Relay for controlling 12V computer case fans

Using Arduino General Electronics
1

Hi all,

It's my first time doing anything Arduino, and I was looking for some advice choosing a relay

I'm looking for a relay that can be switched using the 5v signal from the arduino (the easy bit) and then the 'load' on the relay is going to be a 12v computer case fan.

All relays I am finding are for switching mains voltage equipment, using a 5v signal. Like the below one has a range, but it is 75 - 264, so still not suitable for 12v if I'm reading correctly

Can anyone help spec something suitable please, if such a product exists? Otherwise is there any other way of doing it?

If it is the relay route, preferably something with 8 channels please for 8 individual fans

Any help would be appreciated

Thanks!

2

I'm looking for a relay that can be switched using the 5v signal from the arduino (the easy bit)

No it is not.

The arduino should only be asked to draw 30mA from an output pin so you have to get a relay that will switch on that. There are some but they are not common. Otherwise you will have to use a transistor to switch the relay coil, typically these take 75 to 120mA.

All relays I am finding are for switching mains voltage equipment

No problem, if they switch mains then they will switch lower voltages as well.
The rating of the contacts of a relay and the rating of the coil have no connection except for the fact that contacts that take more current tend to be bigger and require more coil power to move them. But if you find a relay with the right combination of contact ratings and coil ratings go for it as they are interdependent.

Solid state relays of the type you posted are only suitable for AC, they have no contacts as the name suggests.

3

Thanks for the response, maybe it is slightly more technical than I thought then. Just had a quick read up on how relays work to understand your comment properly.

I've found this one, link here. Supposedly for use with an Arduino...

It's working voltage is 5v, and it mentions "relay output maximum contact is AC250V 10A and DC30V 10A"... Would that be suitable? I'm not sure because it doesn't mention what current is actually needed as an input to power the coil and switch it? Unless I've misunderstood.

Any chance you could please link to an 8 channel relay that would be suitable for switching DC12v computer case fans if the one above is not suitable? Would really appreciate it :slight_smile:

4

I'm not sure because it doesn't mention what current is actually needed as an input to power the coil and switch it? Unless I've misunderstood.

You have misunderstood.

That board has an isolator and amplifier built in so it will work when you directly connect it to the arduino. It is active low, meaning you make the arduino output LOW to turn on the relay and HIGH to turn it off.

A rating of 30V DC at a current of 10A is more than enough to drive a fan. In fact it is overkill but if you don't mind the price it will do. There is a 4 relay version of this as well.

5

Thanks for explaining

Price is kind of important so I may try and find a slightly less overkill one... Maybe the opposite of that as well, so I can set the arduino output to high, to turn the relay on. Just seems to make sense that way round lol

6

Just seems to make sense that way round lol

A lot of beginners think like that but in the professional world it is more common for low to be turning something on.

7

Grumpy_Mike:
A lot of beginners think like that but in the professional world it is more common for low to be turning something on.

I'll maybe just go with that then if I can't find anything cheaper or less overkill

Thanks for the help answering all my questions :slight_smile:

8

Gone for the one linked above in post #2, at least it will be suitable for future tasks too then (even if overkill for this project)

Thanks :slight_smile: