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PCB to Control Automotive Relays

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#76637

PCB to Control Automotive Relays | 25 November, 2016

So, project background first. I am in the process of designing a PCB that incorporates a microcontroller, LEDs, capacitive sensors and relays to control auxiliary light in my truck. I have the little stuff worked out and have it prototyped and working, but I want some outside input on the relays on the board.

The relays are 30/40A Bosch Style (5 pin) automotive relays. They are triggered by the microcontroller when it receives a certain input.

I want to make sure that I have adequate trace widths to support the relays when an auxiliary component is triggered. Right now I plan to use 1 oz copper for the board when I have it printed (trace width is 150 mil on the relays and power). I have attached the PCB design to this post.

Each individual relay would have a max of 30A @ 12V on it, and all power lines on the board are fuse protected. In all reality, it is likely that only one relay would be on at a time, and only a single relay will need to support the 30A load, the other relays will only need to handle a couple of amps.

I am new to incorporating microcontrollers and higher amp 12v loads in to a PCB, so I may be approaching this completely wrong. Any input is greatly appreciated!

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#76639

PCB to Control Automotive Relays | 25 November, 2016

ANd the first question is how are you protecting your microcontroller from the back EMF produced by High current relays. Your placement is not well optimised and all your outputs go straight to the relay pins. This is a recipe for disaster!. Read up on protection circuitry or better still pull apart some device that already does this function and look at how they did it!

regards sarason

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