G540 and switching power supplies

[TheGremlin]

I have a quick question on the G540 and switching power supplies. In particular the Meanwell se-600-48 power supply. The se-600 is based off isolation and according to their schematics the -48v dc (common) shouldn't be tied to earth ground. Now it appears the G540 bonds the common to ground internally as it needs to for compatibility with shielded cables.

I also have a bunch of other stuff in my control box (don't we all) but I'll keep this simple. Should I be bonding the common to ground strait out of the psu or should I be looking for a non regulated powersupply or just leave it?

Link to meanwell psu specs (block diagram is on page 2): Meanwell Power Supply Products

[morestuff]

The Meanwell diagram shows that this power supply does not internally connect the negative side of the 48 volt output directly to earth ground, but this does not indicate that you may not do so externally. Indeed, this is a common practice.

Switching power supplies vary in how well they will work when powering motors. I do not know the reputation of the Meanwell units when powering a G540. Perhaps others can comment. There are two main areas of concern.

1) Power up current surge. The switcher will likely have an over-current shutdown circuit. If the stepper driver, or other load, has a significant amount of capacitance across the input voltage, the surge of current to charge this capacitance will cause current in excess of the supply rating to flow. Some switchers will tolerate a momentary current surge, others will shut down and require a power off-on cycle to come back on line. You should not try to put a power switch between the output of the power supply and the input to the motor drivers. It is better to switch the mains power into the switcher because this allows the voltage that must charge the capacitance to rise more slowly, thus causing smaller current surges.

2) Over voltage protection. Most switchers include over voltage protection on their outputs. If the load (stepper driver and motors) should need to return current into the power supply, the output voltage can rise and trigger a shutdown. Usually the supply is running multiple motors and the current returned by one motor can be consumed by one of the other motors and nothing bad happens. If several motors need to return power at the same time, the current must go into the power supply and will cause problems. This is more of an issue for servo systems than it is for stepper systems. Adding a large capacitor externally can help temporarily store the returned current without raising the voltage excessively, but will likely trigger problem #1 above.

Regards,
Steve Stallings
PMDX.COM - Products for CNC and motion control applications

[TheGremlin]

The machine has bee running for some time now with little issue. What triggered this is the recent planned addition of a superpidv2 speed controller. I noticed in their instructions that pin 12 on the G540 goes to ground while in the Gecko instructions they go to -VDC. This didn't correlate with the PSU that says it is isolation based.

Talking to a colleague at work he said the isolation is used so you can wire multiple PSU's in series to bump the voltage. In my application I should be connecting the -VDC to my earth ground. I also received a lecture about how "ground" in this case should be called a common and any -VDC should be bonded to it .