Relay Bounce

Only if your circuit depends on them not bouncing.

I don't know for sure. But I would not only not be surprised if it happened, I would not be surprised if it _didn't_ happen with one brand of relay, and _did_ with another -- so even if you have a dozen on your bench that don't bounce, I wouldn't count on all relays not bouncing.

They can do. It depends on the relay construction and whether you are talking about normally open or normally closed contacts. Solve the bounce on closing though, and you may have fixed both instances! Quite often mechanical switches are worse than relays.

The answer's right, but SOME explanation is useful. Opening the contacts of a relay changes the load forces on springy parts, and all the contact surface forces lift in some complex sequence; so, the metal/metal contact surface changes (and can get light enough to be insulated by any surface film).

Of course, an inductive load can then blast the insulating film with a lightning bolt on the nanoscale.

That's just as well... easier to model ;-) ...Jim Thompson

-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

You bet! I'm of the Greek School... why use a 2" x 4" when you have a

Yes. Reed relays certainly do. There's enough energy stored in their mechanical springiness to get them back in contact at least once.

Unless you go for mercury wetted reed relays, where the mercury film damps the oscillation. Mercury wetted relays do have to be mounted so that the reed is with 15 degrees of vertical, but if you can live with that they are really nice devices - they last ten times as long as conventional reed relays, and the contact resistance is low and stable.

People keep on claiming to make orientation-insensitive mercury-wetted reed relays, but I could never find anyone who actually had any to sell.

-- Bill Sloman, Nijmegen

It runs the reverse of the contact touch then wipe some on close; on open, wipe some then the contacts open.

Grant.

Real men use at least a 2"x12", and prefer pressure treated. :)

I think the right answer is "sometimes". I've observed some that don't appear to bounce on open at all. But I didn't run it through the entire life of the relay, maybe 100 operations. A very nice flat Matsushita power relay design with very compliant contacts.

Best regards, Spehro Pefhany

Imagine the relay contact as a button on a leaf spring. When it's ON, the spring is bent and the button makes contact. When it goes OFF, the leaf spring goes from bent to straight, and the button slips and rotates on the contact surface, then (after spring straightening) the button lifts off. The button rubs and twists before it lifts off the surface, and that's plenty of opportunity for contact resistance to fluctuate or vanish.

George H.

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

Everything bounces if you look at a small enough slice of time. :) (There's a joke in there somewhere...)

But to answer your question - yes, ordinary relay contacts bounce on both open and close events.

Last 5 or 10 percent of standard relay leaf travel is designed to cause a contact wiping action, usually as the leaf deforms to a curve slightly against the solenoid.

Not to be confused with contactor sets that simply slam the contacts together at higher speed and force ;)

There's another jump up to arc quenching techniques as the switched power rises.

Grant.

Yes, but nothing at all like the magnitude and duration of the bounce on closing. In general, you worry more about arcing on break and bouncing on make. For example, if you put an RC snubber across the contacts to minimize arcing, the current that was flowing through them keeps flowing when the contacts open - through the snubber. Thus the rest of the circuit is "unaware" that the contacts have opened, and will also be unaware if the contacts re-close on a bounce. The contacts "appear" to be closed during that bounce.

Ed

All relays i know of are made in such a way that guarantees there is no bounce on opening. They were not designed to not bounce; it is the design that prevents bouncing on opening.