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  1. #41
    Quote Originally Posted by JoeHarris View Post
    Thanks John, I have the din mounted flip down type fuse holder so not sure without looking at it if this would be possible but I understand the principal and I'm sure there would be a way!


    Sent from my iPhone using Tapatalk
    That sounds like you're talking about the AC PSU input fuse. You definitely don't want any diodes in that position!

  2. #42
    Clive S's Avatar
    Lives in Marple Stockport, United Kingdom. Last Activity: 10 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 3,333. Received thanks 618 times, giving thanks to others 77 times. Made a monetary donation to the upkeep of the community. Is a beta tester for Machinists Network features.
    Quote Originally Posted by Agathon View Post
    That sounds like you're talking about the AC PSU input fuse. You definitely don't want any diodes in that position!
    Have you read the post? The diode is to go across the DC fuse output of the power supply to the drivers to give a circuit for the bemf to be able to be dumped into the caps. in case the fuse blows
    ..Clive
    The more you know, The better you know, How little you know

  3. #43
    Quote Originally Posted by Clive S View Post
    Have you read the post? The diode is to go across the DC fuse output of the power supply to the drivers to give a circuit for the bemf to be able to be dumped into the caps. in case the fuse blows
    I have been following carefully. Joe mentioned a single "flip down type" fuse holder which I interpreted as possibly being an MCB - his video shows one on the 240vac side. Just wanted to make sure he wasn't confusing the two lots of fuses with disastrous consequences!

  4. #44
    Clive S's Avatar
    Lives in Marple Stockport, United Kingdom. Last Activity: 10 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 3,333. Received thanks 618 times, giving thanks to others 77 times. Made a monetary donation to the upkeep of the community. Is a beta tester for Machinists Network features.
    Quote Originally Posted by Agathon View Post
    I have been following carefully. Joe mentioned a single "flip down type" fuse holder which I interpreted as possibly being an MCB - his video shows one on the 240vac side. Just wanted to make sure he wasn't confusing the two lots of fuses with disastrous consequences!
    No Prob. But in #39 John show a diagram showing the fuse holder clearly showing the fuse connected to the drive +ve
    ..Clive
    The more you know, The better you know, How little you know

  5. Quote Originally Posted by Clive S View Post
    No Prob. But in #39 John show a diagram showing the fuse holder clearly showing the fuse connected to the drive +ve
    Fear not on this occasion I wasn't confused!!

  6. #46
    Hi Agathon

    the circuit from post 34
    Click image for larger version. 

Name:	power supply output fuses.jpg 
Views:	218 
Size:	48.7 KB 
ID:	22096

    when every thing is working
    the fuse short circuits the diode its connected to
    so the power supplies DC output is connected to the driver

    when a fuse fails power from the DC power supply is blocked
    and now the diode provides a path any for excessive voltage
    generated by the motor to be returned to the power supplies reservoir capacitor(s) and used by any other axis driver

    if the FET's have become short circuit then a large fault current will blow the drivers supply fuse and the motor will be short circuited so no generated current can be returned via the diode


    inside a stepper driver the FET's that form the H bridges
    have built in diodes connected across the drain & source terminals
    Click image for larger version. 

Name:	H bridge inside a TB6600.jpg 
Views:	176 
Size:	37.6 KB 
ID:	22098
    the diodes form a bridge rectifier that converts the AC voltage generated in a mechanicaly driven motor into DC that adds to the external DC supply that powers the stepper driver



    John

    PS
    as an aside
    one of many DIY hand cranked torches using a stepper motor as a generator

    https://www.eeweb.com/blog/extreme_c...otor-generator
    Click image for larger version. 

Name:	Stepper-Motor-Generator-Circuit-Diagram.jpg 
Views:	201 
Size:	40.7 KB 
ID:	22097
    Last edited by john swift; 06-07-2017 at 11:41 AM.

  7. #47
    Quote Originally Posted by Clive S View Post
    No Prob. But in #39 John show a diagram showing the fuse holder clearly showing the fuse connected to the drive +ve

    Yes, I saw that.

    Quote Originally Posted by john swift View Post
    Hi Agathon

    the circuit from post 34
    Click image for larger version. 

Name:	power supply output fuses.jpg 
Views:	218 
Size:	48.7 KB 
ID:	22096

    when every thing is working
    the fuse short circuits the diode its connected to
    so the power supplies DC output is connected to the driver

    when a fuse fails power from the DC power supply is blocked
    and now the diode provides a path any for excessive voltage
    generated by the motor to be returned to the power supplies reservoir capacitor(s) and used by any other axis driver

    if the FET's have become short circuit then a large fault current will blow the drivers supply fuse and the motor will be short circuited so no generated current can be returned via the diode


    inside a stepper driver the FET's that form the H bridges
    have built in diodes connected across the drain & source terminals
    Click image for larger version. 

Name:	H bridge inside a TB6600.jpg 
Views:	176 
Size:	37.6 KB 
ID:	22098
    the diodes form a bridge rectifier that converts the AC voltage generated in a mechanicaly driven motor into DC that adds to the external DC supply that powers the stepper driver



    John

    PS
    as an aside
    one of many DIY hand cranked torches using a stepper motor as a generator

    https://www.eeweb.com/blog/extreme_c...otor-generator
    Click image for larger version. 

Name:	Stepper-Motor-Generator-Circuit-Diagram.jpg 
Views:	201 
Size:	40.7 KB 
ID:	22097
    Sorry about this, I seem to have sowed some confusion about my own clarity. My A-level physics knowledge is a bit rusty but I understand the back emf issue and the role and function of the diodes - excellent and clear explanation though.

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