What’s a Doorbell Transformer?
Everybody starts their DIY journey somewhere, and if you’re just now contemplating that your doorbell has something called a transformer (and that maybe you need to change it out), you’re likely in good company—so don’t sweat it.
A doorbell transformer is a type of electrical transformer called a step-down transformer. It reduces the incoming alternating current (AC) from high voltage (the 120V AC found throughout North American homes) to a lower voltage (because you don’t need 120V AC to drive a simple doorbell system).
While some DC doorbell systems are available, they are exceedingly rare as low-voltage AC is simply better suited for the application. It’s cheaper to implement as it doesn’t require a rectifier to clean up the AC power for DC conversion—if you’d like a concrete example of why that matters, cheap LED Christmas lights flicker because they don’t have a rectifier.
The doorbell transformer supplies power to both the doorbell and its companion mechanical or electric chime located somewhere in your home, typically in the foyer area near the front door. A single transformer can power more than one doorbell and chime (though not many homes have front and rear doorbells).
Doorbell transformer output varies by the home’s age and where in the world you are, but typically they output anywhere from 8-24V to 10-40VA, with the most common transformer type in the U.S. being 16V 10VA. That means the transformer steps down the AC power of the home’s electrical system into a 16-volt AC output with a “power” of 10 volt-amperes.
It’s a bit of a simplification, but volt-amperes function in much the same way as watts do in AC nomenclature. If you’d like to dive deep into the differences, you can start by reading up on power factors, but you hardly need an amateur electrical engineering degree to follow along here.
Just like you can have a 120V laptop power brick rated for a 65W output and a 120V PC power supply unit rated for 800W, different low-voltage devices can have the same voltage but different volt-amperes.
You can find, for example, a doorbell transformer that outputs 16V 10VA and another that outputs 16V 30VA. Both use 16V, but each can only supply up to its VA-rating worth of power, just like a power supply unit can supply up to its rated watts.
Why Does Upgrading Your Transformer Fix Video Doorbell Problems?
Doorbell transfers are very simple and sturdy devices, and it’s not unreasonable to expect the transformer to last for decades or even, potentially, the entire lifespan of the home.
If not for video doorbells, most people would never even think about their doorbell transformer, let alone consider replacing it. Video doorbells, however, change the equation.
Why does it matter? When upgrading to a video doorbell, you may find that your doorbell transformer provided enough energy to supply your old-fashioned doorbell button and the chime—but doesn’t provide enough energy when you introduce the additional power draw of the video doorbell.
Sometimes even upgrading from one video doorbell to another can reveal the problem. I swapped out the original doorbell in my home with a Nest Hello years ago and had no issues. But when I replaced the Nest Hello with the more power-hungry Ubiquiti G4 Pro Doorbell, I suddenly had a problem—the doorbell rebooted every time you rang it because the voltage dropped too low when the mechanical chime activated.
You might find yourself in the same situation if you upgrade from, say, the regular wired Ring doorbell or the Ring Pro to the newer Ring Pro 2. The older Ring models only required 16V 10VA, but the newer models require 16V 30A.
Depending on the combination of chimes and video doorbell hardware you have (or if you want to replace both the front and rear doorbells with video doorbells) you’ll likely need a bigger transformer. Doesn’t matter if you’re installing a Nest doorbell, a Ring doorbell, or even a more DIY-type video doorbell solution like those from Amcrest or similar companies.
Here are some common problems that indicate your transformer is underpowered. These examples presume you’ve tested the wiring with a multimeter and confirmed that there isn’t a dead wire or short in the system.
When attached to the doorbell wiring, your video doorbell cannot maintain a charge. The video doorbell responds when you press the button, but the chime doesn’t. Neither the video doorbell nor the chime responds when you press the button. The video doorbell freezes up or reboots when you press the button.
All of those problems, barring some other obvious issue like a rodent has chewed up your doorbell wiring, indicate that the doorbell transformer is not supplying sufficient power to the system.
How Do You Upgrade Your Doorbell Transformer?
Although swapping out a doorbell transformer is a fairly trivial procedure for an experienced DIYer, on par with replacing a damaged light switch, it still requires you to interact with wall voltage in your home. If done carelessly and without proper safety precautions, it can kill you, and an improper wiring job can cause a fire.
That said, if you feel confident replacing light switches, electrical outlets, or wiring a ceiling fixture in your home, then replacing a doorbell transformer is a breeze.
Identify Your Current Hardware and Video Doorbell Requirements
First, you have a little sleuthing to do. Locate your doorbell transformer. If your home is relatively new, there is a good chance the doorbell transformer is attached directly to (or very nearby) your electrical service panel.
Other common locations besides attached to the junction box include in a closet near the front door, in the utility/HVAC room (in older homes, they were often wired up at the same time as the furnace), in basement stairwells or in storage spaces under the stair near the front of the home, or near your home’s security control panel if the home was wired for a security system during the construction process.
If you have an older home, it’s a crap shoot. My home is nearly a century old, and the doorbell transformer was wired into an old junction box jammed up between two ceiling joists in the basement near the wall shared with the front porch. Working with your head, hands, tool, and work light in a space the size of a breadbox, all while perched on a ladder, is a great time, let me tell you.
When you locate it, check the label. Typically the voltage and VA rating of the transformer is stamped right into the metal.
Most doorbell transformers have two contact points. Some have three in a variable configuration that allows you to select two out of the three contacts for different voltages, such as 8V 10VA, 16V 10VA, or 24V 20A. Even if you have one of these variable models, you may find that none of the variable options meets your needs, and you still need to upgrade.
In addition to locating your doorbell transformer, go to your chime assembly and look for a label. You will likely need to remove the chime cover to find the model number, wiring diagram, or additional information. What we’re looking for is the recommended voltage.
My home has a very old-fashioned brass-tube mechanical chime. The chime is rated for 16V. Using more than 16V, such as replacing the 16V transformer with a 24V transformer, will cause the chime pistons to slam into the chimes harder than normal, generate a buzzing noise, and can even burn the chime out. Considering a fancy brass-tube mechanical chime set can run $500 these days, I really wouldn’t want to burn mine out.
So in my case, I had a 16V 10VA transformer. Rather than upgrade the voltage (or fuss with adding resistors or additional wiring complexity), the wise thing to do is to upgrade the VA output. Thankfully 16V 30VA doorbell transformers are abundant and cheap.
Swap Out the Doorbell Transformer
Once you’ve identified your requirements (and for the vast majority of people, a 16V 30VA doorbell transformer will be the upgrade they need), it’s just a matter of replacing the transformer.
If you know which circuit your doorbell transformer is on, you can turn that circuit off at the electrical service panel. In my case, the transformer shares the same circuit as the basement ceiling lights so it was trivial to flip the breaker and get to work.
If you don’t know which circuit your transformer is on and/or the transformer is wired directly into the side of your electrical service panel, you must shut down power to the entire house by flipping the main breaker.
Once you’ve done so, it’s a simple swap job. Make sure to use a piece of masking tape to label the low-voltage wires going to the transformer. Which wires they are (as in “doorbell button” or “chime”) isn’t important but where they are is.
A doorbell transformer has two low-voltage contact points. It is crucial whatever wires are screwed into each contact point end up on the same contact points for the new transformer. So label the wire (or wires) terminating at each contact before you unscrew them with a simple label like “Contact 1” and “Contact 2” so they don’t get mixed together. If you only have two wires and you can skip labeling anything as doorbell transformers have no negative and positive orientation—as long as you put one wire on each contact, you’ll be fine. All that matters is that the two bundles of wires stay separated in the same fashion they were originally separated to ensure the circuit maintains the same “loop” it had before.
Then just unwire the old transformer and reconnect the hot, neutral, and ground wires as they were to match on the new transformer. Then attach the doorbell wires to the terminals.
Finally, if you want to play it extra safe before you power the system back up, remove your video doorbell from the wall outside your home and disconnect the wires. Separate the wires and energize the system by flipping the circuit breaker or whole house breaker. You can then test the wires with a multimer to confirm the voltage reading is correct (if you have a multimeter handy) or, for a simpler test, bridge the two low-voltage lines at the doorbell site with a screwdriver tip or other conductive tool with a non-conductive handle and confirm the doorbell rings.
This might seem overly cautious, but I prefer not to hook up a new and untested transformer to an expensive video doorbell without first testing it. Multimeters are cheap, but video doorbells are not.
And that’s all there is to it! If you’re comfortable wiring an outlet, wiring up a new transformer is no big deal. Just take your time, double-check your wiring, and if you feel you’re in over your head, call in a pro to ensure everything is safe and proper.
