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Colchester Bantam 1600 3 phase supply

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Gareth Jones 927/09/2016 17:54:27
23 forum posts

A recent advertisement for a Colchester Bantam 1600 lathe indicates that the motor is a two speed 3 phase motor. I'm new to all this but understand that a simple "modern" single phase to 3 phase inverter will not be suitable as the motor is 3 phase 415v, and not 240v. I've been trying to source and learn about high voltage inverters that are suitable for 415v 3 phase motors. Has anyone any experience of installing such a device? The other option would be to replace the existing motor with a single speed 3 phase 240v version. However, I would prefer not to buy a new motor or to lose the two speed functionality. Any other comments?


Gareth Jones

Thor 🇳🇴27/09/2016 18:00:49
1411 forum posts
41 photos

Hi Gareth,

A similar question to yours is discussed in this thread.


Muzzer27/09/2016 18:56:08
2904 forum posts
448 photos

I ditched the original 2-speed motor on my Bantam so I could fit a modern 230V 3-phase motor in its place. The space available is very generous and the motor is foot-mounted which is simple to work with. Modern TEFC (totally enclosed fan cooled) motors are relatively compact, so you can fit a higher power motor in the same space.

I would suggest you go for a 2-pole (3000 rpm no load speed) motor of perhaps 2.2kW or so, rather than the 1.1 - 1.5kW you might otherwise be persuaded to fit. That way you can still get a very similar capability at the lower speed (around 1500rpm) and also get respectable cutting power at the higher speeds that are needed for carbide tooling. With a VFD you get that speed control and only need to make basic speed range selections with the gearbox.

Before anyone says it, you are very unlikely to overheat the motor when it is operating at 1500rpm. You can get a very nice 2.2kW VFD for not a lot of money and a new motor probably not much over £100 if you buy new.


John Rudd27/09/2016 19:21:20
1438 forum posts
9 photos

And to add to Muzzer's comments,

I swapped out the 1.5kw DC motor on my SPG lathe for a 1.5kw 3 phase 2 pole 80 frame size motor which dropped in place quite well with no metal hacking...

I added the necessary vfd and wound the frequency up to make up for the slight shortfall in speed....This has been working well for over a year now with no issue...

The fact that I'm using a 2 pole motor ensures that even at low speeds, the motor doesnt overheat.

A conversion that went well and money well spent, some of which was recouped by selling in the orig motor and speed controller board

Chris Gunn27/09/2016 20:26:17
392 forum posts
27 photos

Gareth, your other option is to go for a Transwave type phase converter, this will deliver 415v which means you can run the original 2 speed motor and use all the carefully selected speeds available. You will also be able to run the coolant pump if you start the main motor first. I have run my Bantam like this for 25 years or so like this, and just connect the unit to the original connections for the incoming 3 phase supply.

Chris Gunn

Muzzer27/09/2016 21:11:51
2904 forum posts
448 photos

I have my coolant pump across the main motor. It means that if I vary the speed, the flow varies too but there is a simple tap on the coolant nozzle and it's not exactly a critical consideration. As well as variable speed, a VFD gives you jog and simple directional control.

I also have a Machtach display to show the spindle rpm. It can also show the actual surface speed if you tell it the radius (metric or imperial) and can be used on milling machines too.

Brian Oldford28/09/2016 08:10:46
686 forum posts
18 photos

"You will also be able to run the coolant pump if you start the main motor first. " A simple wiring alteration can prevent the pump being started first to prevent mistakes.

john fletcher 128/09/2016 09:05:14
725 forum posts

I recently fitted a Huanyang inverter to my friends, I think Harrison 170 lathe. I changed the two pole motor connections from STAR to DELTA, that took ten minutes or less. I fitted a 4 uF capacitor to the coolant pump and reconnected it into delta as well, so it now runs independently from 240 volts 13 amp socket outlet. I wired the lathe so that all the original control are still used, For/rev etc.The inverter bought from E...y for less than £100. Like other readers, I suggest you change the motor and fit an inverter. If you do buy a Huanyang 2.2KW inverter I have made a simplified programing sheet which I could let you have a copy, forget the book. John my friend is a very happy man, programing was easy and I'm no computer expert nor is my friend John. John

Gareth Jones 930/09/2016 09:35:36
23 forum posts

Thanks for all the replies.

I note that all the motor change out solutions have used 3 phase motors. I am aware that single phase motors are not as reliable as 3 phase, however, is it a practical solution to replace the two speed 3 phase motor with a single phase motor. This question is now relevant as I have been offered a Bantam lathe fitted with single phase motor.



Thor 🇳🇴30/09/2016 09:56:17
1411 forum posts
41 photos

Hi Gareth,

It should be Ok to run the Bantam with a single phase motor of sufficient power. You won't get the same speed range as a two speed 3-phase, and of course no continuously variable speed as you get with an inverter.


Muzzer30/09/2016 10:03:07
2904 forum posts
448 photos

Presumably it works after a fashion but as Thor says, you have now lost half of your speeds (most likely the higher ones).

Single phase motors lack the smoothness of 3-phase so it is liable to be noisier and (some say) may produce a poorer finish. A single phase motor is generally larger than the equivalent three phase machine, so check the rating if you intend to stick with it. Although it may look big and beefy it may be underpowered. You should be looking for 1.5HP minimum.

I would look at getting a 3-ph motor and VFD, even if you went for this example. If budget is an issue, keep your eyes open for used components. However, you could get a new motor and VFD for not much over £200.

Ric Goodman23/07/2019 17:00:02
6 forum posts
6 photos

Hi folks - I have a Colchester Bantam lathe with a 3 phase 415v 2-speed motor.

I''m weighting up between installing a single to three phase invertor such as a Transtec STC 2hp, or changing the motor. My household supply is single phase and installing a 3-phase supply very costly.

Does anyone have experience of installing a single-phase motor and what is the precise spec used please? Is a 2 speed single phase motor even possible? Preferably with the same dimensions inclusing foot mounting and arbour.

Are Transtect inverters avalable second hand or is this unwise?

Many thanks for advice.

Ric Goodman24/07/2019 11:57:57
6 forum posts
6 photos

...I meant Transwave above.

Robert Atkinson 224/07/2019 13:39:14
1086 forum posts
20 photos

Hi Rick,

Have you looked a the existing motor to see if it can be re-wired as Delta (lower voltage) for use on a mdern solid state drive? For the reasons described in the original thread above, buing a new single phase (2 Phase) motor is not a good solution. Ideally buy a new 3 pase motor designed for VFD use and a VFD or fit an VFD for your cirrent motor.

Robert G8RPI

DC31k24/07/2019 17:24:38
573 forum posts
1 photos
Posted by Robert Atkinson 2 on 24/07/2019 13:39:14:

Hi Rick,

Have you looked a the existing motor to see if it can be re-wired as Delta (lower voltage) for use on a mdern solid state drive?

He says it is a TWO SPEED motor. Some of these already run delta-connected on 415v. So you cannot delta them again (double-delta?) to make them go on 240v. See:

for typical two-speed arrangements.

I hesitate to mention it here, but the 5hp 240v in, 415v out inverter sold by Drives Direct will do the job but it is rather expensive and it does involve switching downstream of the inverter's output, which seems to be verboten with extreme prejudice on this forum.

larry phelan 124/07/2019 17:27:39
1089 forum posts
14 photos

May not be much help to the above, but when I moved house to the "sticks" 3 phase became out of the question, the cost was -----------------------------? , so I bought a Transwave rotary converter. Problem solved !

Runs the whole shop, planer spindle moulder, bandsaw, lathe miller, the whole works, no messing about.

Baz24/07/2019 18:05:37
578 forum posts
2 photos

I have a Transwave rotary converter, it runs a Colchester Bantam 1600 and a few other machines, it was not cheap but it certainly does the job.

old mart24/07/2019 19:30:50
3345 forum posts
208 photos

The common single phase input inverters require the motor to be set in delta. A motor in star requires a three phase 415V supply. Most modern motors are easy to change.

Two speed motors have a more complicated wiring setup, I'm sure there are experts on this forum who can solve this. Only one of the speeds could be used with a vfd, but that hardly matters.

Simon Williams 324/07/2019 20:45:08
605 forum posts
81 photos

I swapped the original two speed motor on the Bantam 2000 I bought for a single phase motor, hated it. Every start was an adventure, nasty sudden bang on the headstock gears which made me cringe. No clutch on a Bantam, so threading with a tap or die was always an adventure.

So I changed to a 3 phase 4 pole motor (ie single speed) and rewired the controls so that the speed change switch operated the VSD to run at 100 Hz. Obviously that frequency is controllable, but that's a nicety.

With a three phase motor on a VSD comes soft start, DC braking stop, and controllable frequency. With the range of geared speeds on a Bantam playing with the frequency is an option I use very seldom, though it does let me run at very slow speeds if I'm doing something large or chattery.

I have also fitted a 2 pole three phase motor to a Myford S7, this gets the speed up well but you don't really need this with a Bantam where the option for 1600 or 2000 revs is built in. I'm more concerned about using the Bantam with the motor at or close to its normal operating parameters for best power efficiency for operation with carbide tooling so I believe the 4 pole motor is the way to go, particularly as the motor I fitted at 1.1 Kw is a bit underpowered and objects to operating at the highest speed at 100 Hz. Effectively I've forfeited the top speed of 2000 rpm but it's otherwise a lovely machine to use and I'm mighty pleased with it.

HTH Simon

Clive Foster24/07/2019 22:23:22
2836 forum posts
103 photos
Posted by DC31k on 24/07/2019 17:24:38:
I hesitate to mention it here, but the 5hp 240v in, 415v out inverter sold by Drives Direct will do the job but it is rather expensive and it does involve switching downstream of the inverter's output, which seems to be verboten with extreme prejudice on this forum.

Well my Drives Direct 10 HP 415 volt out plug and play box hasn't gone pop despite direct switching on the output. Yet! Date on the label says July 2005. I've had it 10 years and it still seems to be running OK. Although its really due for new capacitors which, apparently, should be considered consumables on any inverter over the longer term. Not cheap in this case. Need to have another go at finding an electrician to hook up my three phase incomers. The Drives Direct box was only supposed to be a temporary expedient. Nowt so permanent as temporary!

Spins up the 3 hp two speed wartime vintage motor on my P&W Model B 12 x 30 lathe a treat on both fast and slow via a splendidly steam-punk set of oil immersed switchgear.

That said I've been very conservative with my rating. No motors above 3 Hp and a set of smoothing chokes on the output which should keep the spikes down.

My view about selecting a motor for VFD control on a lathe is to go by the low speed power and torque requirements. Large jobs run slower and need the oomph. Small fast spinning work rarely needs much power in absolute terms. Give serious consideration to a arranging things so that simply twiddling the VFD potentiometer can substitute for mechanical speed changes over the most used speed ranges. So much easier. Worth changing the pulley sizes to do this. Although a tachometer is fine and dandy a graduated knob is perfectly satisfactory in practice. Low tech reliability and you can see what you will get before starting. Glue a table to the machine to convert knob graduations to speed in the various gear ratios.

Although my Smart & Brown 1024 has a continuously variable mechanical speed control from 40 to 2,300 rpm in two ranges the vast majority of the time its run between 300 and 800 rpm. YMMD.


PS Simon posted whilst I was typing.  Nice to know I'm not alone.

Edited By Clive Foster on 24/07/2019 22:23:48

Edited By Clive Foster on 24/07/2019 22:25:24

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