G540 Spindle Speed Issue

I am building a CNC rounter (it's the GRUNBLAU Platform CNC) I'm using a Huanyang VFD and the typical Chinese 2.2 Kw water cooled spindle. The system uses a Gecko G540 controller which I am connecting to a Windows 10 PC running Mach 4 with a PMDX-411 Smart BOB-USB w/ DB-25 connector.

I successfully hooked everything up and got it to work through Mach 4 to turn on the spindle and to control the speed. Or so I thought. I hadn’t attached the spindle to the machine yet. While I was hooking it up and configuring everything I just had the spindle laying on the table not connected to the machine. Today I finished the machining I needed to do to my spindle mount to get it on the machine and when I mounted the spindle to the machine is when the issue showed up. When I turned everything on and started the spindle up to 24,000 rpm through Mach 4, it would only reach 12,000 rpm. The VFD output was peaking at just over 200 Hz.

I spent the next 2 hours troubleshooting and found that when I removed the spindle from it’s mounting bracket and laid it on the table it would spin up to the full 24,000 rpm/400 Hz. If I took a section of wire and touched one end to the spindle housing and the other end to the machine mount the spindle would immediately drop back to 12,000 rpm/200 Hz.

I took a meter reading of the V1 input from the Gecko to the VFC and the voltage is at 9.8 volt or so when the wire isn’t connected and drops to about 5 volts when it is. It appears there is something that is causing a 5 volt loss in this signal when it is connected.

So my question is; has anyone seen had this happen to them? Or, do any of you know what might be causing this and a possible solution?

I have also disconnected the Gecko board from the VFD and hooked up an independent power supply to the V1 and AMC terminals. When I control the speed with that power supply the issue of contact with the spindle mount dropping the speed goes away.

Any assistance would be greatly appreciated! If you need more information please let me know.

Thanks in advance for anyone’s time

did you ever get this sorted out?

I'm setting up my first CNC and seeing a pretty similar behavior. I've worked around it by setting my VFD min and max to full speed so it essentially ignores the voltage speed input, but I want to figure out why it's happening and get it to work correctly.