AXBB power supply question

[ger21]

It really depends on the power supply.

[GaryLa]

If you use switching power supply, on the output there is earth, V-, and V+. So it is not common ground.

The -V is the DC 'ground' in this example. The earth ground is for the AC input -- to handle faults only.

Are the 5v and 24v grounds not common grounded anyway due to them both being on the 240v ground circuit , or are power supplies normally isolated between the dc and ac ground ?

The ground on the AC is called 'earth' or 'safety' ground. AC supplies don't use ground in normal operation, it's there for faults.

That 'ground' has nothing to do with the ground on a DC ciruit. Often referred to as -V or GND instead of as 'ground'. The switcher produces its own 'ground'. Wall-Wart power supplies produce their own, too. They are isolated via a transformer which is also used to step down the AC.

You must tie the DC circuit GNDs together. For example if you connect a UC100 to an Arduino, their GNDs must be tied together. Otherwise, each PCB has a different opinion of what +5 looks like. The GND is the baseline, or reference.

A good example from the past is the old LPT printer cable. The printer had to connect its GND to the PC's GND. Otherwise, it would not have been able to recognize the +5 (high) and +0 (low) coming from the parallel port. It would've had no reference to compare them with.

[ger21]

You must tie the DC circuit GNDs together.

No, with the AXBB-E, if you tie the two DC grounds (-5 &-24), you lose the isolation. They need to remain isolated.

[GaryLa]

I don't what an AXBB-E is, but if it's using opto-isolators then you're right. It powers its side, and the other PCB powers its side (roughly speaking).

I was addressing the power-supply misstatements that the 5v and 24v might be tied to the earth ground of the AC side.

[ger21]

The AXBB-E is CNC Drives newest controller. http://www.cncdrive.com/AXBB.html

[asuratman]

Another question in the AXBB-E manual drawing about relay (SSR), on isolated output. To trigger DC PS for driver, It uses relay wired from O1 to (-)and 24 VDC to (+), it is a must ? Do we have to config the program CNCDrive or it just automatically ON on every start ? How about if we do not use the relay ?
Sorry, I do not make a new thread.

[ger21]

Another question in the AXBB-E manual drawing about relay (SSR), on isolated output. To trigger DC PS for driver, It uses relay wired from O1 to (-)and 24 VDC to (+), it is a must ?

No, it's just an example of how to wire a relay. You don't have to use one.