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  1. #1
    Hi Everyone !

    I'm coming to you in the hope you would help me with some questions :

    I have BF46 milling machine ( from OPTIMUM ) which is not CNC but that have a big brushless motor driven by a control board.

    Brushless and board : that's why i try to post here hopefully.

    FACTS :

    On a hard work, at low speed, with a large tool, the machine stopped suddenly .
    I looked at the board and found 2 blown fuses ( close to power 220v entry point )
    I changed them and they blew again almost instantaneously.
    Hand turning free the nose of the milling is not as usual : there seems to be a slightly hard point during hand rotation.
    Looks like the motor has passed away...


    -1- if the load on these type on motor overpasses the torque capacity, there is no other protection than fusing the engine together with the fuses ( and may be the board as well )?

    -2- the controller board is not able to stop the work and let the engine cool down ?

    -3- there were a little bit of oil into the motor : is that bad for the motor ( does it crunch the varnish on copper wires ? or dissolves the glue fixing the magnets ? ) - oil was left in gear box -located below motor- during machine transportation to another workshop and milling was tilted down to horizontal for the trip.

    -4- the motor ( fit vertically ) has 2 end caps, top one with some circuitry : i could not separate the rotor neither the top, only the bottom cap came apart from end shaft bearing : is there anything of some interest to visually check out the rotor ? ( should it be a smooth solid uniform part or are there some magnets that can be split out from that bit ? )

    -5- do you think, in case the motor ( rotor ? ) is damaged, that the board could be damage as well ?

    -6- i changed the board not so far ago, and it cost me 1000e.... is there a mean to repare those board rather than changing as a whole at customer cost ? ( i'm not a businessman, i'm working by my own... ) That is to say : manufacturer is not very helpful except at heavy cost.

    Sorry for my mistakes in English language, and many thanks for reading and helping if you have any idea !

  2. #2
    Looks like the motor is inverter driven.
    1- Some inverters will shut down depending on what type of fault they see on the motor windings and some don't, they just blow up.
    2- As above
    3- Any oil should not have been able to pass between the gearbox and the motor as there should be oil seals on the shaft connecting them so I wouldn't think that would be the problem.
    4- You would need to separate the motor from the gearbox first before stripping down the motor. Testing it electrically would be the first step. Disconnect it from the inverter and check each winding to ground. They should all show a high resistance between the windings and ground, in the megaohms range. Then test each winding to the other two. They should show equal resistance for each winding between each other and depending on the motor this could be quite low, ie a few ohms.
    5- If the motor has gone down it could quite easily take the inverter with it if it does not have any overload or short circuit protection.
    6- These inverters are normally repairable particularly if it is a standard pcb type. Most decent electronics repair shops should be able to do this.
    If this is the second time this has gone down I would get the motor checked out to ensure it is ok and seriously think about upgrading the inverter to give you some protection from the motor faults.

    Meant to add that most manufacturers will quite happily sell you another board as its good for their sales figures and dont do repair work.
    Last edited by Web Goblin; 31-12-2013 at 07:12 PM.

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  4. #3
    Agree with Web Goblin,
    3. A small amount of oil would not be of much concern, but obviously better without it, it's the oil seal that is suspect. It may also be that it's the gearbox at fault, maybe it lost oil during transportation and that oil has not been topped up.
    4. It sounds like the circuitry on top might have something to do with speed or position feedback.
    Web Goblin is talking the stator, the rotor you mentioned is the rotating part in the middle and in an ac induction motor would be extremely robust, look like a solid lump of metal with laminations, and unlikely to be a problem, though joints on the end of the cage have been known to fail.

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  6. #4
    Thank you guys for your comments and brain storming's.
    I got the motor out again and clamp it into a vise.
    Eventually took some pics.
    Oil seems to come from weak seals letting thru during horizontal transport.
    I found one tiny wire i had to sold again on the Hall sensor on top of motor ( inside top cap )
    All wires are rigid and insulating plastic of bad quality.
    Observing the main control board, there are no hot points or burned points or inflated condensators, any other ideas for what to look for ?

    Another question : i can't figure out what is the metallic box under the main control board ? is it a rectifier ? it is sealed ( by soldering stuff ) and written in Chinese on top of it.
    I would be happy to find out that the problem is there.... who knows ?
    Click image for larger version. 

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    Last edited by BILLYBOUM; 01-01-2014 at 02:15 AM.

  7. The metallic box in the last pic with the chinese writing is an EMI filter to stop interference & noise from the VFD getting back on the mains supply.

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  9. #6
    I was busy looking at the pictures when irving replied. The box is as he says a mains filter. If this was faulty it would cause the fuse in the supply plug to blow and not the ones on the control pcb.
    You could remove the heatsink clamps from the six power transistors at the rear of the board and check to see if any of them look cracked or burnt. If the motor windings check out ok with your test meter you would need an insulation tester to further check for any insulation faults to other windings or ground.
    Have you tried powering up the control pcb without the motor attached to see if it blows the fuses?

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  11. #7
    Didn't know about EMI filter !

    Thank you both : you are clever !

    I will remove the heatsink clamps this afternoon to see if any cracks/burnt appears.

    Motor checks out OK ( as far as i know ... )

    ALL THE BEST AND A HAPPY NEW YEAR GUYS !!!!!!




    PEACE

  12. #8
    Happy New Year !

    See the circuit board mounted on the end of the motor, make sure it goes back in exatly the same position. You can see it has slots to allow rotation.
    If you are using a 500v Megger type insulation tester keep it well away from the same circuit board, only test at the windings (U, V, W), if it's just a multimeter that will not be a problem.

    On the main board there is a white connector with 2 white wires going to it, beside it is a 3 leg component mounted on a small vertical heatsink, well the legs on that do not look good, it looks in fact like someone has changed it before. Maybe this is a component that blows often ?

    There is a rectifier with GBU 12G written on it, this could also be causing the problem.
    http://www.datasheets.pl/bridge_rectifiers/GBU12A.pdf
    Last edited by EddyCurrent; 01-01-2014 at 08:16 AM.

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  14. #9
    Hi Eddy, many thanks for your helping documents and comments, and i'm impressed by your sharp eyes and knowledge !!!

    -1- Yes i ticked marks to position-back the rotary circuit on top of the motor, but yes i try to test everything on this circuit - including small Hall-effect tripods - is that deadly for them ( my multimeter is a FLUCKE, switched to BuzzerOhm-meter ) ?

    -2- I suppose i have to de-solder the GBU12G to test it correct ?

    -3- you are right as well for the 3 legs that look re-soldered : do i have to de-solder this component as well and how come is possible to test it ?

    -4- i have the "old" contol-board where i plugged by mistake ( at the wrong place ) the rpm information : may be it is easier to check and repair this board ? ( the present board is burning the 2 protective fuses almost instantaneously, the previous one just doesn't work and leaves the fuses OK by the way )

    Thanks Eddy for your time and ideas !

  15. #10
    Quote Originally Posted by BILLYBOUM View Post
    Hi Eddy, many thanks for your helping documents and comments, and i'm impressed by your sharp eyes and knowledge !!!

    -1- Yes i ticked marks to position-back the rotary circuit on top of the motor, but yes i try to test everything on this circuit - including small Hall-effect tripods - is that deadly for them ( my multimeter is a FLUCKE, switched to BuzzerOhm-meter ) ?
    Using the Fluke meter is okay.

    Quote Originally Posted by BILLYBOUM View Post
    -2- I suppose i have to de-solder the GBU12G to test it correct ?
    Yes

    Quote Originally Posted by BILLYBOUM View Post
    -3- you are right as well for the 3 legs that look re-soldered : do i have to de-solder this component as well and how come is possible to test it ?
    ideally, can you see a number on this component ?

    Quote Originally Posted by BILLYBOUM View Post
    -4- i have the "old" contol-board where i plugged by mistake ( at the wrong place ) the rpm information : may be it is easier to check and repair this board ? ( the present board is burning the 2 protective fuses almost instantaneously, the previous one just doesn't work and leaves the fuses OK by the way )
    You can use this to make a comparison with the other board, you can test the components without de-soldering them for a start then if you find a difference you can de-solder it to test it properly.

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