A milling machine problem

[Paul CampbellParticipant @paulcampbell97533]

My first post and a bit of a long one! Anyway, hello from Canada.

I recently got an ex-school milling machine, namely an Excello 602 vertical mill. A fine Canadian (1970's vintage) vertical mill resembling a Bridgeport, but better, being heavier and the quill extends further. It has a 1.5 hp, 220 V 3 phase motor drawing 5 to 7 amps for which I bought a Newton Tesla CL1500 (2 hp) inverter drive. The inverter has a maximum output of 7 amps. The unit came pre-programmed and I had it hooked up to the mill by an industrial electrician. Everything works fine but after 5 minutes or so the inverter trips off and the motor feels hotter than I think it should be for such a short period of operation. This happens with the the motor simply being on without actually working under load apart from turning the spindle. I did remove the motor and had it checked by a good motor specialist who found no electrical or bearing problems when bench tested. I have checked the motor for amp draw when running on the mill turning the spindle and it constantly shows 8-9 amps instead of the rated 5 to 7 noted on the motor plate. I should note that I have a gear head 12" X 30" lathe with a 1.5 hp 220 V 3 phase motor (which is brand new), and this machine runs for hours off the inverter with no problems! My question is that given the motor has no known wiring or bearing problems, and the inverter happily runs the other motor with no trips, could the mill motor be drawing too much and tripping the inverter because of resistance in the spindle from a "drive train" problem? The mill is a vari-speed type and has a full gearbox. I have installed a new drive belt from the motor to the spindle. There was good oil in the gear box, and I've changed this oil anyway. When I rotate the spindle by hand it turns with minimal resistance in high gear, but significantly more in backgear. Any thoughts about what to try next would be GREATLY appreciated. Thanks. Paul

[Paul CampbellParticipant @paulcampbell97533]

[MuzzerParticipant @muzzer]

If you were managing to gobble up this power in the machine itself due to friction it would become extremely hot in no time It would also make quite a smell and most likely quite a racket. I doubt there is anything wrong with the mechanical aspect of it. It should only take a fraction of a hp to spin up and sit there.

You should only see the rated 5-7 A with a full load (cutting some serious swarf), so if you are seeing 8-9A with no load and a hot motor, something is seriously wrong with the motor and/or wiring. If it's got a 220V 3-ph motor rather than a 220/415 motor, there is very little you can do wrong. But I'd be looking at the motor and the direction switch (FWD/REV) connections to see if there is a neutral wire or any other way to miswire the thing. If the motor runs by itself at a 3rd party, it must surely have been miswired.

Could you post a picture of the motor connections and also confirm if the direction switch has been opened? Sounds like a nice machine you have there. But most likely a couple of wires crossed over.

Murray

[Nigel McBurney 1Participant @nigelmcburney1]

Varispeed machines can be a real pain when powered from artificial 3 phase supplies,I very quickly disposed of a good condition varispeed colchester student ,it would not start the spindle if in the mid to top speed range,it would start when in the lower end of the range,and some owners have had trouble with vary speed Bridgeports.

[Chris Evans 6Participant @chrisevans6]

I have a Bridgeport 2HP varispeed with 415/220 motor. When wired to a Transwave static inverter it would only run for 5 or 6 minutes then stop. The motor did not sound happy running from the static inverter, I also ran the 3HP lathe from the same inverter and that did and still does work well. I switched the Mill over to a separate VFD three phase at 220 volts (wiring star/delta changed) the original forward reverse switch was disabled. I did not do this wiring myself so have no other knowledge. The mill will now run for hours very smoothly and draw 4 amps or slightly more when working hard. My VFD is a cheap £90 Chinese job so nothing fancy. I do wonder if you are trying to run mill and lathe from one VFD if it is a parameter setting issue. A friend of mine (who wired my VFD) has a separate Chinese VFD on all his machines about 6 in total.

[vintagengineerParticipant @vintagengineer]

I would have thought that the inverter is going to run at near maximum load most of the time. I was always taught to spec equipment 25% higher than the maximum running draw. That way machinery will never be running flat out. Also maximum and minimum power outputs are normally measured under ideal conditions.

[Ian S CParticipant @iansc]

How cold is the workshop? If too cold the oil in the mill maybe too heavy, I find in the winter here in NZ(not too cold) that my lathe needs to be run for 10 minutes to warm the oil in the bearings, and it just won't run in a high speed until warm(it's a belt head lathe).

Ian S C

[John RuddParticipant @johnrudd16576]

Paul,

If you remove the belt from the motor/gearbox and run the motor, this will tell you if the gearbox is loading up the motor…..

When you run without the belt on, what is the motor current then?

If nothing changes or there is little change, then I'd agree with Muzzer's thoughts on a wiring issue…

Edited By John Rudd on 17/02/2017 11:05:15

[MuzzerParticipant @muzzer]

Vintageboy – the VFD load will be a function of the cutting load so it will only operate anywhere near max load if you are generating serious swarf.

Nigel – he said it starts and runs fine.

Paul – although you say it was "preconfigured", that might assume no humans were involved. You have to program the parameters correctly using the data on the nameplate, such as voltage, rated current, number of poles, frequency etc. So if you get the voltage and/or frequency wrong you can magnetically saturate the windings. That would make things hot and trip the VFD…..

[Simon Williams 3Participant @simonwilliams3]

It's possible (though perhaps unlikely) to connect the three coils of a three phase motor so that one is in opposition to the other two. If so, the two correctly connected coils will establish a rotating field, which the rotor will follow, but the reversed third coil hinders not helps, taking more current in the process.

If I've understood correctly you have connected the motor in delta to run from 220 volts. Did your test house do the same, or did they run it in star on their 400 volts supply? Can you post a diagram of how the motor terminal box is wired?

I would suggest that the reversing switch is an unnecessary complication at least until you can get the motor running comfortably. It's just adding to the confusion at the moment.

If it is the motor heating up and the machine stays cold its unlikely to be the mechnicals downstream, the problem is in the motor or the drive settings. Ive also heard tell of problems with some motors on chopped up supplies generating. internal circulating currennts but I'm pretty sure if that was your problem you would get the same heating effect on a vfd.

Rgds Simon

[TobyParticipant @toby]

Posted by John Rudd on 17/02/2017 11:02:50:

Paul,

If you remove the belt from the motor/gearbox and run the motor, this will tell you if the gearbox is loading up the motor…..

When you run without the belt on, what is the motor current then?

If nothing changes or there is little change, then I'd agree with Muzzer's thoughts on a wiring issue…

Edited By John Rudd on 17/02/2017 11:05:15

that is definitely where I would start……….

[Stuart BridgerParticipant @stuartbridger82290]

+1 on running the motor on the machine without the belt.
If it is A VFD with a 7A output and the motor is drawing more than this, then it will trip!

[Paul CampbellParticipant @paulcampbell97533]

Dear All

Thank you for all the help and advice.

I will add a bit more info:-

My workshop is heated and even though it is presently minus 20 deg C outside, the shop is a warm 19 deg C, so the oil is warm all the time!

Yes I do run two 1.5 hp machines off the same 2 hp inverter, but only ever one at a time. I can only physically plug one machine into the inverter.

Given the other machine runs fine and its brand new motor (which has an amp rating on the motor plate of 4) never trips the inverter, does this still leave the possibility of the inverter being incorrectly programmed?

The original reversing switch is gone. The lead from the inverter goes straight into the motor.

How would one tell if one of the coils was wired up to be in opposition to the other 2? If I'm wired wrong but when at the motor shop they tested it with the input power connection "done right", could this result in them finding nothing wrong with the motor at least when just running with no belt or load on?

Thanks again to everyone for the ongoing advice.

Paul

[Chris Evans 6Participant @chrisevans6]

Paul, I know little about VFDs but they may need differing parameters from motor to motor. Could be all down to a settings problem. I cheated and had mine set up for me.

[Stuart BridgerParticipant @stuartbridger82290]

Perhaps we should go back to basics. It has been implied that the inverter trip has been due to overcurrent, but this hasn't been confirmed. Paul, can you advise the exact trip message/code and the model of the inverter.

I find it a little odd that we would get an overcurrent trip after 5 mins. If the system was was waming up, then I would expect the running current to decrease. This is of course unless something is tightening up on the mill.

As others have indicated, the inverter parameters do need to be matched to the motor, particulalry the Full Load current setting which is there to protect the motor from overload.

[TobyParticipant @toby]

What Paul has said is that the motor is drawing 8 to 9 amps on the mill (without any cutting load?) against a plate rating (FLA?) of 7 Amps. So it is no surprise it trips. I think the question is, why such a high current.

I think Paul really does need to go back to basics but he needs to do what John Rudd suggested. i.e test the motor disconnected from the mill (but with his inverter) so he knows if the excessive current is due to load from the mill or a problem with the motor and/or inverter.

We know the motor has been bench tested by a motor guy so it should be easy enough to compare the non-load current on the bench test with the non-load test with Paul's inverter. One assumes that, if the motor specialist says the motor is fine then the non-load bench test current is much less than the plate current. But it would be good to confirm that.

I also have another question, what voltage was used for the bench test and is that the same voltage Paul's inverter is giving? (ie 220V 3 phase) And is the motor definitely wired delta and this hasn't been messed with since the bench testing? (ok, that is two questions…)

 

Edited By Toby on 17/02/2017 18:53:21

[Ian ParkinParticipant @ianparkin39383]

Given that Paul is in Canada the motor is probably star wired for 220v….here it would be 415v for star 240 for delta/mesh

Could it be that the motor has been wired delta rather than star..that would cause it to draw too much current and get hot if Paul is feeding in 220v into his VFD

[TobyParticipant @toby]

Posted by Ian Parkin on 17/02/2017 19:00:06:

Given that Paul is in Canada the motor is probably star wired for 220v….here it would be 415v for star 240 for delta/mesh

Could it be that the motor has been wired delta rather than star..that would cause it to draw too much current and get hot if Paul is feeding in 220v into his VFD

a good point!

[not done it yetParticipant @notdoneityet]

Before we get too deep into this one, where is the current draw measured? If it is the inverter draw, then that may be misleading somewhat.

It might be useful to know the current draw of the motor that gives no running probem. VFDs are certainly not 100% efficient and single phase draw will be different from the phase draw of the motor. It might not be important, but needs clarification I think.

[Paul CampbellParticipant @paulcampbell97533]

Dear All

Thanks for the still ongoing help.

I am away from home for the next few days. In the meantime I have borrowed an "over the wire" meter and when home will disconnect the belt from the mill motor and run the motor on my inverter with no load. We'll see how those values compare to the 8 to 9 amp draw when the motor is turning the spindle. I'll send an update as soon as I can.

Thanks again

Paul

[Ian S CParticipant @iansc]

I think Ian Parkin and Toby have it. The voltage in Canada is 110/120 V single phase, and 220 V three phase, at 60Hz.

Ian S C

[Ian ParkinParticipant @ianparkin39383]

But one would have thought that his industrial electrician would have known about that

[Neil WyattModerator @neilwyatt]

The inverter should current limit if set up with the correct motor parameters and it is 'modern' enough.

Neil

My own inverter reduces motor amps when it calculates the motor is likely to be overheating.

Neil

[Paul CampbellParticipant @paulcampbell97533]

Gentlemen (and Ladies)

Hello again from the still frozen wastes of Northern Ontario, Canada.

The diagnosis of the problem has been made!

The essential problem is that the Ex-Cell-O 602 mill was made in 1971 and as such has a 1971 vintage motor on it. Recall that when connected to the inverter the motor ran for a few minutes but seemed to get hot then the inverter would trip off. The inverter however would run a 2009 vintage motor of the same hp and specifications with no problems at all on my lathe!

At a motor shop today, a new 1 1/2 hp 230 V 3 phase motor ran off the inverter with no problems and an amp draw of about 1/3 of the motor's maximum rated amp draw (whereas the old motor would draw 8-12 amps despite the motor plate saying 5.1 amps max and this with the motor not even connected to the mill spindle!)

Some research has shown that a number of companies that supply motors and inverters for industry all state that older (pre 1990 in North America) motors are often not inverter rated and as such will not run well off such a unit. This appears to be due to various things related to type of wire used, insulation class, and other things beyond my simple brain.

I thus feel that the first motor shop found no problems with the old motor when they benched tested it because they had it hooked up to a "pure" 3 phase supply and as such it ran drawing only around 1/3 of it's rated amperage as expected rather than almost twice the rated amperage that it was drawing when running on my inverter at home.

So I must advise fellow enthusiasts to consider this possible cause if they find their "older" 3 phase motor does not run well off their lovely, shiny new inverter.

Thanks for all the help and suggestions.

A grateful member.

Paul

[SillyOldDufferModerator @sillyoldduffer]

More information about inverters and older motors in this document.

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