RC unit

[TarHeelTom]

Trying to salvage a few of the mechanical relays from the Bridgeport under rehap.

No problem, pretty straightforward.

But have noticed that almost every relay has a component between the first of the common points and the first NO points.

It's marked:

RC Unit
630 vdc, 250 vdc (or thereabouts)
.1 mfd 100 ohms

Looks like two separate components with amber colored epoxy or similar cast around them.

Any idea why these were there?

Thanks

Tom

[Al_The_Man]

Are you sure it is not across the coils, snubbers are used on AC circuits to quench back emf or spikes that may occur when the coil releases, the DC equivalent is the reverse EMF diode across the coil.
Al.

[mike_Kilroy]

Al, I've seen some designs where the rc networks were put across the contacts also to try to mitigate the sparking on opening an inductive load.

[TarHeelTom]

Originally Posted by Al_The_Man Are you sure it is not across the coils, snubbers are used on AC circuits to quench back emf or spikes that may occur when the coil releases, the DC equivalent is the reverse EMF diode across the coil. Al.

Yeah, Al, I was expecting them to be across the coil, and was surprised when they were not across the coil.

Most of relays are 11 pin tube socket type. Pins 2 and 10 are always (on these, at least) the coil, and the snubbers are connected from pin 1 to pin 3.

And by the way, mine look exactly like the picture you posted.

Thanks

Tom

[Al_The_Man]

Iv'e found them fitted to contacts on rare occasions, but usually the relay has been under rated and the 'fix' is to add a snubber instead of using the correct size contacts.
If the contacts are switching a high energy DC inductive load, you can get relays fitted with magnetic arc-blowout feature, this is a magnet adjacent to the contacts.
Al.

[mike_Kilroy]

or an engineer who added snubber across the contacts instead of the proper design of adding a diode across the dc inductive load itself to supply path for the inductive voltage spike....