What Is a Stepper Motor Transformer? Types and Selection Criteria
A stepper motor transformer steps the 220 V mains down to the low AC voltage that AC-input stepper motor drives require.
A stepper motor transformer is a supply transformer that steps the 220 V mains down to a low AC voltage within the supply range of AC-input stepper motor drives. The drive rectifies this voltage internally and applies it to the motor windings in pulses. In systems with several stepper axes, such as CNC machines, cutting and packaging machines, several drives are supplied from separate outputs of the same transformer. DC-input drives use a DC power supply instead of a transformer.
Models in the catalog
| Model | Power | Output voltage | Number of outputs |
|---|---|---|---|
| GMT TRF060-220-070-1 | 60 W | 70 V | 1 |
| GMT TRF120-220-070-2 | 120 W | 70 V | 2 |
| GMT TRF180-220-070-3 | 180 W | 70 V | 3 |
The numbers in the code show the power, the input voltage (220 V), the output voltage (70 V) and the number of outputs in that order.
Selection criteria
- Drive's AC input range: The transformer's output voltage must be within the drive's AC supply range. The GMT GSTD2860, for example, accepts 18–80 V AC, and a 70 V output is within this range. A transformer output is not connected directly to a DC-input drive.
- Number of outputs: Supply each drive from a separate output; the number of outputs must not be less than the number of drives.
- Power: The total power must cover the power of the motors under working conditions. Use the supply power recommendation in the motor and drive datasheets; a transformer running at its limit heats up.
- Protection: Protect the transformer's input side with a suitable fuse or circuit breaker, earth the housing and mount the transformer in a ventilated place.
Common mistakes
- Connecting the transformer output to a DC-input drive: The drive does not work on AC and may be damaged.
- Connecting several drives in parallel to one output: The outputs are made for separate drives; load is shared unevenly and the output is overloaded.
- Applying a voltage above the drive's range: Higher voltage gives torque at high speed, but if the drive's limit is exceeded, its power stage fails.
Stepper transformers at Welibaba
The Stepper Transformers category has 3 active products from GMT, all listed with prices: TRF060-220-070-1, TRF120-220-070-2 and TRF180-220-070-3. Drives are in the Stepper Drives category, and matching motor, drive and transformer is explained in the stepper motor systems guide.
Frequently asked questions
What does a stepper motor transformer do?
It supplies AC-input stepper drives from the 220 V mains with the low AC voltage the drive accepts.
How many drives can one transformer supply?
As many as it has outputs; one drive is connected to each output. The catalog has models with 1, 2 and 3 outputs.
Can a DC power supply be used instead of a stepper transformer?
Yes, if the drive also accepts a DC input; the DC voltage must be within the drive's DC range. Check in the drive's datasheet which supply is permitted.