G540 VFD output floating ?
Just a quick question about hooking up a G540 to a harbor-freight mill that has been CNC'ed.
On the geko there is
pos 7 -X- VFD Ground
pos 8 -X- VFD Output
pos 9 -X- VFD +10v
Inside the spindle on the mill there is a DC motor controler it connects to the existing controls that are just a variable resistor to set speed they are
Red Wire -X- Vin sets speed [more volts the faster it turns]
White wire -X- +10V
Black wire -X- Gnd
The catch is on the mill Gnd is about 50V above Ground everywhere else so measuring from black wire to Ground gives me about 50V and red gives about 60V. This seams to be common on DC motor controlers with a resistor for current scene.
In the papers for the geko it calls the VFD output a opto-isolated output is this just from the computer or is it from the rest of the geko. I'm hoping its from the rest of the geko then floating it at 50v will be no problem if it is just from the computer then I need a analogue opto-isloator.
Thanks Tesla^3
ps Thanks to geko for a Excellent little stepper driver my mill is running about 3x faster then my previous home brewed steprep drives
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Many simple SCR (across the line) DC controllers do not have isolation from the input supply when feeding the internal control logic.
This is fine when the speed is controlled from a self contained pot.
If interfacing with a source that provides analogue control then isolation is needed.
The rest of the machine and motor frame etc, should be at earth ground potential.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
That makes since. The drive for the spindle is in a plastic box inside the head of the mill (seemed like they worked to make sure it wasn't at ground potential) the mill its self is grounded tho. I am hoping that the necessary isolator is in the g540 already. Some people talked about using the vfd out to run a DC drive off a treadmill but didn't tell much more than that. That gave me the idea that maby it could work with it directly if the gecko is already isolated on those 3 points. They seem to have included everything else needed for a small mill except maby a kitchen sink. A quick test with a ohm meter shows ether those 3 are isolated from the rest or the resistance is higher than my meter can read, all other pins on it show a pull up or down internal connection.
Thanks Tesla^3
The analog output is optically isolated from both the G540 and the PC.
Mariss
Thanks Cool
It will work just fine floating then.
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