PWM Output Voltage Drops from 100%

[JohnT1]

I am using Mach3 to control one of those cheap 500W Chinese spindles via a uc-100 and Gecko 540.

With the spindle disabled at the VFD I am getting 0 to 10 volts at pin 8, proportional to the spindle speed percentage as set in Mach3. Just like you would expect.

If the spindle is then enabled at the VFD, the output voltage drops to about 5.8 volts on pin 8, and the spindle runs at only about 70% speed even though Mach3 is set to 100%.

Now for really strange part.......

If I just take the tip of a screwdriver and just touch pin 7 on the Gecko, the voltage jumps up to 10v and the spindle speeds up to 100%. If i then stop touching pin 7 the voltage drops to about 9 volts.
Similarly, If I touch pin 8 with the screwdriver, the voltage drops to about 2 volts, and returns to about 5.8 when I stop touching it.

The spindle works fine when controlled locally at the VFD over it's entire speed range, so motor loading doesn't seem to be the problem. I have also verified that all connections are tight and the local speed control pot on the VFD is disconnected when hooked up the Gecko. Changing the settings on the Spindle Pulley in Mach3 makes no difference.

I sure would appreciate any suggestions relative to the source of the problem and the means to fix it!
Thanks In Advance for any help!

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[mactec54]

I am using Mach3 to control one of those cheap 500W Chinese spindles via a uc-100 and Gecko 540.

With the spindle disabled at the VFD I am getting 0 to 10 volts at pin 8, proportional to the spindle speed percentage as set in Mach3. Just like you would expect.

If the spindle is then enabled at the VFD, the output voltage drops to about 5.8 volts on pin 8, and the spindle runs at only about 70% speed even though Mach3 is set to 100%.

Now for really strange part.......

If I just take the tip of a screwdriver and just touch pin 7 on the Gecko, the voltage jumps up to 10v and the spindle speeds up to 100%. If i then stop touching pin 7 the voltage drops to about 9 volts.
Similarly, If I touch pin 8 with the screwdriver, the voltage drops to about 2 volts, and returns to about 5.8 when I stop touching it.

The spindle works fine when controlled locally at the VFD over it's entire speed range, so motor loading doesn't seem to be the problem. I have also verified that all connections are tight and the local speed control pot on the VFD is disconnected when hooked up the Gecko. Changing the settings on the Spindle Pulley in Mach3 makes no difference.

I sure would appreciate any suggestions relative to the source of the problem and the means to fix it!
Thanks In Advance for any help!

If your spindle only has 2 wires like in the snip then you don't have a VFD Drive, your spindle is a DC motor and driven by a DC drive

It sounds like you have a Ground problem as pin 7 on the G540 is GND

Your PWM or 0-10v has to connect through where the pot is wired the other connection is just the On/Off

[ericvic]

Sounds like noise. I am having a very similar issue but with a different controller (Pokeys57CNC). With the spindle not running I can vary the speed in Mach3 and see the frequency on the VFD change and go all the way to 300 (Max for my spindle). But if I start the spindle the frequency drops to about 270 and if I measure the voltage it is somewhere around 8v. Ordering an EMI filter and some ferrite cores to see if that fixes my issue.

[mactec54]

Sounds like noise. I am having a very similar issue but with a different controller (Pokeys57CNC). With the spindle not running I can vary the speed in Mach3 and see the frequency on the VFD change and go all the way to 300 (Max for my spindle). But if I start the spindle the frequency drops to about 270 and if I measure the voltage it is somewhere around 8v. Ordering an EMI filter and some ferrite cores to see if that fixes my issue.

He does not have a VFD Drive, this is a totally different setup than yours, if you have a VFD Drive

Correct Grounding and Shielded cable termination in your case has to be correct if you have a noise problem

[ericvic]

He does not have a VFD Drive, this is a totally different setup than yours, if you have a VFD Drive

Correct Grounding and Shielded cable termination in your case has to be correct if you have a noise problem

He stated

With the spindle disabled at the VFD

so how is that not a VFD drive?

[mactec54]

He stated so how is that not a VFD drive?

Because he is confused as to what he has, he does not have a VFD Drive

[CitizenOfDreams]

Your problem is not noise. Your problem is that the junky DC motor controller (I had one of those in the past) is not properly isolated from the AC mains. That's why everything changes when you touch the pin with a screwdriver. It is a very good way to blow up your Gecko, UC100 or the PC if you are unlucky.