I have stock K8200 and I print PLA at 50C and try to print ABS at 90C but the most the bed will
heat up to is about 64C max. I can tell it to print at 90C but it will never reach it.
What is the recommended bed heat temperature for Velleman 3mm brand ABS filament?
My other printer [Robo3D R1] runs it a 100-105C for 1.75mm filamentr.
What is the max current I can use with the heatbed if I use the current connections to control
a relay and use an separate 15v DC power supply? Do I need to be this hot for ABS?
I upgraded the power supply mainly because of the slow heat-up of the print-bed.
The built in Mosfets can handle greater voltage and current and there is a convenient place to cut a PCB track to separate the heater and main board supplies. The screw terminal becomes the heaters supply and the coaxial connector becomes the main board. I’m still mostly using PLA and heating the bed to 70C. The hot-end is quite happy at the higher voltage after tuning the PID loop.
[quote]What is the max current I can use with the heatbed if I use the current connections to control
a relay and use an separate 15v DC power supply? Do I need to be this hot for ABS?[/quote]
With a separate 15VDC power supply the bed will not take a higher current and therefor will neither heat up faster nor reach a higher temperature.
You will need a power supply with a higher voltage.
You could use a laptop power supply at 19…19.5VDC or even a 24VDC power supply (for the bed only).
With that you’ll be able to reach at least 100°C, or the 50°C in much less time.
It’s not recommended to switch the power supply by a relay.
You can find a nice little external circuit using a MosFET in this forum.
I installed a separate 24V DC 6 Amp Meanwell powersupply, switching the secondary by means of a RepRap Power Expander solid state relay controlled by the THERM2 output on the controller board. The first time I switched on, the Power Expander burnt out, so I replaced it with a simple relay and have had no problems. Another solid state relay has been sourced and will be installed at the first sign of a problem with the relay.
The heated bed now reaches 90 deg C in 6 minutes and can go past 100 deg, but I am loath to see how high it will go!
[quote=“Paul Compton”]It’s not recommended to switch the power supply by a relay.
You can find a nice little external circuit using a MosFET in this forum.[/quote][quote=“WallyL”]Hi,
I installed a separate 24V DC 6 Amp Meanwell powersupply, switching the secondary by means of a RepRap Power Expander solid state relay controlled by the THERM2 output on the controller board. The first time I switched on, the Power Expander burnt out, so I replaced it with a simple relay and have had no problems. Another solid state relay has been sourced and will be installed at the first sign of a problem with the relay.
The heated bed now reaches 90 deg C in 6 minutes and can go past 100 deg, but I am loath to see how high it will go!
Wally[/quote]
I chose a desktop Power Supply from Meanwhell 24V/120W because of better electrical safety wtith closed housing.
(looks just like some of the usual Laptop power supplies, see link below)
[quote]It’s not recommended to switch the power supply by a relay.
You can find a nice little external circuit using a MosFET in this forum.
[/quote]
Avoid using a relay because :
it will give you less accurate temp control by suppressing the PWM modulation of the Velleman Board (relay gives you just plain on or off)
it could easily blow your onboard Mosfets due to the voltage spikes generated from the relay coil. (at least without using a flyback diode at the relay coil)
You should use the mentioned circuit to switch the heater. I did so too. Parts are cheap and it’s easy to build.
I already thought about starting a PCB version of it via Fritzing Fab. If anyone wants one, just let me know and i will make a PCB and do a bulk order.
The circuit and parts list of the MOSFET circuit for interfacing the 24V supply to the 15V control voltage supplied by the printer board
can be found here at the forum. (link below)
I added some cheap thermal compound between the heatbed PCB and the glass plate i use on top to have better heat transfer.
Now it heats up nearly as fast as the extruder and easily reaches 100°c.