Recommend sources for DC motors

Yes, cooling fans, but 230V AC from memory.

that and the basic economics of cheap, maintainance free transformers all over the place instead of rotary machines, it's also far easier to switch.

People should treat mains voltages as deadly since they can be, yes ok plenty of us have had shocks and are still around but when you get too comfy with something that's the time it bites back. I've had a 2kV shock off a scope but that doesn't make it safe 8-).

That's the point, everyone's different.

Greg

As no one has mentioned it, no you can't change the number of poles internally, a motor is wound one way or the other, the more poles the slower it turns for a given mains frequency.

Greg

I see.

I was thinking of the star vs delta winding pattern which some sources suggest is a common thing to have configurable by the user.

Pete Harrison

Star Delta only applies to 3 phase motors.

-- Regards,

John Stevenson Nottingham, England.

Visit the new Model Engineering adverts page at:-

Oops didn't read the first post correctly, thought we were talking about single phase.

-- Regards,

John Stevenson Nottingham, England.

Visit the new Model Engineering adverts page at:-

assume that

Do I not remember 'pole switching motors' that varied the speed by switching the number of poles? iirc my 23 Swiss Launderette washing machines inherited when I bought my shops used this system to give three speeds. I scrapped them in the first year as they were over 30 years old and I thought it unsafe that the local kids could poke fingers through the rust holes in the panels

AWEM

It should be noted that the nice people at Myford's will sell motor pulleys in two diameters and for several shaft sizes.

Mark Rand RTFM

There are a few rare three phase motors which have a tapped winding connected to a multi-pole switch which allows the number of poles to be changed by a factor of 2. Somewhere I have a diagram explaining how the arrangement works. I can dig it out if anyone is interested. There are also a few three phase motors which have two main windings, and I've even read about one which has two tapped main windings, giving a total of four speeds. But in general you can't change the number of poles.

Chris

The option to connect a three phase motor as either star or delta offers a choice of two operating voltages. The operating voltage required for the star connection is approximately 1.7 times the operating voltage required for the delta connection. Most small three phase motors operate at 240 V in the delta configuration or 415 V in the star configuration. This doesn't affect the shaft speed.

Chris

Well, it looks like a trip to Newton Tesla. They have a ready-to-go motor which they claim is a drop-in replacement. Their motor also has the appropriately sized output shaft so that is one less task to do. It would appear that their motor is not a totally enclosed type which might have been better. There is, of course a premium for this at £100 inc Vat collected from the door but I can't seem to find much else that I can rely on as an alternative - unless anyone knows better.

Thanks for the help

Pete Harrison

Hi Peter,

I have just been through the same for my Myford ML7. I bought the Mitsubishi S520 Inverter and a motor from John at Newton Tesla and I can say i am very happy with the end result. John is very helpfull with setting up the motor with the inverter even though he didnt supply it.

The difference in motor poles is what sets the rotational speed. For a 50 hertz system, the formula would be:

Most 3 Phase motors are wound for both Star and Delta and on smaller motors this can be changed to suite the electrical supply you want to run on. But mostly high torque motors are started in Star (Initial high torque for starting under load) and then when up to speed switched to Delta to run. But ignore this because if you stick with Newtons motor it comes correctly configured.

Roy

Peter Harris> Well, in a fit of madness, I bought a variable frequency inverter. These

That is all good to know. I shall be calling in to pick up a motor tomorrow (Thursday). Hope they have some 4 core flex. That seems unnaturally hard to find in small amounts.

Then all I shall have to do is persuade My wife to hold up one end of the lathe while I change the motor. Shouldn't take long, better have her eat extra weetabix though - just in case.

Pete Harrison

B&Q normally has 4 core flex in 1.5mm2, quite good enough for a small motor as fitted to a Myford.

Wayne...

I've bought 4-core flex with a braided shield (which is recommended for inverters to reduce RF interference) by the metre, from City Electrical Factors. This was in Cambridge, but they have branches all over the place.

-adrian