Arrow 750 - regen resistor glowing red hot.


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Thread: Arrow 750 - regen resistor glowing red hot.

  1. #1
    Member Burf86's Avatar
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    Default Arrow 750 - regen resistor glowing red hot.

    I was sitting in front of my Arrow 750 the other day, deburring a part, when the external regen resistor burst into flames. I quickly hit the emergency stop and the flames died down and the resistor cooled off.

    The next day I was able to make the spindle do its thing. i.e. spin and stop as it should, but when the machine was sat idle the regen resistor would then start to overheat again.

    Please help me Cincinnati brain trust!



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    Default Re: Arrow 750 - regen resistor glowing red hot.

    Hi,
    a regen braking resistor is place directly across a the DCLink by a MOSFET or IGBT switch.

    I assume your machine is three phase? Is it 380VAC? Lets assume for the moment that is is 380VAC. The input AC is rectied and smoothed by the DCLink
    capacitors to 380 x square root(2)=537VDC.

    If your braking resistor has a resistance of 100Ohm and its switched across the DCLink then the power dissipated in it would be 2883W or nearly 3kW. It will get hot quick, real quick!
    In reality the braking resistor is switched onto the DCLink only for very brief periods, say a few seconds while the spindle is decelerating.

    It sounds like your machine is switching the resistor on but not off again. I would guess the MOSFET/IGBT is faulty, or the circuit which controls it.

    In lager machines its quite common for the braking MOSFET/IGBT to be on a separate board so that they might be replaced as a spare part, they have a reputation for failing.
    You should replace the resistor now too. It will be unreliable after catching fire.

    Craig



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    Default Re: Arrow 750 - regen resistor glowing red hot.

    What Joe said. The power transistor is definitely dead. The driver stage for the transistor is very likely damaged as well. And it's probably a good idea to replace the flaming resistor, even if it checks out OK.

    It's not a particularly complicated repair, but it needs to be done by someone who knows what he's doing.



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    Default Re: Arrow 750 - regen resistor glowing red hot.

    Do you have black Kollmorgan drives? If so, it could be that the DC bus voltage is to high, it should be about 320 VDC. The regen resistor may be trying to keep it lower if it is a lot higher 380 VDC. I would think you would get a OVER VOLTAGE alarm on the drives.

    Mike CNC Machine Services INC | Cincinnati Milacron MachinesCNC Machine Services



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    Default Re: Arrow 750 - regen resistor glowing red hot.

    Thanks for the information, much appreciated.
    The machine does have the black Kollmorgan drives.
    I've used a company to fix the drives in the not so distant past but this is the third time they have gone down, so my assumption is they are ripping me off. The drive they sent back has a sticker on it that says "SQUIRES" and this is not the name of the company I was working with. Does this name Squires ring any bells when it comes to Killmorgan drive repairs? I'm based in the U.K.

    I also very much appreciate the advice to use someone who knows what they are doing, but it's no longer an option I'm afraid. I've already sunk 6k on repairs and I only spent 2k to get the machine in my door. It's at the point now where I either learn to do the repairs myself, or she goes to the big scrapyard in the sky.
    I taught myself to use the machine having never even looked at a CNC machine before she arrived. Can't be too much harder to learn how to fix it. I have a friend or two in the area that know more about electronics than I do so I will be roping them in as well.



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    Default Re: Arrow 750 - regen resistor glowing red hot.

    We suggest that you send the unit and call Kilroy Corp. 937-660-5313. We have used them for years with Kollmorgan drives and have been very happy, they are in Dayton Ohio.

    MIKE CNC Machine Services INC | Cincinnati Milacron MachinesCNC Machine Services



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    Default Re: Arrow 750 - regen resistor glowing red hot.

    Howsit chaps?
    Thanks again for the help and input, very much appreciated by this CNC/electronics n00b.

    So, my friend and I have done a little digging in the power supply and spindle drive but have not been able to locate the fault. So I request some more help if you don't mind.

    We have checked the IGBT modules that regulate the 3-phase supply inside the power supply and the spindle drive but they all seem to check out fine. We then did a bit of poking around on the circuit boards inside the spindle drive (VFS5) but weren't able to find anything obviously at fault. I'm hoping someone will be able to give me some more specific advice on what to look for or test...

    A bit more info on the problem; The spindle drive is showing the red fault light when the machine is giving power to the drives. The regen light on the power supply is flickering and the regen resistor starts to heat up and glow red hot.



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    Default Re: Arrow 750 - regen resistor glowing red hot.

    Quote Originally Posted by CitizenOfDreams View Post
    What Joe said. The power transistor is definitely dead. The driver stage for the transistor is very likely damaged as well. And it's probably a good idea to replace the flaming resistor, even if it checks out OK.

    It's not a particularly complicated repair, but it needs to be done by someone who knows what he's doing.
    You say the power transistor is dead, how do I go about identifying this transistor and checking to see if it is in fact deaded?
    I know I am a n00b asking such basic questions, but as mentioned before, I need to learn to fix it myself or the machine is not going to live any longer...



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    Default Re: Arrow 750 - regen resistor glowing red hot.

    Quote Originally Posted by Burf86 View Post
    You say the power transistor is dead, how do I go about identifying this transistor and checking to see if it is in fact deaded?
    A typical VFD would have 6 transistors for the motor outputs and 1 odd transistor for braking. Sometimes that 7th transistor is a separate part. Sometimes all 7 transistors are packaged in the same module. If you can read the part number on the module, you can check whether it has the braking transistor inside. If it does not, look for a large transistor elswhere on the circuit board.

    A blown power transistor will typically have a dead short (0 ohms) between emitter and collector (source and drain for an FET).

    A healthy transistor will typically check as a diode. Most high power FETs and IGBTs have a built-in diode between source/drain (emitter/collector).

    Post some pictures of the board, that may help us identify the parts. And, of course, always be careful while repairing high voltage devices. Good luck!



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    Default Re: Arrow 750 - regen resistor glowing red hot.

    Thanks, CitizenOfDreams.

    I have uploaded pictures from the inside of the spindle drive. There are a bunch of 5-pin transistors on the circuit board and then three with three pins attached to a bit of sheet metal to act as a heat sink (I assume).

    The regen resistor is connected to the power supply, but the red fault light is showing on the spindle drive. So that's why I have taken to looking in the spindle drive for the fault rather than the power supply. Although the IGBT that was replaced previously was in the power supply.

    I've had a quick poke around with a multi-meter to try and find the faulty transistor, but I'm fairly clueless. The unit has been out of the machine for a good few weeks now so there shouldn't be much chance of me getting a shock...

    Attached Thumbnails Attached Thumbnails Arrow 750 - regen resistor glowing red hot.-img_20220905_200515_818-jpg   Arrow 750 - regen resistor glowing red hot.-img_20220905_200734_326-jpg   Arrow 750 - regen resistor glowing red hot.-img_20220905_201822_502-jpg   Arrow 750 - regen resistor glowing red hot.-img_20220905_201833_605-jpg  

    Arrow 750 - regen resistor glowing red hot.-img_20220905_201845_968-jpg   Arrow 750 - regen resistor glowing red hot.-img_20220905_201901_155-jpg   Arrow 750 - regen resistor glowing red hot.-img_20220905_201911_639-jpg  


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    Default Re: Arrow 750 - regen resistor glowing red hot.

    I have been speaking to a friend and he suggested it could be a short in the spindle motor causing the resistor to be fed current.
    Does this make sense to anyone else?



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Arrow 750 - regen resistor glowing red hot.

Arrow 750 - regen resistor glowing red hot.