First Proper CNC Router

**diycnc** · 05-11-2019

Just been watching some of Joe Harris videos, and have had discovered the world of DIN rail connectors!
I finally understand what the rows and rows of plastic blocks are in everyone's control boxes now.

**JAZZCNC** · 05-11-2019

Originally Posted by diycnc

Thanks for the MCB advice. Will try 6A type D to start with.

Nearly always needs a 10A

Originally Posted by diycnc

What's the recommended connectors for the high voltage wires from the PSU to the drivers?

Directly wire from the transformer output to Fuses then to drives. Fewer connections the better. Every connection or connector is a potential problem area so fewer the better.

**routercnc** · 05-11-2019

I guess you are referring to the fact that the psu will have a single positive cable and single negative cable output, and you need to connect these to 3 or more drivers.

Daisy chaining the drivers power input is not advised, so separate runs should be used.

Maybe Jazz has a neater solution but most people use a distribution block to connect each power output to multiple outputs, often mounted on the psu board.

**JAZZCNC** · 06-11-2019

Originally Posted by routercnc

Maybe Jazz has a neater solution but most people use a distribution block to connect each power output to multiple outputs, often mounted on the psu board.

Every connection is a potential problem down the road so if you can limit connections you eliminate potential problems. So why have connection blocks on the PSU when you can remove those connections by wiring directly to fuses.? Put the fuses on or close to PSU.

Also, note that when using AC drives your only using a Transformer so often there's no PSU board involved because you don't need Caps or Bridge.

**diycnc** · 06-11-2019

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** · 06-11-2019

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** · 06-11-2019

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** · 06-11-2019

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** · 06-11-2019

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** · 08-11-2019

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?