Inverting 5V out of control box for P.P. PWM

Discussion in 'The Projects Forum' started by Fleck, Oct 30, 2013.

  1. Fleck

    Thread Starter New Member

    Oct 29, 2013
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    I am new to this forum and getting this in depth with the electronic side of things.
    I run a Flashcut CNC control box with PWM out to a Digispeed polarity protected/isolated speed controller to a KBIC manual motor controller.
    Presently I have to set my RPM 2800-0 as opposed to 0-2800 as I only have isolated +5V and common ground out from CNC box, no hi low choices in software.
    This is causing the spindle to start 100% when I power up if I forget to switch to manual and off at power down the day before, potential safety issue.

    Wondering if with only the isolated +5V PWM and common ground out there is a way to reverse the polarity of +5V PWM signal?
    Thank you for your time,
    Mike
     
  2. wayneh

    Expert

    Sep 9, 2010
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    You've lost me. PWM works by varying the duty cycle, not the polarity. So for instance you have 0% (always 0V), 50% (half the cycle at 0V, half at +5V) and 100% (always +5V).

    If you leave your device set high, and this is a problem when you come back later and forget it was set high, then nothing you do with the controller will mitigate your bad memory. You need some sort of auto-reset to slow.
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I "think" he means that currently when PWM is 100% its 0 RPM and when 0% PWM its 2800 RPM and he wants to invert that so that when PWM is 100% its 2800 RPM and when 0% PWM its 0 RPM.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Normally the KBIC min-max rpm is 0-10vdc If you are not obtaining the 12v for the isolated analogue from the KBIC and are only using two control wires to the KBIC then I suspect you have the two connected from slider to +10v instead of the slider and 0v.
    BTW you can obtain the 12v from the KBIC if you need to, to feed the isolated analogue output.
    This will give you the effect you are seeing.
    Max.
     
  5. Fleck

    Thread Starter New Member

    Oct 29, 2013
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    Yes, I described incorrectly. It is 2800 RPM @ 0%0V now. I would like to change the PWM voltage to travel from 0V to -5V as Digispeed was designed. 0RPM @ 0%0V 2800 RPM @ 100% -5V.
    Thanks
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Still not with you?
    The KBIC takes 0-10vdc normally.
    I will have to pull the manual on the Digispeed as normally the analogue output is for standard controllers which are 0 to +10vdc, not -5v?
    Looks like you have the wrong model, there are other models that are 0-10+v.
    Max.
     
  7. Fleck

    Thread Starter New Member

    Oct 29, 2013
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    I do have the option of a 0-10V analog out on box. The DigiSpeed DC04 supports (PWM) 0V,5V pulsing and Synchronous Serial command interface. Not sure if the latter of the two is an analog type control. I purchased the Digispeed interface because it was my understanding that the KBIC needed a isolated signal to avoid damaging my machine controller.

    Thanks for the information
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The way I read the DC04 it outputs 0 to-5v, I haven't come across that method before, but if your KBIC is standard, the control is 0 to 10+.
    Many of these PWM to Analogue convertors, often obtain the +12v from the drive in question, many times it is a VFD.
    If the +12 or +10v is not available, it is customary to supply a separate isolated supply.
    You could invert this signal somehow I guess?
    Max.
     
  9. wayneh

    Expert

    Sep 9, 2010
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    I'm glad the folks with the know-how have shown up to help you and maybe it's obvious to all of you, but how do the electrical details address this safety concern?
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I find the manuals very poor, one sentence it mentions the DC04 being suitable for the average VFD etc, but don't go into details?
    You need to chose the PWM to 0-10v if it is an option.
    This way you should have the right control.
    In the case of the KB I can direct you to the 12VDC output, it requires unscrewing the board and soldering a couple of wires, or you can supply a separate 12v supply.
    BTW, you should be using the I1 & I2 for stop start, this way you can restart where your previous setting was in necessary and the drive will go through the acceleration process.
    Max.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    We do not know at this point what/how is the system controller.
    If wired correctly, it is normal for a controller such as Mach or any other similar system to cancel all spindle outputs at power off or reset, therefore if the unit is connected the way it was intended, when re-powering up of the system or restarting, all motion will also require restarting through the operator.
    Max.
     
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  12. Fleck

    Thread Starter New Member

    Oct 29, 2013
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    Not to be misunderstood, the way that I have wired the control box to the Digispeed is the reason why the spindle is starting when the control box is powered up (if the software is not running). Digispeed and Flashcut controller are two unrelated products not designed together. I believe the DigiSpeed was designed with Mach in mind. I will hook my old spindle relay back up in tandem with Digispeed invert its polarity and solve the potential spindle starting issue, but I am still wondering about inverting a 5volt PWM signal and if it is possible. Thank you for being so generous with your information.
     
    Last edited: Oct 31, 2013
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