> Are you using the relay to reverse the motor?

One of the relays, yes
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> a series connected MOSFET does the current switching

In this design, one of the relays connects one or more of the other
relays to 12V power. I change the state of those things before
energising that power relay, so it is the only one to experience
any arcing

There's a common point where I can insert a PWM FET. It's
the hot end of a low-ohms current sense resistor. Whatever
path the motor current takes, in any direction through a series
of relays and/or switches, it goes through that resistor. The PIC
uses it to detect an end-stop microswitch opening, so any added
resistance from a FET can be accounted for in the comparator
setting

Looking at the suppression ideas in David's link, it will take too
many components to cover all the paths. Some paths go through
manual switches instead of relays, so they need protection as well

Joe


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