have any links!

Would this one on ebay be any good for using with 220 volts? http://www.ebay.ie/itm/Solid-State-Relay-SSR-10DD-DC-DC-10A-3-32V-12-220V-DC-3-25mADC-/390840299311?pt=UK_BOI_Industrial_Automation_Control_ET&hash=item5affe5af2f

Thanks!

Yes. That's fine.

** WARNING !**
SEE REPLY #7 !

I looked it up and an opto-isolator was what I read can prevent interference from the mains voltage, can't find the exact article though.
Do you think it's necessary in this case? Swithing on and off mains fans/coolers. Sensors are air temp/humidity, water pH, water EC (electrical conductivity). Thanks.

I think you misunderstand the purpose of the opto-isolation. The opto is necessary to sense the zero crossing point in the waveform without having a direct connection to the mains. The 220vac part of the circuitry is on the top half of the relay and the dc input terminal are on the bottom .
[EDIT]:frowning: I changed the wording to "top half " and "bottom half" because the way the wording is oriented that makes my statement corrent. I normally turn the device 90 degrees clockwise so my input comes in from the left (ignore lettering orientation) and my output , the SPST switched side is on the right )

The zero crossing circuitry is part of the right half of the circuitry. It does not mean the switching at 50 or 60hz will or will not interfere with electronic equipment but such a low frequency normally does not. You must excercise
care to make sure the 220v power is off when wiring it.

Hi, I've bought the relays as above but looking up aduino relays online they are all shown on a board with other parts (looks like resistors and more). Do I need some kind of board to attach to the relays or can it go direct to the Arduino?

You need a transistor to switch the relay (Arduino cannot provide enough
current) and that usually means a base or gate resistor too. Across the
relay coil there must be a freewheel diode (or snubber circuit) to prevent
the inductive kick-back from destroying things. Those are the components
you get on a relay shield.

The circuit is shown here: Arduinoos » Blog Archive » Relays (Part 1)
(the one with the transistor)

MarkT:
You need a transistor to switch the relay (Arduino cannot provide enough
current) and that usually means a base or gate resistor too. Across the
relay coil there must be a freewheel diode (or snubber circuit) to prevent
the inductive kick-back from destroying things. Those are the components
you get on a relay shield.

The circuit is shown here: Arduinoos » Blog Archive » Relays (Part 1)
(the one with the transistor)

Ah, that's not good :frowning: Thanks for the good info, looks like I'm better off getting ready-made boards (I need a couple of relays and things could get messy very quickly).

Am I better off getting a 5v or 12v relay? I've seen both for sale online but don't understand the practical differences.

Hi, I've bought the relays as above but looking up aduino relays online they are all shown on a board with other parts (looks like resistors and more). Do I need some kind of board to attach to the relays or can it go direct to the Arduino?

THE ONES HE IS TALKING ABOUT ARE THE SOLID STATE RELAYS REFERRED TO IN FOLLOWING COMMENT

** WARNING !**
I just noticed the labeling on the SSR linked from ebay said 12-220VDC NOT 12-220VAC.
Sorry , I (WE) didn't catch that.

Note the labeling on this shows AC .

I have never heard of DC solid state relays but if it means what it says then IT WON'T WORK for switching AC because the polarity is only one way.

HEY GUYS. FYI, THE OP DOESN'T KNOW THE DIFFERENCE BETWEEN A SOLID STATE RELAY AND A REGULAR RELAY SO YOU SHOULD CLARIFY WHICH ONE YOU ARE TALKING ABOUT because he is actually asking you if he needs all the extra components you normally use for a relay driver if he is going to use SOLID STATE RELAYS (which don't require any of that)

Read the OP's Reply#4 and then look at the link he is referring to when he says ("as above") In reply #4 he is referring to SSRs.

(this thread is spinning out of control....the OP wants to switch AC MAINS and everyone is talking about using ordinary relays, which will arc if you try to switch 220vac off while it's running and it will heat up and melt the plastic relays and start a fire.)