Yet another Beaver resurection (TC20F)

[philf]

Instantaneous starting current on mine, which probably has a similar sized spindle motor, is over 100 amps. Needs a type C at least, but preferably a type D breaker.

(My spindle motor is a 27.5 kW Mawdsley DC motor with an appropriately large KTK-Mentor drive )

Andrew,

Doesn't the drive have adjustable ramp times? 100A just to start seems almost unbelievable. If that's the best it can do then I can only think it's a crap design!

Phil.

[awemawson]

Phil, I went back and re-read my notes to check - actually the figure I'd remembered was the DC to the motor spindle, and was 109 amps. The inrush mains current was 90.5 amps

[JeffK]

I spent a bit of time this afternoon prodding and poking to try to find out what was causing the EMG. Turns out thermal overload switch 2 had tripped. I reset and tried again but same thing (several times). They say something about doing the same thing over and over expecting a different result means something don't they?
Anyway the overload switch feeds the hydraulic pump etc as well as the spindle drive field current. I finally disconnected the field current wires and tried again just running hydraulics and ancillaries. No problem with no thermal trip.... I am now making the assumption there is too much current draw on the spindle field circuit - something I know nothing about and sounds like it could be expensive.
The other option could be the overload switch faulty but I suspect not. I have attached a few photos of the spec plates on the motor and field drive. If anyone knows anything about what I now need to do I would certainly appreciate the help....  As you will see it is a Siemens motor.
cheers

Jeff

[JeffK]

Woops - just noticed I put the same (upside down) photo in twice One of those days....
Here's the right one.

[awemawson]

Oops 

Had it been a field drive for a Mawdsley I know where there is a spare, but yours seems to be a Siemens.

I don't often say this, but your pictures are too small to get the detail - I'm usually banging on asking people to make them smaller !!  If you load them up at 640x480 or 800x600 the writing becomes readable.

[philf]

Andrew,

Our hydroelectric scheme uses Siemens permanent magnet servo motors rated at 55 kW. To spin the 6 ton Archimedes screws up to speed before we let the water in only takes about 2.5 kW. It does ramp up slowly.

Phil.

[JeffK]

Try these - the main plate does say the high running current is 78 amps but I didn't expect it to draw this for a low load cut.....I have got a couple of 63A type D breakers heading this way - if it needs more I will have to do something different with the distribution board....
Anyway got to fix the field current issue first. Hopefully the high draw is related to that.

cheers

Jeff

[awemawson]

Although obviously an AC 3 phase rather than DC motor, it's rating is (perhaps not surprisingly) very similar to mine 

My field driver gives about 160-170 V DC at about 7 amps so circa 1 kW so about 1/27 of the motor rating

Are you sure that the second plate you label as the field is not the cooling fan for the main motor ? Certainly a 2cw6-145-8 is a blower motor but a quick google doesn't show your 2cw6-166-8.  The first plate is giving the specs for the motor in-built tacho.

[ddmckee54]

I've been working with American motors and their data plates for 40 years and I've got no clue what those data plates are trying to tell us.

Stupid question/s, does this spindle motor have a separate cooling fan motor and is that motor running?  It looks like your spindle motor has a thermistor/s to monitor winding temperatures.  Siemens will do that on a lot of motors as an option, on their "bigger" motors thermistors are pretty much standard equipment.  If the spindle motor has a separate motor for cooling, this motor should basically come on when you power up the system.  If the cooling fan wasn't running you'd get over-temp alarms.  Maybe not when the spindle motor is running no-load, but it would happen with a load on the motor.

You might get "lucky" and have a spindle cooling fan motor problem instead of a spindle motor problem.
Don

[awemawson]

Sorry Don I got into your post erroneously intending to edit mine 

[JeffK]

I guess all 3 plates are mounted on the main spindle motor body, though 2 are together on one end and the other (main) is at the other end of the assembly. As I said I have very little knowledge of these type of motors so it may well be that one plate relates to the cooling fan (which is at the same end as what I call the field plates) and the other to the main motor.
I have been doing a bit of internet searching and realise that there are several different tacho's, encoders etc to monitor position etc on the main motor but am a bit lost with this.
My gut feel is pull the whole thing off, clean it and see what is worn out. That is ok with a V8 petrol engine but with servo motors I am afraid I might do more damage than good with settings etc for encoders.
I can certainly check in the morning if the motor fan runs but will be away from tomorrow night for 2 weeks so don't want to pull too much apart just now. The whole thing is pretty clagged up with gunge so a clean mat well do some good but....

Again thanks for all of the replies. I am a bit out of my depth here so don't want to mess too much up.....

cheers

Jeff

[awemawson]

Assumptions here Jeff, but I THINK what you have there is a fairly normal 3 phase motor driven by a probably pretty big inverter whose speed can be controlled. As it is needed to run fairly slowly at times it has a separate cooling fan. Embedded in the motor is a tacho to let the controller know what speed it's turning at.

At a pinch you could probably run that motor at a fixed speed directly off 3 phase so long as the voltage is ok

[JeffK]

I will hopefully dive into it tomorrow and get the motor off the lathe then try to see what is going on. As I said I will be away for a couple of weeks after tomorrow so apologies for the discontinuity but will get back after it when I get back. I think you are right with the separate cooling fan but will confirm when I get it in bits. As for the tacho / main motor I am a bit less confident there. However I guess if it is broke then the worst thing that can happen is that its broke. If I am lucky it may end up fixed... nothing ventured nothing gained...  into the unknown.

[cnc-it]

I would test the motor without removing it to save a lot of hassle as it looks heavy!.. then if it's ok service the drive.  I've had lots of spindle and servo drives go down but never had a motor go bad. Could be a bad capacitor or other component that has failed due to age?

[JeffK]

Well - I got back from my travels (eventually) and though time to dive into the lathe again....
Pulled off the fan motor at the back of the spindle motor (Andrew was right with his diagnosis of the spec plates) and found it totally choked up with caked on crudd. https://madmodder.net/Smileys/default/confused0068.gif I though this must be the problem - overloading the motor and causing the thermal switch to trip..... Once upon a
time there used to be a filter at the inlet to the cooling fan but that had long since gone....
After much solvent, scraping etc I relieved the fan blades and casing of a significant weight of sticky gunge. Tested the motor and all was well so re-assembled and put it
back on the machine confident I had fixed the problem. I even fabricated a new filter out of fishtank filter mesh.
Alas on starting up again the same thermal trip problem
More head scratching and chasing wiring revealed nothing new so I decided to get some new classD breakers and a new thermal switch. Off to ebay and picked up everything
at a bargain price.... Installed the new breaker and changed out the thermal switch - got to be it now.... Not a chance.
I was now getting really frustrated so thought back to basics. Lets do what I should have done at the start and get the multi-meter out.....
With power on I was getting strange voltage readings at the switch across phases.... 130V, 330V and 415V. Can't be right methinks.... Worked my way back to the main fuses
to find voltage ok upstream of them.... one 80amp fuse blown and the fan motor was trying to run on 2 phases..... this had not affected the PLC side of things or anything else
that was kicking in prior to the thermal switch tripping.... I thought I had better check all of the 5 main fuses and found 3 out of 5 had blown - obviously when the whole
main breaker thing had gone. Back to ebay and found 5 surplus used fuses (these are not cheap new...) so bought them all. They arrived middle of last week adn I duly installed
them and - hey presto all was working again......
I guess the excercise was not all a waste of time as otherwise I would have kept running with a bad cooling fan with no filter so at least that got fixed but just shows sometimes it
is better not to jump to conclusions and to check the basics first.....
Got the first metal cut on Thursday in MDI mode so just got to figure out Symbolic FAPT now..... Off to order some new tooling......

[awemawson]

Excellent that you found it.

I'm reminded of once years back when I was called in to a fault at the CEGB National Control Room at Park St SE1. (*) We had two suites of Argus 500 computers, a main and a standby monitoring the grid network, and smoke was coming out of the Burroughs 2 mByte fixed head disk on the stand by side. They were on separate phases running off a huge battery bank and invertor set up. They had a high resistance neutral bond, so one suite was getting about 150 V AC and the other something like 350 hence the smoke. Fortunately only a fan but you see even the best people can get it wrong !!

(* all moved to Winersh near Reading now)

[JeffK]

Well I guess its been a while since I last posted,,,, been busily making parts with the Beaver  I finally discarded FAPT and figured out how to program the machine without it. Apart from a few issues with tooling and getting feeds and speeds right all was going really well with until the CRT went 'Ping'. I managed to source a replacement LCD monitor at a cosy and everything went back to normal.
Then the other day I was trying to cut an acme thread. I had done this before and had the program I had used previously successfully so was a bit puzzled when the end product was more like a series of razor blades than a nice square acme profile
I tried a few things, bought a new insert holder etc but to no avail. Finally figured out the spindle encoder was slipping
To retrieve the missing grub screw that held the encoder shaft in place I had to disconnect the encoder and pull the whole drive wheel off. Retrieved and re-secures all of the bits and all seemed to be well except now when I use MDI mode the feed works perfectly but when running a program the machine stalls on the first line where there is a feed command - even on programs which worked perfectly before.
eg. If I enter G01Z-3F0.01; in IPR feed mode in MDI it will work fine but if I enter the same line in a program the program stalls at this line and will not execute the command.

I am pretty sure disconnecting the encoder has messed something up either in the spindle synchronisation or just with the parameters - the question is what? 

Any ideas would be most welcome as this one has had me stumped for days and despite reading manuals etc I have not come up with anything useful yet.

cheers

Jeff

[awemawson]

Bad luck Jeff. Mines a Siemens control unlike your Fanuc, but I seem to remember that the encoder has an index pulse once per rev as well as the quadratue A & B pulses. Could it perhaps be missing.

A ‘scope job I think.

[JeffK]

You may be right but I wondered if just disconnecting the encoder could create an issue? May have to go out and buy a scope to check it with as I don't have such a beast. Got by over the last few months with a simple multimeter (believe it or not!!). The thing that confuses me is why everything worked ok before I disconnected the encoder but now doesn't. If I had inadvertantly broken a wire or something in the connector surely MDI would not work? Unless I am unlucky enough to have damaged the actual encoder (I was pretty careful with it). Any recommendations for a decent scope?

cheers

Jeff

[awemawson]

s/h Tektronix scope off eBay  They are robust and professional. You don't need a particularly high spec one.

[JeffK]

Thanks Andrew 

[chipenter]

Do you have a G20 line before it locks up , if its default is G21 the feed will be 0.01 mm a minuet , a bit like watching a clock .

[JeffK]

Sorry for the delayed reply - I was called away for a couple of weeks.
I have tried adding a G20 to the code but no difference. Checked the wiring and all seems good.
I think the answer must lie with parameters somewhere but just can't find the right one. At one stage
the diagnostic code 1000 showed a 1 on bit 3 which indicates an interlock or the start lock is on but
that has since stopped coming up. The status display on the bottom of the screen indicates that the
turret is moving but the position display shows no movement and the turret doesn't actually move.
More head scratching I think.....

cheers

Jeff