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I don't have any experience with star delta starters but on doing some research I concluded that 2 push buttons(NO and NC) are required to turn on or off the system. I have a pump which is star delta controlled, turns on when I push green NO button and turns off when I push red NC button. Now I want to control this via Arduino rather than manually pressing buttons. What I thought so far is to replace push buttons with relay(NO with NO and NC with NC respectively) and control those relays with Arduino. But I've seen many systems of star delta connection where motor turns on or off with just a normal on/off switch i.e. no separate push buttons. That will be more feasible to control via Arduino since only one relay is required. But I nowhere found a way to replace 2 push button circuit with normal on/off switch. Please help out.

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  • \$\begingroup\$ Questions on the usage of products aren't on topic here, because they ultimately come down to needing to know things which are not knowable from the outside. Before you contemplate "hacking" this motor controller and all the potential dangers thereof, you need to thoroughly understand both how it works internally, and applicable external requirements - eg, what happens if it turns back on after you turn it off or trip the e-stop or overload? \$\endgroup\$ – Chris Stratton Oct 20 '20 at 14:10
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You could maybe use a two pole relay if the starter doesn't mind the buttons being held

schematic

simulate this circuit – Schematic created using CircuitLab

Or if one of the buttons has priority over the others you could hard-wire that button and just use the relay on the other.

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  • \$\begingroup\$ Thanks for your interest Jasen. I don't know whether starter mind the buttons being held or not. That's what I want to know. Star delta connection is pretty common (with two push buttons), but I don't know the functionality of it. Also I kind of have a constraint of using 30amp 5v single pole relay only. But as I told that I've seen systems where single on/off switch controls the system, this relay will be perfect for that. \$\endgroup\$ – Rishabh Oct 20 '20 at 8:06
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Actually you need three(3) power contactors, and not a single relay for star/delta. But I suppose you have these contactors and timer unit in a box that is mounted on a pump itself.

schematic

simulate this circuit – Schematic created using CircuitLab

Usually the star/delta schematics for the 1st contactor is as depicted. You have a start and stop button that are series wired with motor protection device and possibly an emergency stop. The strat button is self retained by using an auxiliary contact of the power contactor.

schematic

simulate this circuit

For use with your Arduino, you have to replace start/stop button combo with a relay, also yo have to remove the aux. contact from power contactor.

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For safety reasons, it would be advisable to keep the Star - Delta Starting circuit 'as is' and interface it with Arduino only for 'Start' and 'Stop' pulses.

enter image description here

Hence having two relays for the interface is a must.

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