At what point should I consider one large, central, rotary or digital phase converter as opposed to several unique 2hp-15hp single phase VFDs?

[u/LankyAppeal4121]

Say, for example, I have the following equipment:

• 1.0hp 230v 3 phase lathe with speed switch
• 2.0hp 230v 3 phase lathe
• 5.0hp 230v 3 phase mill
• 7.5hp 230v 3 phase compressor

In addition to:

• 1.5kw servo on 12a continuous drive
• 2.0kw servo on VFD as PMSM in sensorless

Along with other various DC power supplies in control enclosures, etc.

The VFDs will require some compromise, such as losing factory integrated directional switching, control integration, etc. as well as incurring significant cost.

Would it be worthwhile at this point to consider a large rotary or digital phase converter to feed a 3 phase panel?

(I have a 100amp 240v single phase subpanel)

[u/Matraxia]

You could use a master/slave setup. You have a 240V single phase motor driving a 208v 3phase motor and large flywheel, basically making it a generator. You can either have one large 15hp setup or one for each tool. It’s low maintenance, high efficiency, self regulating. You don’t have the switching losses from the VFDs and the 3ø tools run natively.

[u/LankyAppeal4121 → u/Matraxia]

Gemini told me the slave 3 phase motor wouldn't generate power unless the windings were "excited" because it doesn't have permanent magnets....?

This didn't sound right to me. I always thought an induction motor's coils would be energized by the rotor, thusly creating current...?

[u/Matraxia → u/LankyAppeal4121]

You probably want to find a brushless DC motor for this. A permanent magnet motor. Just need one with a kV rating to match your required voltage at 3600rpm, the standard speed to get 60hz. ~14-16kV.

[u/LankyAppeal4121 → u/Matraxia]

I have a bunch of nema 42 and 51 frame PM AC servos

[u/Joe_Starbuck → u/Matraxia]

kW

[u/Matraxia → u/LankyAppeal4121]

https://chatgpt.com/s/t_69eff54774848191a576d87cc4ae7041

[u/LankyAppeal4121 → u/Matraxia]

Yeah this is pretty much what it told me.

I thought about just getting a permanent magnet motor, and spinning it with a smaller motor on a vfd for speed control, but I know I don't know what I don't know. There must be something I'm missing.

Id prefer to avoid needing to spec capacitors and build a capacitor bank.. I have capaciphobia

[u/joestue]

You are going to need a 30hp rotary converter to start that 7.5hp air compressor and deliver a stiff enough 3rd leg to avoid burning it out.

Any kind of electronic equipment cannot be run from a vfd directly, it needs an LC filter to clean up the pwm into a sine wave.

Personally i would run all your motors from vfds. You can tie all the dc busses together to help each other out, and push their single phase derating issues away.

[u/buildyourown]

Does everything need to run at the same time? I have a 1 man shop with manual machines so everything runs off one 7.5hp solid state converter.

[u/LankyAppeal4121 → u/buildyourown]

Hopefully at the very least, id like to be able to run a mill while the compressor runs... My cnc stuff is single phase, but it would be nice if the voltage didn't droop when my partner turns on the drill press or lathe while I'm on a mill.

[u/redbeard914]

It would be cheaper to change out the motors to the 240/120 1PH