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Will my transformer power a video doorbell?
Most "my video doorbell keeps rebooting" problems are a power problem, and most power problems are the VA rating rather than the voltage. This works out whether your existing transformer has enough capacity, how much voltage you lose down the wire run, and what your chime needs.
Power & chime checker
Verdict
Calculating…
How this is calculated
Volts tell you compatibility, VA tells you whether it will actually work
Voltage and power are different questions and people conflate them constantly. Voltage (VAC) has to fall inside the range the doorbell accepts — too low and it won't boot, too high and you risk damaging it. VA is capacity: how much current the transformer can deliver before its output sags.
This is why a 16 V 10 VA transformer — extremely common in houses built before video doorbells existed — passes the voltage test and then fails in service. It's the right voltage but roughly half the capacity. The symptoms are distinctive: the doorbell works, then reboots when it starts streaming video, or the night-vision LEDs cause a brownout, or it drops off Wi-Fi under load.
Voltage drop over the wire run
Doorbell wire is thin and the runs are often long, so a meaningful amount of voltage is lost as heat before it reaches the doorbell. The calculation is Ohm's law over the round-trip conductor length:
current (A) = VA ÷ volts
resistance (Ω) = 2 × run length (ft) × Ω per foot for the gauge
voltage drop (V) = current × resistance
The resistance figures used are the standard values for annealed copper: 20 AWG at 10.15 Ω per 1000 ft, 18 AWG at 6.385 Ω, 16 AWG at 4.016 Ω. A 60-foot run of 20 AWG carrying 20 VA at 16 V loses over a volt and a half.
Two caveats on how to read that number. First, the current used is peak draw at the doorbell's full rating — during a video call with the infrared LEDs on. Idle draw is a fraction of that, so the drop you'd measure most of the time is smaller. Second, a transformer's nameplate voltage is its output at rated load; lightly loaded, real transformers commonly measure a volt or two above nominal. This is why the tool treats voltage drop as a margin warning rather than a hard failure unless the loss is extreme.
Why the chime type matters
Mechanical chimes generally work directly. When the doorbell isn't ringing, the chime coil acts as a load that lets a trickle of current pass through to keep the doorbell powered — which is exactly what these devices are designed around.
Digital chimes usually don't tolerate that trickle current. The result is a chime that hums, buzzes continuously, or repeatedly self-triggers. Most video doorbells ship a small bypass module — a diode or resistor pack — that wires across the chime terminals to solve it.
No chime at all breaks the circuit entirely. You need a jumper or resistor across the chime terminals to complete it, or the doorbell simply won't power up.
Upgrading the transformer
A doorbell transformer is an inexpensive part, but it's a mains-voltage device. It is typically mounted on a junction box near the electrical panel, on the furnace, or in an attic. Replacing one means working on a live circuit unless you kill the breaker, and in many jurisdictions this is work an electrician should sign off on. The common upgrade target is 16 V at 30 VA, which comfortably covers current video doorbells.
Common questions
What transformer do I need for a video doorbell?
Most current video doorbells want 16–24 VAC and at least 20 VA, and 16 V 30 VA is the safe general-purpose choice. Always check the specific model's spec sheet, because the requirement varies and models with floodlights or larger sensors draw more.
Why does my video doorbell keep restarting?
The most common cause is insufficient VA. The doorbell boots fine on standby power, then browns out the moment it starts streaming video or turns on infrared illumination. Check the transformer's VA rating before assuming the doorbell is faulty — a 10 VA transformer will do exactly this.
Can I use a 10 VA transformer with a video doorbell?
Usually not reliably. Some basic wired doorbells manage on 10 VA, but most video models specify 20 VA or more, and running under-specified is what produces intermittent faults that look like network problems. If the voltage is right but the VA is low, the transformer is the part to change.
Will a video doorbell work with my digital chime?
Generally yes, but usually only with the bypass module the manufacturer supplies, fitted across the chime terminals. Without it a digital chime commonly buzzes or triggers repeatedly. Check what's in the box before you start the install.
Does wire length matter for a doorbell?
More than people expect. Thin 20 AWG wire over a long run can lose one to two volts, which is enough to take a nominally compatible 16 V supply below a doorbell's minimum once it's under load. If your run is long and the verdict here is marginal, a higher-voltage transformer is often easier than rewiring.