| Need | Choose this family | Example products on this page | Why it fits | Watch out for |
|---|---|---|---|---|
| Sense AC voltage safely in a measurement circuit | Voltage transformer | ZMPT101B precision voltage transformer, ZMPT107 high-accuracy voltage transformer | A voltage transformer steps voltage for sensing and provides isolation. The ZMPT101B uses a 1000:1000 turns ratio with 4000V isolation, and the ZMPT107 also uses a 1000:1000 turns ratio with 4000V isolation and up to 2.5mA output. | These are for isolated AC voltage monitoring, not for powering loads or microcontrollers directly. |
| Measure AC current in a wire or load | Current transformer | ZMCT103C 5A/5mA current transformer, ZMCT102W 5A/2.5mA current transformer, ZEMCT303A 40A/40mA current transformer | A current transformer measures current through a magnetic core. The ZMCT103C is a 5A input/5mA output CT with a 1000:1 turns ratio, the ZMCT102W is 5A input/2.5mA output with a 2000:1 turns ratio and 4500V isolation voltage, and the ZEMCT303A provides a 40A/40mA range with ±1% accuracy for higher-current sampling. | A CT does not step voltage down. It only measures current, so it is the wrong part if you need voltage conversion. |
| Dim a lamp, heater, or control motor speed | SCR AC regulator/dimmer | 2000W SCR AC-AC dimmer with external potentiometer, 5000W SCR dimmer with aluminum case | These parts control AC power rather than measure it. The 2000W module provides 50V–220V AC adjustable output using a 25A bidirectional thyristor, while the 5000W regulator adjusts from 0V to input voltage for heavier AC control jobs. | This family is for AC power control, not isolation and not sensing. |
| Power low-voltage DC electronics | Neither of these families directly | — | No — you still need rectification and regulation after the transformer before powering a microcontroller. Measurement transformers and regulators feed sensing or control circuits, not DC loads. | If your project ends at a controller, plan the bridge rectifier, regulator, and protection stage as well. For controller-based monitoring builds, these parts feed an Arduino board or similar ADC stage rather than the load itself. |
| Add isolation to a mains-facing measurement build | Voltage transformer or higher-isolation current transformer | ZMPT101B PCB-mount voltage transformer, ZMPT107 voltage monitoring transformer, ZMCT102W ultramicro CT | These parts fit when the goal is isolated AC voltage monitoring or current sampling. Of the 5A CTs here, the ZMCT102W is the stronger isolation choice at 4500V. | The isolation rating still needs to match the risk level of the installation. |
| Need adjustable AC output | SCR regulator/dimmer, not a fixed ac power transformer | 2000W SCR regulator dimmer, 5000W cased SCR voltage regulator | Choose these when the job is light dimming, motor speed control, or trimming AC delivered to a load. | Many variacs and other autotransformer-style variable transformers are not isolated, so adjustable AC is not the same as galvanic isolation. |
| Step voltage down with a current transformer | Do not choose a CT | — | “A current transformer can be used as a voltage step-down” is a common beginner mistake, but the simpler and correct explanation is this: a CT only measures current. | If you need isolated AC voltage measurement, choose a voltage transformer instead. |
| Product name | Family | Electrical rating | Turns ratio or control range | Isolation | Accuracy or linearity | Frequency | Mounting or form factor | Best-fit use |
|---|---|---|---|---|---|---|---|---|
| ZMPT101B 2mA/2mA precision voltage transformer | Voltage transformer | 2mA rated input/output | 1000:1000 turns ratio | 4000V isolation | ≤0.2% linearity | — | PCB-mounted; requires PCB mounting with pin length greater than 3mm | Isolated AC voltage measurement on a PCB |
| ZMPT107 2mA/2mA voltage transformer | Voltage transformer | 2mA primary/secondary current; 2.5mA max output | 1000:1000 turns ratio | 4000V isolation | — | — | Epoxy encapsulation | Isolated AC voltage monitoring where a compact encapsulated part fits |
| ZMCT103C 5A/5mA precision current transformer | Current transformer | 5A input / 5mA output | 1000:1 turns ratio | — | 0.2 accuracy class | 45-55 Hz | Compact 18x24 mm body | Compact current sampling where the line frequency matches |
| ZMCT102W 5A/2.5mA current transformer | Current transformer | 5A input / 2.5mA output | 2000:1 turns ratio | 4500V isolation voltage | ≤ 0.2% linearity | — | Ultramicro form factor | Precision 5A current sensing with higher isolation |
| ZEMCT303A 40A/40mA current transformer | Current transformer | 40A / 40mA rated current | 1000:1 turns ratio | — | ±1% accuracy | — | Epoxy encapsulation; red and black output leads | Higher-current motor sampling and overcurrent detection |
| 2000W SCR AC-AC regulator dimmer | SCR regulator/dimmer | 2000W max power | 50V–220V AC adjustable output | — | — | — | External potentiometer control with mounting nut | Light dimming, motor speed control, temperature regulation |
| AC 220V 5000W SCR voltage regulator dimmer with case | SCR regulator/dimmer | 5000W power capacity | 0V to input voltage adjustment range | — | — | — | Aluminum alloy case; SCR control | Higher-power enclosed AC regulation |
Check the device label for “100–240V 50/60Hz”; if it already accepts that range, you do not need a transformer, only a plug adapter. Buy from this category only when the device or circuit specifically needs AC output, sensing isolation, or adjustable AC.
No — an AC-AC transformer still outputs AC, so you need rectification and regulation before powering a microcontroller. In practice, that means adding a bridge rectifier and a regulated DC stage before the controller.
VA should be at least voltage × current, plus 20% safety margin; for motors or heaters, allow 2–3× startup headroom. That extra margin helps prevent voltage sag, nuisance heating, and overload during startup.
A current transformer measures current through a magnetic core, while a voltage transformer is used to step voltage for sensing or isolation. Choose a CT for current sampling in a conductor and a VT for isolated AC voltage monitoring.
Not always — many variable transformers are autotransformers, so they do not provide galvanic isolation. If the install or bench setup needs shock separation from mains, treat adjustable output and isolation as two separate requirements.
A small 12V AC transformer can read about 16–18V with no load, and forum reports say 20–40% high unloaded is common. The voltage drops closer to its rated RMS value once the transformer is under its intended load.
Some hum and operating heat are normal; 40–60°C is common, and loose laminations or mounting can cause buzz. What matters is whether the temperature and noise stay stable under the rated load rather than rising rapidly with normal use.
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