Electronic – DC Relay overrated for max. 100ms


In my case I need a relay to switch continous 0.5A at 24V DC, but in time of closing the contacts there will occour an inrush current from the further circuit of 6A, but only for max. 100ms because there is a contactor (DC) in line of the switch.

I dont know the exact amount of damage of the contacts in that case, because its only for milliseconds. Do I need a Relay with max. switching current rating of 5A or 8A rating?
Could there be a significant amount of damage in general?

I already checked the datasheets according to that, but the graphs are ending at the rated current.

I personally think I schould just take the overrated big one, but in my case a smaller component size would be better and it will be fully underrated wit 0.5A for the continous time

At a 5A type I would take the omron G6B-2214P-US or the Panasonic DSP2a-DC5V.
They are DPST relays, the second pole will be used for a signal.

Thanks for your help!

Best Answer

In-rush current is a killer for contacts in relay (and elsewhere). A short current spike during operation, when the relay is properly closed might be tolerable (ask the manufacturer).

In-rush current on the other hand is much worse: It starts flowing at the very first instant the contacts barely close. Usually contacts bounce for a short moment, causing a current arc and extensive heating of the contacts. The same holds true for high currents when switching off the relay (i.e. when shutting down an inductive load).

As a result, the rating of relays are typically for resistive loads only. As soon as the load gets capacitive or inductive, the allowable limits are much lower.

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