I want to control speed of an AC Motor using phase cutting.. Well, I already have zero cross detector and SSR but don't know how to program Arduino to phase cutting using SSR.. And to connect the motor to SSR, do I need some protective circuit or not? Thanks!

closed as off-topic by MatsK, sempaiscuba, Dmitry Grigoryev, SDsolar, jose can u c Jun 21 '18 at 20:15

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    you want to use the zero-cross to trigger an interrupt that saves the millis() value. in loop(), you can (millis() - lastCrossTime) to find out where on the phase you are, and control the relay based on that. youtube has several detailed video on the topic, recommended. – dandavis Mar 8 '17 at 1:12
  • In practice a packaged SSR will not be suitable for partial-phase activation. You need a bare triac, and to use that safely you need some fairly serious electronic design experience. This is not in any practical sense an Arduino question. – Chris Stratton May 30 '17 at 16:38
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    I'm voting to close this old abandoned question as off-topic because it is primarily about electrical engineering not Arduino, and because it is not specific enough to survive on any stack exchange site. – Chris Stratton Jun 11 '18 at 15:06

First of all no protective circuit is needed in order to connect an arduino with an SSR. SSR input is isolated from the load. Now answering your question you better go with an inverter, forget the SSR, and let arduino control the inverter. Using DOs from an arduino you can command the inverter to start/stop the motor or change the motor direction. Using an AO e.g provided by a DAC like MCP4921 you can control the motor RPM, too. There are a lot of inverters available for different loads and also different controls (Manual, Digital/Analog, Serial)


As per Your question You must need a protective circuit to save the Arduino from Back Voltage.

Take reference from this Link AC Motor Speed Control

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