latch 3 soft switches with one relay?

Hi,

Like the title says, I'd like to know if it's safe to latch multiple "soft" switches with a single relay.

I plan to build a thermal control and a delay switch to add temperature controlled logic to the vehicle for the defrost and seat heaters so that they will come on if the temp is below "x" (say around 40 degrees).

The thermal control part should be obvious. The delay switch is so the car is given time to start and the HVAC system to initialize (2010 Mercury Milan with electronic controls, a clone of the Ford Fusion). Both of these parts will be off the shelf (kits, CanaKit and Vellemann items).

What I need to know is how to safely latch all three of the switches. These switches are triggers for the vehicles onboard relays, I know from the wiring posted here they get latched to ground to trigger the relays, but do I need to diode protect the ground connections I'm latching?

The relay on the Vellemann VM188 kit is 16A/230V, so I'm certain it's up to the task.

I figured I should ask for some advice here before I let any of the smoke out of my climate controls.

The diodes aren't needed for protection, they are needed for isolation. If you connect all the switches together to one set of relay contacts with no diodes you will short all the switches together and when you turn one on, the other two will turn on with it. With diodes in line for each switch they will prevent backfeeding of one switch to the others.

One relay going through three diodes should work with no issues.

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Kevin Pierson

Thanks for the reply! I didn't think about the need for isolation.

I'll definitely make that a part of my plans, then.