This is from Joe2014
Using the MX4660 Controller with a VFD
The 6 outputs of the MX4660 are each an optical isolator in series with a 1,000 ohm resistor and this limits how the outputs can be used. If you want to control a device that uses 12 volts, the 1,000 ohm series resistor limits you to a maximum of 12 ma current, probably not enough to do much more than light up an LED. To use the outputs to control the Forward and Reverse signals of a VFD you will need to add some type of driver device, typically a relay with a driver on the coil side since the 12 ma output is not enough to reliably control even a small relay.
I used a simple relay driver board similar to
New 4 Channel 5V Relay Module Board Shield for Pic AVR DSP Arm MCU Arduino H | eBay . These are quite small and inexpensive, under $3.00 for a quad relay board and the 4 relays not only let you control a VFD using 2 of the relay circuits but you will also have an additional 2 circuits to control a mist pump, dust extractor or spindle cooling system. The relay board also provides isolation protection for the MX controller which is important since you don’t want to destroy such an expensive device. You could also go with just a similar 2 relay board if all you want to do is control the VFD.
Attachment 307848