Relay Contact Protection

GA to AH.

There are some special contactors which are current-zero sensing ones, but big and expensive i guess. Lots of electronics in it.

Randomising by design is interesting, never occurred to me Do you have any simple method to do this AH?

About the OP, this Tyco paper gives some methods....you can try. (why would you bother at a voltage level of 5V though?)

http://relays.te.com/schrack/pdf/C0_v4bg_4.pdf

An extract from that paper....

If you are using a microprocessor to engage the relays simply make sure that either the CPU clock rate is not a multiple of the line frequency and/or the interrupt that drives the process is not somehow tied to the line frequency.

If it is an external source that drive the relay closure it is usually rare that this stimulus is tied to the line frequency, but a little detailed checking should answer that question.

<...bother at a voltage level of 5V...>

Er, it reads as though the relay coil is 5VDC and the contract rating is 250VAC, 16A, here or is that a misinterpretation?

Schweitzer Engineering Labs (SEL) has a small module called the SEL-9502 Contact Arc Suppressor available for this purpose. Check out their web site www.selinc.com for info. They are kind of pricey ($105 each), but if you cannot control your switching as AH recommends, this might do the trick.

Red Lion R-C Snubber Noise and Arc Suppressor at Newark on line for $6.00

Model Number SNUB0000

There's a PDF from Red Lion showing how to correctly place it in circuit and it's specs on the Newark site.

That is an RC snubber for the coil side of the relay. It is a smart addition to the total circuit, but the original poster seems to be concerned with the actual contact points of the relay, which this will not help.

Suggest you download the PDF from redlion.net. I can't seem to get the hyperlink to work or the pdf to upload to CR4.

I use them on the contacts for hvac apps.

redlion.net/Support/Virtualhelpdesk/search for snub0000

Data sheets normally give some data on spark quenching networks.

Check with the manufacturer or any equivalent relay.

Hi, I just ran the figures you gave and if you put a resistor and a capacitor, in series, across the relay contact points it will give a simple, but effective spark suppression. For 16 Amps at 250 Volts: Use a Capacitor of about 25 Mfd., at a Working Voltage of at least 500 Volts. With a Resistor of 0.1 Ohm, rated at 5 to 10 Watts. This ought to get going. Success.

Why not simply use a solid state relay? Various manufacturers make them. The ones we use are Potter Brumfield.

A caution. If you use 25 μF of capacitance, it will pass about 2 amps reactive current @ 230 VAC, 50 Hz - when your contact is open and supposed to be OFF.

When the contact closes, the capacitor may be at 325V and peak current could be 1000 amps, you should consider if the contact is rated to switch such a capacitor at that voltage (if not, the contact may weld closed or be damaged more when closing than opening.