Inverter Output to Spindle Questions

[Tioga]

I had the opportunity to help diagnosis a dead spindle problem on my Laguna. Whilst doing this I measured 130 volts AC to ground at each of the three leads that feed the spindle. The voltage between any two of them was 0. At the time of measurement the spindle should not have been spinning (no program being run). So here's my question - what does the inverter do to to control the speed of the spindle ? Does it change frequency or voltage or something else ?

BTW I'm new to the CNC world.

Tom

[rtibbs]

The output to the spindle is 3-phase 0-400Hz. The RPM is controlled by varing the frequency.
I’m sure one of our EE types out there can give a better explanation however, that’s my take

[wmgeorge]

Three phase out of an Inverter should read Nothing to ground, phase to phase while its running you will get varying voltage and Hz (cycles for us old timers). Having said that you could be getting some stray leakage and its very easy to see that with the good DVM used today. What is important is if its working ok or not?

You do have your control box and power wiring properly grounded, correct? Otherwise your going to have stray voltage and other issues.

[Mobius]

Three phase out of an Inverter should read Nothing to ground

Why would you get nothing to ground? Voltage is potential energy. If there is electrical energy present at the terminals, then you should have a reading based on the potential energy at the terminals vs. 0 potential (ground)?

[Tioga]

So I did some research (talked to a tech). My master power on/off is mis-wired. One of the line-in wires by passes the switch, hence there's one live line feeding the inverter. Then speculation has it that with just one line hot, the act of putting putting the volt meter leads on ground and any one of the inverter outputs causes a small current sufficient to have the inverter generate voltage.

This is now mute as I have rewired the switch to interrupt both line-ins.

Thanks for the input.

Tom

[wmgeorge]

Three phase out of an Inverter should read Nothing to ground

Why would you get nothing to ground? Voltage is potential energy. If there is electrical energy present at the terminals, then you should have a reading based on the potential energy at the terminals vs. 0 potential (ground)?

Depending on if the power source has a grounded secondary. Not all three phase or single phase transformers have a secondary leg grounded if it did, that leg becomes the neutral or grounded conductor. Not to be confused with grounding conductor used as an equipment or system ground. However the new DVM are so sensitive they can pick up stray voltage or phantom voltage on just about anything. This is based on over 60 years in the electrical field most of which was industrial or commercial.