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Author Topic: Triac vs Relay  (Read 1026 times)
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Hi There!

I want to control (on and off) 1.5 HP, 220VAC motor from Arduino.  I am thinking of controlling the motor by building a solid state relay using MOC 3021 and triac BTA16.  Is this the best approach? or using a relay is the simple and better option?  Need to know any advantages and disadvantages of both the approaches.  Any suggestions are welcome.  Thanks in advance.
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Best is to buy a ready-made random turn-on SSR, but they are expensive compared to making your own. If you use a mechanical relay, you should connect a snubber network across the contacts to control arcing. You may need to use a snubber network with the home-made SSR too.
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Induction motors are a nearly pure inductive load (tricky for triacs) - do you have specs / datasheet for the motor?
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At that power it's time to look for properly sized 'motor starters', which is just a fancy name for a electromechanical relay built for such service.

Lefty

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Thanks all for your responses.  I have decided to go with 10 Amps relay.  For the snubber network, If have one capacitor of 10nf/680V and one resistor 39R in series across the relay switching terminals, is that sufficient?
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I suggest you check the starting current of your motor, to see whether a 10A relay is sufficient. Regarding the snubber, I'm not an expert in this area, but 10nF sounds way too small to me, I suspect you need at least 1uF for a motor of that size.

There are vendors of alternative arc-suppression devices who claim that snubbers are useless in high-power applications, for example http://www.arcsuppressiontechnologies.com/Documents/Lab%20Note%20103%20-%20NOV2011%20-%20Snubbers.pdf.
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Thank you dc42.  After doing some research on internet, I too realized that snubber circuits may not be useful in suppressing the arc totally.  So I am left out with the option building my own SSR.  Good news is there a snubberless version available in BTA16 Triac series for inductive loads.
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