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I have below circuit employed at my home.

Since I used 2 way wiring between relay and manual switch, during power failure, I face problem of Lamp turning On or Off depending on switch position.

Out of 4 positions of two way switches 2 are working fine and other 2 are working opposite.

Please help me with some circuits preferably using relays or switches to overcome this problem during power failure. Other design are also welcome.

UPS takes over without any issues but SPDT relay 2 used for home automation system loses power from mains, changing contacts thereby toggling the lamp.

Since the space is limited, kindly give me some idea, where after power failure SPDT Relay 1 switches to UPS mode but due to power loss SPDT Relay 2 changes contact there by Lamp is toggled.

Suggest me to keep the state of Lamp, when taken over by UPS (SPDT Relay 1 works fine and Phase from UPS) after mains power failure (SPDT Relay 2 changed state).

enter image description here

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  • \$\begingroup\$ Your requirements are unclear. When the power dies does the home automation system switch off? Do you want your lights to come on, stay off or maintain its previous state? Your mains relay contact is drawn incorrectly: When the mains relay turns on the relay will switch to UPS supply. Hit the edit link ... \$\endgroup\$
    – Transistor
    Commented Nov 15, 2020 at 9:38
  • \$\begingroup\$ When the power dies does the home automation system switch off? - Yes since connected to mains; Do you want your lights to come on, stay off or maintain its previous state? Need to keep the lamp state as it is even after power failure (SPDT Relay has toggled at power failure); When the mains relay turns on the relay will switch to UPS supply. Hit the edit link - Edited as suggested. Thanks for the advice ☺ \$\endgroup\$
    – Kumaran
    Commented Nov 15, 2020 at 14:50
  • \$\begingroup\$ Why do you need SPDT Relay 2 and the 2 way switch? Wouldn't an SPST switch alone serve the purpose? \$\endgroup\$
    – vu2nan
    Commented Nov 15, 2020 at 17:33
  • \$\begingroup\$ Use of SPDT Relay 2 and 2 way switch is to operate the lamp both from home automation system and also using local 2 way switch, as it is connected to lamp as staircase wiring. During power failure Phase from UPS reaches to terminal 3 of 2 way switch by default. \$\endgroup\$
    – Kumaran
    Commented Nov 16, 2020 at 1:48

3 Answers 3

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Finally powered my Home automation relay board through UPS. Solved the problem.

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Here's how you would need to wire it.

enter image description here

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  • \$\begingroup\$ SPDT Relay 1 is wired this way only. Further I have a SPDT Relay 2 which toggles at power failure changing the state of lamp. I need to keep the lamp state even after power failure. \$\endgroup\$
    – Kumaran
    Commented Nov 15, 2020 at 14:54
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schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. A possible solution - but it relies on RLY2 having a much faster drop-out than RLY3.

How it works:

Mains on

  • RLY2 is energised.
  • RLY3 just repeats the operation of RLY1.

Mains drops out

  • If RLY1 was off then RLY3 will be off and will not change state.
  • If RLY1 was on then RLY3 will have been on. If RLY2 drops out quickly it will maintain the status of RLY3.

It's up to you to see if you can find a quick and slow response AC relays.

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  • \$\begingroup\$ I will try this idea. I have DC relays used in the system. I will try to modify and fit into the system and post the output shortly. Thanks, it really helps mentally. \$\endgroup\$
    – Kumaran
    Commented Nov 15, 2020 at 16:40
  • \$\begingroup\$ I replaced SPDT Relay 2 to a DPDT relay, then Relay 2 is a DC Relay of 5V coil powered by a 5V mains adapter with added capacitor to hold its contact during transient period from mains to UPS. Added new home automation relay to trigger DPDT relay. Thanks. Anymore possibilities also please share. \$\endgroup\$
    – Kumaran
    Commented Nov 16, 2020 at 2:00
  • \$\begingroup\$ It's not clear from your comment whether it worked or not. \$\endgroup\$
    – Transistor
    Commented Nov 16, 2020 at 7:20
  • \$\begingroup\$ still working on it, will post the update. \$\endgroup\$
    – Kumaran
    Commented Nov 17, 2020 at 9:49
  • \$\begingroup\$ If power fails Home automation loses power, thereby RLY1 contact opens same time RLY 3 opens. My assembled UPS takes approx 45 secs to cut in. 5V DC relay used in place of RLY 2 can hold contacts for few seconds only. Cannot succeed. Any other suggestions please \$\endgroup\$
    – Kumaran
    Commented Nov 17, 2020 at 15:50

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