[quote=“Paul Compton”]I’ve upgraded my K8200 here at work, with a 24v heater supply.
There is a convenient place to cut the PCB track between the screw terminal power connector and the coaxial power connector. I’ve removed the coaxial connector and replaced it with a screw terminal connector (at 90 degrees to the original) and use that for the 15v supply. The original screw terminal connector is now the 24v supply.
It’s been working just fine. The mosfet doesn’t get too warm and I have a 12v volt fan running at low speed from the 5 volt supply pushing a little air through the box (not the printed one).[/quote]
Hi Paul,
Can you post a picture of the pcb modifications you made? It seems a nice solution to have a 24V switched by the available mosfet, by cutting some PCB trace… According to the datasheet of the mosfet it should be able to handle the 24V and amps.
Since I had a powerfull AC transformer in stock with several outputs (3-24V AC, 10A) I have made
a cirquit which can handle this current. Actually for heating no DC current is required at all.
However, the solid state relay used, only works well with DC current. Therefore the 24V AC output
is connected via a rectifier. The DC current is not stabilized. A mechanical relay connects the on board
15V in the case there is no external power. The solid state relay (0-100V DC, 10 A) connects the
current (15 or 24V) to the heated bed when 15V comes up. Since I had only 12V mechanical
relays in stock a cheap dc/dc converter has been used to reduce the 24V.
[quote=“kvandt”]Can you post a picture of the pcb modifications you made? It seems a nice solution to have a 24V switched by the available mosfet, by cutting some PCB trace… According to the datasheet of the mosfet it should be able to handle the 24V and amps.[/quote]It’s the track between the screw terminal block and the coaxial power connector.
The stepper drives end up getting the high voltage too, but that’s not necessarily a disadvantage.
[quote=“edirol”]The original ribbon cable goes to the X Support. From there is use a 2x0.75mm2 cable along the cable chain.
Buttom of the X support
Connection to the heatbed[/quote]
Does anyone know if this item is availiable as an STL file. Just adding a upgraded heated bed to my K8200 and this looks like the perfect item for a neat completion
I like the fast heating of the flatbed so much that I also consider to increase the voltage of the heating element of the extruder during heating up. Is it known what maximum voltage can be supplied to that element?
Since I use PLA the external power supply is only used for reaching the maximum temperature. When the flatbed left his home position a switch is activated causing that the original power supply takes over the feeding of the heating elements. This means that the voltage is not significant for the control dynamics of the element.
Update
In the meantime I have tested the behaviour of the heating element by myself. The hotend was disconnected from the
printer and tested in an external setup. In the tabel below it is shown how much the time is shortened by increasing the voltage. The resistance of 0.55 K-Ohm is equivalent with about 200 deg.
Next step to see if the hotend can be warmed up (perhaps partly) during heating of the flat bed. At least I do not see
a reason why this cannot happen simultaneously if there is enough power available.
Hi all, having done a few modifications it’s now time to look at the heat bed. Mainly the time it takes to heat and its ability to maintain that temperature with the fan running on full.
Using a 24v power supply appears to be a proven method. Not surprising as it more doubles the effective standard wattage. The problem is that I don’t have a 24V power supply, but have some really good 12V ones.
My thoughts are, if I find the centre point of the heating element (pcb track) and attach a wire, I effectively have 2 heaters both half the resistance which can be connected in parallel and fed with 12 Volts.
If current = Voltage / resistance and power = Volts x Amps and my heater measures 5 Ohms.
At 24 Volts: 24 / 5 = 4.8A 24 x 4.8 = 115.2 Watts.
At 12 Volts: 12 / 2.5 = 4.8A 12 x 4.8A = 57.6 Watts
But I have two of these so: 57.6 x 2 = 115.2 Watts & a current of 4.8 x 2 = 9.6A.
The heating effect should be the same, the standard ribbon cable certainly won’t be able to handle the 10 A so will need to be changed. Then come some interesting questions:
Can I just change the printer supply from 15V to 12V or would I need to switch using a relay?
Will the K8200 control board run on 12V?
Would a 12V supply have any implications for the stepper drivers or motors?
Will the pcb tracks, connectors and FETs handle 10A without any modifications?
I look forward to your thoughts.
I used a old Notebook PSU (19.5 Volt, 120 Watt output) switched over a car relais. Now it heats up much faster andthe Velleman PSU stays much cooler while printing. The Car Relais gets warm, but not hot.
[quote=“sauntson”][quote=“edirol”]The original ribbon cable goes to the X Support. From there is use a 2x0.75mm2 cable along the cable chain.
Buttom of the X support
Connection to the heatbed[/quote]
Does anyone know if this item is availiable as an STL file. Just adding a upgraded heated bed to my K8200 and this looks like the perfect item for a neat completion[/quote]
I would be interested in the STL too.
Barnabybear, the mainboard will rin at 12 v, but the motors will loose torque, due to the lower voltage.
And you’re right, wether the PCB traces nor the Flat cable will withstand 10Amps.
I Would go for a relay switched heatbed or use the PWM circuit (will easily handle 15Amps) posted here on the forum.
[quote=“sauntson”][quote=“edirol”]The original ribbon cable goes to the X Support. From there is use a 2x0.75mm2 cable along the cable chain.
Buttom of the X support
Connection to the heatbed[/quote]
Does anyone know if this item is availiable as an STL file. Just adding a upgraded heated bed to my K8200 and this looks like the perfect item for a neat completion[/quote]
I don’t remember where it came from but I still have it and you can download it here
[quote=“ichbinsnur”][quote=“raby”]
I don’t remember where it came from but I still have it and you can download it here[/quote]
Thanks a lot man!
I already thougt about desinging one myself, to get rid of the buggy ribbon cable …
cheers,
hristian[/quote]
You’re welcome.
I’ve added it to the Wiki.
[quote=“raby”][quote=“ichbinsnur”][quote=“raby”]
I don’t remember where it came from but I still have it and you can download it here[/quote]
Thanks a lot man!
I already thougt about desinging one myself, to get rid of the buggy ribbon cable …
cheers,
hristian[/quote]
You’re welcome.
I’ve added it to the Wiki.[/quote]
Great idea!
[quote=“raby”][quote=“ichbinsnur”][quote=“raby”]
I don’t remember where it came from but I still have it and you can download it here[/quote]
Thanks a lot man!
I already thougt about desinging one myself, to get rid of the buggy ribbon cable …
cheers,
hristian[/quote]
You’re welcome.
I’ve added it to the Wiki.[/quote]
Just wondering.
Why would you need one for the X axis?[/quote]
I want to exchange the ribbon cable with round ones that have bigger cross section.
But if i do i need som guidance for them. They won’t fin in the gap where the flat cable lies …
For the X axis I did exchange the flat cable for a round one. I just used a spiral band to hold things together and it works well (it rubs a bit on the desk where the printer stands but it’s not a problem).
