Hello
thingiverse-production.s3.amazon … _large.jpg
is it possible to post an image of the ready-fitted board ?
regards,
Phijol
[quote=“edirol”][quote]Well: What could happen?
The bed is a resistor, designed to produce heat
[/quote]
Acually your are right. So I build a prototype of a 24V MOSFET controller, but to completely decouple the extra voltage from the controller board, I changed the electronic design and use now a optocoupler. Now I can keep the bed at 60° even with 2 fans at 100% speed ;-). 3.9A@24V=94W
(With 12V input will you have to change R2 and R3 to 1.2k !)
Edit: The MOS-FET can also be the IRLU8743PbF (I-Pak version).
Edit2: Note that schematic signs and hardware pinouts generally do not correspond! This may be a trap for less experienced users. If you have built this circuit and you get a “alway on” output, check wiring and pin numbering of the optocoupler.[/quote]
So I just breadboarded this circuit and am getting odd results. When the controller board power turns on, I am getting the full 24 volts across the 24v positive and the drain of the MOFSET. But with no power from the controller board, I’ve still getting about 5.5-5.7 volts of power between the 24 v positive and the drain of the MOFSET? Circuit “seems” to match the schematic… Ideas?
Something similar happened to me, turned out part of the stripboard I was using had a fault and two of the strips were joined by a little piece of stray copper (manufacturing fault). Make sure your breadboard isn’t shorting out internally somewhere and that you’re not running a common ground between the input and output.
FYI for anyone else, the optocoupler I used was a 4N25 and the mosfet was an IRF540N. Been working fine (although a couple of different valued resistors) and the transistor doesn’t even get warm with only a tiny little heatsink on it.
Checked and doubled checked, and replaced both I/C’s with new ones. Now the circuit seems to work as advertised, although the voltage on the drain is still maybe .4 volts when the opto-isolator is disconnected from the 15volts. Is that normal? Once connected to the bed, would that mean a tiny current will be draining all the time? Seems like it should go to 0 volts when the 15v is not on the opto-coupler.
mine fluctuates between 0.0mv and 0.1mv while the heater is off. Granted though, it’s connected to the bed so that might be affecting the test. I’m printing something now so can’t disconnect it to test it
That would be great, thanks! I image with the bed connected it would act like a pull-down resistor, but seems like there shouldn’t be any voltage to pull down in the first place…
That would be great, thanks! I image with the bed connected it would act like a pull-down resistor, but seems like there shouldn’t be any voltage to pull down in the first place…[/quote]
Did you get a chance to check?
[quote=“Mikeb69”]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.[/quote]
Mike (or anyone),
So, what did you do to convert it back to not being a PWM? I’m in the Merlin v2 board, and I want to change the firmware of the board over to a regular off/on.
according to Configuration.h I have Motherboard=77
The Pin.h code looks like this:
#if MOTHERBOARD == 77
#define HEATER_0_PIN 10 //E0
#define HEATER_1_PIN 12 //E1
#define HEATER_2_PIN 6 //BED
#endif
#define TEMP_0_PIN 13 // ANALOG NUMBERING
#define TEMP_1_PIN 15 // ANALOG NUMBERING
#define TEMP_2_PIN -1 // ANALOG NUMBERING
#define HEATER_BED_PIN 9 // BED
#define TEMP_BED_PIN 14 // ANALOG NUMBERINGSo, what part of this code would I have to change to make the pins not behave like PWM?
Would it be just as simple as adding the variable ‘HEATER_BED_PIN 6’ and setting the HEATER_2_PIN to -1 and then making sure all of the other settings/programs for Motherboard=77 are in line to use HEATER_BED_PIN as the controller?
Or could I just figure out which pin is pin 9, and run my heater off of that pin?
Thanks.
Yet another person asking about alternatives for the mosfet
I can acquire a IRF1405 with fair ease, it pretty much is set for current and voltage but the rdson (5.3m) is quite a bit higher than the one you recommend (3.1m), is this going to be an issue?
I bought 24V power source for hot bet (can by adjusted +/-10%) /150W … cca €13
When I tried it (without controling) on 25V => 115°C in 25 minutes (I am using on bottom of cariage … aluminium layer + some plast)
I will make controling with Relay into PCB (€2) without FET’s. Less work… less money.
(power expander on net … $20 + shipping ? Crazy ? … FET cca €0.75, opto cca €0,25)
can I use this to power up my heated bed?
FINDER - 6012-9012-0040 - RELAY, DPCO 10A 12VDC
Hi Guys, this board could work for a mk2 heatbed at 24v? http://reprapworld.com/?products_details&products_id=576&cPath=1591_1600_1669
I don’t think that kit will work as the k8200 is already powered by 15 v.
I would just get me a 12V or 24 volts print relay and us an appropirate current limiting resistor and flyback diode at the coil of the relay.
This is what i built myself, the relay is taken from some switching electronics i had lying around:
Has anyone had this circuit fail on them? I made the opto-isolator circuit from this thread and it worked great for a week, but now the 24volts just remains on all the time and my bed has uncontrolled heat. Will test it to see what failed (opto-isolator?) but curious if anyone else has experienced this?
For what it’s worth, the MOSFET went bad and was connecting the power regardless of its input. Time will tell if it was just a random part failure or if something is taking it out…
Did you accidentially swap drain and source?
I don’t think so. It wouldn’t work at all if I did, would it? Mine worked for several days, then just started outputting 24v all the time. After replacing the MOSFET, it seems to be working fine again. If it fails again, I’ll have to investigate further I guess…
Well, then it’s likely connected correctly.
I only said that as it happened i soldered mine wrong way (twisted) so it gave me the same as you described befor going up in smoke … 
I used 500 W power supply out of free broken Toshiba LCD TV. I used 24v for control board and 5 volt to raspberry pi.
Its working fine.
[quote=“Battman540”]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.[/quote]
For those of you that are concerned about my method of adding in a heat bed power supply with no additional parts, I have an update. The controller board is still working perfectly and so is the LED.
I have now worn out the bearings on the X & Y belt and also the extruder (all replaced with quality sealed bearings) and everything is working fine.
I have lost count on the number of hours on my K8200 but it runs about 20-30 hours per week.