motors & inverters

[billy]

How can you tell if a motor would be compatible with an inverter, I have bought a 3ph lathe & would like to have speed control as well as running it on 230v.

[meow2222]

give far more info, incl all tech specs

NT

[billy]

From the motor plate

Hoover AC Motor

TYPE 3029HAF 1633Y RATING Machine CYCLES 50 VOLTS 220/240 380 440 INSUL. CLASS E WDG S/D AMPS 2.08/1.2 H.P. 3/4 PH 3 R.P.M. 1425

[Andy Dingley]

Assuming bog-standard UK 3 phase, then you compare the VA rating on the inverter to what you need the motor to deliver, and you compare the pricetag of the inverter to the size of your wallet. These things are still _very_ expensive. You can use a smaller inverter than motor (within reason), but you lose total power accordingly.

If you can live without variable speed, then a DIY rotary converter made from a large 3 phase motor is a good, cheap choice. Capacitor boxes are a bad idea though. Read the electrics section of

for lots of good advice.

[dom]

You've got a 750W motor (1HP = 746W to be precise) and it's dual voltage rated.

You must open up the little electrical box on the motor and change the links inside it from Y configuration as it is now, to delta (symbol like a traingle) configuration. This is usually very easy - probably a diagram on the inside or outside of the coverplate - but check it now before buying anything. (Remember a 230V inverter produces 3 phases at

230V, not 3 phases at 400V as most machine shops would have).

I bought one of these from this selller:

my 1100W bandsaw (an old 3-phase startrite 352) - extra power above the rated power of the motor is a good thing.

You'll have a big fat manual to read, that isn't terribly clear. But, virtually all inverters can be set up with something called "2 wire control" or "3 wire control".

By using this, it is possible to wire up your machines existing controls to control the inverter directly - a true fit and forget solution.

My bandsaw (which obviously only runs in one direction) has the go/stop buttons wired through to the inverter - and the speed control knob (which I never use) is just left at max on the inverter.

For a lathe you will probably want 3-wire control (which allows reversing) and you'll want to wire in the footbrake emergency stop if you have one.

I think the best solution is to use the lathe gearbox to change speed, and the inverter speed adjustment to vary the speed in that gear - and most of the time to run the inverter at full speed (the inverter varies the speed by reducing the mains frequency from 50Hz, which reduces the power).

If your lathe has a clutch (so that the motor remains running whilst the chuck comes to a quick stop) you could possibly wire the inverter to power the motor only and no control wiring (nice and simple), but you will need to use the little control panel on it to turn the motor on and off (important: inverters must start the motors themselves - no suddenly dropping the load onto them with a big clunky switch - or disconnecting the load the same way - the inverters internal electronics must be allowed to do this).

Overall. Checking your motor is suitable - easy. Buying something suitable - easy. Wiring it up requires some confidence with wiring machinery and understanding a fairly complex electronics manual. But the overall solution is worth it. I'm very happy at the solution I arrived at.

[Jonathan Schneider]

Specs aside you should be aware that a cheap inverter outputs something far from a sine wave and makes motors run less efficiently/smoothly/cool.

Jon

[dom]

I think the OP means VFD's

are specifically intended as motor drives and (AIUI) the new ones don't attempt to produce a synthetic waveform - the output is pulse width modulated to full voltage.

[Aidan]

The cooling fan on most motors is on the end of the shaft. If the motor is run at reduced speed then less air is delivered, so the motor runs hotter even without the additional heating due to non-sine wave inverter output.

[cupra]

You can turn the switching frequency down on most inverters these days if you're worried about heating up the windings (if you can put up with the noise!) - a 5:1 speed range is probably OK without external cooling.