A couple of other factors:

– start/stop – if you are frequently starting and stopping the machine, 3-phase is generally better than single-phase.

– speed control – possible with 3-phase but not single-phase.

My vertical mill has a motor with electronic speed control of something like 200-10000 rpm, nominal 2HP, which I believe was designed for washing machine use. It has one useful thing for heavily-loaded slow speed motors – a separate cooling fan. Even with 3-phase motors with a VFD for low-speed control, a built-in fan might not be enough at those lower speeds.

Those wishing to change motors is quite limited. Generally failed motors are exchanged for a direct replacement – the original was carefully chosen by the manufacturer.

It was only the minority that changed motors, from 3 phase, to single in years gone by (before cheap VFDs became available) because used commercial machines wee cheap – for that very reason.

Nowadays, it tends to be the other way round because the 3 phase motors were always superior – given a suitable power supply was available.

Then, along came cheap brushed DC motors – but the cheapness often led to failures (often not so cheap for the user) – and now brushless, but also cheap, DC motors. An improvement but not idiot-proof, all the same.

Changing from DC or single phase induction is always a matter of what modifications need to be made to accommodate the new drive. Every situation may be different. The induction motor is the usual choice but universal motors can be found – snd require a different means of speed control.

Bearings are, I think, more likely to be ball bearings on 3 phase motors ( more long-lived). Changing from DC to single phase my include other bearing arrangements.

Foot or flange mounted motors are often not (easily) interchangeable. Foot mounts come in various sizes/congiurations.of corse.

There are plenty of cheap, light-weight, chinese motors around these days. Price usually denotes som advantage/shortcomings.. There are different ranges of motors, even from one brand. Cheapest, less cheap, lower starting torque torque or the increased starting torque range. Braked or unbraked is yet another category.

Your choice, of course, but there is rather more to motor choices than initially meets the eye. You may even think ahead and decide to buy dual voltage 3 phase motors – yet another choice to consider.- before jumping in on the girst available option. As is the options of powering the machine to which the motor is to be fitted,. VFD or historic static (or rotary) converter, for instance.

I tend to look for brushless if I'm choosing

It's like electronic ignition for cars in the 1980s, it's just better

In the beginning there was darkness and then Faraday and Edison gave the world Light. DC was their vision and then Tesla got in on the act and the world became AC mainly because it enabled easier power distribution.

However DC motors are in many ways better than AC and the latest permanent magnet brushless motors are very compact and powerful. An electronic controller for a brushless DC is very similar, electronically, to a VFD for an AC motor so if you want variable speed the cost difference between AC and DC is minimal.

AC motor are best used at a fixed speed with variable load. DC motors can handle variable speed and high load as can be witnessed on a fully loaded Lisbon tram starting on a steep incline.

I'm for BLDC motors every time.

CS

Many old AC motors had internal fan driven air ventilation but modern motors do not hence the fins. This is because if there is a severe overload situation or winding failure and the stator winding catches fire this remains contained within the case improving safety. The downside is that although the stator can be conduction cooled the rotor temperature becomes a limiting factor and frequent starting cycles is a frequent cause . The issue here is that heat is conducted from the rotor into the bearings through the shaft. However since the shaft is hot and the outer bearing race is being cooled by the case fins issues with bearing load arise. Unlike plain bushes used on early motors ball races can be lubricated for life so give better reliability especially for motors located where regular maintenance is difficult. Rather like long case clocks nobody thinks they need looking at until they stop. So it is with motors and lathe motors with their frequent stop/start use profile do suffer.

The soft start of a VFD in itself is a worthwhile feature for a lathe without a clutch with the variable speed as a bonus.

BLDC motors with a permanent magnet rotor don't suffer from rotor heating to the same degree that an AC motor does and they don't need as much iron in the stator so are more compact and lighter.

CS

Bigger brings greater mass and inertia. This can be a benefit or detrement depending on application. Good for constant running with variable not good for frequent stopping and starting.
BLDC has a lot of advantages but it's not perfect. Not an issue for us but they don't like high temperatures. For machine tool use they have to be well sealed or ferrous particles will foul the magnets.

Well In usually look for cheaper second hand motors from respected manufacturers. 3 phase or single phase. I avoid cheap new motors from China. Found them noisy and not well balanced. Blow the nitty gritty technical stuff. Never had a failure with this philosophy and there are a lot more £s left in my pock.

Andrew.

Not exactly a "drop in" for my Myford 254 both in terms of the space available and the connexions, but I do know what you mean.

As Mike says, 3-phase squirrel cage motors are widespread for a good reason.

Myford did a version of the 254 with 3 phase motor and vfd. It had a poly vee belt drive to the spindle. I think it was 2 speed (2 lots of pulleys, but I might be wrong.

Whilst searching for a suitable brushless DC motor for a friend in the States to fit to his BCA jig borer I came across eBay Item number 225 466 391 205.

This is a motor and servo controller sold as a plug and play system without the hardware associated with the Sewing machine offerings. The motors and matching controllers come in several power rating from 550W to 2.2kw so should suit someone wish to use this technology.

CS

Clive,

Doing the due diligence thing and checking the feedback none of those units have ever been sold by that seller.

All the similar sellers have similar low feedback and sell the same gun related gear, but no electric motors so far. it's likely you would end up waiting a long time for them to ship.

Picking up on what Robert is saying the connectors appear to be quite lightweight for what would be UK 4A or US 8A if fed straight off the mains so the controller must be pushing significant DC voltage.