Conect 121 CNC Lathe Project

[JohnHaine]

That's presumably for the spindle motor? Important to check if the pot is isolated from the mains to determine how to control from Mach.

[mtrehy]

That's presumably for the spindle motor? Important to check if the pot is isolated from the mains to determine how to control from Mach.

Thanks John, how would I determine that?

[JohnHaine]

Well I would normally say, look at the documentation! But there probably isn't any.

A lot of lower-end motor controllers, especially ones using Triacs, do not have an isolating transformer so that, though the control electronics may be working at "safe" voltages like 12v the actual common side (-ve supply) can be floating at half mains voltage. I have a KBE speed control on my Novamill where this is the case. If you then try to connect the control voltage input and Gnd connection to your properly grounded BoB and motion controller the ground connection puts a dead short across the internal rectifier which blows up - worse it may take the other electronics with it. There are ways to isolate the control electronics using opto couplers so it is operating safely with a proper ground connection. I see that the description includes the cryptic phrase "4, high and low voltage signal is completely isolated, the use of safer" - which is hopeful.

To check, you need an AC voltmeter such as a digital multimeter capable of measuring mains voltage. Have the unit wired up (including to mains earth) and running the motor. Set the meter to its max AC volts range, and using INSULATED probes measure the voltage on each of the 3 terminals connected to the pot - if they are all at or around zero volts it should be OK. And, before doing this test, set the meter to measure ohms and check that the black wire has continuity to mains ground (unit switched off of course).

[mtrehy]

Hi John,

So I checked all that and all seems t check out ok so pretty confident it's isolated.

I have a attached an image of the terminals on the motor controller.

The board I have is a cheap USB board

https://buildyourcnc.com/item/electr...ach3-USB-Board

I'm not at all sure of how the board will connect to the spindle controller. In the description of the spindle controller it states:

7. the given signal mode (V / mA): the default potentiometer, 0-5V, 0-10V, 4-20mA, PWM, button type




Be very grateful for any ideas!

Cheers

[JohnHaine]

Sorry for slow reply. This came up in another thread either here or in the Mach support forum and I posted some info gleaned from data sheets & manuals. Some searching should turn it up.