On Monday, 29 October 2018 00:18:32 UTC, Dave W wrote:
On Sat, 27 Oct 2018 08:43:44 -0700 (PDT), PaulS
wrote:

Hi Everyone,

I have a frustrating door bell extension situation.

When the house was rewired many years ago a cable (bog standard 2 core bell wire) was passed through the cavity / under floors from the under-the-stairs transformer adjacent to the breaker panel, to the front door bell push via an over the door bell (https://www.screwfix.com/p/byron-120...ll-brass/14337) providing a simple door bell setup.

Mains
| |
____|__|_____
| | ______
| Transformer |------------------------| |
| | | Bell |
| 8VAC |---------Switch---------|______|
|_____________|

When I built my office I ran a cable from a second bell in the office back to the under-the-stairs panel. From past experience I knew i wouldn't be able to hear the existing bell when working.

Initially I tested each bell individually - both ring when they're the only one on the circuit. I then wired the bells in series. No sound. I hadn't really expected them to as the 8 Volt transformer wouldn't have the oomph to drive 2 bells in series.

______
Mains | |
| | | Bell |
____|__|_____ |______|
| | | | ______
| Transformer |-----| |-------------| |
| | | Bell |
| 8VAC |---------Switch---------|______|
|_____________|

I replaced the 8 Volt transformer with a transformer tapped at 8, 16 and 24 and tried again. Still no go.

______
Mains | |
| | | Bell |
____|__|_____ |______|
| | | | ______
| Transformer |-----| |-------------| |
| | | Bell |
| 16-24VAC |---------Switch---------|______|
|_____________|

The bells are similar and when poked with my multimeter I can see what appears to be an adequate voltage across the terminals (testing from where the wires terminate near the transformer).

My next thought was that it might be something to do with the way the bell mechanisms work - making and breaking the circuit and that being out of sync in such a way as to prevent either bell from working - so I modified the circuit and added a 12VAC relay.

______ ______
Mains | |------------| |
| | | Relay| | Bell |
____|__|_____ |______|------------|______|
| | | | ______
| Transformer |-----| |-------------| |
| | | Bell |
| 16-24VAC |---------Switch---------|______|
|_____________|

When the bell push is pressed, the relay operates, but the bell in series with it doesn't. Frustrating!

Somewhere in the dim recesses of my memory I can recall adding a capacitor in parallel to an inductive load (such as the bell or the relay) might be of some use in such situations. But what type of capacitor and what value? Anyone?

Could anyone explain precisely why the original 2 bells in series with what appears to be adequate voltage and the bell and relay in series don't work?

Any other novel solutions I might use given that:
- There is only one 2 core wire in place to the front door where the first bell and switch (bell push) are and no option of adding another.
- There is only one 2 core wire to the second bell.
- I only have access to the wires where they terminate near the transformer. This in effect means I CAN'T wire the bells in parallel.
- Wireless is not an option. I need a fix and forget set-up with no batteries.

Long read I know, so thanks for reading.

I'd welcome some words of wisdom / experience of similar situations.

I notice you haven't replied to any posts. I can't understnd your
relay circuit - where does the second bell get its power from?

I would try adding two diode rectifiers to the transformer, charging
two electrolytic capacitors. A capacitor would also be needed across
at least one bell to make it independent of the other one's
interruptions. Each diode would peak rectify the 8VAC to give about
20V across the two bells in series. 1000uF might do for the
capacitors.

Mains
__|__|__
| | diode ______
| |--o-||-o---o---| 2nd |
| | | |+ |+ | Bell |
| | | cap = = |______|
| 8VAC | | | | |
| | | | o------o
| |--|-----o |
| | | | |
|________| | |+ | ______
| cap = o-----------------| Door |
| | | Bell |
o-||-o------------Switch---|______|
diode

Or you could use your 16V transformer feeding a bridge rectifier
instead of the diodes and two capacitors above.
--
Dave W

Hi Dave,

The second bell gets its power from a separate (the original) transformer (not shown - my bad). I'll try some of the simple solutions first and if they son't work I'll give yours a go.