PCB Relays

Other Hardware General Electronics
1

Hi guys I am in the process of designing my first PCB which will be controller the turbocharger in my truck depending on several analog and digital inputs. My question is what type of relay would you recommend? A reed relay or a normal 5V coil relay?
What i need it to do is when i command the relay closed, it sends 12V to the brake pedal switch circuit for 1 second to fool the truck into thinking that the brake pedal has been pressed to disable cruise control if it was on.
Here are a couple links to the relays i was thinking about.

I wont need more then 50mA for this circuit but i may also want to add a second relay which will disconnect the wire between the wastegate solenoid and the computer in order to keep the wastegate closed when i want it to be and i am not sure how much current that solenoid runs at. i will try and find out asap.
Which relay will last longer? handle the harsh automotive environment better?

Thanks

Mitch

2

Of the ones you cited, both are woefully under-rated to switch the stop lamps. They may be adequate to switch another automotive relay. You will also need a heavier relay to control the waste-gate solenoid.

To cancel cruise control, you use whatever circuit monitors the clutch pedal. This circuit only switches the logic in the Cruise Control.

3

For the driving of the relays i would go for 12V coils and open collector drivers. Don't forget the freewheeling diodes.
When it comes to contact ratings the following is worth considering.

  • Every time you break an electric current you will get an electrical arc. It is this arc that limits the lifespan
  • The intensity of the arc depends on the current
  • The length and burning time depends on the voltage across the contact surfaces. This voltage is affected both the voltage-source (voltage, ac or dc) and the load (inductive loads increase the voltage over contact surfaces)
  • Using some kind of arc suppression like snubber circuits, varistors or diodes will increase contact life considerably
4

nilton61:
Using some kind of arc suppression like snubber circuits, varistors or diodes will increase contact life considerably

Though not for a non-inductive load on 12V.

5

Thanks for your input guys. I tested the brake light circuit and it only pulled 20mA so one of those relays would be fine. Would i be better off going to a solid state relay? From what i have read they dont require a freewheeling diode and would also last longer correct?