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
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
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
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
Sod it that's it for tonight my finger is getting tired.
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John Stevenson said
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
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.
JG wrote in message ...
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.
Thanks for that insight Bob.
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!
JG wrote in message ...
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
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.
"Bob Minchin" said
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
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 -
"JG" wrote in message off.
Brook Compton have a very good technical department.
For small motors call 01484 422 150.
Take all the information from the plate including the serial number. ( I now
need to write it down large enough to read at arms length :-) ).
They can trace any motor they ever made, but if it's older than 7 years they
have to dig out the records from an archive, which can take a day or two.
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.
Any pointers greatfully received :)
What does this invertor say on the makers plate, not the book, about
phases and voltages in and out ?
ON NO ACCOUNT PUT EARTH TO ANYWHERE OTHERT THAN THE
HEAT SINK TERMINALS.
If not marked L and N then put live to R and neutral to S, leave T not
Best to send plate details first as there are some 240 volt three
phase input invertors on the market
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John Stevenson said
Input : 50Hz, 60Hz 200-230V 1Ph
Output : 0 01 - 400Hz 200-230V 3Ph 7.0A
I thought that ought to be the case :))
Thanks John - that makes sense. A pity that the manual uses
questionable 'English' and goes out of it's way to confuse the ageing
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'.