# Need some help for the cables.

Posted by BoByS
 Need some help for the cables. March 16, 2014 05:37AM Registered: 8 years ago Posts: 38
Dear friends!
It's Bobby here. I'm living in Bulgaria and I'm a mechanical engineer (bach and master degrees in Automation and Robotics) and now I'm studying PhD degree in Machine Elements.
I'm building my first printer now. I was looking for a good platform for me for about 6 months (yeah, I know it's a loooot time) and chose the Prusa i3 3D printer. I modified it a little bit and start building it. I have all of the parts, with a laser cut frame (b=10mm).
So, in short, I'm a mechanical guy, not an electrician.
I need some help with the cables from my power supply to the RAMPS 1.4 board. I bought 12V, 360W DC power supply on a sale in a local electronics shop. I know, that from the socket (~220V) I need to put 1.5mm^2 cables to the power supply (Yeah, I have a good jack from an ATX power supply). But from the output of the power supply, cables with which diameter I need to put? Based on the formula, I think that 4mm^2 will be good enought, but I still need a help..
I've made a quick and ugly diagram. Please, excuse me for it! In short:
1) 1.5 mm^2 - for the LNG cables;
2) ??? - for the yellow and black cables;
3) ??? - for the heated bed's D08 purple cables.

Sorry about the metric units, too, but I'm really poor in AWG conversation.
Best regards,
Bobby

P.S. Sorry about my lame questions, but these 30Amps really confuse me. The RAMPS board have only 11 and 5 Amps sockets...

Edited 1 time(s). Last edit at 03/16/2014 05:44AM by BoByS.
 Re: Need some help for the cables. March 17, 2014 04:59PM Registered: 8 years ago Posts: 869
Quote
BoByS
Based on the formula, I think that 4mm^2 will be good enought, but I still need a help..
RAMPS has 5 and 11amp fuses for the main electronics and heated bed respectively. 11 amps chassis wiring is a 20 AWG cable or approximately .5mm^2 for you metric loving builders. That's the bare minimum and doesn't give you any safety margin. Anything 1.5-4mm^2 will be fine with the larger the better up to what will fit in the connector.

Quote
BoByS
1) 1.5 mm^2 - for the LNG cables;
2) ??? - for the yellow and black cables;
3) ??? - for the heated bed's D08 purple cables.
1. Pretty much any old extension cord will work. An old computer cable is fine with the connector cut off. 360 watts / 220 volts = 1.46 amps. Even if your power supply has awful efficiency converting AC to DC, you're still only drawing a couple of amps.
2. The yellow and black cables between the power supply and the RAMPS are mentioned above. They carry 12v but higher amps, up to 11amps (or possibly more if your heated bed is out of usual spec. The 1.5-4mm^2 mentioned above applies here.
3. The same applies from #2.

Quote

P.S. Sorry about my lame questions, but these 30Amps really confuse me. The RAMPS board have only 11 and 5 Amps sockets...
The sockets normally only have 11 and 5 amps. They can have higher demands for short periods of time. Also many power supplies are a little overly optimistic in their rating and they can't produce that full current 100% of the time. Or in the case of many computer power supplies, the power supply is incapable of delivering the full power on the +12v rail. Instead, the total wattage is the optimistic sum of all the rails, or a combination of rails. The good news is that oversizing the power supply doesn't hurt anything and the printer will only draw what it needs. You may however pay extra for additional capacity you really don't need, or your supply won't operate at it's peek eficiency.
 Re: Need some help for the cables. March 18, 2014 09:39AM Registered: 8 years ago Posts: 38
Wow, thank you very much for all of the interesting stuff in your answer. It's really clear now!
Best regards,
Bobby
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