Inverter driven motor as replacement for two speed motor

[Dave WoottonParticipant @davewootton]

Hi

I have just started looking in detail at an Aciera F3 bought some time ago as a project and put into storage while we moved house. It is fitted with a nominally 900/3000 RPM motor which runs fine on a rotary converter, however in my new workshop I’d like to eventually move away from the rotary converter hence the question. The existing motor is rated at 1HP at 900 revs and 2HP at 3000. Also have a new Mitsubishi 2.2kw 240V inverter bought for another project that did not materialise. Question is would I be better off buying a 4 pole motor and running it under the nominal frequency to give 900rpm and over to give 3000rpm, which was my original intention or alternatively a 6pole motor run at 50hz to give 900rpm and over the nominal frequency to give 3000rpm , I have read on some of my internet searches that a 6 pole motor can be safely run at 180% of its design frequency which seems to me would also allow the motor to be run at under 50hz to give a useful low speed range without concerns of the motor getting too warm. Has anyone any experience of running a 6 pole motor under similar conditions? I would be very interested and grateful for any advice.

My workshop is still in storage but I have the mill at home and couldn’t resist the temptation to have a little tinker with it this afternoon as a diversion from the evils of paperhanging!

Thanks

Dave

 

[Pete RimmerParticipant @peterimmer30576]

I would run the 4 pole and just reduce the frequency for low speed. I run mine down at low frequency and don’t find that it gets unduly warm. I have actually re-configured the windings on my mill’s 2-speed motor to change it to a 4 pole and I run that off a vfd at 2 different frequencies to mimic the original 2 speed operation.

Heating up issues are not as prevalent as people try to make out. The motor will only use as much power as it requires to try to stay synchronous so if the load is low then the heat generated will be low also. There are a lot of factors involved but so far I have yet to get a motor warm enough by running at low frequency to need to shut it off and I’ve run them as low as15hz for extended periods.

[Robert Atkinson 2Participant @robertatkinson2]

No Question. Go for the 4 pole motor.
This will give you full torque at the original low speed (same 1HP as existing) and you can increase the frequency to get the higher speeds at full rated power.
Any 50/60Hz motor can run at 120% of 50Hz speed. In practice the the 4 pole motor will use the same bearings etc as 2 pole of the same model so will happly run at the 2 pole motors rated speed.
Check the data sheet. You can buy motors specifically rated for a 8:1 speed range (50-400Hz) but they cost more.

Robert.

[Dave WoottonParticipant @davewootton]

Thank you Pete and Robert, that’s just what I needed to know, I’ll get a motor ordered and make a start on the machine, It’s in very good condition but has been greased up and stored for nearly thirty years so needs a very good clean, to say the least, and a careful recommission. Workshop has been in storage for seven months now cannot believe how much I miss it, this at least will be something to do that does not involve DIY!

Thanks Again

Dave

[John HaineParticipant @johnhaine32865]

An F3 – nice! I inherited an F1 which was lovely but too small for what I needed then. I refitted the original 3 phase motor and a vfd and it ran sweet as a nut.

[Dave WoottonParticipant @davewootton]

This is the machine, looks dreadful in the pictures but been stored well greased for nearly thirty years, previous owner bought it from his employer but had no 3 phase so never got around to using it. The protective grease has done it’s job well but is an absolute horror to remove, should keep me amused for a while. Underneath the grease and grime it is in great condition, a friend who is a dealer put me on to it as I’m the only person he could think of that is mad enough to take it on! Can’t wait to make a start.

[Pete RimmerParticipant @peterimmer30576]

That’s a lovely little machine.

Get a gallon of duck oil and another of brake cleaner. from the auto parts store. Mix it up about 20% oil 80% brake cleaner into one of those pressure pot sprayers you can get for about 15 quid from motor factors. spray that onto the cosmoline grease and let it do its magic for a minute, wipe it off with scott blue workshop towels or rags. If it’s stubborn take a 1.5″ paint brush and cut the bristle down to between 3/4″ and 1″. Makes for a great little scrubbing brush for degreasing grubby machine parts.

This makes a great cleaning/degreasing spray for your machine tools and is also good for keeping condensation at bay to stop your surfaces rusting. If you use neat brake cleaner you might invite rusting especially this time of year.

[duncan webster 1Participant @duncanwebster1]

I’ve been running a 1500 rpm motor at 75hz for years with no ill effect. Leave the lathe belts on one setting most of the time, only change if on large diameter job so that motor isn’t labouring. When supplied as factory fit they just had a 2 belt ratios, mine has 5 as I don’t fancy changing the input pulley

[noel shelleyParticipant @noelshelley55608]

WARNING ! Brake and clutch cleaner is HIGHLY inflammable and will ignite VERY easily . Makes a very good engine starter but in an enclosed space could be like a demolition charge.

Only use in an open space with good ventilation or outside. I will not allow its use in the enclosed confines of an engine room. A small spark from a light switch or motor is all it will take.  Noel.

[Robert Atkinson 2Participant @robertatkinson2]

Noel raises a good point. A look at the datsheet shows it contains normal heptane amongst other solvents. N-heptane is used for explosion proof testing. During testing the vapour has to ignite from a 200 microjoule spark. That is less than 1/30th of the energy of an electrostatic spark you might get from walking on a nylon carpet.

Robert.

[Dave WoottonParticipant @davewootton]

I’m always careful with any sort of solvents and fumes, working in the HV switchgear industry I’ve seen the results of a few fires and explosions, the most dramatic being when someone decided to hire contractors to refloor an underground canteen one Sunday, without obtaining any permits or notifying the engineering department. The room was next to a plant room with an old non room sealed boiler next to it, the adhesive fumes built up and were ignited when the boiler lit. The damage was unbelievable, doors blown off their hinges and windows blown out one floor above, the resulting fire took out the rest. By an incredible stroke of luck the bang happened when the contractors had gone to McDonalds, and their were no injuries (could this be the first instance of a McD being good for you!).

Back to the little mill. i ran it up today on my rotary phase converter and it does run very well indeed, but looking at the motor pully was confused as it really didn’t seem to be running at 3000 rpm as stated in the manual. I can’t see a motor plate on the outside but taking off the terminal cover it shows the motor connections and states the motor speed to be 690 and 1410 RPM, a bit of googling shows some earlier machines did have this lower speed range, so mine must be an early model. Another question (sorry) would it be possible to reconfigure this motor to run in delta on a 240v inverter, or alternatively if buying a new motor should I still buy a 4 pole as recommended before? Any advice much appreciated.

Dave

[Robert Atkinson 2Participant @robertatkinson2]

The motor has 6 windings, 3 pairs. For low speed each pair is in series and the 3 are wired in Delta. For high speed the pairs are connnected in parallel and the 3 are wired in Star. This gives the higer voltage . around 400V as well.
For Low voltage, 230V you can connect the pairs in parallel  and then the 3 pairs in Delta. This will of cours give you low speed. The VFD running at 100Hz will give you high speed.

Six windings is 12 “ends”. You only have 6 terminals with two ends on each terminal. This does not allow the desired connection. So you will have to split out the connections. This is easy if there are two wires on the back of each terminal stud. Not easy if the connections are at the windings.
So first hting is to look at the back of the motor terminals to see how many wires there are.
A photo would help.

Robert.

[Dave WoottonParticipant @davewootton]

Thanks Robert, that’s what I was hoping, I’m away during the week but will post some pictures next weekend.

Thanks Again

Dave

[Pete RimmerParticipant @peterimmer30576]

Short answer is no, you can’t just re-configure a pole-changing 2-speed motor to act as a delta-wound motor. What you can do is strip the thing down and find the winding ends then permanently re-connect the 12 ends to create a delta configuration which is what I have done on my TOS mill but you can’t just do it at the terminal block and it’s not as simple a matter as finding the star point, it’s quite involved.

If you want to see what I went through (and I can assure you I won’t be repeating the process) you can see it here:

TOS mill 2 speed motor converted to delta.

[Dave WoottonParticipant @davewootton]

Managed to have a quick look in the terminal box of the motor this morning and there are definitely only six wires connected, so any other connections must be in the windings, impossible to photograph while in the machine, had to use a dentists mirror and torch to peer at the terminal block. I’ve seen your TOS restoration posts Pete, very impressive, at one time I had a Thiel 158 which looks to be very similar, I used it for cutting traction engine gears and some of the heavy machining (great as a horizontal borer) and then sold on to a friend who still has and uses it. Wonderful machine but I ran out of space! I must admit I don’t really fancy poking around in the windings of a 60-70 year old motor, so I’ll order a modern replacement to use with the Mitsubishi inverter I have. Does give the option as Duncan states of going over 50hz to get a little higher top speed if required, looking at the workshop manuals the mechanical arrangements are the same in the earlier and later higher speed machines.

Incidentally Aciera, and other Swiss machine manuals are freely available to download on the Anglo Swiss Tools website.

Thanks for your very helpful replies, still awhile before the restoration can start but nice to have something to think about and plan in the meantime.

Dave

[Robert Atkinson 2Participant @robertatkinson2]

Hi Dave,
As the winding ends are not brought out it is likey that there is just a tap into the winding. This will not be easy to locate and bring out as separate connections. Not least because there will very little wire to connect to.
I think you are right to go for a new motor.

Robert.

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