I'm considering solutions for a particular high-current switching application. My preference is to use dual-coil latching relays. The only such relays which meet the power requirements are SPST configuration.
Among my many design constraints is a requirement that the switching cannot occur under live conditions. However, as I'm using high-current relays I must ensure a minimum contact (wetting) voltage/current (100mA @ 5V in my application).
The switched loads and supplies are both variable. The supplies can range up to 120V or 33A, although there are no guarantees except that the supplies will not be live during switching. There may or may not be a load present during switching. The coil supply is 24Vdc.
I'm curious what ideas everyone has to ensure my minimum wetting current requirements. My best idea at present is to use an ancillary non-latching relay operated by the same control pulse to switch the 24Vdc (used to drive the relays) across the power relays' contacts during switching (current limited, of course). It goes without saying that there are drawbacks to this solution.
Best Answer
I don't see a problem with doing absolutely nothing. If your contact switches and a load isn't connected and then, some time later, it gets connected, if the relay contact is a bit "dry" it will "wet" when at least 5 volts appear across it then behave normally.
If you were trying to switch loads that run from less than 5 volts it might be a problem of course.