Calling all electrical experts - DC motor conversion

[neevo]

Great day for the Hercus today, not only did I finally get all my imperial gears (big thanks to pipeclay) but I took a gamble on an eBay auction for a treadmill:

http://i258.photobucket.com/albums/hh270/edneeves/B1F702F2-6502-4258-8DC5-E1BA657983A8_zpsl6kiiafs.jpg (http://s258.photobucket.com/user/edneeves/media/B1F702F2-6502-4258-8DC5-E1BA657983A8_zpsl6kiiafs.jpg.html)

Plan for the treadmill was to try my hand at a DC motor conversion. 99c later I was the proud owner of a Avanti 006 Treadmill:

http://i258.photobucket.com/albums/hh270/edneeves/2F2CDDBC-05F6-4B66-B63D-9C48030F53B8_zpsfxvl0afi.jpg (http://s258.photobucket.com/user/edneeves/media/2F2CDDBC-05F6-4B66-B63D-9C48030F53B8_zpsfxvl0afi.jpg.html)

My father in law hand already given me a treadmill motor and this was designed to provide the electrical bits but unfortunately the motor he gave me was 0.5hp AC :(

Shame, because I really needed to replace the old motor on the lathe:

http://i258.photobucket.com/albums/hh270/edneeves/B4823362-F75D-43F6-8BC6-F76FA951F737_zps7bwvze9j.jpg (http://s258.photobucket.com/user/edneeves/media/B4823362-F75D-43F6-8BC6-F76FA951F737_zps7bwvze9j.jpg.html)

Pulled the Avanti apart this afternoon and was delighted to find this with a fan attached at the end too:

http://i258.photobucket.com/albums/hh270/edneeves/5F0B771C-311A-421F-9ED9-5D53B9DA80F7_zps2v4fu2st.jpg (http://s258.photobucket.com/user/edneeves/media/5F0B771C-311A-421F-9ED9-5D53B9DA80F7_zps2v4fu2st.jpg.html)

A bit too powerful for my little 9" lathe, but I plan on keeping the flat belt, so that will provide a little insurance against the hp.

I pulled the pwm and tested the motor:

http://i258.photobucket.com/albums/hh270/edneeves/D44B4D4E-62DA-4C06-94B0-7BBD095B3585_zpsjh5lcqol.jpg (http://s258.photobucket.com/user/edneeves/media/D44B4D4E-62DA-4C06-94B0-7BBD095B3585_zpsjh5lcqol.jpg.html)

The motor made a horrible noise, which was the reason nobody bid on it, I pulled the motor apart and found something had been through it. There was some damage to some of the inner motor spindle. I filed down some nicks and flattened the brushes and it worked perfectly afterwards. RESULT!


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[neevo]

Now to the questions.

1) There is a Hall effect sensor that connects to the PWM. What is this for and should I look to keep it?

2) This is the speed control module. I am keen to remove this and use my potentiometer instead. There are 5 wires to the speed control unit and I would assume 2 are the power for the LEDs and maybe 3 could control the speed. But really I have no idea. Anyone know what's going on here and if I can replace with a pot?

Front panel

http://i258.photobucket.com/albums/hh270/edneeves/560C3BCA-BE84-4F26-926C-D4D0DA97F078_zpsjxuy1pgg.jpg (http://s258.photobucket.com/user/edneeves/media/560C3BCA-BE84-4F26-926C-D4D0DA97F078_zpsjxuy1pgg.jpg.html)

Wires into speed control and Hall effect sensor:

http://i258.photobucket.com/albums/hh270/edneeves/0A9A152E-3F77-4E37-AD19-5DEA06082C59_zpsjzz6mbh2.jpg (http://s258.photobucket.com/user/edneeves/media/0A9A152E-3F77-4E37-AD19-5DEA06082C59_zpsjzz6mbh2.jpg.html)

Hall effect pickup:

http://i258.photobucket.com/albums/hh270/edneeves/89336ACD-C03A-4323-903A-1A0FA39D949A_zpsxdrjemj0.jpg (http://s258.photobucket.com/user/edneeves/media/89336ACD-C03A-4323-903A-1A0FA39D949A_zpsxdrjemj0.jpg.html)

Speed control module:

http://i258.photobucket.com/albums/hh270/edneeves/CA3ACBF1-C3DD-4413-AFDB-06099770F7DB_zps15dzwbe4.jpg (http://s258.photobucket.com/user/edneeves/media/CA3ACBF1-C3DD-4413-AFDB-06099770F7DB_zps15dzwbe4.jpg.html)

The pot I'm trying to use:

http://i258.photobucket.com/albums/hh270/edneeves/65582972-398B-41ED-B45D-22939BCCCD3F_zpsf3p4z4cw.jpg (http://s258.photobucket.com/user/edneeves/media/65582972-398B-41ED-B45D-22939BCCCD3F_zpsf3p4z4cw.jpg.html)


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[RayG]

The hall effect sensor is probably speed feedback. Might be worth keeping.

Ray

[neevo]

The hall effect sensor is probably speed feedback. Might be worth keeping.

Ray

Thought that might be the case. I assume it varies voltage to maintain speed.


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[NCArcher]

I'll have a go.
Prox switch is speed feed back as mentioned. I think for the digital display only.
I think the speed control is multi speed not variable.
Pressing the up/down buttons increases or decreases a counter that varies the pulse width to a pre determined value that corresponds to the counter value..
Pressing the stop button resets the counter to zero.
Only a guess but if it is correct I don't think you could adapt a pot easily if at all.

[neevo]

Got it NCArcher. Looks like I need to incorporate the button module into my control box then.

I will check where the wiring goes for the hall sensor too. If it goes to the display can I assume it's not of benefit as it doesn't interact with the motor?

Thanks for the advice.

[NCArcher]

Again, I'm only guessing.
If the prox switch goes straight to the display then I think it's pretty safe to say it will have no effect on speed control.

[neevo]

Yeah I does go straight to the display.


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[NCArcher]

I've been googling. The motor control board appears to be a generic one. probably made in china. I'm almost certain that you can connect a pot in place of the speed control unit. I'm just not sure yet how to do it. The red and blk wires are probably +5V and 0V supplying the speed control board. The Grn/Wht/Gry wires are the speed control inputs. It may be as simple as placing a 10k pot on these terminals but I can't find any specific info or cct diagrams on these boards.

[neevo]

Interesting. Maybe the pots not completely out yet then. I assume I have no need for power if I replace the board with the pot?

Eg remove the red/black (if they are power for the board) and work out which ones go to which of the 3 connections on the pot.

Is there a way to test resistance across each wire to see which is ground and which is the in/out for the pot wiring when the board is live?

[neevo]

Looking at the back of the board there is a common connection between all the switches (up, down, off). Would that correspond to the ground on the pot?

If so what's the risk of I get the other 2 connections on the pot mixed up?

[Ueee]

Hi Neevo,
The biggest problem you will have by far is keeping to motor cool. Have a look here http://www.woodworkforums.com/showthread.php?t=159263
I ended up cooking my motor, i think the braking didn't help but i just could not keep it cool.
Nearnexus may still have some KBIC controllers left if you want an easy hookup solution. They are not that expensive.

Cheers,
Ew

[neevo]

Cheers Ew. I will keep an eye on that. Just run the motor on the bench with no cooling and it didn't even get warm after 2 mins on 20% power. No idea how that will translate in the real world though.

Also tried to wire up the pot but it did nothing. Looks like I might use the board for the moment, plus I get cool lights to see where the motor is at.

[jhovel]

I'm no expert, but for a pot to work, the speed control would have to react to either a variable resistance or a variable voltage or a variable current.
The output of the push button controll might be any of these or it might be digital (some sort of numerical count) - in which case a pot is not going to work.
I suggest you firstly put a multimeter across the control lines and if that doesn;t tell you anything find someone with an oscilloscope to have a look at what the output is doing. That would clear it up I think.
Good luck and let us know what you find out!

[neevo]

This is probably getting a little beyond my abilities. Plus the original board works a treat and has speed indicator leds.

I think I will rework/make my control box and include the board as the speed control instead.

Cheers all.

Ew I will let you know how the temp goes on the motor. I need to make a fan for it as the one I have is the wrong way round as I need to reverse the motor.

[KBs PensNmore]

This is probably getting a little beyond my abilities. Plus the original board works a treat and has speed indicator leds.

I think I will rework/make my control box and include the board as the speed control instead.

Cheers all.

Ew I will let you know how the temp goes on the motor. I need to make a fan for it as the one I have is the wrong way round as I need to reverse the motor.


Shouldn't reversing the polarity of the motor reverse it??? I'm no sparky but that isn't that what the beauty of DC motors are, or are you saying the fan would run in reverse then?
Kryn

[simonl]

Most of these DC treadmill motors are designed to spin in one direction. They will spin the other way if you reverse the polarity but they are not designed for that. If you look at the brushes in the motor you will see that they do not make contact at 90 deg, they make contact with the commutator at some angle so as to point "away" from the rotation. Like I said, they will run in the other direction, but for how long I don't know.

Simon

[neevo]

My motor looks like the brushes are 90 degrees, plus reversing the polarity works fine. Problem is the attached fan which now works great for sucking air out of the motor, not pushing air in.

[KBs PensNmore]

My motor looks like the brushes are 90 degrees, plus reversing the polarity works fine. Problem is the attached fan which now works great for sucking air out of the motor, not pushing air in.

I would have thought that as long as air was moving through, that was the important thing. I could stand to be corrected, I usually am.
Kryn

[neevo]

Dunno. I was going to run it and see what happens. Worst case I make a replacement.

[simonl]

Give it a crack, see how it goes. At least you won't die wondering!

Simon

[neevo]

True.

[BaronJ]

The problem with fans is that the efficiency drops off faster as it gets slower. Forced air cooling from an independent fan would be better. The major problem with these permag motors, is that apart from the air flow through them, the only other way heat can be got rid of is by conduction through the armature shaft and bearings. Where as an induction motor has good thermal conduction directly to the case.

[cba_melbourne]

Most of these DC treadmill motors are designed to spin in one direction. They will spin the other way if you reverse the polarity but they are not designed for that. If you look at the brushes in the motor you will see that they do not make contact at 90 deg, they make contact with the commutator at some angle so as to point "away" from the rotation. Like I said, they will run in the other direction, but for how long I don't know.

Simon

This is called "commutator timing" in DC motors. Motors designed to run in both directions sacrifice some efficiency by using a symmetrical commutator timing. Motors designed to run only or mostly in one direction use an asymmetric (aka advanced) timing. Asymmetric means that the brushes are advanced a few degrees against the rotation direction.

- Motors with asymmetric timing do not run well in the other direction, the commutator sparks and power/speed is reduced.
- It is usually easy to change motor timing from L or R to symmetrical, and vice versa. Often just the brush carrying flange needs to be rotated. Sometimes a little locating notch needs to be filed away first to allow rotation.
- Sometime though a motor with asymmetric timing uses a brush setup, where the brushes are set at an angle to the commutator (not at 90 degrees to the commutator, but angled in rotation direction). In this case it is not possible to change rotation direction, because the brushes would quickly wear away and possibly even chip.

As a practical example: You may have noticed that some better handheld drills (metabo, bosh come to mind) have a reversing lever that mechanically rotates the whole brush carrier. This is a superior method to change rotation direction, over the cheaper handheld drills that have a fixed symmetric timing and only switch direction by reversing polarity. It allows for best efficiency and performance in either direction.


see here if you like to know more about this:
http://en.wikipedia.org/wiki/Commutator_%28electric%29

[mike48]

I'll have a go.
Prox switch is speed feed back as mentioned. I think for the digital display only.
I think the speed control is multi speed not variable.
Pressing the up/down buttons increases or decreases a counter that varies the pulse width to a pre determined value that corresponds to the counter value..
Pressing the stop button resets the counter to zero.
Only a guess but if it is correct I don't think you could adapt a pot easily if at all.

I think that this is probably correct, and any modification to use a pot to achieve variable speed is most certainly unlikely to work without some additional Analogue to Digital interface electronics.

I would try to adapt the push button "speed up down" aspect which is already built in.

mike

[neevo]

Will do, watch this space as I've ordered a larger control box and will look to incorporate the control buttons and leds.

[neevo]

Parts ordered, plan is to redesign the control box, a little larger so I can include the control unit for the motor.

Also ordered a few fans so I can try and get the cooing right once I get the motor running.

Also finalising the motor mount which should be relatively easy as I have a TIG here, just need to find some steel plate.

[neevo]

I'm really annoyed with myself. After receiving all the necessary parts to build my new box, building the box, chasing out the lid to incorporate the control board and speed indicator leds... I accidentally let the smoke out of the board by shorting it on my welding plate!

BALLS!

I found the buttons were the things that took the hit and went to an electronics store today to buy replacements. Soldered them in fine but unfortunately it's not come back to life :(

No burnt looking parts on the board so probably not worth chasing the damaged parts.

Looks like another box ruined (shame as I had done a good job on this one):

http://tapatalk.imageshack.com/v2/15/01/09/494d139ae7e7e232eed23a5da7870df9.jpg

So now I'm on the hunt for either another replacement board, I may pop down to a local treadmill repairer to see if they have anything or I may go down the new PWM route.

[simonl]

Sorry to hear about your magic smoke early release program. Been there & done that!

Is it a standard treadmill speed controller you have used? If so then I may have one or two floating around. I could post them to you if you think it will help you out. They may or may not work but they may be worth a try.

Simon

[neevo]

Cheers Simon, appreciate the help. I've been in contact with a treadmill repairer in Penrith who may have a replacement controller board.

If not I will let you know and see if you have something that can help.

Appreciate the offer.

[simonl]

Cheers Simon, appreciate the help. I've been in contact with a treadmill repairer in Penrith who may have a replacement controller board.

If not I will let you know and see if you have something that can help.

Appreciate the offer.

No worries. Happy to be a backup plan. :U

Simon

[cba_melbourne]

I'm really annoyed with myself. After receiving all the necessary parts to build my new box, building the box, chasing out the lid to incorporate the control board and speed indicator leds... I accidentally let the smoke out of the board by shorting it on my welding plate!....................
.

You are a FOOL!!!!

Sorry to offend you but I have to.

Only a fool can be so foolish, as to test a board with life mains components on a STEEL PLATE COVERED BENCH. Be very grateful to still be alive. You should NOT do this sort of work as you are clearly not suitably qualified.




PS: you did a nice job on the housing. But it is still not worth to risk your life. Go and buy a ready made speed controller.

[neevo]

I will take my chastising as its due. Appreciate the comcern though.

[neevo]

New plan. Turns out the lead I had to replace the board wants $250 for it, maybe not.

For that price I can buy a KB Electronics DC motor controller which will let me use a pot on it and get total variable speed control... So that's the plan.

Question: where is best to buy them from? Also what else do I need to set it up for my 2.5HP peak DC motor?

On a side note I finished motor mount. I didn't have any large plate so I cut 2 x 75mm wide lengths and TIG'd them together. I cut 2 x 10mm holes and used a Drexel with cutting disc to join them:

http://i258.photobucket.com/albums/hh270/edneeves/D713D2F5-DAB8-4234-A813-C427A80AB0E5_zps7p00riik.jpg (http://s258.photobucket.com/user/edneeves/media/D713D2F5-DAB8-4234-A813-C427A80AB0E5_zps7p00riik.jpg.html)

Then I welded the motor mount to the plate:

http://i258.photobucket.com/albums/hh270/edneeves/9EF73649-A498-4A6A-8E07-1A091445C0E8_zpsiq5wglzq.jpg (http://s258.photobucket.com/user/edneeves/media/9EF73649-A498-4A6A-8E07-1A091445C0E8_zpsiq5wglzq.jpg.html)

Fits perfectly and has about 1" of adjustment, plus it's much smaller than the AC motor on there now. Just needs a nice coat of gloss black paint.

Also got the remainder of my enclosure bits but now I'm changing the design again I may need another box unless I can use the original one again.

[cba_melbourne]

New plan. Turns out the lead I had to replace the board wants $250 for it, maybe not.

For that price I can buy a KB Electronics DC motor controller which will let me use a pot on it and get total variable speed control... So that's the plan.

Question: where is best to buy them from? Also what else do I need to set it up for my 2.5HP peak DC motor?

..........................................................

KB DC controllers are obsolete designs. 15 to 20 year old fossils. They have not designed a new DC controller since probably 2000.

In my honest opinion, you would be better off selling that DC motor, and invest instead in a 3-phase motor and VFD.

[neevo]

I don't disagree cba, but I don't have the budget at the moment for a 3 phase motor and VFD, whereas I currently have all I need to get the DC motor running, bar the PWM.

Is there another PWM you could recommend?

If this experiment with the DC motor doesn't work, a VFD is definitely next on the cards.

[BobL]

I don't disagree cba, but I don't have the budget at the moment for a 3 phase motor and VFD, whereas I currently have all I need to get the DC motor running, bar the PWM.

Is there another PWM you could recommend?

If this experiment with the DC motor doesn't work, a VFD is definitely next on the cards.

I agree with cba_m, a suitable used 3phase motor will set you back ~$30 and a a budget Level VFD is ~$140.
Since you only paid 99c for your DC motor it's not like you have a lot to lose.

[neevo]

Everyone talks about cheap 3ph motors but I've never found one for less than a hundred plus.

[BobL]

Here's one for $50,.
http://www.gumtree.com.au/s-ad/hornsby/miscellaneous-goods/electric-motor-3-phase/1066053005

[neevo]

400v, don't I need 240v?

[BobL]

400v, don't I need 240v?

Technically yes but if you run a 420V 3Phase motor, connected in "star" or "Y" connection at 240V you will get about half the power.
So 3HP becomes ~1.5 HP but for a small Hercus like yours 1HP is more than enough.

More explicitly, that motor looks like its a 420V "Y" , or 400V "∆" 3HP
If you don't know what "y" and "∆" mean you will need to do a little bit of homework.

Running in Y Mode will give 420/240 = ~1.7HP
Running in ∆ mode = 400/240 = ~1.8HP

To get the full 3HP at 240V the Y connection inside the motor will need to be converted to ∆ connection.
This requires internal motor surgery and is not for the faint hearted or inexperienced to tackle

The ideal sort of motor for your lathe will have a nameplate like this.
These specs are the same as what I have on my hercus and I have only felt the need for more power than this a couple of times a year.
http://www.woodworkforums.com/attachment.php?attachmentid=319037&d=1404795931

[neevo]

Got it. Thanks Bob.

[simonl]

Keep looking for 3 phase motors. They pop up from time to time real cheap. My motor on my VFD mill conversion was $40 brand new, the one for my lathe was $30. Both are 3 HP. I did need to re-wire them internally to bring out the star point though. The first time was interesting, after the sixth time it's routine.

Just have to keep looking.

Simon

[neevo]

Ok, on the look out for 3ph stuff now to see how that would pan out. Made an offer on that motor and waiting to hear back. Pricing up the DC motor drive and it's the same as a 3HP VFD delivered.

Also checking VFD options and have some questions.

1. Would I buy a VFD based on listed HP of the motor? Eg 3HP?
2. I would look to mount the VFD under the bench and then build a control box for it with my RPM display, will that work? Assume I can run a pot for the speed control.

[cba_melbourne]

Ok, on the look out for 3ph stuff now to see how that would pan out. Made an offer on that motor and waiting to hear back. Pricing up the DC motor drive and it's the same as a 3HP VFD delivered.

Also checking VFD options and have some questions.

1. Would I buy a VFD based on listed HP of the motor? Eg 3HP?
2. I would look to mount the VFD under the bench and then build a control box for it with my RPM display, will that work? Assume I can run a pot for the speed control.


1.

Modern VFD's (those not older than say 15Y) are very intelligent and adaptable. It is customary to have the VFD rating match the motor rating. Depending on application, it can be of advantage to have the VFD rated one or two size steps larger than the motor, especially if the rated motor power is required at elevated room temperatures and/or it is desired to run the VFD at the highest possible chopper frequency in order to reduce motor noise (or motor singing). Also Motor braking can be improved this way. Motor protection always remains fully assured. Downside of doing this is actually only the extra cost for a larger VFD.

That said, it is also perfectly possible to run a motor one or two size steps larger than the VFD. The motor output is then of course limited to the VFD rating. The downside of doing this is the extra cost, extra weight and extra inertia of the oversized motor, meaning reduced accelleration and braking performance. It will still perform better overall than the overrated treadmill motor setup you were looking at before. This is certainly not something you would do on purpose when buying new components. It is something that you can do in order to reuse existing components, or to make use of components that by coincidence just happen to be available to you at an irresistible price.

2.

Yes that would work very well.


PS: when buying a motor, also make sure the number of poles match your application. A 2-pole motor has about 3000rpm at base frequency, a 4-pole motor about 1500rpm, a 6-pole motor about 900rpm. The selection is a little different than it is with a DC motor. For example, a 4-pole motor will have the best power at about 1700rpm, but will remain usable up to at least 3000rpm, and it will provide constant torque down to about 500rpm with a cheap VFD and down to near standstill with a slightly more expensive "vector" type VFD.

[neevo]

Thanks cba, very helpful. Will grab a motor and then size the VFD from there.

[Stustoys]

More explicitly, that motor looks like its a 420V "Y" , or 400V "∆" 3HP
If you don't know what "y" and "∆" mean you will need to do a little bit of homework.

Running in Y Mode will give 420/240 = ~1.7HP
Running in ∆ mode = 400/240 = ~1.8HP

To get the full 3HP at 240V the Y connection inside the motor will need to be converted to ∆ connection.


Hi Bob,
That doesnt sound right. If the motor is ∆400/420.... then there is no star point to dig out, you already have it.:? But if its a Y start ∆ run motor why doesn't the plate say that?

Stuart

[BobL]

Hi Bob,
That doesnt sound right. If the motor is ∆400/420.... then there is no star point to dig out, you already have it.:? But if its a Y start ∆ run motor why doesn't the plate say that?

Stuart


Good point.
I didn't look at the pic closely enough.
It looks like the 400/420 refers to the ∆ connection side of the motor so running this connection at 240V will generate ~half power.
Running it on Y will generate 1/4 power.

[neevo]

Still plenty of go at 1.5hp, especially vs what I have on there at the moment which is 0.5hp and probably only 0.15 of those left and working properly ;)

What are the pitfalls in looking for motors? Will any 3ph motor work? 230, 400, 420, with the only impact being final HP when run on 230v or are there some that will never work?

I assume a 1-2hp 230v 3ph motor is the ideal purchase for my little 9" Hercus?

[BobL]

Still plenty of go at 1.5hp, especially vs what I have on there at the moment which is 0.5hp and probably only 0.15 of those left and working properly ;)
Even really old motors still tend to generate their rated HP. The oldest motor (rated at 0.5HP) I have tested was 105 years old and it still generated 0.5HP!


What are the pitfalls in looking for motors?
Pitfalls include
Dud Bearings, its not a proper test by any means, but the rotor should spin freely and noiselessly by hand.
Uneven coil impedances (resistances). Also not a complete test but the resistance across each coil should be the same. If these resistances are not the same the motor will overheat
Low insulation resistances. These should be tested with a Megger type instrument.
Running Noise/squeal. This may be indicative of some other problems and can be VERY irritating. This can be tested just by running the motor



220 - 250V rated connection, connected to 240V should produce full rated power
380 - 440 rated connection, connected to 240V should produce half rated power
The motor also should be a 1400 rpm motor

[QUOTE]I assume a 1-2hp 230v 3ph motor is the ideal purchase for my little 9" Hercus?

On my Hercus I started with a 1/2HP 415V Y connected motor (so only 1/4 HP) and as I do mainly small stuff I thought I would be OK but found it quite restrictive especially at lower frequencies (<40Hz) and so I was constantly changing gears, especially.
Then I upgraded to a 1 HP 240V ∆ motor (so full 1HP) and I now can get down to about 20Hz without changing gears for most things.
2 HP should theoretically allow me to operated down around 10Hz but this is also problematic as operating the motor lower than about 20Hz may running into cooling problems.
The other advantage of more power is being able to take deep cuts but I really question whether extra loads on the bearings on these small lathes are up to this for extended periods.

[neevo]

Great info, thanks Bob. Just heard back on that motor on gumtree. It's 400mm x 280mm diameter, that sounds huge for a 3HP motor doesn't it?

No way can I fit that on the mount unfortunately

[cba_melbourne]

Still plenty of go at 1.5hp, especially vs what I have on there at the moment which is 0.5hp and probably only 0.15 of those left and working properly ;)

What are the pitfalls in looking for motors? Will any 3ph motor work? 230, 400, 420, with the only impact being final HP when run on 230v or are there some that will never work?

I assume a 1-2hp 230v 3ph motor is the ideal purchase for my little 9" Hercus?

For a 9" Hercus I would recommend a 3 phase 240V 4-pole TEFC motor as follows (based on personal experience with my 10" Hercus 260 fitted with 3/4HP VFD and motor)
- a 1/2HP motor would be the smallest choice. If 90 % of what you do fits over the cross slide, you will be happy.
- 3/4HP would be what I regard the ideal size for either a 9" or 10" light duty lathe such as Hercus.
- 1HP if you do a lot of large diameter work or like roughing with deep cuts at the limits of the lathe's rigidity (or slightly beyond).
Make sure you buy a motor that is a drop-in replacement to your existing motor (meaning the pulley fits the motor shaft, and the mounting holes line up). So first thing you need to find out what frame the existing motor has, is it a metric IEC frame or an imperial/American NEMA frame. If its a very old lathe you may not find a simple drop-in replacement - or it may be cheaper to modify the mounting/pulley to suit whatever motor you can get for cheap.

Pitfalls when looking for a used motor? I would personally NEVER buy a used 3phase motor under 2HP! There is no simpler and cheaper motor than a 3 phase motor. In the power class of 1/2 to 1 HP, these are really dirt cheap: you are looking at between $80 and 150 brand new off the shelf. Sometimes it pays off at visiting a motor dealer, telling him its for a hobby lathe, and asking if he has some one-off "new old stock" motor that would suit. If you must buy second hand, choose at least something that looks near new or well looked after. There are some motors on eBay auctions..... old and rusty and grotty on the outside.... that actually belong in the tip. I have found bargain NOS motors on eBay, like never used at 1/4 the former list price, but you have to be patient and look up regularly and just buy it when one pops up. If you need a motor NOW, all I can recommend is buy a new one off the shelf. Whatever the salesman tries to tell you, you do NOT need an expensive VFD rated motor, you want a stock standard low cost off the shelf motor.

[neevo]

Thanks all. Search continues. Will see if I can find a local place for motors near/around Penrith NSW.

[BobL]

Great info, thanks Bob. Just heard back on that motor on gumtree. It's 400mm x 280mm diameter, that sounds huge for a 3HP motor doesn't it?

No way can I fit that on the mount unfortunately

Another reason to get a smaller motor. :)

I'm very happy with all the small used 3P motors I have acquired over the last 5 or so years.

These include

The 2 x 1/4 HP, 1 x 1/2 HP and 1 x 4HP I picked up for nothing.
All except the 1/2 HP have been converted to 240V/∆ operation
The 1/4HP motors are being used on Blowers to vent the shed - these motors are more than 40 years old and were left out in the open for some time (so quite rusty) but they still meggered and ran OK, although one had a noisy (corroded) bearing. I converted and restored these more as a challenge than any sort of practical consideration.

I bought a never used 240V/∆ 1/5 HP motor for $20 because it looked cute and for a project that never eventuated, so it now sits in the back of a cupboard.

Two 1HP motors I bought are on my wood and MW lathes each cost $30 and both are running fine after 3 and 4 years of operation respectively.
Another 240V/∆ 1HP (Danish ASEA) motor cost me $70 as felt sorry for the old guys selling it. This has become a sort of a test motor.

The 240V/∆ 1.5HP Leeson on my DP also cost ~$30 and probably gets more use than any of them - running well after 3 years.

A never used 2HP 240V/∆ Fasco cost me $50. I was going to put that on a home made linisher until I picked up a 3HP linisher for nothing.

A never used 3HP 380V/Y, dual speed ABB that I bought for $30 has been converted to 240V/∆ single speed - awaiting a future project.

A 4HP GE 240V/∆ -415V/Y motor cost me $35 awaits a future project.

The near new 5HP 240V/∆ - 415V/Y cost me $35 and is on my compressor.

As others have said there are motors out there, you just have to be patient and wait for then to come up.
At our mens shed we have more than a dozen, mostly quality never used 3P motors. About half of these have come as a donation from an air con company that closed down. Most of these will not be used so we will eventually look to move these on as they do take up considerable space.

[neevo]

I actually have updates!

I ended up going down the PWM drive path, mainly because it was $200 delivered and I could use the existing motor.

Step 1 was to get a fan that would blow air into the motor when I reversed it. I bought a PC fan with a housing and turned up a custom mount for it on the lathe plus made a sheet metal frame for the fan housing:

http://i258.photobucket.com/albums/hh270/edneeves/A494E007-C8C7-4509-BFDA-4036A1434F70_zpsmboitlng.jpg (http://s258.photobucket.com/user/edneeves/media/A494E007-C8C7-4509-BFDA-4036A1434F70_zpsmboitlng.jpg.html)

http://i258.photobucket.com/albums/hh270/edneeves/A494E007-C8C7-4509-BFDA-4036A1434F70_zpsmboitlng.jpg (http://s258.photobucket.com/user/edneeves/media/A494E007-C8C7-4509-BFDA-4036A1434F70_zpsmboitlng.jpg.html)

I've hooked it up to the motor and spun it and on mid speed the motor actually gets colder to the touch!

I freshened up the motor with fresh brushes which caused some issues as I though the system was broken, until I worked out the brush guide was bent and one of the brushes wasn't touching the motor.

The next part was to work up a proper control box. 1) to house the DC drive and 2) all the controls.

The box also has a 12v feed which turns on the RPM sensor, plus also a fan in the top of the box to draw out air around the drives cooling fins. Works a treat.

Also all input wires are detachable so I can separate the box from the motor and power socket.

Here she is in all her glory:

http://i258.photobucket.com/albums/hh270/edneeves/9AEE485E-079B-4110-AC4C-9B0E3C0F9864_zpss62oxkli.jpg (http://s258.photobucket.com/user/edneeves/media/9AEE485E-079B-4110-AC4C-9B0E3C0F9864_zpss62oxkli.jpg.html)

http://i258.photobucket.com/albums/hh270/edneeves/5321AE4C-FCA4-4A8E-9A08-2EB98953C778_zpsebmyyynk.jpg (http://s258.photobucket.com/user/edneeves/media/5321AE4C-FCA4-4A8E-9A08-2EB98953C778_zpsebmyyynk.jpg.html)

http://i258.photobucket.com/albums/hh270/edneeves/B7825609-095F-41C4-9734-0DB21E18FED7_zpsrsokmrdc.jpg (http://s258.photobucket.com/user/edneeves/media/B7825609-095F-41C4-9734-0DB21E18FED7_zpsrsokmrdc.jpg.html)

http://i258.photobucket.com/albums/hh270/edneeves/025C11B8-F0EB-43A1-814E-65E1E4E69789_zps3e2nufzd.jpg (http://s258.photobucket.com/user/edneeves/media/025C11B8-F0EB-43A1-814E-65E1E4E69789_zps3e2nufzd.jpg.html)

It works a treat. Just need a slightly shorter a section v belt.