Comments sought on new build: A CNC Router for RC Gliders and Planes

[routercnc]

Hi Neil,

Ok, thanks. Then I'll stay with my original plan which is 6A MCB type D on AC side of PSU, and automotive blade fuses on the 70V DC side. I plan to fit a trial 1A fuse on the DC then jog an axis to deliberately blow the fuse. Then I can make sure that it blows cleanly and there is no residual arcing from the 70V. I'll then fit the intended rating. I think Eddy and Irving both went this way.

But the DIN mounted fuse probably is the way to go for how your machine will be used industrially. Do you know if the 5x20mm fuses need to be specific for DC? This was where I got stuck with this option because reading around AC and DC currents seem to require a different type of fuse and so I went back to the automotive type which are definitely for DC. I wondered if that was why the fuse wire was such a curly shape on the DC blade fuse instead of the straight wires in the AC ones, to make sure there was a clean burn/break rather than continual heating, expansion, and arcing.

I'm not coming from a strong electronic knowledge-base so the above are just my views / thoughts.

As for the rest of your build looking very professional now, well done.

[Jonathan]

Ok, thanks. Then I'll stay with my original plan which is 6A MCB type D on AC side of PSU, and automotive blade fuses on the 70V DC side. I plan to fit a trial 1A fuse on the DC then jog an axis to deliberately blow the fuse.

Interrupting the supply to a stepper motor driver (or many drivers for that matter) whilst running can damage them, so I wouldn't recommend that test.

Do you know if the 5x20mm fuses need to be specific for DC? This was where I got stuck with this option because reading around AC and DC currents seem to require a different type of fuse and so I went back to the automotive type which are definitely for DC.

I read somewhere that if the DC rating isn't specified for an AC fuse, you can use it with DC but only at half the AC voltage rating. Don't quote me on that though...
I would trust the 5x20mm fuse more than the blade fuses - running a 240V AC fuse at 70V DC seems more reasonable than using a 12V DC fuse at 70V DC.

[routercnc]

Interrupting the supply to a stepper motor driver (or many drivers for that matter) whilst running can damage them, so I wouldn't recommend that test..

OK good point, but out of interest is that any different to an e-stop? My latest control box (when finished!) will cut power to the drivers via a relay which seemed to be a common approach.