Use 12-gauge wire for your heated bed, and upgrade your E3D to a 40-watt cartridge.

[626Pilot]

I built a Rostock MAX v1 way back in 2013. At the time, the strategy for wiring the Onyx heated bed was to use 4-conductor speaker wire, which was either 16- or 18-gauge. You'd use two wires for + and two wires for -. This worked alright, but I noticed that the connectors kept melting! I would have to chisel the remnants of the destroyed plug out of the sockets, and then screw down the wires into a new plug. I also noticed that the colored insulation was blackening near the plug! I bought some tiny Raspberry Pi heat sinks to ameliorate the problem, but they were still so hot that you couldn't touch them for more than five seconds.

Last week, I got some 2-conductor, 12-gauge speaker wire from Amazon for $17.95. I cut a length of it, and stripped about 2/3" of insulation off one end. I fanned out the individual strands so that they were flat, and then soldered them to the Onyx's solder pads. I figure fanning the strands out lets them make better contact. Then, I stripped about 1/4" of insulation off the other end of the cable and screwed it down into the green Molex plug. I also have an Auber SSR on the way (thanks for the recommendation, mhackney), and I will continue to use the 12-gauge wire with it once it gets here.

Benefits:

• Fatter gauge wire "fills" the Molex plug's receptacles more, allowing for a larger contact area - the wire, being thicker, is also able to conduct more heat away from the plug
• Heat sink is now SIGNIFICANTLY cooler, whether the Onyx is initially heating or holding temp (70C)
• With the old wires, the Onyx could only hover anemically around a max of 73C. With the old Viotek 450-watt power supply feeding the controller through two pairs of skinny wires, it took awhile, but I was able to achieve 90C! Haven't tried anything higher. I'm going to switch to a 350W "LED power supply" that will let me use whatever gauge of wiring I want (it has screw terminals), and I think it will probably get up to temp more easily.

Another good "mod" for your heated bed is to fold a dish towel over, and put it on the glass while it's heating up. It will reach temperature MUCH more quickly!!!

I also replaced the somewhat weak 30-watt cartridge heater on my E3D Cyclops and V6es with these 40W ones. I had to wrap them in a little bit of aluminum to get them to fit properly. Both hot ends heat up more quickly now. I'm going to stop using the Cyclops because even with a 40W cartridge, the massive surface area on the heater block makes it too susceptible to heat loss from cooling fans. I'm also a little worried about not being able to trim excess aluminum foil inside the heater cartridge bore. The V6 has neither of these problems. It can get by with a 30W element, but who doesn't like a faster warm-up time and more resistance to part cooling fans? I will be using these cartridges from now on.

[mhackney]

12 guage wire is a great choice and fanning the Onyx side does reduce resistance.

A BerdAir or similar directed airflow will work with the cyclops. I wrap the heat block in silicone tape too.

[DeltaCon]

I used ÖLFLEX® HEAT 180 SIF 1 x 6 mm² wire (compares to AWG 9.5) for my 20V setup. And did the same fanning at the onyx side before soldering. The only downside is that it does not flex very easy. I was thinking about using an XT60 between the bed and the SSR/PSU to make it easier to lift the top-baseplate, but hey, how many times does one do that...

[KAS]

Obviously it depends on the manufacture of the wire, but most cheaper speaker wire is copper clad aluminium. Not exactly the best stuff.

Edit: i'm just mentioning this for anyone else looking to do the same. Get decent pure copper wire

[626Pilot]

I got this stuff because it was two-conductor "zip wire," and I wouldn't have to use heat shrink to keep the wires together.

What I would really like is 12-gauge (or lower) twisted pair. I think that would yield less EM noise, particularly when it's running in PID mode (sustaining heat by rapid cycling) and generating what amounts to AC. I didn't see any of that on Amazon.

[Eric]

Twisted pair is easy to make yourself. Take two wires of the same length, preferably of different colors. Put them together and clamp/tie one pair of ends to something sturdy. Put the other pair of ends into the chuck of your drill. Stretch the wire out and keep light tension on it until you're done. Run the drill at a slow speed (or crank if you used a hand drill) until you get the twist you want. Don't cut the wires to the required lengh until after you've twisted them, as the twist will shorten the wire pair.

[626Pilot]

That much I know, but then I have to jacket them somehow (heat shrink) or they will tend to unravel. I have had a little success getting the insulation to stick together with a heat gun. It's just that it seems easier to buy it pre-done. More flexible as well, as I wouldn't have to cover most of it with heat shrink.

[Mac The Knife]

Or, instead of heatshrink, you use some thin CA, (hobbyshop superglue) and spot tack the wires together. A little trick I picked up from RC car onroad racing.

[geneb]

Waxed lacing tape.

g.

[gchristopher]

To improve the wiring when the bed was still 12V after the screw terminal melted, the dinosaurs went with Deans Wet Noodle wire for the heat bed. Teoman recommended bullet connectors, which was another great idea that makes taking the bed on and off easier. Lastly, replacing the stupid screw terminals with plug connectors was great for peace of mind, but required rework on the RAMBo.

I don't see how I could possibly have been more careful to get good insertion and contact on the screw terminals with the original RAMBo wiring. Given that, the volume of reports of them failing, and accompanying scary pictures, I wouldn't recommend using the screw terminals for the heated bed to anyone.

The screw terminal block on the RAMBo specifies a max 14 AWG wire, and is rated for 16A current. If the nominal resistance of the Onyx is 1.1 ohm, that's 10.9A at 12V, so that's about 32% derated? I don't know if that's good/adequate/bad.

Upgrading the bed to 24V with an SSR obviates that problem, since the only thing they'll be driving is the relay. (Though I still consider the wet noodle wire and bullet terminals the best option I've heard of so far.)

Edit: found:

The version of the connector that Ultimachine ships with their "generic" RAMBo is much better - it's essentially the same as the style used for the power connections, but is broken up into a series of pluggable 2 pin terminal blocks. I really wish they'd use those in the SeeMeCNC boards.

Erm, what Gene said. That'd be great.

[geneb]

For all the v3 machines, they've gone to the "generic" pluggable compression terminals.

g.

[Reikal]

I used Silicone wire on my V2 build as it's designed for high current very high temperature usage. Easy to get from model shops as its used on almost all high load electric motors (cars, multi-copters etc). Easy to solder and very flexible, comes in a good selection of gauges too.