View Full Version : CNC newbie electronics query II

09-07-2014, 01:03 AM
Hi, I need some final advice on wire choice for my CNC electronics. Ive had great advice on previous post.

Firstly, the power supply Im using is a PS408-12 type (http://www.leadshine.com/productdetail.aspx?type=products&category=power-supplies&producttype=linear&series=PS&model=PS408-12)
What would be the recommended fuse to use on the power plug, and is this based on the power supply output which is 36V/8A?

Secondly, for my connection between PSU and driver, i want to buy this wire of ebay due to cost.(http://www.ebay.co.uk/itm/FLAT-TWIN-AUTO-CABLE-2-CORE-THINWALL-CAR-VAN-MARINE-CAMPERVAN-WIRE-UPTO-50M-/251433953875?pt=UK_BOI_Electrical_Components_Suppl ies_ET&var=&hash=item3a8aa1aa53).
Is this OK to buy the 11A wire, considering the current and voltage output from PSU being 36V/8A?

Thirdly, what wire can i use between BOB and driver for signal, Im not considering CAT 5 cable just yet and only want minimal for playing with my CNC electronics at moment. Any recommendation of ebay? :eagerness:

Thanks in advance

09-07-2014, 10:07 AM
Oh dear, you have a lot to learn. Current is like water flowing in a pipe. If the pipe's too small it'll burst (get hot), but it doesn't matter if the pipe's too big. Voltage is like pressure making the water flow. A smaller pipe won't burst but the pressure is reduced (voltage drop) so indeed the bigger the better within reason, as the voltage drop is less. So 0.5mm wire rated at 11A is OK. For BOB to driver you need, ideally, 3 core screened (STEP/DIR/GND+Screen), but you can use the same 4-core CY cable as the driver to stepper, just don't use one of the cores.

A 5A fuse should be sufficient but its not critical, a 13A is OK.

09-07-2014, 10:51 AM
For BOB-> drivers, I would suggest a short length of 4-core screened from Maplin as the quick option. I doubt if you will need enough to bother with eBay. Just ignore one core as Irving suggests with CY. The thinner stuff is a bit easier to use as it's more flexible in tight spaces but electrically there's no real difference in this application. The screening might not be quite so effective as a better quality cable but for these short lengths I wouldn't worry too much. However, it is also a bit more fragile so for the finished item, either make sure that it is well-secured to avoid any fracturing, or just use CY.

Lots of misunderstanding around about mains fuses. They are there to stop the mains cable bursting into flames in the event of an equipment failure, primarily. They need to be big enough to take the load (but so should the mains cable) but otherwise as low as reasonable to provide more protection. I would use a 3A fuse here as it's a standard value but 2A or 5A would be fine, if you can find them, and assuming you are using any reasonable mains lead.

Lee Roberts
09-07-2014, 09:44 PM
If you've got a spare USB cable cut the ends off and use that, you could also use screened alarm cable.

How much do you need as I've got 10 rolls of 4 core and 8 core sat in the shed not doing anything?


09-07-2014, 10:33 PM
Thanks lee. Ive ordered some 4 core already:upset:. But the usb cable is something ill definitely consider. cheers