Supply Current for Lathe

[GrahamWarks]

I would be very grateful for any advice on the following:
I have a large wood turning lathe with mechanical variable speed drive which (the VSD) became u/s, one sliding pulley ran directly on the motor shaft and the shaft worn down after 20 years! The 0.75kw 1 phase motor, with a special shaft, is not easily replaced so I decided to go for an inverter and 3 phase motor driving through fixed ratio pulleys.

I decided my new 3 ph motor should be a bit more powerful to compensate for the lower torque available at low motor rpm and no gearing so bought one with 1.1kw and a 1.5kw inverter to suit. The latter is 1 ph in and 3 out which I intended to supply from a 13amp socket in the workshop.

On receipt of the inverter I noted that the rating plate says max supply current is 17.4 amps. Presumably to allow for losses in the inverter and surges at start up etc.

I am hoping this will still be ok plugged into my 13 amp socket on the basis that my smaller motor will not draw the full current: 17.4A/1500w * 1100w=12.76A drawn and within the rating of the 13A socket.

1) Have I got this wrong and 2) Any tips for setting up/running the inverter. I think it is probably not wise for example to program in extra torque especially as I have already upsized the motor relative to the original

Thanks for any comments
Graham

 

[Balenza]

Why not just fit a single to three phase convertor. Just state your requirements to the supplier and they will do the sizing for you.
Their the specialists after all who deal with this every day.
Or alternatively install a three phase generator. We did.
Two of em in fact. One is 25 kva and the other one is a 100kva beast powered by diesel engines. 45 hp/3 cyl Perkins and 300 hp/ V8 Deutz respectively.
I think this invertor malarkey is way beyond your scope and probably beyond most on this forum.
Try this link below.

http://www.isomatic.co.uk/3phConverter.htm#General

 

[Paper Spark]

The maximum input current (for the 1.5Kw) of 17.4A is too much for it to be taken from a normal 13A socket outlet. Normally this size inverter would be fed from a 20A radial.

A 3ph 230V 1.5Kw motor draws at max load approx 6A per phase, as you only have single phase input this is why it requires the higher input current.

A 3ph 230V 1.1Kw motor draws at max load approx 5A per phase, so your 1.1Kw inverter would require in the region of 15A input current, which again would require it's own radial circuit feeding it.

You should be able to limit the max output current by adjusting the relevant parameter so that you could run the motor from a 13A socket. A lot will depend on if the lathe load is at full load for excessive amounts of time, which in this case I don't think it would be as originally it was using a 0.75Kw drive.

What is the make & model of the inverter as I may be able to assist in the setting up of it?

 

[ColJack]

you can set some inverters to use variable torque, or torque boost at low speeds..

speed control can be either variable via a potentiometer or "digital" by use of pre-set speeds and a multi-stage switch..

 

[GrahamWarks]

Thanks for your replies.

Paper Spark, the inverter is a Mitsbishi FR-E520S-1.5K-EC complete with the EMI filter unit and the FR-PA02-02 control panel. Output voltage is 200 to 240V. I bought this secondhand advertised as tested and ok. I have the instruction manual downloaded from Mitsubishi.

The 3 phase motor is a new 1.1 KW (1.5 HP) 1400 RPM, 220/380V 4 pole motor, type T90S4, Current is 3.8A at 220V and 2.77A at 380V from manufacturers data sheet.

The lathe capacity is 28" diameter by 40" long but it would never be asked to tackle a piece of wood that large. Apart from anything else I probably could not lift that size piece of wood to place it in the lathe! Turning a 3" diameter spindle might require 2000rpm but at that speed taking very light cuts. Turning a large bowl of 28" diameter would require about 200rpm but a good amount of torque. Of course the tool is hand held so one gets direct feedback of how much cutting force is being applied.

I wouldn't expect the motor to be working near its maximum power output but I can see how at low rotational speed but high torque it could draw a lot of current.

I would be grateful for your comments.

Balenza, thanks for link to Isomatic. One of those would be ideal if this lathe was earning money but its only my hobby and £575 (plus the cost of the new 3 phase motor) is a bit expensive. If I had that much to spend I could have the worn motor shaft reground a few thou smaller, the key ways reground, new oversize keys made and a new pulley made to fit. To put it in perspective the cheapest new electronically variable speed lathe is about £900 I think. The advantage of going the inverter route is the very low rpm possible.

Thanks to all, Graham.

 

[Paper Spark]

Hi Graham

Have worked with some of the earlier Mitsubishis and found them easy to install & commission.

IMO I would install the inverter into a separate control panel with the Stop/Start controls on the front along with a speed control potentiometer.
Ensure ventilation to the panel as well, I wouldn't mount the inverter externally in case of sawdust getting into the vents & possibly causing it to overheat.

As you have a 4 pole motor (base speed 1500rpm) and you say you require a max speed of 2000 rpm then parameter Pr1 (max frequency)would need to be set to 68Hz, from the formula

rpm=base frequency X 60 divided by No of pairs of poles.

Also set Pr9 (max current) to the motor name plate rating for 220V.

If you'll be running the lathe as low as 200rpm a 6 pole motor will give the same power but increased torque at the lower speeds. For the max speed just increase Pr1 to 100Hz.

Hope this helps in any way

Regards Andy

 

[GrahamWarks]

Hi Andy,

thanks for your advice. I will find or make an enclosure as you suggest with a dust filter in the bottom and an extract fan in the top. I will use a 1 watt 1k linear potentiometer for speed control.

Thanks also for advice on the parameters for current and speed range. The motor I ordered is 4 pole 1.1 kw. they delivered a 6 pole 0.75 kw motor by error which I sent back. It is difficult to choose the best motor power/poles and I may end up putting a step pulley on the motor to improve low speed torque.

I have looked at all the commercial lathes and some of the best specified ones use an inverter and a stepped pulley system with motors up to 3kw!

Out of interest I will try plugging this into a 13A socket, on a 32 A ring and observe the current on the display but I do, from advice on current in your last post, expect it to blow the fuse in the plug. I have no spare ways left in my distribution board but have a 32 amp outlet in my garage which I haven't used for ages so will probably relocate/rewire that to where the lathe is.

I appreciate your help and will let you know how it goes once I have it together. It may be a week or so as I have to get my new pulley machined to fit to the new motor and a couple of new threaded holes in the end plate of the motor, B14 but my machine has three bolts at 120 degrees not 4 at 90 degrees as current standard.

Best wishes

Graham

 

[Paul Barker]

Hi Andy,

I have no spare ways left in my distribution board

Get an electrician to put in a new meter block and a garage consumer unit at source? Or a new DB?

but have a 32 amp outlet in my garage which I haven't used for ages so will probably relocate/rewire that to where the lathe is.

Is this an unused 4mm or 6mm radial from the DB? Fuse it down to 20 amps more appropriate for the load and use it then.?