Short answer
A video doorbell usually needs 12 to 24 volts and considerably more power than a classic bell. The old transformer of 8 volts and a few VA is too light for that and has to be replaced. The existing doorbell wire is often usable for the power supply over short distances. With consumer models the video goes over wifi, with real intercom systems over its own cable.
Who this article is for For anyone who wants a video doorbell. You can do the measuring on the low-voltage side yourself; the transformer in the meter cupboard is work for an electrician.
Three ways of powering it
On battery. Easy to fit, but you charge it periodically and in cold weeks that comes round faster. The picture also starts more slowly, because the doorbell is in sleep mode.
On the existing doorbell transformer. Only possible if that transformer supplies enough. Almost always it does not.
On a new transformer. The most sensible option. A transformer with the right voltage and enough VA on the DIN rail in the consumer unit, with the existing doorbell wire to the door.
Why the old transformer is usually not good enough
A classic bell needs 8 volts and a few VA. A video doorbell has a camera, a processor and wifi on board, and often needs 12 to 24 volts with more power. If you connect it to a transformer that is too light anyway, you get:
The old eight volt transformer almost never copes with a video doorbell.
- a doorbell that restarts during a call
- a picture that becomes blocky
- a transformer that gets warm
What a doorbell transformer does exactly and how to find it is in doorbell transformer.
Reusing the existing wire
There is usually two-core doorbell wire to the front door. For the power supply that is often fine, provided the distance is limited and the wire is not too thin. Over long distances the voltage drops and the doorbell keeps restarting.
That does not apply to the video. Consumer models send the picture over wifi to your router. With wired intercom systems it runs over its own cable, usually two cores or a network cable.
Wifi at the front door
In practice that is the biggest stumbling block. A front door is often far from the router, with a wall or a metal frame in between. Test it before you fit it: stand at the door with your phone and see how much signal you have. Two bars is too little.
Solutions: an access point in the hall, or a wired system where the video goes over the cable.
Linking to a chime and door release
If you want the existing chime to keep working alongside the app, you usually need a module that passes the ring on. Each brand does that slightly differently.
To open the door you need an electric door release, and that in turn needs its own power supply and sometimes its own transformer. See electric door release.
Privacy and the neighbours
A camera at the door may film your own property. If it routinely films the pavement or the neighbours' garden, there are rules you have to follow. So aim it as tightly as possible at your own door and path, and use the masking function if your system has one.
From my own work
A customer in Geleen had bought a video doorbell that could run on batteries, but he was charging it every three weeks. The old doorbell transformer was 8 volts and far too light. With a 24 volt transformer with enough VA on the DIN rail it now runs on a fixed supply. No more hassle since, and the picture starts straight away instead of after three seconds.
When to call an electrician
- You do not know which transformer is in your meter cupboard
- The doorbell needs to be linked to a door release or a chime
- There is no usable cabling to the front door
I look at what is there and test it before you order a doorbell. See also doorbell transformer and request a quote.
Frequently asked questions
Can I use my existing doorbell wire?
Often for the power supply, provided the distance is limited. With consumer models the video goes over wifi, not over that wire.
Why is my video doorbell always flat?
Because it runs on a battery instead of a fixed supply. With a transformer of the right voltage on the DIN rail that is a thing of the past.
May my doorbell camera film the pavement?
Your own property is fine. If it routinely films the public road or the neighbours, rules apply. Use the masking function and aim it tightly.
Further reading
Doorbell transformer: what it is for and why your doorbell is not working
If your doorbell is not working, it is usually the push button and not the transformer. Search in this order and you will usually have it within a quarter of an hour.
The intercom is not working: troubleshooting in four steps
If it does not work in one home, the problem is in that home. If it works for nobody, the problem is at the entrance or the power supply.
Intercom in a block of flats: how it is put together
In a block of flats the work is in the riser cable and the door entry panel, not in the handsets. That decides whether replacement turns out easier or harder than expected.
Questions and comments
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