# 220V AC detection for relay switch

1. ## 220V AC detection for relay switch

Help solve the problem.
I have a relay that should switch at 220V (COM from NC to NO), and at 110V remain unchanged (COM remain on NC).

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2. ## Re: 220V AC detection for relay switch

Do you expect the relay coil to energize for 220 VAC, but not 110 VAC?
Where do you want the transition?

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3. ## Re: 220V AC detection for relay switch

Originally Posted by wwfeldman
Do you expect the relay coil to energize for 220 VAC, but not 110 VAC?
Where do you want the transition?

I have 2 heating elements that operate from 115 volts.
At a voltage of 115 volts, I want to connect them in parallel.
At a voltage of 230 volts, I want to connect them in series.

The input voltage varies from 115 (100, 110, 115, 127) to 230 (220, 230, 240) volts.
I need to switch the relay at a voltage of 230 volts and thus ensured a series connection of the heating elements.
At a voltage of 115 volts, the relay should not switch and thus ensured the parallel connection of heating elements.

The circuit shown does not work. For some reason, the relay is switched at 115 volts.

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4. ## Re: 220V AC detection for relay switch

The circuit shown does not work. For some reason, the relay is switched at 115 volts.
Sure, the relays has a wide range of set and reset voltages and is not suited to discriminate between 115 and 230 V. In addition, the TVS diode circuit makes no sense.

The worst point is that releasing the relays with applied voltage can cause an arc shorting the mains voltage. The only way to handle this properly in an automatic switch is to have two relays switching with intermediate delay, as e.g. performed in automatic wye-delta motor starter.

5. ## Re: 220V AC detection for relay switch

Originally Posted by FvM
The only way to handle this properly in an automatic switch is to have two relays switching with intermediate delay, as e.g. performed in automatic wye-delta motor starter.
Explain, please, in more detail, I do not know what it is about.
Thank you.

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6. ## Re: 220V AC detection for relay switch

You need two relays.
One relay to connect or disconnect the parallel arrangement.
One relay to connect or disconnect the series arrangement.
The relays must work together in break (the current connection) wait make (new connection) when the power changes.
It has to work this way regardless of going from 115 V to 230V or 230 V to 115 V.

The two anti-series zener diodes clamp the voltage across the relay coil to 120 V.
If the voltage is less than 120 V, the diodes do nothing, and the coli voltage is whatever is applied.
If the applied voltage is greater than 120V, the diodes clamp the voltage to 120 V.
So, no matter what voltage you apply, from 115 V to 230 V, the coil will see about 120V

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