Advise on relay to purchase

Hi Folks,

I'm new enough to this so excuse the lack of knowledge. I'm based in Limerick in Ireland. I'm looking to purchase a solid state relay for a project. Basically I'm trying to use the relay to switch on and off a 100w light bulb. I'm intending to use the mains as power (ac current). I understand the relay acts as a switch similar to a transistor. I've worked with transistors before. So essentially if you want to switch a 100w bulb at 240v the bulb will draw .41ma. (wattage divided by voltage). Once I do this I intend to switch the light bulb for a heat pad which draws 1.5 amps. What I'm really looking for is what relay to purchase. Any help on this would be greatly appreciated.

Thanks folks

Hi, A solid state switch will also to the job for the heater, just make sure it is capable of switching the current.

In fact if you measure the COLD resistance of the heater, it will tell you via OHMS LAW how high the switch ON current will be. Usually heaters change resistance as they heat up, the highest current being at switch ON.

Tom... :)

Hi Tom,

Very much appreciate the reply. Do you know of any solid state relays that would suit?


If you won't be switching ON/OFF frequently, why not use a $2 10A 240VAC relay module? That's the low end for those, 10A. IIRC they can switch more amps of lower volt DC.

If you see Watt ratings, W = V x A.

Thanks go for smoke, I was looking at one of these:

Relay module 1 channel 5V - 10A 240Vac 30Vdc

I think this might work.

It should handle the lightbulb (incandescent bulb?) and 1.5A (360W, as compared to blow dryer at 600W-1500W) heater.

If you write the relay control part of the sketch as a separate task that other parts signal through a variable value, that task can run a timer whenever it is switched and not switch it again until the timer is up. If you don't know how, the "do many things at once" lesson shown on this forum and many places (1st link in my sig space below is to Nick Gammon's tutorial and there is a sticky thtread at/near the top of this forum section with the same basic lesson by Robin2 in IIRC Dublin for example) on the web.

Such a task can simplify the rest of the sketch to safety the relay and what's connected to it where say watching temperature and switching on above or below could burn the relay in a day or less... the code would be simpler till then.

Hi, Lots of info and examples on both relays and solid state relays HERE