I have a Rasberry Pi running inside a device, which I want to connect to a relay to switch a 220VAC/20A load. The load 'spikes' to 20A when the motor is starting up, but then runs nominally at 7.7A when the motor reaches it's max.
I currently have an electro-mechanical relay rated for 10A contact current and am afraid that the 20A peaks from the motor startup (~7-8 spikes each for ~1.0 second) will cause the contact to 'arc and stick,' if not cause a worse failure.
I do not want to use a SSR, bc of the heat dissipation requirements, if I can help it. I was thinking I might use the 10A-rated relay to drive a contactor switching the higher-power load, but Im not confident in that design.
Thanks!
Answer
Rather than guess at how much to oversize the relay, it is best to use a relay that is rated based on motor power. The IEC motor standards include a rating system that rates relays on more specific application information. In the USA, relays that are suitable for use with AC motors have a horsepower rating.
Look at my more specific answer to this more specific question: Max allowed inductive load (pump) for a given relay
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