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Author Topic: Spindle speed control  (Read 8421 times)

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Re: Spindle speed control
« Reply #10 on: January 16, 2006, 09:55:55 AM »
Vmax - Try measuring the voltages at the speed control pot relative to the AC line neutral. While the control is indeed using low DC control voltages, the entire drive electronics, including those DC voltages is floating at the AC line voltage. You can not connect those control voltages anywhere without isolation and indeed you can be electrocuted working on the "low voltage" control signals if you are not careful.

Remember, everything is relative, and even though the leads on the speed pot only show low DC voltages relative to each other, this does not mean that they do not have a different voltage realtive to something else like ground.

Pete C.


Re: Spindle speed control
« Reply #11 on: January 16, 2006, 10:30:16 PM »
I am well aware of floated voltages I retired out of the power industry we worked from 24vdc to well over 500kv. I don't see from looking at the board schematic how you can have that voltage level present at the pot hookup. I double checked the readings from the pot leads to GRND, AC neutral, dc common. Both Aver and RMS. Where exactly is the voltage sourced from that could be present. I do not see it nor can I measure it. Both leads are hooked to a computer mother board and I do not see any means that the manf has isolated it.???? Help me to understand the problem. Now of course if a component failure occured anything is possible. Same is true with any ac/dc conversion where you do not have an isolation transformer to step the needed voltage down before it is rectified.( even then you could have a shorted transformer H-L that is where the chassis grnd comes into play. Not failsafe for sure but if properly connected it is a good safety net. (;~)= Terry


Re: Spindle speed control
« Reply #12 on: January 17, 2006, 12:17:57 PM »
Ok lets see if I have this figured out. The Speed control board if completely floated from any reference could be energized at full potential? That "is" a scary thought. I guess I cannot see it here because the board and components are all bonded and cannot float from the reference neutral or common. Definantly something to keep in mind. We always lived by the Checkit before you touch it and groundit or gloveit. Except for those that did barehand work.( Energize yourself to the same potential 500KV and isolate yourself from any reference.) those were the Brave(nutty)ones.

(;~)= Terry
Re: Spindle speed control
« Reply #13 on: January 18, 2006, 07:14:33 PM »

Just found this thread. :) The speed control potentiometers on these controllers are fed by a DC voltage of approx 14Vdc, derived from a zener diode style regulator.

The positive side of this voltage  (P3) basically sit at mains potential. The 0V for the potentiometer sits at mains potential minus 14V. The KBiC controller speed trimpot just sits in series with the manual speed potentiometer to reduce the maximum speed.

As the voltages are around mains potential, you need to have isolation from any control voltage being generated from Mach2/3. This is where the DigiSpeed comes in. http://www.homanndesigns.com/DigiSpeedDeal.html It isolates the PC control voltage from the mains referenced control voltage in the KBIC controller.


Homann Designs
email: peter at homanndesigns.com