I've just bought a 5M strip of SMD 3528 blue leds for the interior of my chicken coop.
They have a stated output power of 24w / 5 m with 60 Leds per metre. (i'm probably not going to need the full 5M)
My Arduino Mega is running the show, powered by its own 9v supply into the jack from Mains.
My 12V DC motor runs through a L298N powered with its own 12V supply.
I have an 8 channel 5v Songle Relay strip, which i'm planning to run a heat lamp and a cooling Fan.
What will be the best way to wire these LED's, i've read too many horror stories and "The magic smoke appears" to go forward without asking advice.
run the led's via the relay with their own power supply?
I don't need flashing effects or anything fancy, i may need to dim them slightly depending on how bright they are in the coop (they state 270-300 lumens /metre)
You can switch the leds on and off with a relay. You cannot dim them with a relay. You will need a power mosfet for that. An N-channel one with a logic-level gate. Or simply use a shorter strip. You can cut them after every 3 leds.
Why are you using a mega for this project? What a waste!
I'm using the mega as I got it as a gift. Plus it means I can add on in the future.
If I went down the Mofset route I could use pwm to dim them to an acceptable level.
I have a feeling that a 255 they will be too bright.
I think the max length will be 2.5 metres in length of strip so 120 leds. I see from looking there's lots of choices and different ampere values. Based on 120 leds at 12 Watts. Which would be the best to buy?
Your 2.5m strip will draw around 1A @ 12V = 12W. Each group of 3 leds shares the same 20mA current.
There are many mosfets to choose from, so pick whatever is cheap and convenient to have delivered. I suggest something in a TO-220 package so you don't have to deal with a surface mount component. Almost anything in TO-220 size will be more than adequate for your strip. Examples include irl510, stp16nf06l or buk553. As long as it is rated for more than 1A, more than 12V, is n-channel and has a logic-level gate, it will be fine.
Anode (+) of led strip to 12V
Cathode (-) of led strip to Drain pin of mosfet
Source pin of mosfet to ground
Gate pin of mosfet to pwm output of Arduino. For safety, connect via ~200R resistor.
Pwm output of Arduino to either 5V or ground via 10K resistor. This prevents the mosfet turning partly on, while the Arduino is starting up, and getting hot.
Ground of 12V and 5V/Arduino connected.