FP5NC Spindle Motor Noise

BBC Thyristor drive, 7.5kw spindle motor 0-6300rpm

Was operating the machine the other day making a cut, hit stop and once the spindle was stopped I could hear an unusual noise. There is a growl in the motor even while it is stopped. The noise stops when the system is disabled but returns when the system enable button is pushed. It seems to be electrical noise in the motor armature as it goes away if I disconnect the armature power plug. Spindle will turn when started but does not sound good.
I will post a list of everything I've tried so far but was hoping someone would jump in and say: Oh yeah! I know exactly what that is, here's what you need to do to fix it.

Sent from my Moto G (5) Plus using Tapatalk

Well, further troubleshooting and a bit more info. The "growling" noise in the motor also goes away when the field voltage is removed. Guess that makes sense..... Field or armature needs the other energized to act against.

Note: The growling noise in the spindle motor includes a physical vibration and this is all going on with the motor stopped.

Have checked all 6 Thyristor and all seem to be workings ok, no short circuits and each one conducts when power is applied to the gate. In my mind I think one of them is "leaking" allowing voltage thru to the armature.

I have swapped out the 3 control boards of the drive, the pulse generation card (AE6003) the speed/current control board AM6002 and the AF6002 module. None of them produced any change in the motor noise.

Sent from my Moto G (5) Plus using Tapatalk

The embarrasingly obvious thing I have not yet checked is that Im getting all three phases into the BBC itself. Find out tonight.

Maybe a dumb question, but does it have a cooling fan that runs from a separate power source?

The spindle motor has an integrated fan that is working. The BBC drive does not have a dedicated fan, it is cooled via the fans in the doors of the cabinet.

Once the weather improves a bit I am going to get my o-scope on the 12ea. thyristor gate drive signals. I assume there should not be any output signal to any of the gates when the spindle is off. Hopefully more information by the end of the weekend.

Erik

Never mind the 'scope, do you see any armature (Anker) voltage with a voltmeter, when the motor is stopped?

With motor stopped, correct, I see no reason why there should be any signal to the thyristor gates if the motor is stopped. I expect there may be field voltage.

Which brings up a point.... you probably should check the rectifiers in the field circuit. (Thyristors if it has "field weakening" type control).

If there is field voltage, but it is partly AC due to the failure of a diode, then one might expect a bad noise, and also probably some noticeable effect on performance, and noises during operation. if two diodes failed, it would probably open the field supply fuse.

Thanks for jumping into my mess JST. A volt meter shows 0 VDC and .13VAC on the armeture before you hit the system enable button, after enabling, it is still 0 VDC and jumps to .9 VAC. The field is powered all the time. It shows 320VDC with a 180VAC component. However, there is a field power supply board (I have two of them) and swapping it out does nothing, noise and vibration remains the same. I assume the AC component I am seeing is left over ripple as the supply is simply a diode network to rectify the incoming AC. Not sure if I mentioned above but the noise sounds like it is 60hz.
In the attached picture there are three inductor L1 L2 L3 on the AC input side of the thyristor array. Do not have a micro ohm meter, a fluke meter shows between .4 and .5 ohms. How critical are these inductors to the Thyristor drive? I can get a battery and get an accurate resistance if necessary.

320V with 180V AC component sounds wrong for 3 phase input. Sounds like you lost a phase, maybe. 3 phase should make a DC that has only about 15% ripple, way less than 180VAC. That might make the field buzz.

The low volts on the armature with it off may be fine. Not clear about the enable, I assume that is not running the motor.

Check to see if all 3 phases are coming to the field rectifier.

JST said:

320V with 180V AC component sounds wrong for 3 phase input. Sounds like you lost a phase, maybe. 3 phase should make a DC that has only about 15% ripple, way less than 180VAC. That might make the field buzz.

The low volts on the armature with it off may be fine. Not clear about the enable, I assume that is not running the motor.

Check to see if all 3 phases are coming to the field rectifier.

Click to expand...

The 3phase input to the machine is 380ish VAC via a step up transformer from my Phase Perfects 220VAC output.The field supply gets it power from 2 legs of the input.

Sent from my Moto G (5) Plus using Tapatalk

OK, then the ripple makes more sense. What sort of rectifier setup does it have? Probably a full wave bridge, in which case check to see that all the diodes of the rectifier are good.

The description of the problem seems to point at the field, since it is noticed even when the armature is not powered (but field is).

Believe I've figured out the problem: Prior to hearing the noise from the motor: There was no power to the field. A few weeks before the problem started I had moved the wire on the R5 resistor seen below to the center tap to get 50 ohms instead of full 100 ohm value of the resistor. Never put a meter on it, but powered up and everything worked the same with no odd noises etc. Once this noise problem began, I looked at everything. including checking the R5 resistance (100ohm overall and the tap at 53ohms) With the system enabled and the noise occuring I could also feel heat off the resistor as expected. The other day I swapped in the spare A7 power supply board I have and hurray the noise was gone. Machine sounded and ran like I was used to. The next day I tidied up wiring in the cabinet, powered up and the noise was back.

Pulled out the R5 resistor and (luckily) removed the variable adjustment clamp band and found that the resistor wire under the contact pad was broken.
My moving of the lead to the variable tap probably disturbed the broken bits of wire under the contact pad. Worked OK for a couple weeks then general vibration must have finally closed the circuit and started applying power to the field.

I have been running the machine the last few years with no power applied to the separately excited field! I didn't understand how that could be but then looked at the motor lead diagram shown below and realized there are also field windings that are powered by the armeture power supply.

I have never seen any weird issues with the spindle the last few years. I assume since it has tachometer speed feedback the system could control any potential runaway behavior?

Does all of the above seem plausible?

:

Sent from my Moto G (5) Plus using Tapatalk

yes, you effectively had a (probably crummy) series motor, but between friction and speed feedback, it could be controlled and be reasonably stable.

I don't think you really found the problem, though. You just found out what was wrong. Is there any procedure for adjusting that resistor? Why did you decide to move the tap?

It does not seem correct that the field should vibrate etc. usually the field is quiet and just "there". It sounds as if something wrong is going on, for an unknown reason.

I would start by determining the field current. Some clamp-on ammeters will read DC, although you usually need to set zero with an adjuster. If you do not have one, you may need to set your DMM for current, connect it in series with the field, and see if you have the current you should have. Might be more, might be less, it would surprise me if the current reads right at the 0.56A or close to it.

I still suspect some issue with field current

I agree with you except re: the motor. Made by Kessler Group. It is top notch quality. Lot more troubleahooting to do. Your right, I've not found the root of the problem as yet.

Sent from my Moto G (5) Plus using Tapatalk

Here is a print from a BBC drive pdf I have:


my control cabinet does not include the two inductors L4 and L5 that are shown in the print.

The field supply itself is simplicity. Just a full bridge rectifier.

So... does the field current jive with what it is rated to be.... fairly closely?

If it is less, that may indicate an issue with the rectifier. Might be one "leg" of it not working OK.

The vibration, to me, suggests a lot more variation of current than there should be. That would be consistent with a bad rectifier. But that is nt the only possible problem.

By any chance, is the "R2" MOV getting hot? if there is a bad rectifier (open) then the varistor/MOV may be getting hammered, and may already have failed.

Solved

Well......... We have a saying in my industry: "Go where the airman was last!" (I work as an avionics technician on Airforce aircraft)
Embarrasing I didn't find this sooner. I am using weather, fulltime work and family as excuses.

I had this motor rewound about 3 years ago. In that period I've probably only put 10-15 hours of run time on the spindle motor, if that much.


Anyway; there is a short between the separately excited field windings and the series field windings.
Back to the motor shop tomorrow!

Good that you found it.

Yeah, I can see that causing some trouble, depending on just where and how it was shorted.