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| | |-+  Pokeys57cnc 10v spindle control only reaches 8.1v
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Author Topic: Pokeys57cnc 10v spindle control only reaches 8.1v  (Read 3715 times)
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NeoTO
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« Reply #10 on: May 20, 2017, 12:43:18 AM »

The adjustment pot is really small and relatively stiff. Are you sure that you indeed rotated it? Observe the flat region on one side of the pot head.
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www.poscope.com home of PoKeys USB HID, IO, USB, Ethernet controler and PoScope USB PC oscilloscope
cncprint.blogspot.com
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« Reply #11 on: May 25, 2017, 10:21:48 AM »

I'am sure that i can turn the pot without any problems. I've bought a special small screwdriver for it. In Mach3 it works without any problems.
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garyhlucas
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« Reply #12 on: May 25, 2017, 06:45:03 PM »

Simple test. With the vfd disconnected put a 20K resistor across the pokeys output and vary the input across the range of speeds. If you see the voltage drop off same as for VFD then you will be sure the problem is a combination of low output current from pokeys combined with low input impedence of the VFD.  Back before you youngins were playing with this kind of stuff we had to resort to vacuum tube voltmeters so the meter itself wouldn't pull the voltage down!
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Peter Knell
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« Reply #13 on: January 25, 2018, 06:18:57 PM »

Cncprint did you fix this in the end? I am having a similar problem. Works perfect when not connected to VFD (even with 15k ohm across it.) As soon as its connected to VFD voltage drops. The max voltage i can get is 2.8 even trimmed with POT. This is Pokeys57cnc
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garyhlucas
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« Reply #14 on: January 25, 2018, 06:35:37 PM »

The pokeys output current is too low to drive the input impedance of the VFD. So you will need an amplifier circuit that can provide more drive current than the Pokeys. I know the why, but I am not not an electronics guy to suggest a circuit.
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Peter Knell
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« Reply #15 on: January 25, 2018, 06:48:02 PM »

The measured impedance of the VFD input which is the same on most VFDs is 19.8kOhm. If you do the math the input pulls almost nothing. Also with the wires disconnected from the VFD and 1kohm load between the wires the voltage does not drop.
Im stumped on this one.
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Peter Knell
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« Reply #16 on: January 25, 2018, 10:55:55 PM »

THANK THE F@#KING LORD!!
I have figured it out!
I figured it must be high frequency noise coming out of the VFD but dont have an osiliscope so i wrapped both the 0v line and the 10v line around some ferrite chokes as many times as i could and boom off she went perfect speeds and perfect voltages.
Photo for others struggling with this. Only took me about a solid week to find it dam it!


* IMG_20180126_164616-1728x2304.jpg (658.95 KB, 1728x2304 - viewed 49 times.)
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TOTALLYRC
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« Reply #17 on: January 26, 2018, 06:21:50 AM »

Nice work Peter.
Thanks for posting so that someone else can benefit from it.

Mike
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We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.
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