I had a problem today which made me think that I needed to replace the motor on my ML7.
While screwcutting - and therefore switching from forward to reverse every minute or so - turning on caused the main RCD to trip and eventually the main switch became in-effective. As it turns out I'm up and running again as I found a wiring fault but not before I had checked eBay for a new motor.
Irrespective of this problem I have often thought about replacing the
1/2HP unit with something more powerful. I didn't find anything as a direct replacement currently up for auction but I did find some 1.5HP units but they are 2800rpm and now wonder if I could use one of these. The current spec is 1450rpm so the speed may be an issue but it might be posible to change the drive pully size (make it smaller?) to compensate.
Does anyone have experience of changing the motor on an ML7 or can comment on the viability?
If you have got to this stage of thinking about a motor transplant then think very seriously about going the three phase invertor route.
Fact is you are stuck with a 1425 rev 4 pole motor. Two pole 2800 rpm motors can't be made to run slow enough without some serious work done to the pulleys and at the expense of having a very small motor pulley and loosing the wrap around of the belt with slippage.
Second hand single phase motors are usually expensive and an unknown quantity, shipping is also high as they are heavy and this adds to the cost.
Going onto a three phase motor has advantages. A 3/4 Hp motor will be smaller than your 1/2hp one, they are smoother and cheaper. Anyone trying to sell you a S/H unit for more than 15 quid is ripping both arms off.
Next the magic box of tricks, the invertor or Variable Frequency Drive. Loads available all work the same way, they take 240 volt single phase in and put 240 volt 3 phase out. Some have more knobs levers bells and whistles than others, - not needed you just need start stop reverse and a speed pot. Buy a modern unit, one with flux vector control. You don't need to know what it is it just works better.
Now for features, even the simplest one will give you soft start, controlled braking, variable speed and take care of the motors overload and thermal trips. No bulky MEM starters, no rotary Dewhurst start for/rev switch. In fact these sell for up to 1/2 the cost of a new VFD on Ebay.
One thing to watch with a VFD is that it comes complete with programming panel and filters, many sell these as extra's. Mitsubishi is a bugger for that. VFD at £130 to £140 quid, panel £23 quid extra and filters £20 on top of that. That makes it a dear job.
Best bang for the buck is the Telemechanique Altivar ATV11 series. RS Components do this to anyone for £95 their part number 431-9178 including filters and keypad, all you need are stop start switches and a pot.
Sod it that's it for tonight my finger is getting tired.
This has occured to me and been dismissed on the grounds that I don't know what I am doing with 3 phase power !
The speed difference now makes sense I hadn't thought about 2/4 pole.
That is what has put me off in the past.
eBay item 7502724810 is a Hyundai N100 Plus - is this the thing you mean? It is described as a "Vector Invertor".
Looking on the RS website seems to confirm that the Hyundai is similar and may well be a more powerful unit at 1.5Kw so I've put a 'watch' on that.
Due to lack of knowledge I can't tell whether the Hyundai is complete or if I would also need any other accessories such as the "stop start switches and a pot." you mention, the photo shows buttons for 'stop', 'start' and 'Min-Max' which could be just that.
Thanks very much indeed John for your speedy and informative response.
Having run a ML7R for 26 years, I'd be surprised if any job would really need any more power than the 1/2 or 3/4 horse motor that is fitted as standard. Many years ago I had the loan of power meter I was surprised to find that the input power when plunging a 1/2" drill into mild steel (no pilot hole) with swarf coming off with blue edges was less than 1/4HP.
A further 'advantage' of not having excess power is that when the inevitable 'snarl-up' occurs, a stalled motor or slipping belt is prefereable to breaking a tool or worse still bending something expensive.
I would add that I have a 3/4hp motor and invertor on my ML7. Whilst I do use the lathe quite hard at times (blue swarf is so pretty), I find that belt slip prevents me using the full potential of the motor.
What made me consider changing the motor was the fact that a 0.05mm cut has often stalled the motor. On the other hand I have also produced 'Blue swarf' - but I had put that down to the material rather than the power being used.
I did have problems with belt slip when I first aquired the lathe last year but adjustment to the lay-shaft sorted that.
Now that I have done some further investigation into 'Vector Inverters' (thanks to John Stevenson) the fact that going that route would also mean 'variable speed' may well become the motivating force that gets my purse strings mobile!
Stalling on a 0.05mm cut? That sounds serious. I assume you have a good tool so it sounds like your motor is in trouble. Is it a capacitor run type? maybe the capacitor is open circuit or on its way out.
Original equipment normally has a capacitor start motor. One bulge on the motor body and a noticable click as the motor slows down after switching off. Next most suitable/likely motor will be a capacitor start & run type. Two bulges and the same audile click on slowing. If someone has changed the motor, then you might have a capacitor run type. One bulge and no click on slow down. These are least suitable for lathe work as they have low starting torque and if loaded to near full output, they will slow down, not have the torque reserve to recover speed, slow down more etc etc until they stall. With a knackered capacitor (under the bulge!) this type are worse than useless and may exhibit the symptoms you describe.
Capacitors are not too dear (few quid) and may get you back to the days of blue chips and oil smoke.
I note you said you were too familiar with matters electrical. Are you anywhere near Southampton? I could come and have a looksee if that would help?
After further research - more questions . . . . . .
Assuming I do get a Vector Inverter, what specification motor would be ideal?
What are the advantages/dis-advantages of 2 pole, 4 pole, 6 pole?
Does the following text from an inverter manual have any relevance to the choice of Inverter to buy . . . .
" Sensorless Vector Control - The inverter has a built-in auto-tuning algorithm. The inverter can be possible to do high-starting torque and high-precission operation. ... The required torque characteristic or speed controll characteristic may not be maintained in case that the inverter capacity is more than twice the capacity of the motor in use"
I ask this because I will be looking for a 0.37kW or 0.55kW motor but I am watching a 1.5kW inverter on eBay.
I don't think so - if I understand correctly, a capacitor would be a 'cyinder' attached to the outside of the motor casing.
The paint colour is the same as the lathe paint so I assume that it is original equipment.
No bulges at all - it is a Brook Crompton Parkinson KP6345 - 370W -
220/240V with C77 stamped on the top left corner of the spec plate - The only 'click' is from the master 'on-off' control which is an Allen West & Co unit attached to the lathe base. I switch on and off via the rotating switch on the front of the lathe base which gives alternate fwd-rev with each 90° rotation. There is no 'click' when using this.
Thanks for that gererous offer Bob - unfortunately the trip might turn out to be a holiday :) I live at the northmost tip of Warwickshire - (Atherstone).
All these questions were answered by John Stevenson in an e-mail with the net result that I now have an Inverter and am awaiting the re-direction of a motor (I took delivery of a reduction gear unit which should have gone to Hampshire :(( ).
I knew (as I'm sure you did) that there would be more questions.
I am confused by the input conections. There are three terminals (for input) marked 'R' (L1), 'S' (L2) and 'T' (L3), additionally there are two 'Earth' terminals on the heat-sink. From the standard 230V supply is it simply a matter of connecting 'Live' to R, 'Neutral' to T and the Earth to the heat-sink or have I got it completely wrong?
It could be L>R, N>S & E>T or any combination thereof since the manual makes no reference to the input other than to say "Connect the power supply to R S T".
As far as remote control is concerned I can understand what the appropriate connections are but can find no reference to whether the connection needs to be 'pulse' or fully switched. Similarly, there doesn't seem to be a 'Stop' function.
Thanks John - that makes sense. A pity that the manual uses questionable 'English' and goes out of it's way to confuse the ageing brain.
Within 5 minutes of sending this question I found a clearer definition of the action requird for remote control and I now understand that I need switches that remain 'ON' when actioned rather than 'Pulsed'. Your description of automatic stopping by fixing a switch to the lathe bed also makes sense now thanks.
I presume that it is unwise to connect the unit to the mains until I have the motor and can therefore have an applied 'Load'.