First Proper CNC Router

[diycnc]

Just wondering is there a reason why we use a MCB before the PSU, but then a fuse before each driver?
Do they not both perform the same job? Why not use the same everywhere?

[AndyUK]

One drive should only ever pull x amps. Multiple drives connected to the same PSU can draw more than x amps quite normally. That's the theory at least - although at this point I think we're trying to stop things going up in smoke rather than protecting the drives themselves.

[diycnc]

Totally understand the need for protection before and after the PSU, just wondering why we don't use MCB on both sides, or fuses on both sides.
I still have a lot to learn about the electrical side of things, so this might be a silly question.

[AndyUK]

Ah yes now your question makes more sense. I'm no expert so I'm sure someone will put us right, but the way I see it is the MCB is placed before the PSU because it's 3-4x (however many drivers you have) more likely to trip, so easy and inexpensive resetting is helpful. It's also very obvious when it's tripped rather than digging out fuses. There's also the chance of inrush to the torroidal tripping it, so again more likely. It's also a convenient way to isolate the PSU. As for the fuses on the drivers, they're cheaper than adding an MCB.

[JAZZCNC]

The main reason is protection.
The MCB protects the transformer in case of a short circuit. You don't actually need an MCB type fuse, any fuse type of correct size will work but due to the nature of Transformer and inrush, etc MCB is just easier to reset when trips.

The fuses for the drives protect each drive in case of short circuit or excess current draw. The transformer can supply many more amps than each drive can handle so if, for instance, motor shorts out the drive will keep dumping current up to it's rated output or until it destroys its self. some drives have built-in current protection but it's not advised to rely just on this, hence why a fuse.
Fitting a fuse same size or just slightly higher than the drives rated load will offer it some protection. In fact, I often fit fuses at a lower rating than the drives max rated current if the motors are not rated at or close to drives Max current.

[diycnc]

Drivers are rated to 7A, and motors just to 4.2A. Probably will be running them at over 3.14A ref I think.
Would a 4A fust be okay?

Currently looking at the industrial DIN rail fuses holders like this one, unless anyone can suggest anything better/cheaper.
https://www.rapidonline.com/mersen-c...holder-26-5786

Also looks like most people are using double pole MCB's on the live and neutral before the PSU. Is this essential? I thought only the live would need one?

[JAZZCNC]

Drivers are rated to 7A, and motors just to 4.2A. Probably will be running them at over 3.14A ref I think.
Would a 4A fust be okay?

5A would work better. Gives some safety to drives but won't trip when motrs are being worked hard.

Currently looking at the industrial DIN rail fuses holders like this one, unless anyone can suggest anything better/cheaper.

These are what I use, cheap and easy to wire and change.

https://www.ebay.co.uk/itm/5X-FS101-...72.m2749.l2649

Also looks like most people are using double pole MCB's on the live and neutral before the PSU. Is this essential? I thought only the live would need one?

No don't need double pole.

I prefer these to Din rail connectors when creating Busbars. Lot cheaper as well.

https://www.ebay.co.uk/itm/Set-6Posi...72.m2749.l2649

[diycnc]

Thank for your help JAZZCNC.

When it comes to settings the driver current, the drivers have peak and REF values labeled on them. Which one should I be concerned with?
I found the same question in routercnc MK3 build thread, but couldn't find an answer.

[JAZZCNC]

Thank for your help JAZZCNC.

When it comes to settings the driver current, the drivers have peak and REF values labeled on them. Which one should I be concerned with?
I found the same question in routercnc MK3 build thread, but couldn't find an answer.

Use Peak values.

[diycnc]

Transformer, fuses, mcb, and terminal block on order. Wish me luck!