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Project ultimate heatbed cable.  

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Ilkka
(@ilkka)
Active Member
Project ultimate heatbed cable.

Hi.

I want compact enclosure for my printer, and i dont like how heatbed supply and thermistor leads are routed.
They are spiralwrapped and take too much space to rear of device. This is also one reason to do something radical.

I do not have my printer yet and i cant do any more investigations so i need your help.

*3 or 4 core cable
First question: I assume that heatbed supply has (pwm controlled) 24v + and -, and thermistor has two wires also.
Is there same potential at thermistor, does these share common ground (negative or positive)
Same again simplified, can i in theory use three core cable between and separate common ones at the ends of cable?

My intention is investigate how to make possible route these wires under the bed using some ultra-soft FLAT silicone cable, or mini chain, etc...
If i desolder those supply wires, clean all solder from pads, and drill about 2mm holes through from center of both pads, i could route new wires
from under the bed...

*Drill on not?
Second question: Are there heating element layer right under the connector tab?
I do not want to drill and cut any of those.

*Estimating cable sizing
Third question: How much power (W) or current (A) @24v heatbed can draw max?

Posted : 25/01/2018 3:46 pm
Paul Meyer
(@paul-meyer)
Honorable Member
Re: Project ultimate heatbed cable.

I would use a 4 wire cable. Make sure the heater cables are the same or larger gauge then the originals.

The reason I would not share ground: the thermistor is going to be a sensitive resistance measurement. This will likely be a voltage divider circuit with a resistor on the Einsy somewhere connected to VCC and an analog input. That input will also be connected to one end of the thermistor and the other end of the thermistor to ground. This "voltage divider" will allow the analog input to measure the resistance of the thermistor indirectly by measuring the voltage on the analog input.

The heater circuit will be using PWM toggling 24v on/off on the positive heater wire. All of the current will be returning on the heater ground wire. This will raise/lower (slightly) the voltage of the heater ground.

If you shared the ground between these two, I wouldn't be surprised if there were noticeable shifts in your temperature reading as the heater turns on/off. Because that temp reading is feeding into a PID algorithm that is driving the heater on/off, coupling the heater state back to the temp reading would significantly complicate the system.

An extra wire would be cheap insurance in this case.

Posted : 25/01/2018 6:55 pm
thrawn86
(@thrawn86)
Honorable Member
Re: Project ultimate heatbed cable.

regarding the pic, that's an mk2, the cable gland is in a different place and he's also missing the cable support on the back of the carriage. the instructions go into pretty excruciating detail about how to avoid that.

I'm not sure where 8-10" of slack is going to go, properly supported, without taking up at least a few inches somewhere or having super tight bends. My first printer, an MP mini, had the heatbed and thermistor wires very cleverly routed underneath the bed and through the frame (no protruding wires) and tons of them broke off. The solution was just to route them outside the frame with a drag chain or wrap.

Posted : 25/01/2018 6:56 pm
david.s86
(@david-s86)
Eminent Member
Re: Project ultimate heatbed cable.

A response from an electronics/wiring newb here...but...how hard would it be to change the bed/wiring and route the wires vertically, instead of horizontally? (I'm not asking for me, I have plenty of room to build it stock :P)

Posted : 25/01/2018 7:10 pm
Ilkka
(@ilkka)
Active Member
Topic starter answered:
Re: Project ultimate heatbed cable.

4 wires it is.

If nobody cant say more, i have to wait few months and then use my flir and multimeter to find out the rest...

Posted : 25/01/2018 8:07 pm
thrawn86
(@thrawn86)
Honorable Member
Re: Project ultimate heatbed cable.


4 wires it is.

If nobody cant say more, i have to wait few months and then use my flir and multimeter to find out the rest...

since you mention a flir, there are shots of the MK42 floating around and pcb layouts as well showing the location of the heating elements. There are no heating elements underneath the power wire pads, if thats what you're asking. The bed is something like 150w iirc.

Definitely advise you to take a look at the EINSY documentation on github if you want more specific schematics.

Posted : 26/01/2018 12:37 am
JoanTabb
(@joantabb)
Veteran Member Moderator
Re: Project ultimate heatbed cable.

when I repaired my mk2 heatbed wiring, I used an old kettle cable as the source for reasonably flexible wire, and I used 2 lengths for the + cable and two lengths for the - cable, running them in paralell. I made them slightly longer than standard and routed them the same as the original wiring, with spiral wrap...

that bodge is still working fine.

I did however buy some Silicone insulated RC Buggy wire, in black and red, to use next time I needed to do the job... this cable has lots more, finer diameter conductors in each wire, making the resulting wire much more flexible and way less likely to break due to repeated flexing.

if you are looking for ultimate cabling I would suggest this sort of cable for the job...

I would also use single wires rather than a 4 wire cable, because single wires are again less likely to suffer flexing damage than a multicore cable

14 AwG should be more than adequate for the heatbed power wires
24AWG should be more than adequate for the thermistor

this table is from an ebay supplier

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 26/01/2018 1:33 am
maxx78
(@maxx78)
Estimable Member
Re: Project ultimate heatbed cable.



My intention is investigate how to make possible route these wires under the bed using some ultra-soft FLAT silicone cable, or mini chain, etc...

Do you know the cable chain mod for the MK2 & 3 ?

https://shop.prusa3d.com/forum/original-prusa-i3-mk3-f30/cable-chains-for-mk3-t12543.html

Posted : 26/01/2018 11:46 am
Ilkka
(@ilkka)
Active Member
Topic starter answered:
Re: Project ultimate heatbed cable.

Yes i have found that, and i like it, possibly will do that to extruder wiring.

But this heatbed... there is a cut out at back of cabinet :mrgreen: 😉
That is the main reason why i want to try something diffrent solution, i have a wall there.
I have allready old cabinets in my garage and those will stay. (sideways setup is my only backup if this fails)

So under the bed chain, or silicone extrafine stranded flat cable (oooo), routed nice U-shape like they use with chains.

If it is only 150w@24v = 6.25A Because silicone can stand high temps and distance is so short, i could use really thin wires. 22AWG...
Maybe i will do 4x20gauge

If i cant find suitable flat cable, i have a way in my mind to make a flat chain using 4 separate wires, but i need my printer first....

Posted : 26/01/2018 4:10 pm
Ilkka
(@ilkka)
Active Member
Topic starter answered:
Re: Project ultimate heatbed cable.

Something like this maybe?

Posted : 03/02/2018 12:12 pm
Ilkka
(@ilkka)
Active Member
Topic starter answered:
Re: Project ultimate heatbed cable.

I have learned fusion 360 so much that i managed to make this model to move like a real one.
Just simulated it with a chain, this can be done and it is possible to modify my mk3 to fit my tight cabinet.
I will use existing heatbed and sensor cables loosely nylon sleeved inside a 7x7 chain.
That nylon sleeve inside chain will make chain move smoothly.

I expect my printer to arrive at the end of next week... 🙄

Posted : 18/03/2018 11:11 am
maxx78
(@maxx78)
Estimable Member
Re: Project ultimate heatbed cable.

Nice idea for the heatbed cabeling, maybe i try something myself 💡

Posted : 19/03/2018 10:47 am
Ilkka
(@ilkka)
Active Member
Topic starter answered:
Re: Project ultimate heatbed cable.

Got my printer and i am sure now this can be done, but i didnt have to.

I made extra short lcd bracked and heatbed cable cover and got enough space.

Posted : 27/03/2018 2:46 pm
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