# What is 1-phase variac

## Forum: Microcontrollers and Digital Electronics 1-phase AC motor on 3-phase frequency converter

Hello I have a 1-phase AC motor with 75W nominal power and would like to operate it via a frequency converter. Now I can get a cheap frequency converter with a 3-phase output. Is it possible to operate my 1-phase motor with this 3-phase frequency converter? Incidentally, the frequency converter is also supplied with 1-phase. Greetings Johann

If you mean a capacitor motor: yes and no. It doesn't work directly, because the capacitor only generates the appropriate phase shift at a certain frequency. And if you connect the motor without a capacitor, it will run, but a little out of round.

This will only work if the FI also accepts single-phase alternating current as a voltage source, with three-phase current the intermediate circuits are charged to 550 volts, which the alternating current motor will not like. I could also imagine that a.) The frequency converter will have a problem with one phase remaining empty b.) The auxiliary winding of a capacitor motor does not tolerate direct connection, during operation there is still a capacitor in series.

of Probably the unsuspecting one (Guest)

The small FU's are at least available with a Schuko plug (or 1-phase). Gives 3x 230V sine waves.

So, first of all thanks for your answers ... My motor is a capacitor motor. As already mentioned, the frequency converter is suitable for 1-phase alternating voltage as a voltage source. What do you think of the idea of ​​running the motor via a variac instead of a frequency converter? Then the supply voltage would always have a nice 50Hz and you could simply set the voltage between 0 and 230V.

ElektroJohann wrote:> What do you think of the idea of ​​running the motor over a variac instead of> a frequency converter? Then the supply voltage would always have> 50Hz and you could simply set the voltage between 0 and 230V. This changes the torque. This also has an indirect effect on the speed, but do you want that?

I use the motor as a fan. The torque doesn't play such a role here. Less torque means less speed and therefore less air flow. Or did I misunderstand something?

You could hang a resistor in front of each winding, which would make the voltage a little more tolerable for you. Then a capacitor must be connected in series with a winding to allow the current to lead by 30 °. It will be a little smaller than the one that comes with the engine. In order to bring the third phase into play, there are balancing circuits. I only know them for balancing ohmic loads. But this is also possible with inductive / capacitive loads, it only requires a little more computing effort. But it's up to you yourself. I don't have time for that ...

### Write an answer

Providing an email address is voluntary. If you would like to be automatically informed by e-mail about replies to your post, please log in.

### Important rules - read first, then post!

• Use upper and lower case
• Do not insert longer source code in the text, but as a file attachment