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I have recently purchased a doorbell camera for the front door. It has the ability to ring my current doorbell but I use an intercom system with an electronic chime module. After watching many you tube videos and doing research I have determined that I must use a relay between the doorbell button and the chime module. The intercom system uses two (2) 16 volt AC transformers that are hidden behind the intercom which I would like to use to power the doorbell circuit and relay. However there are no 16 volt AC relays, only 12 V or 24 V. I could purchase a 24 Volt AC transformer, but there is no way to hide it inside the intercom master station and so it would look unsightly, and I prefer not to go that route.

Can I use the 16 V power supply with a 24 V relay, which would be 75% of the relay's rated voltage? This would not be a constantly energized relay, but only a momentary contact closure to trip the relay and complete the circuit to ring my intercom's doorbell chime. I feel this would work, but I'm checking with those who should know if there might be any problems or unforeseen consequences?

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  • What does the relay data sheet say about the pull-in voltage?
    – Andy aka
    Commented Feb 2, 2021 at 15:57
  • 24Vac transformers can be hidden and don’t have to fit inside
    – Tony Stewart EE75
    Commented Feb 2, 2021 at 15:58
  • Search for Omron's G6B-1114P-US-DC20 relay. That's a 20 V and closer to your 16 V need.
    – jonk
    Commented Feb 2, 2021 at 20:39
  • My post was about an AC Relay. Several have suggested a 20V DC relay or a circuit using a bridge rectifier for a DC Relay. Doorbell circuit use AC not DC.
    – IWatson
    Commented Feb 3, 2021 at 5:32
  • Just to clarify: Your doorbell button is just a passive button, not an electric circuit that energizes when you press it, correct?
    – pion
    Commented Feb 3, 2021 at 6:24

3 Answers 3

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Use a multi-voltage relay

The good news is that you're not stuck with single-voltage relay coils; a RIBU1C's low-voltage coil is rated for anywhere from 10-30VAC, for instance. That, a plastic "handy box" with ½" KOs on it, and some wirenuts and cableclamps, will get you what you need.

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  • Great minds think alike. Advantage of this solution is that all the components are ul listed and packaged well. The underlying relay can probably be bought for a few dollars on an electrinics supply shop website
    – gbronner
    Commented Feb 11, 2021 at 13:37
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Addition of a bridge rectifier and a filter capacitor would yield an open-circuit DC voltage, higher than 20 V, to energise a 24V DC relay.

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  • This'll yield about 20VDC BTW
    – ThreePhaseEel
    Commented Feb 11, 2021 at 0:33
  • The voltage would be (16 * 1.414) - 1.4 = 21.2 V. It would definitely work, with the 'must-operate' voltage of a relay generally being not greater than 80% of its rated coil voltage (in this case 24 * 0.8 = 19.2 V).
    – vu2nan
    Commented Feb 11, 2021 at 3:06
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    Yeah, it'd work but it'd be a bit tight (I was counting the diodes as a ~1V drop as that's more typical for 1N400x type diodes)
    – ThreePhaseEel
    Commented Feb 11, 2021 at 3:13
  • The key phrase in my earlier comment is 'not greater than', which means that a relay could operate at a voltage even lower than that.
    – vu2nan
    Commented Feb 11, 2021 at 4:32
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I would use a 12VAC Relay with Resistor in series to drop the Voltage by around 2-3 Volts to make it save to use with the Relay.

Or if you are feeling extra bold you could just use a 12VAC Relay that can handle up to ~14VAC and it should work just fine if it is only used as a momentary contact. But i wouldn't recomend it :)

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