4' x 4' x 8" Router Build

[Neale]

1) What are the consequences if I’ve under rated the transformer? The motors will struggle in the situation that they’re all maxed out? How does this actually manifest itself? Motors stall? Feed slows down and start to get rubbing on the cutter?

2) You mentioned checking the motor temperature and adjusting the current - how do you adjust it? Is it a software setting?

3) If I want to add an extra motor sometime in the future (4th axis) I can just add another transformer and wire it in parallel to the first one to give more grunt?

4) The drive accepts AC, I don’t need any kind of smoothing or additional circuitry - just wire direct to the drives from the transformer?

1. With a significant overload, the transformer will overheat leading to breakdown of insulation and/or burnt out winding. However, with short-term overload (say, no more than a few seconds with 2x overload) you will not see any significant effect and the transformer isn't likely to suffer. Output voltage will drop slightly below the nominal value but not enough to worry the stepper drivers. The motors will not notice. And even that level of overload is unlikely. Go 625VA and be safe to add a fourth axis if you like.
2. After my last posting, I went back and looked at your picture of your drivers. I was surprised to see that there was no current control setting. Usually, some of the switches are used for setting maximum current. So maybe these drivers have some kind of software setting, or they are pre-configured for a particular current. Did they come with specific motors? If so, ignore what I said because the manufacturer has already dealt with this one!
3. As per 1 above, if you go for an over-rated transformer you could safely add a fourth axis - just wire it in parallel with the existing drivers. Fourth axis is usually rotary and unlikely to even take as much current as the XYZ motors. Or add another dedicated transformer? Do not wire a second transformer in parallel with the first! Their output voltages unlikely to match closely enough. You do not need any connections between the two transformers. However, I doubt that you would need that anyway.
4. Yes, just connect transformer secondaries directly to the AC in terminals on the driver. If at all possible, you are recommended to wire each driver directly to the transformer, probably via a terminal block of some kind which can take all the wires. Do not daisy-chain more than one driver together (i.e. wires go to first one then continue to the next). Whatever rectification and smoothing is needed by the driver is handled by its internal circuitry.

[m_c]

Just to clarify something on the current requirements, a 5A stepper motor won't draw 5A from the power supply, except in very specific circumstances which are not actually likely to occur.

Say a stepper is rated 5A at 10V while stationary (nice round figures for simplicity, but voltage is likely to be 3-5V for most common steppers), that means at idle, it will consumer 50W (5V x 10A).
If you power that via a 50V transformer, that means at idle the drive is only going to pull 1A (50W/50V). (assuming 100% efficiency - typical efficiencies are going to be in the 90s)

However, once the motor starts spinning, the motor requires more voltage to maintain the rated current due to the generated back emf, so at some point the drive will reach a point where there is not enough voltage for it to maintain the full 5A current, and this is the point where maximum power supply draw will be pulled. As you move above that point, which I'll call the peak power point, current draw will actually decrease.
However (yes another however!), stepper motors are not that efficient, so in practise the current actually drops of before reaching the peak power point, due to that pesky inductance which limits how fast the current can be changed in the coils.

[m_c]

@Neale those drives are software configurable.
I'm not entirely sure why they bother with microswitches for some settings, given other critical settings have to be set in software.

@JonnyFive if you need the software, I've got the install file for V2.1.8, which lists your drives.

[JonnyFive]

@Neale those drives are software configurable.
I'm not entirely sure why they bother with microswitches for some settings, given other critical settings have to be set in software.

@JonnyFive if you need the software, I've got the install file for V2.1.8, which lists your drives.

So there’s an app I need to configure the drivers? I did not know that. Presumably they are set to 6A from the factory, am I likely to need to change it?

[JonnyFive]

Just read the manual for the driver, looks like you need to connect via the comm port to tweak the current. I ain’t gonna do that The manual says the current will be adjusted automatically.

[JonnyFive]

Let’s talk fuses, how does one work out what amperage to use? Just add up all the current draws within the circuit? Add a bit on top for luck?

[JonnyFive]

I've been researching wire sizing for my build and here's what I've come up with:

1) Cable from wall socket to cabinet - 3 core, 2.5mm² flex
2) 240Vac within cabinet - 2.5mm²
3) Earthing - 1.5mm²
4) 24Vdc signals - 0.5mm²
5) Proximity switches - 3 core 0.5mm² CY
6) VFD to spindle - 4 core 1.5mm² CY
7) 55Vac within cabinet - 2.5mm²
8) A+ / A- / B+ / B- - 4 core 1.5mm² CY
9) EGND / VCC+ / EA+ / EA- / EB+ / EA- - 1mm² CY
10) PUl+ / DIR+ - 0.5mm² twisted

How does that all sound?