I want to implement a 12V relay (https://www.mouser.com/ProductDetail/Panasonic-Industrial-Devices/TX2SA-12V?qs=HLLy2pIPwuuBcCVwky7PWw%3D%3D) in an automotive application.

I will be using the car's 12V battery power to control the relay coil. The signal I am switching is battery 12V going into a high impedance input, so very little current will flow through the contacts, necessitating the use of a small signal relay.

Using a transistor is not possible as there would be no voltage drop between gate and source since this is not a low/high side switch.

I am concerned because I cannot find a small signal relay rated for automotive use, particularly vibration. I am also concerned how the relay coil will respond to the noisy battery power, and whether I will experience unexpected switching under conditions such as load dump or starting.

Is this a valid concern, and if so, what measures should I take to prevent issues?

  • 2
    \$\begingroup\$ Have you thought about using an automotive rated relay? \$\endgroup\$
    – Passerby
    Oct 26, 2018 at 3:31
  • \$\begingroup\$ I have updated the post to include why I am not using an automotive relay \$\endgroup\$
    – user202237
    Feb 10, 2019 at 1:37

1 Answer 1


I was incorrect in one of of my assumptions in this question.

The input I am going into is an ignition input on an ECU. These are generally pulled down internally, which means you can use a MOSFET to switch the signal, since the drain will be at 12V and the source will be at ground.

I did end up using the small signal relay, and one of the surface-mount legs of the relay eventually broke due to vibration. My solution was to epoxy the body of the relay to the board, but in the future I would use a through hole relay.


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