Fried a power supply


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    Default Fried a power supply

    Hello all,

    I am getting very close to the completion of my new cnc router that i have been building for a couple months. Yesterday I finally started doing a test cut which was to surface my table so that is is true to the machine. Durring the cut my bit came loose, and I quickly hit the e-stop button and then poof my power supply for my spindle fried.

    My spindle is of the DIY variety with a large RC airplane brushless motor. To power the motor I am using a Meanwell 350 watt 24volt power supply rated at 14 amps. I have been using this same setup for about 6 months now with no issues including stalling the motor to the point the speed control went into lock out and the power supply was fine. From my testing the most current i am using is around 8 amps durring a cut. On my old machine jthe power supply was not included in the e-stop loop and i would just turn the motor off at the speed control if there was a problem. My new setup uses a relay to cut the main power to the power supply when the e-stop is initiated. I suspect that this may have been what fried the power supply but i dont know enough about them to be sure.

    Durring initial inspection of the blown power supply i found that the internal fuse was not blown. I did find several resisters (i think too black to really tell but they had an "R" on the board next to them) that were blown along with either a mossofet or a voltage reg, and another IC that had all blown.

    I have a spare supply that i was going to wire up but i dont want to blow it again. should i move the relay to the dc side of the power supply, or keep it where it is? My plan is to install an inline fuse on the dc side just to make sure i do not over amp the power supply.

    Thank you for the help

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    Default Re: Fried a power supply

    Quote Originally Posted by rotccapt View Post
    Hello all,

    I am getting very close to the completion of my new cnc router that i have been building for a couple months. Yesterday I finally started doing a test cut which was to surface my table so that is is true to the machine. Durring the cut my bit came loose, and I quickly hit the e-stop button and then poof my power supply for my spindle fried.

    My spindle is of the DIY variety with a large RC airplane brushless motor. To power the motor I am using a Meanwell 350 watt 24volt power supply rated at 14 amps. I have been using this same setup for about 6 months now with no issues including stalling the motor to the point the speed control went into lock out and the power supply was fine. From my testing the most current i am using is around 8 amps durring a cut. On my old machine jthe power supply was not included in the e-stop loop and i would just turn the motor off at the speed control if there was a problem. My new setup uses a relay to cut the main power to the power supply when the e-stop is initiated. I suspect that this may have been what fried the power supply but i dont know enough about them to be sure.

    Durring initial inspection of the blown power supply i found that the internal fuse was not blown. I did find several resisters (i think too black to really tell but they had an "R" on the board next to them) that were blown along with either a mossofet or a voltage reg, and another IC that had all blown.

    I have a spare supply that i was going to wire up but i dont want to blow it again. should i move the relay to the dc side of the power supply, or keep it where it is? My plan is to install an inline fuse on the dc side just to make sure i do not over amp the power supply.

    Thank you for the help
    Hitting an Estop will do it every time, unless the power supply has regen protection you need something like this, between your motor and power supply, something as simple as a diode may solve the problem also, the regen clamp is the best way to protect the power supply

    Attached Thumbnails Attached Thumbnails Fried a power supply-regenclamp_920-0024-pdf   Fried a power supply-ametek_freewheeling_diodes_provide_power_supply_protection-pdf  
    Last edited by mactec54; 01-08-2018 at 08:38 AM. Reason: added more
    Mactec54


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    Default Re: Fried a power supply

    Meanwell is a good brand, 2 year warranty on most power supplies, Having just a large cap helps as well. A fuse will not react not fast enough.



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    Default Re: Fried a power supply

    Would moving the relay to the DC side eliminate the problem?



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    Default Re: Fried a power supply

    I cannot say the relay caused the problem, On the DC side that may cause the drives to see all the regen voltage. mean well power supply does have over voltage protection. What model PS is that?



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    Default Re: Fried a power supply

    Quote Originally Posted by sparkness View Post
    I cannot say the relay caused the problem, On the DC side that may cause the drives to see all the regen voltage. mean well power supply does have over voltage protection. What model PS is that?
    They have no protection from back regen from the DC motor, this is a common problem with switch mode power supplies, when the back voltage exceeds the output voltage it will fry what ever is in its path

    Mactec54


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    Default Re: Fried a power supply

    Quote Originally Posted by rotccapt View Post
    Would moving the relay to the DC side eliminate the problem?
    It may help, but the relay may be a potential next fail point

    Mactec54


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    Default Re: Fried a power supply

    dc side relay

    Attached Thumbnails Attached Thumbnails Fried a power supply-estop-relay-png  


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    Default Re: Fried a power supply

    So what blows up in the PS? the switch is opto isolated

    Attached Thumbnails Attached Thumbnails Fried a power supply-mean-well-se-power-supply-jpg  


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    Default Re: Fried a power supply

    if the returned energy increases the powers supply voltage above the voltage its set to

    the first thing that happens is the power supply will shut down as it attempts to protect itself

    in a 48V @7.3A power supply there is only three 680uF 63V capacitors across the output

    the switch mode power supply has no way to absorb the returned energy and excess voltage can damage the output capacitors ,
    the output rectifier diodes and possibly the feedback circuit resulting in the catastrophic failure


    all the stepper driver manuals I have read advise against switching the DC supply

    a better solution will be to have a current dump circuit to limit the maximum voltage rise due to any returned energy from the stepper motors and disable the driver

    with servo motors to switch the AC supply to the power supply to stop a runaway

    John

    PS
    simple switch mode power supply
    Fried a power supply-switch-mode-power-supply-jpg

    Last edited by john-100; 01-08-2018 at 03:46 PM.


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    Default Re: Fried a power supply

    I am using a lrs-350-24. My driver's are powered by a sperate unregulated supply. this ps is only for the spindle and the cooling fans. The ps runs an electronic speed control that then runs the brushless motor. I can run it without the e-book stop but I like the idea of killing the spindle in case of an emergency.

    My other option would be to switch the 5v that controls the speed control



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    Default Re: Fried a power supply

    I would expect the brushless motor and speed control to generate similar returned energy voltages as stepper or servo motors can

    so you need to protect the power supply possibly with a diode to stop current flowing back into the supply
    or a returned energy dump circuit that connects a low value resistor across the supply to dissipate the excess energy until the voltage drops to near normal limits

    John



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    Default Re: Fried a power supply

    Quote Originally Posted by rotccapt View Post
    I am using a lrs-350-24. My driver's are powered by a sperate unregulated supply. this ps is only for the spindle and the cooling fans. The ps runs an electronic speed control that then runs the brushless motor. I can run it without the e-book stop but I like the idea of killing the spindle in case of an emergency.

    My other option would be to switch the 5v that controls the speed control
    And that is the correct way to switch it, for what you are doing, you still need a dump or clamp of some kind to protect the power supply

    Mactec54


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    Default Re: Fried a power supply

    would this be a good circuit to build? http://www.cnczone.com/forums/attach...2&d=1497491089



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    Default Re: Fried a power supply

    Quote Originally Posted by rotccapt View Post
    would this be a good circuit to build? http://www.cnczone.com/forums/attach...2&d=1497491089
    Why over-complicate things? Just use an analogue power supply, or simply connect a diode in series with the + output of your PSU. The diode will protect the PSU from reverse current flow. Though, not 100% sure that the PSU was fried because of reverse current in this case.

    During the cut my bit came loose, and I quickly hit the e-stop button and then poof my power supply for my spindle fried.
    Your conclusion may be wrong and the PSU may have been blown by the time you hit the e-stop. After all, to hit the e-stop you had to notice that the bit came lose, and the time between those two events is enough to blow the PSU. Maybe the internal fuse is intact because it is the wrong type or wrong dimension...

    https://www.youtube.com/c/AdaptingCamera/videos
    https://adapting-camera.blogspot.com


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    Default Re: Fried a power supply

    The spindle was still running when I hit the estop. Also my fans were still running. I noticed the burnt ps when I went to reset the system and the ps would not turn on and I started smelling the burnt components.



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    Default Re: Fried a power supply

    Quote Originally Posted by rotccapt View Post
    The spindle was still running when I hit the estop. Also my fans were still running. I noticed the burnt ps when I went to reset the system and the ps would not turn on and I started smelling the burnt components.
    That's what makes this happen, spindle is running, you cut the power and the spindle turns into a generator and the regen power goes right back to the source

    A simple Diode will give you some protection, but not complete, and my be all you need

    Mactec54


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    Default Re: Fried a power supply

    Quote Originally Posted by A_Camera View Post
    Maybe the internal fuse is intact because it is the wrong type or wrong dimension...
    The fuse is only for the main input power supply 120v / 240v Ac there is no protection on the DC side of these power supplies

    Mactec54


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    Default Re: Fried a power supply

    Your power supply got toasted during a feedback power of a freewheeling DC spindle, moving your relay to the DC side will eventually solve the feedback issue, just use a high amp relay to be able to carry the FLA of your spindle.



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    Default Re: Fried a power supply

    Thank you for the info, I'm going to build the circuit I posted and am looking at switching the 5v control. If I can't do that I will move my relay to the DC side between the ps and the protection circuit



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