3 phase BLDC controller blown - Burst MOV and capacitors - any Ideas why this may happen.

Discussion in 'Technical Repair' started by aspiespot, Jan 4, 2019.

  1. aspiespot

    Thread Starter New Member

    Dec 14, 2018
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    Hello,

    I am pleased I have found your brilliant site and am trying my best to digest and understand motor controllers.

    The attached pictures show what I think is 3 phase BLDC motor and controller / uk 230v 50hz / 750w / we have a couple of these which have failed in exactly the same way with less than 5 hours use.

    Picture B shows a MOV which has burst in half / small capacitor burst / large capacitor burst.

    I would very much welcome any Ideas or suggestions on why this could be happening,

    Thank you Darren.
     
  2. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    Most likely excessive input voltage.

    I'm curious that the motor seems schizophrenic as it says "Brushless DC Motor" and "AC 230V"
     
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  3. aspiespot

    Thread Starter New Member

    Dec 14, 2018
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    Hi,

    Sorry I did not explain this very well in my first post, the supply to the machine is 230v 50hz (UK).
    And im sure the output from the pcb is 3 phase DC to a brushless motor ?
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Not if the circuit board shown is also a AC to DC inverter/power supply also.
     
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  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    My guess too, it is usually excessive or over-voltage time that kills a MOV.

    The motor also resembles the modern ECM (Electronically Commutated) motors now fitted to HVAC systems where the input is AC and internal electronics control the DC commutation.
    Max.
     
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  6. AlbertHall

    AAC Fanatic!

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    If this was connected directly to a standard UK mains supply then you might look at whatever else is connected to that same supply.

    I was once called to repair a high power DC power supply on industrial premises which kept blowing the triacs on the mains input.
    After some investigation there were sometimes ±700V spikes on the mains supply caused when a large 3-phase fan was switched on or off. The spikes killed the triacs. They installed a clean mains supply line.
     
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  7. shortbus

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    But those usually aren't called BLDC motors, but by their real name SRM switched reluctance motor.
     
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  8. MaxHeadRoom

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  9. shortbus

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    We'll have to agree to disagree Max. There is a difference, between the ECM and SRM. The ECM is like a BLDC in that the rotor has magnets. The SRM rotor has no magnets, but is ferromagnetic. The ECM is just a BLDC that senses it's load and makes changes to keep up the set speed. The only thing in common with them is that they are electronically commutated.

    The SRM is actually an older motor, it was invented in the 1880's.
     
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  10. MaxHeadRoom

    Expert

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    Yes I agree there is a difference, ECM is a loose term for Electrically Commutated Motor which can cover a wide variety of technology, SRM is as you say, it has a ferrous rotor in place of the PM rotor of a BLDC or ECM motor.
    The term ECM has been used principally since the 1980's when it was first developed by GE for HVAC fan motor applications.
    The electronically commutated SRM is I believe a newcomer on the scene as far as HVAC goes as far as I have seen.

    Variable Reluctance Motor (VRM)
    The variable reluctance motor is an evolution of the stepping motor and is generally designed for use in low power, open loop position and speed control systems where efficiency is not of prime importance.

    Switched Reluctance Motor (SRM)
    The switched reluctance motor was designed for use in high power, high efficiency, variable speed drives able to deliver a wide range of torque.

    Synchronous Reluctance Motor
    The Synchronous Reluctance Motor is similar to a synchronous AC machine.
    The rotor has salient poles but the stator has smooth, distributed poles whereas both the switched and variable machines have salient poles for both the rotor and the stator.

    Max.
     
    Last edited: Jan 5, 2019
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  11. MaxHeadRoom

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    BTW, here is the story from GE themselves.
    Max.
     
  12. Hymie

    Active Member

    Mar 30, 2018
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    Interestingly the failed electrolytic capacitor in photo E is rated 22uF 25V, this suggests to me that the failure mode is the circuit which is generating the low voltage dc from the mains.

    The damaged MOV might be part of this low voltage circuit, rather than being across the mains – I suggest you take a close look at the MOV markings to determine its voltage rating.

    The large (fusible?) resistor (R2 47Ω) may be part of the voltage limiting circuit.

    What is the voltage rating of the two large electrolytic capacitors (from the markings I can discern, they appear 1000uF 200V).
     
  13. shortbus

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    My thought would be possibly the motor is being back driven by what ever it is used on. The OP never mentioned what or how it's being used.

    Some times stuff fails because it wasn't the correct thing for the project. Having multiples of the same motor fail the same way in the same machine makes it sound like that is the problem.
     
  14. aspiespot

    Thread Starter New Member

    Dec 14, 2018
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    Thank you all very much for your suggestions,

    I have attached some more pictures and added some more info below,

    On the MOV is has 471KD 14.

    The two large capacitors are 1000uf / 200V.

    On the new picture added it shows two short wires fitted with closed end connectors ,Looks like they could be somthing to do with changing the voltage depending on the county.(230v or 115v)
    At first I did wonder if the pcb was set to 115v instead of 230v ?

    The motor is fitted to a Metal cutting bandsaw.

    Regards Darren.
     
  15. AlbertHall

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    What are the two red things covered in pale yellow tape?
    What are they connected to?
    One of them appears to be connected to the point labelled 115V.
     
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  16. MaxHeadRoom

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    They appear to be wire nuts with some kind of insulation over them.
    IIRC they were banned in the UK a long time ago.
    Max.
     
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  17. Hymie

    Active Member

    Mar 30, 2018
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    471K is a generic marking for an MOV having a rating of 300Vac. It’s hard to imagine external mains noise destroying the MOV, otherwise I’d expect other electrical equipment to have been damaged. Therefore I would think that it likely that the electrical noise (which destroyed the MOV) is generated internally for some reason.

    The photos suggest that the unit can be configured for either 115V or 230V operation, but if set to the wrong voltage I would not expect the unit to last longer than 5 seconds, let alone 5 hours.
     
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