AC Relay EMI Suppression

[NavMicroSystems]

We keep getting whacked by these huge spikes when we switch off the loads.

Are you sure that the noise isn't coming from the coil of the relay? Can you hook a relay up to your pic without a load and fire it and scope the noise?

I have had a simmilar situation,
with no load I could switch all relays without seeing any spike,
but with (inductive) load on the large relais I had huge spikes about 1 or 2 times out of 10.
The spikes were definitely comming from the relays contacts when opening.

Since the "power-side" of the project was an existing installation, replacing the relays was no option.

This is why I went for the "ZeroCrossing" solution.

@CocaColaKid,

However you should doublecheck you have done everything to suppress noise comming from the coils.
Make sure you have proper grounding and no Ground loops.
Use a separat PSU to drive the small relays.

@Melanie

Isn't this one of the areas you are experienced in?