Single phase motor basics

[GraemeVW]

I've been keeping an eye open for another motor for my lathe, but usual story, the more I look, the more I realise I don't know!
I could do with some basic schooling in machinery motors.

I'm mainly looking at old british motors but I see lots of different terminology, ones with capacitor start, ones without etc.
What should I really be looking for?

I haven't measured the pulley to see what shaft dimension I need yet, but I need foot mount, 1/2 or preferably 3/4hp and I want to be able to reverse it.

Looking at the usual listings you see on FB marketplace, eBay etc, what should I be looking for? Any particular type of motor best? How can i tell if it's reversible?

I see terms like cage, induction etc and I don't really know if it matters.

I know some folk will say to go 3 phase, but that's a whole different set of issues. I'd rather stay single phase I think, even if it's not as smooth etc.

 

[Seadog]

3 phase really is the best option, Graeme. It will transform your lathe experience.

 

[GraemeVW]

3 phase really is the best option, Graeme. It will transform your lathe experience.

Yeah, at the moment that's not where I want to go with it.
Maybe in future though.
I'm just not ready to go down the whole vfd route. I wouldn't even be changing the motor but the one that's in it is a giant lump of explosion proof iron with an odd switch set up which I don't think is reversible.
Easiest, quickest, cheapest route for me right now is to just find another single phase motor. Plenty out there, cheap, easy.

I'll be buying a mill in the next 6 months/year. That will force me to deal with 3 phase, maybe I'll revisit it then.

 

[Guineafowl]

The only advantage of a single phase motor, is that it’ll run on single phase. Granted, that’s often the overwhelming factor.

In every other way, 3ph motors are better. Run on a VFD (TEC or Newton Tesla will set you up with a package), you get soft start, reverse, speed control, optimised power delivery, etc, etc.

Edit: X-post with yours.
Start with the motor rating plate, which should give the important details.

 

[GraemeVW]

The only advantage of a single phase motor, is that it’ll run on single phase. Granted, that’s often the overwhelming factor.

In every other way, 3ph motors are better. Run on a VFD (TEC or Newton Tesla will set you up with a package), you get soft start, reverse, speed control, optimised power delivery, etc, etc.

Edit: X-post with yours.
Start with the motor rating plate, which should give the important details.

The motor that's in it, shouldn't be in it. The plate will tell me about that motor but not what motor is best to replace it with.

 

[6ply]

Get these.

 

[6ply]

 

[GraemeVW]

Get these.

View attachment 402778

I believe this may be under control.
I'll have a read. Always nice to understand reasons.

 

[m_c]

Typical squirrel cage induction single phase motors come in three types.
Capacitor Start. Capacitor Run. Capacitor start/capacitor run.

Capacitor Start option typically uses a centrifugal switch to disconnect the capacitor once the motor reaches a certain speed.
Capacitor Run has the capacitor permanently connected.

Benefit of Cap Start, is you get more starting torque.
Benefit of Cap Run is you have one less thing to go wrong, and the motor runs slightly smoother.

Single phase motors essentially rely on inertia/momentum to keep spinning, as due to only being powered by 50Hz single phase, they only produce torque 100 times per second.
Cap Start/Run use additional coils, and the capacitors produce an offset phase/voltage in those coils to get the motor spinning.
Direction is reversed by swapping the start/run coil connections.

As for sizing, most modern motors will be built to IEC Frame sizes. (quick google gives this - https://electricmotorwarehouse.com/content/PDF/Metric_frame_chart.pdf )
If your lathe is an older imperial machine, you'll likely have to modify the mount, and that a modern motor will be far smaller for the same power rating.


However, as has been said, 3 phase and VFD is the better option from a functionality point of view.

 

[Agroshield]

Get these.

Your wish is my command:

https://archive.org/details/16electricmotors. (note that for some reason a full stop is needed at the end of this URL to make it work. This disappears when pasted into the forum)

24 Electric Motors In The Home Workshop : Free Download, Borrow, and Streaming : Internet Archive

69pg How to identify and use discarded and surplus motors. Examples of actual workshop applications

archive.org

 

[6ply]

I've been keeping an eye open for another motor for my lathe, but usual story, the more I look, the more I realise I don't know!
I could do with some basic schooling in machinery motors.

I'm mainly looking at old british motors but I see lots of different terminology, ones with capacitor start, ones without etc.
What should I really be looking for?

I haven't measured the pulley to see what shaft dimension I need yet, but I need foot mount, 1/2 or preferably 3/4hp and I want to be able to reverse it.

Looking at the usual listings you see on FB marketplace, eBay etc, what should I be looking for? Any particular type of motor best? How can i tell if it's reversible?

I see terms like cage, induction etc and I don't really know if it matters.

I know some folk will say to go 3 phase, but that's a whole different set of issues. I'd rather stay single phase I think, even if it's not as smooth etc.

You may wish to avoid the old British motors (any old motors, actually) unless you are willing to sort out dodgy connections, cracked insulation, broken and bodged connection blocks, etc. Some of course are in fine condition.

 

[GraemeVW]

Typical squirrel cage induction single phase motors come in three types.
Capacitor Start. Capacitor Run. Capacitor start/capacitor run.

Capacitor Start option typically uses a centrifugal switch to disconnect the capacitor once the motor reaches a certain speed.
Capacitor Run has the capacitor permanently connected.

Benefit of Cap Start, is you get more starting torque.
Benefit of Cap Run is you have one less thing to go wrong, and the motor runs slightly smoother.

Single phase motors essentially rely on inertia/momentum to keep spinning, as due to only being powered by 50Hz single phase, they only produce torque 100 times per second.
Cap Start/Run use additional coils, and the capacitors produce an offset phase/voltage in those coils to get the motor spinning.
Direction is reversed by swapping the start/run coil connections.

As for sizing, most modern motors will be built to IEC Frame sizes. (quick google gives this - https://electricmotorwarehouse.com/content/PDF/Metric_frame_chart.pdf )
If your lathe is an older imperial machine, you'll likely have to modify the mount, and that a modern motor will be far smaller for the same power rating.


However, as has been said, 3 phase and VFD is the better option from a functionality point of view.

None of the motors I already have seem to have capacitors though. Unless they are hidden inside? So what kind if motors are those?

 

[GraemeVW]

Your wish is my command:

https://archive.org/details/16electricmotors. (note that for some reason a full stop is needed at the end of this URL to make it work. This disappears when pasted into the forum)

24 Electric Motors In The Home Workshop : Free Download, Borrow, and Streaming : Internet Archive

69pg How to identify and use discarded and surplus motors. Examples of actual workshop applications

archive.org

It's ok, I've kindly been e.mailed pdf's.
I'll have a read up.

 

[GraemeVW]

You may wish to avoid the old British motors (any old motors, actually) unless you are willing to sort out dodgy connections, cracked insulation, broken and bodged connection blocks, etc. Some of course are in fine condition.

I'm ok stripping, cleaning, redoing connections etc, I just can't to anything with the internal wiring.
I may have just been lucky, but the 6 or 6 old British motors I have all run spot on.
I het your point though. I'm not married to the idea of it being an old motor I get, Its just they are what you normally see and I'm sure I've read they are more likely to be reversible. I've also read they are normally more powerful for the same rating, but that may be a bit of a rose tinted glasses thing.

 

[m_c]

None of the motors I already have seem to have capacitors though. Unless they are hidden inside? So what kind if motors are those?

There are numerous other types, which were historically reasonably common for smaller motors.
I'd guess most are either likely to be shaded pole motors, or motors that had the capacitor remotely mounted.

 

[GraemeVW]

There are numerous other types, which were historically reasonably common for smaller motors.
I'd guess most are either likely to be shaded pole motors, or motors that had the capacitor remotely mounted.

All the motors I have are 1/2hp or under, my drill, my small lathe, a belt grinder, power hacksaw etc, but none have capacitors. One of them has starter windings though and I then have to switch it over onto the running windings.

I'll read the books I've been sent, I'm sure they will explain everything.

 

[GraemeVW]

I've skimmed the books, I'll read properly over the weekend, but I get it now.
I understand the main differences in motors, and how to reverse them.
It seems I can probably reverse the one I have, but I still dislike the huge built in switch and excessive weight of it!

 

[piman]

Hello Graeme,

all induction single phase motors have capacitors, usually located inside the terminal box. I've not seen a centrifugal switch motor for I don't know how long. They are superceded by the start and run permanently connected capcitor type.

Alec

 

[123hotchef]

I've skimmed the books, I'll read properly over the weekend, but I get it now.
I understand the main differences in motors, and how to reverse them.
It seems I can probably reverse the one I have, but I still dislike the huge built in switch and excessive weight of it!

What lathe is it?
Why would you not just use a switch and reverse the motor you have already.
I did that to my one years ago with some help from here.
I would still like to do a VFD conversion at some stage though.

 

[GraemeVW]

What lathe is it?
Why would you not just use a switch and reverse the motor you have already.
I did that to my one years ago with some help from here.
I would still like to do a VFD conversion at some stage though.

It's an old fortis lathe.
It came with no switches at all and a random clunky old motor.
The motor is fireproof, has a built in switch that tales up loads of space so can't easily be fitted and removed through the opening in the cabinet, is daft heavy, has a noisy bearing, and will need to be opened to see if I can find enough wires to reverse it.

It also has loads of exposed 240v contacts as all the covers are missing. Making new ones will be tricky as they aren't flat.

I thought it may be easier to just pick up a replacement.