Hello
I had the same problem with low temp and it took forever to reach 60 deg.
Now I have bought and mounted a silicone heatpad from keenovo.com/products/silicone-heater.html
I must say its fantastic! 22 -> 110 deg in less than 2 min. I bought it on ebay and a SSR to go with it. The relay 12v DC to 220v AC.
This is the best upgrade Ive made to my K8200 
I find a simply solution using a 12V 30A Relay. Then I convert the heatbed output of the controller from PWM to Digital 0/1.
Untill now it works fine and I printed for 12hours at 110°C without problems. Using a 12V 150W power supply for both controller and hotbed.
It is not clear why Velleman decided to have the heatbed output in PWM instead of a common 0/1 output.
Is there some reason?
The original Marlin Firmware is built to work in “bang-bang” mode (ON / OFF) for the hot bed.
Inside the firmware into the pins.h file , all the other board have this code:
#define HEATER_0_PIN 10 //E0
#define HEATER_1_PIN 12 //E1
#define HEATER_2_PIN -1
#define HEATER_BED_PIN 6 //BED
Velleman converted in
#define HEATER_0_PIN 10 //E0
#define HEATER_1_PIN 12 //E1
#define HEATER_2_PIN 6 //BED
So the hotbed works like a thirth extruder, using PWM output controlled with a PID.
And this causes the need to built complex electronics schemas instead of using a normal relay.
I just finished installing a 24VDC power supply to heat the heat bed and did not use any additional electronics. Look at the controller schematic and you will see that the MOSFET for the heat bed is used to sink current. I simply connected the +24 volt supply directly to the heat bed (through the ribbon cable ) and made the new power supply share a common ground with the controller. When the heat bed MOSFET turns on it completes the path to ground. No other modification is needed. Very simple and is working great!
Just to avoid to destroid my controller, did you connect the parts as the following schema? I did in Italian but
“PIATTO” means PLATE and “ALIMENTATORE” means “power supply”
[quote=“Mikeb69”]Just to avoid to destroid my controller, did you connect the parts as the following schema? I did in Italian but
“PIATTO” means PLATE and “ALIMENTATORE” means “power supply”
You understand perfectly what I did. It works!!!
There is absolutely no reason to add additional circuitry to add in the second 24 volt supply. I have been working in electronics for many years and this will work without any issues.
Tim
Hi Battman540,
with that experience, you should however note that LD4 will have to handle a reverse polarity voltage of 9 V during all times the heatbed is off. Depending on the exact type of LED chip installed there, that may be well beyond the rating.
Cheers,
kuraasu
[quote=“kuraasu”]Hi Battman540,
with that experience, you should however note that LD4 will have to handle a reverse polarity voltage of 9 V during all times the heatbed is off. Depending on the exact type of LED chip installed there, that may be well beyond the rating.
Cheers,
kuraasu[/quote]
Good point!
My printer has about 40 plus hours of operation since the addition of the 24 volt supply and the LED is working fine so far. I tried to fine the LED specs but was not successful in locating a part number. I was considering changing R15 to higher value (it is 1.8K).
Thanks for the input!
Tim
Hi Tim,
current flow in reverse polarity should be very small, i.e. the resistor is not important there and the diode will see the full voltage drop. You would have to increase the resistance by several orders of magnitude to see an effect. But then the LED won’t light up anymore in forward direction anyways, so you could just as well remove it in the first place.
The reverse voltage is still moderate in the 24 V configuration, so worst case would probably be that the LED dies off with a small ‘pop’ some day. Or maybe it is a type with 12 V rating, or the (more common) 5 V rating includes a large safety margin and it’ll be ok. As you said - without the specs, we can’t be sure. Nonetheless, I think it’s worth noting what could happen when connecting another power source.
Cheers,
kuraasu
The led is a 0805 . You can find the components list used on the controller here :
http://www.open-electronics.org/a-new-board-for-the-3drag-theres-more-than-sanguinololu/
And the Led’s datasheet I think is this
http://www1.futureelectronics.com/doc/EVERLIGHT/17-215-G6C-F5M1N2B0E-3T-AM.pdf
If this can help…
Hi Mikeb69,
thanks a lot, but I’m afraid that’s not the right datasheet: LD4 (at least here) is red, not “Brilliant Yellow Green”.
Furthermore, such standard components can easily vary between the boards from Open Electronics and the ones from Velleman, or even between different production lots.
Cheers,
kuraasu
I just got through making the opto-coupled version to supply 24v to the heatbed. You might not need this step but since absolutely no one local sells spare parts for this thing I can’t risk frying my controller board.
Reaches temp really quickly but one concern is the bed is unevenly heated. In the center where the fans are, the bed is much cooler than at the extremities. Has anyone ever tried to add more temperature sensors to the bed, get an average temp and then send that average into the controller board? Yes the bed moves around so it’s not always in the center of the bed, but I mean the part of the bed near the fans is always a lot cooler. So if the temp sensor is under the cooling fan then the rest of the board gets really hot, if the temp sensor is away from the fans then the part of the board under the fan is under temperature.
[quote=“ntoff”]I just got through making the opto-coupled version to supply 24v to the heatbed. You might not need this step but since absolutely no one local sells spare parts for this thing I can’t risk frying my controller board.
Reaches temp really quickly but one concern is the bed is unevenly heated. In the center where the fans are, the bed is much cooler than at the extremities. Has anyone ever tried to add more temperature sensors to the bed, get an average temp and then send that average into the controller board? Yes the bed moves around so it’s not always in the center of the bed, but I mean the part of the bed near the fans is always a lot cooler. So if the temp sensor is under the cooling fan then the rest of the board gets really hot, if the temp sensor is away from the fans then the part of the board under the fan is under temperature.[/quote]
Using a glass surface will help keep the temperature even across the bed. The thermal mass increases a lot with the addition of the glass. After switching to a glass surface I installed a fan that I use to cool the heat bed after a print. The glass was taking a long time to cool down and release the printed object.
[quote=“Mikeb69”]The led is a 0805 . You can find the components list used on the controller here :
http://www.open-electronics.org/a-new-board-for-the-3drag-theres-more-than-sanguinololu/
And the Led’s datasheet I think is this
http://www1.futureelectronics.com/doc/EVERLIGHT/17-215-G6C-F5M1N2B0E-3T-AM.pdf
If this can help…[/quote]
0805 is the physical size of the LED and not a part number. The resistor and LED are both 0805 in size.
Hi,
I have bought a 24V power supply and need a MOSFET relay to control it.
Where can I buy one like that shown in the photos?
Which photos, or which post do you mean?
Thanks Duragz, I will buy there.
Hi Kuraasu, I will need a solution to my bed heater software not working when I install this psi.
Regards,
Wally
Suddenly my bed heater is working again!
I dunno what I did or what happened to do that.
Wally
Update on my no additional electronics needed to add in a separate 24vdc power supply.
I have just completed printing THREE “build your own jet engine” projects (thingiverse.com/thing:392115) and the printer is working fine. This job was about 30 plus hours of printing which puts the life cycle test at around 70 hours total with no problems and the LED is still working fine.
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).
