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this should be a simple question, but no product pages seem to describe this situation. I want to hook up a wired doorbell with two buttons and two chime units. Both bells should respond to both buttons (i.e., one chime back door, two chime front door). However, my dad tried this years ago and the result was the transformer burned out. I'd like to try again. Can anyone tell how to build such a circuit properly?

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  • Does each doorbell have its own transformer or are you trying to use the same transformer for both? – Vince Patron Jan 23 '18 at 18:07
  • I can do it either way. The wires from both buttons and both chimes go to the utility room so I can hook up whatever is needed there. – Dwight Galster Jan 23 '18 at 18:09
  • Oh you might be asking about integrated transformers, but that's not what I had in mind...I thought of putting one or two transformers in the utility room. – Dwight Galster Jan 23 '18 at 18:10
  • Old fashion dual chimes had Ding for the Back door and Ding Dong for the front door. What kind is this? – Sunnyskyguy EE75 Jan 23 '18 at 18:13
  • Yes that is the kind I am talking about. But instead of just one chime unit ringing, they should both do their thing. One upstairs and one downstairs, if front door button is pushed, both should go ding-dong and if back door both should go ding. – Dwight Galster Jan 23 '18 at 18:15
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You don't need a relay and you don't need two transformers. You do need a transformer powerful enough to operate both chimes, so you can't buy doorbell kits with transformer included. You'll need to select the transformer separately.

You should purchase two identical chime units. If the chime units are different, their voltages must match. The transformer voltage must match the chime unit voltage, and the transformer amperage must equal the sum of the two chime unit amperages.

A single dual-tone chime is easy to wire up. Usually there are wiring diagrams in the package and sometimes they even make sense.

Select one low-voltage terminal on the transformer to be the supply leg and the other to be the return leg. It doesn't matter which because it's AC and isolated from your house mains. Connect the supply leg to both doorbell buttons. Connect the other terminal on the front door button to the ding-dong terminal on the chime, and the other terminal on the back door button to the ding terminal on the chime. Connect the common terminal on the chime to the return leg on the transformer.

Now, to wire two dual-tone chimes is almost as easy. You just connect the second chime unit to the first in parallel, ding-dong terminal to ding-dong terminal, ding to ding, and common to common.

This diagram has the transformer at the circuit breaker service panel, but you will probably put yours in your utility room. In any case, for safety reasons, please mount your transformer on a junction box.

double dual doorbell

The aqua ring indicates where all the wires come together in your utility room. Black indicates the low-voltage supply leg, and white the low-voltage return leg. Of course, the colors are in the diagram only; I'm not trying to suggest that you buy red and blue wire.

  • Thank you very much. I believe I'll try to follow this advice. – Dwight Galster Jan 24 '18 at 2:15
  • can this arrangement support lighted buttons? (those are always nice and easier to find) – dandavis Jan 26 '18 at 5:15
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    @dandavis: Lighted buttons should be possible. - Lighted buttons that do not require an extra wire are vampires, that is, they operate by allowing a small current to flow through the load. Since the load here is two chimes in parallel, in theory the button lamp will sense a less resistive load and must be slightly more robust. However this should not be a problem since almost all the resistance in the vampire circuit is in the lamp, and the tolerances of this kind of product must be enormous. – A. I. Breveleri Jan 26 '18 at 13:35
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For the sake of completeness, and in honor of Thevenin and Norton, I offer a circuit to use when the amperage requirements of the two chimes are equal, and a transformer is available with that amperage rating and an output voltage equal to the sum of the two chime units' voltages:

Norton-Thevenin doorbell circuit conversion

In the special case of this doorbell arrangement, the loads can be connected in series. This circuit is suitable only for low voltage applications. Never wire household power loads with the switch in the middle.

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Wire the two buttons together parallel to each other and then connect one end to the bells, the other end to the transformer then take the other end of the bells to the transformer.

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    This is too general for an answer. – Eugene Sh. Jan 23 '18 at 18:29
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    And what little there is of it is wrong -- connecting the buttons in parallel will make the front door and the back door sound the same. – A. I. Breveleri Jan 23 '18 at 19:33
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The proper way to connect a 2 chime unit two 2 door switches is to connect one side of the transformer low voltage to both switches each return line from the switch will go to a separate chimes. The other side of the transformer low voltage is connected to the chime common.

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