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  1. #1
    Am having problem with the spindle revs on this machine .

    I fitted a Sprint 340 i DC drive unit quite a while ago in place of the lenze controlller which had gone pop .

    All was fine for a couple of months and I had no detectable problems . It then began to fluctuate in speed but this could be "tuned out " using a range of adjustments in particular the IR compensation pot. It soldiered on for a while until the fluctuations returned accompanied by some apparent light knocking which seemed to be coming from the back end of the motor, ( or possibly from the Choke which is a 40 mH unit fitted as standard) . There also appeared to be significant arcing at the motor commutator in time with the knocking

    I should add that this can be intermittent but often shows itself when the machine has been on for 20 mins or so.

    I took advice from the suppliers of the DC drive unit (https://inverterdrive.com/group/DC-T...0-Isolated-1Q/)
    (they assured me that these drives either work or go bang, they do not behave in this way)

    On their advice I carried out extensive checking to ensure that the mains supply was not being interrupted . Checked all mains connections, replace any crimps which seemed dubious , isolated the drive from the bob relay and used a simple link to put it into the "On" position, and fitted a pot in place of the 0-10v analogue input . I then ran it essentially bare except for the control signal from the pot .

    It was not long before the problem returned. At a speed of about 600 revs I was seeing a steady control input of about 2.6v but the output was fluctuating wildly around 45v , on occasions dropping to zero . The spindle speed on the computer display was also fluctuating
    I concluded that the erratic output was causing the knocking which I felt I was hearing from the choke , along with the arcing at the commutator . The supplier assures me though that the problem is external to the drive unit.

    The same motor connected to a 42 v regulated PSU runs sweetly at steady 42.3v and steady 650 revs showing on my computer screen.

    Is it possible the choke is faulty? Can I test it ? Can I leave it out of the circuit to see if it runs better without? Indeed , Is it needed anyway? Can I replace it with something different ?
    Is there anyone out there with a spare one lying about ?(I dont see any on Ebay)

    If I try to run a program it will run relatively sweetly ( slight fluctuation )on straight cuts , but on thread cutting it will just drag the spindle down to a stall.
    Likewise on parting.

    Clearly the machine is useless until I can get this sorted .. Any thoughts folks ?

    No doubt there will be suggestions to go to 3 ph motor and inverter but there is no room. This motor sits in a space 125mm wide /deep
    The nearest 1/2 hp motor I can find is 145 Diameter , 3/4 hp which I understand would be correct for the machine is 165 so neither will fit.

  2. #2
    The choke is simply a wire wound around magnetic core - usually either ferrite or iron. If it's mounted on the motor, if there's access, you could migrate it to the controller (so it's still in circuit, but mechanically separate and not subject to vibration) That's the only way I'd suggest testing live. The choke is a "good thing" - it'll help to suppress high-frequency, high energy noise coming off the commutator - wouldn't recommend running without. You can replace the choke - obviously it needs to be suitably rated, value isn't quite so critical (+100%/-25%) - if it came down to it you could wind your own - plenty of resources to explain how online.

    But, the behaviour you describe - "it was not long before...." - suggests the problem isn't immediate - but after a period ("not long") of operation - my money is on a temperature-related fault in the controller. Now here's a question - does it similarly fail under no-load? (on a lathe I'd suggest removing the chuck, or the drive-belt, or whatever to remove the mechanical load on the spindle and therefore the current drawn. If it works off-load, but fails under load, that's really a strong indication of the controller failing. If it fails off-load as well, then depending upon buggerance of strip-down, I'd be inclined to get everything together on a bench, video it, and send the video to the supplier and ask them to explain.

    If it helps for bench-test - I could post you a (100mm dia, 180VDC spindle motor - only 1/4Hp, unfortunately, just to bench test? (an excuse to post back your old controller at the same time!).

  3. #3
    Actually.... thinking about it - might be worth throwing a test-lamp in place of the spindle motor - just an incandescent (if you can still find them!) - if you can pursuade that to flicker then that takes all the motor/choke out of the equation, and very visual for a blame-vid. Just another option.

  4. #4
    The guy did suggest that. (Even in parallel with the motor) Havent got round to it yet .
    Would it be a bad Idea to take choke out of circuit for trial purposes

  5. #5
    Removing the choke would remove some protection from the drive and increase the electrical noise in the system - at least with the motor attached. I'd be cautious with the motor in circuit - but very more relaxed with just a lamp.

  6. #6
    Just a follow -up

    Used the lamp in parallel with the load and it was flckering up an down,
    Took motor belt off and not much better .
    Tried with only lamp connected and it was steady (able to turn lamp up and down) so sounds like drive is OK.
    Bypassed the choke and tried briefly with just the drive and motor and we are back to flickering so pointing to motor.
    It seems the Drive regulates motor using armature voltage feedback so may well be that a surging motor sends all kinds of rubbish back to the drive .

    Took motor off and found a worn brush, andd one which had a loose connection.
    Switch brushes , tweaked brush springs , and ensured brush connections were tight and all seems much improved .
    Proof of the pudding tomorrow when I try some screw cutting and parting off.

    Thanks for the pointers Doddy
    Will PM shortly

  7. The Following User Says Thank You to John11668 For This Useful Post:

  8. #7
    Not there yet .
    More Consistent spindle speed , and pulsing and knocking all but gone , but not a lot of torque and a very slow ramp up despite adjustments to ramp time .
    Am thinking the dead brush has left a bit of carbon shorting at the commutator . New brushes on way so a thorough clean of the comm, and a new pair of brushes and we will see what then transpires

  9. #8
    All cleaned up , New brushes carefully bedded and thoroughly run in.
    Motor runs sweet, lamp steady, holds speed consistently, until you load it with a cut , then it just droops away to a stall.
    I am thinking the Armature voltage feedback function has fallen over . I guess this would tie in with slow ramp up!
    (Checked brushes again and they have run in to a nice polish over the faces)
    But still gutless.

    Anyone had such experience or able to throw any light?

  10. #9
    No. The offer remains of a 180V 0.5 HP spindle motor to test. If problem remains its the controller, if not it's the motor.

  11. #10
    Kind offer but did you not say it was 1/4 Hp.
    Would take you up at a stroke but not sure if it would help . My problem only shows when I start cutting,. On the bench mine runs like a sewing machine

    Will see what suppliers say tomorrow. Failing that it is maybe a 3 phase option .
    Or someone told me you might be able to point me to an economic servo set up. Any I have seen seem well beyond my DIY budget

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