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Locating electronics and needed AWG?

Posted by aamcle 
Locating electronics and needed AWG?
October 17, 2020 07:10AM
The mechanical portion of my build should be finished today all I need to do is assemble the hotend and put the end stops in place.

Then it's the electronics which should be easy enough although getting it tidy will be fiddly.

However my inability to decide were and how I should mount the board and power supply is frankly doing my head in.

The 24v power supply is bulky so fitting it into the base would raise the printer up more than I would like.

Fitting it on the back would work but when the printer is in an enclosure the board could get too hot.

A separate control/power supply box is my favourite option but that requires some sort of plug/socket with very many connections including a high amp connection for the bed.

In addition there is the connection to the temperature sensors that must have exactly the same resistance (Ohms) each time they're made.

The bed will take 12A (300x300mm) and the steppers 2A what AWG should I be aiming to use?

Any advice gratefully received!

Thanks All. Aamcle
Re: Locating electronics and needed AWG?
October 17, 2020 08:16AM
Installing Business radios and Repeaters have a lot of left over wire. I power my controller with a Radio Power cable Motorola HKN4191 20 amp, 12 AWG

My Cables are left over and missing fuse holder and Motorola power cable connector as these part are used on when installing radios.
You may ask your local Business radio company they may have a throwaway piece they would give you really cheap or even free.
myself would use at least a AWG 12 20 amp cable for power the controller, these power cables are really flexible.

Computer Programmer / Electronics Technician
Re: Locating electronics and needed AWG?
October 17, 2020 09:04AM
It's usually easier to accommodate an increase in the height of the printer than an increase in the footprint. That means putting electronics on the top or the bottom. It's easier to access the electronics if they are on top of the printer- you won't have to turn the printer over or on its side to access the controller, etc., and you can access electronics while the machine is in a functional state to test your repairs/modifications. If you put electronics on the bottom, it's a good idea to use a drawer so you can access things without turning the printer over. A drawer will require a clear space to open it however, and can still be a PITA to work with if the printer stands on the floor.

It's always a good idea to put the electronics outside a warm/heated enclosure, so enclose first, then add electronics. You can design the enclosure to have an isolated area for the electronics so the whole thing looks neat.

You only need connectors on wires that will be frequently connected and disconnected, such as the stuff on the extruder carriage. The rest of the wires can go right to the controller board or SSR's, power supplies, etc. The more connectors you put between the fans, thermistors, heaters, LEDs, etc., and the controller the more unreliable the whole thing becomes. Every one of your connections is suspect when there's a problem, and the more connections there are along a given wire, the greater the chance of there being a bad crimp, etc.

Some guys put a lot of effort into using industrial wiring guides and tracks and lacing wiring harnesses to make the whole thing look super neat and "professional", but I question the value of it when it's time to fix or modify something. I favor a haywire approach (it's really not just laziness) with wires labeled with the name of the connection instead of a number/letter combo so I know which is which when they are disconnected from the controller. It makes it fast and easy to disconnect and reconnect things. Hide the rat's nest inside the enclosure. I'm also not a fan of putting covers on the extruder carriage. The covers block the view and access to wiring on the carriage and have to be taken off every time you need to make a change. The extruder carriage is where you'll have to do most of the repairs/mods/maintenance in the machine, so fast easy access is nice, as is an unobstructed view of the wires and connectors. I like to use velcro straps to position the wires on the extruder carriage so I don't have to keep clipping off zip ties.

On the bed I like to make connections to the heater and thermistor on terminal blocks that are mounted on the bed support. If I need to replace a bed heater or need to take the bed off the machine I can disconnect the heater and thermistor, remove the bed without disturbing most of the cabling. I like Wago 221 lever nuts to make the connections. No tools are needed and they are good for moderately high currents. I designed and printed some clips to mount Wagos on t-slot. Anderson Power Pole connectors are also good for bed heaters as they are cheap, easy to install and allow polarized connections in case that's needed. You can get them in different sizes rated for as much current as you might need.

Wire current ratings are based on temperature rise which is a function of the current, the gauge of the wire (which determines resistance), the insulation material, and whether or not the wire is exposed to air or in a bundle of wires. A 20 gauge wire insulated with PVC can handle much lower current than a 20 gauge wire insulated with silicone. So the question of wire gauge for the bed heater is one of what's available to you. If all you have is 20 gauge wire, you can always braid/twist several of them in parallel to ensure that each individual wire isn't going to carry too much current. If the bed moves in Z or Y, you need to use flexible wire for the heater connection, which rules out super heavy gauge cable. As a reference, I have an extension cord in front of me that is UL rated for 13A at 125V. It uses 3x 16 ga, PVC insulated wires. So for a 12A bed, I'd probably get some 14 or 16 gauge silicone or teflon insulated wire or the equivalent copper cross section in smaller gauge wires.

Edited 1 time(s). Last edit at 10/17/2020 09:10AM by the_digital_dentist.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Locating electronics and needed AWG?
October 17, 2020 02:32PM
Thanks to you both smiling smiley

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