Good Automotive Solid State Relay?

Forum 2005-2010 (read only) Hardware Interfacing
1

I plan to use my Arduino to switch an ignition coil (I am making a Rev-Limiter). I need a solid state relay that can:

  1. Handle the current to drive an ignition coil (I did not measure but most coils draw a few amperes)
  2. Have an output range that includes 12v DC
  3. Accept a 5v DC input (from arduino)
  4. Switch fast
  5. Be cheap :slight_smile:
  6. Be normally closed (The arduino will switch the relay causing an OPEN circuit, disrupting power to the coil).

Since I am using a solid state relay would I need a transistor to drive it? If I do need a transistor will I need a protection diode?

Any suggestions?

2

Power MOSFETs.

Some of these have fantastically low on resistances of tenths or even hundredths of an Ohm, which allows them to switch big currents without even breaking a sweat.

If you need one end of the load (coil) to be connected to ground then you should use a P-Channel device. You can arrange for them to be normally-closed with a resistor from the gate to GND.

http://www.armory.com/~rstevew/Public/Motors/H-Bridges/Blanchard/figure-1.htm

Explains how to use them. You don't need an H-bridge, you just need the top left mosfet in the design above.

Draw yourself a schematic, make sure you understand it and try it all on breadboard switching a light bulb before you make it for real.

Mosfets have built in diodes that will provide some protection against back emf, but I would beef them up with a decent higher power diode.