Heat Beds wiring and terminals block.

[Torgeir 250]

Hi Folks,

 

I've seen so many times that the double wire (+ and -) 24 VDC used for the heat bed become burned, this frequently occur on the heat bed connect block or on the block at main PCB.

Ultimaker changed those screw terminal blocks later on in the production and I'm not sure if there is some blocks of this new spring tension blocks that has failed.

However, there is a fix for anything so lets go..

 

Those terminal blocks are really well selected as they are designed to cope with up to 20 Ampere!  So what is the problem?

Well, since we are using less than half of this max current we do not need this "heavy" wires, so the wires selected might only need to take about ~ 10 Amps max..

So the selected wire is well AWG 18 (cannot confirm this, but should at least be), can cope with 10 Amps continuously and  intermittent up to 16 Amps.

 

As this block terminal can handle 20 Amps, the contact surface clamping area is big - for a single AWG 18 wire.

In order to increase the contact area we often use the fold back method, this in order to increase the number of strands that is clamped into the contact area.

By doing this, the contact resistance decrease and heat build up is avoided here.

 

Here is some pictures:

 

Here is a picture of how to do this.

The orange wire is AWG 18 and the red is AWG 14 (hold 20 Amps Continiously).

 

Here is the AWG 18 fully folded..

 

 

Here is the specs for the screw terminal block at Phoenix Contact web site in US. Can be found any places..

Here is the terminal block.

 

Thanks

 

Torgeir.