stepper driver curcuit

Discussion in 'General Electronics Chat' started by dobrodewed, Jan 10, 2017.

  1. dobrodewed

    Thread Starter New Member

    Jan 10, 2017
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    Does anyone have a schematic for a A3979 stepper driver? My controller uses these and my x and z axis are set to 1.4A, my y and a axis is set to 1.8A. They drive nema 17 motors at 30v. I would like more torque!
    Question: is there anyway to use the outputs to the motors from the A3979s to drive an additional higher output h-bridge. My controller works well, it's just under powered. I'm thinking of it as a preamp. All the signal shapes are correct, so just amplify them? Power these new h-bridges with the new 48v as well and voila I can drive bigger motors
     
  2. DNA Robotics

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    Jun 13, 2014
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  3. ClassOfZero

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    Dec 28, 2016
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    http://www.automationtechnologiesinc.com/products-page/kl-stepper-drivers/kl5056

    The above linked drivers are rated at 20 - 50V and 5.6 amps

    I run KL-6050 and never had a issue with them.

    Just upgrade your stepper drivers, if of course they are compatible with your motors. What sort of machine are you running ?

    Hopefully max will chime in he has some pretty good advice & knowledge regarding cnc.
     
  4. dobrodewed

    Thread Starter New Member

    Jan 10, 2017
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    it's a stepcraft 840. Everything is built into the controller. Their schematics are proprietary.
     
  5. ClassOfZero

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    Dec 28, 2016
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    Maybe it doesn't require more torque.

    What are your reasons for wanting more torque ?
    Is there enough stiffness in the machine to accommodate the extra cutting forces ?
    Are the stepper motors already at their max specs or can they take some tweaking ?

    I'm not trying to be a downer, when I was going through the conversion process for my mill there were so many people basically overpowering their machines, well at least trying to, some to a point where the stiffness of the machine wasn't enough to take the extra cutting forces. Then you had the whole "my rapids are greater than your rapids" posturing. I just had a look around on cnczone and basically went with what the majority were getting good results with.

    The thing is about CNC machine for home use is that they are limitations on material and speeds, you either have to work within those parameters or upgrade. A lot of these machines are used well beyond their original design specs.

    Or you could just replace the whole controller box.
     
  6. dobrodewed

    Thread Starter New Member

    Jan 10, 2017
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    it had 40mm nema 17 on the x and z and 48mm on ltthe y. I replaced the x and z nith 48mm. If it got slightly dirty from cutting it would lose steps, mostly z, then x then y in order of exposure. I couldnt get through one job. The x and z replacement helped alot, but current limit at 1.4 isn't the 2A the motor uses. The driver is a 2.5A , but set by resistor on A3979. I could change the values if I knew what to change to. The y is 840mm with belt on other lead screw. I want 1000mm to allow vertical e milling at the end. With the added length and stiffer c beams I thought a dual drive would work better. I could just add a 4th axis and drive it. 4th and y are set to 1.8A but could use 2A setting as well. I was hoping someone had a schematic and resistor values.
     
  7. dobrodewed

    Thread Starter New Member

    Jan 10, 2017
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    or a way to boost the output externally of the controller pwb.
     
  8. dobrodewed

    Thread Starter New Member

    Jan 10, 2017
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    since the 4th isn't installed I thought I might drive stronger drivers with it for the new y, then move the x to the 1.8A old y wich would solve changing the driver resistor values.
    p.s. I've also ordered a dust collector boot!
     
  9. ClassOfZero

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    Dec 28, 2016
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    The data sheet should have an equation to calculate the resistor value required, then all you wold have to do is identify the resistor on the pcb.

    According to the datasheet pin1 & pin14 are your sense pins.

    Which is RS = 0.5/ITRIPmax

    If you work out the resistor to change I'd make an incremental change and keep an eye temperature, probably not a good idea to go full bore and rupture a smoke valve.

    I am barking up the right tree with this suggestion ?

    The dust boot sounds like a good idea.

    Good luck :)
     
  10. dobrodewed

    Thread Starter New Member

    Jan 10, 2017
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    yes, thanks for the help
     
  11. ClassOfZero

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    Dec 28, 2016
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    No probs mate. Let everyone know how you get along, you never know someone else may be looking to do the same thing in future.
     
  12. DNA Robotics

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    Jun 13, 2014
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    The data sheet says that chip is good for 2.5 Amps. A Google search shows links to tweaking them.

    If you want to use another driver, just intercept the step & direction signals where they go into the A3979 chips.

    A3979 stepper driver.jpg
     
  13. dobrodewed

    Thread Starter New Member

    Jan 10, 2017
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  14. ClassOfZero

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    Dec 28, 2016
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    As long as the torque ratings are greater than what you have you should be good, all you have to do is make a new mounting plate.


    Yes that does seem like a good idea (and the simplest), but I thought of a few things that may add complication. And in the common vernacular "I'm not trying to rain on your parade".

    Since the OP doesn't have access to the original schematics there's no way of telling what other signals the driver board does or does not use and how it would affect operation. I thought about mentioning that option as well and figured it'd require a whole lot of circuit tracing.
     
    Last edited: Jan 11, 2017
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