I will use a different controller for my K8200 soon and that means I should try out what the normal controller can survive…
I connected a variable power supply in series between the heat bed output of the controller and the heatbed to see what would happen.
At first I’ve set the additional PSU to 9V so there’s 24V on the heat bed and it went without problems to 80°C and then I cranked the voltage slowly up to the max of the PSU. The temperature went from 90°C to 105°C in under one minute at full power (34V PSU+ 15V Controller). The controller got a little bit hot but nothing that should be a problem. And the controller was able to switch the power on and of without problems when I was using 15V for the PSU.
I didn’t try if the controller can switch with 34V because it will take a day or two for the new hardware to arrive but I will test it for you if you want as soon as I get it.
I tried this because I thought that there has to be a better way than to use a relays…
I might use a reprap power expander to do it but I’m just curious.
Try that on your own risk. It worked fine for 5 minutes but I can’t guarantee that it won’t brake after 5 minutes…
Some of us have been using the on-board MOSFET as a low side switch and supplying the high side of the bed with an external supply for a long time.
It’s been documented several time on the forum. Well within the FET’s ratings.
I went one stage further and cut the track between the power connectors and used both; 24v on the barrel connector (actually changed to a screw terminal) and 12V on the screw terminal (giving the onboard regulator an easier life).
[quote=“Paul Compton”]Some of us have been using the on-board MOSFET as a low side switch and supplying the high side of the bed with an external supply for a long time.
It’s been documented several time on the forum. Well within the FET’s ratings.
I went one stage further and cut the track between the power connectors and used both; 24v on the barrel connector (actually changed to a screw terminal) and 12V on the screw terminal (giving the onboard regulator an easier life).[/quote]
Yep, the onboard FET should be able to handle up to 15A easily even without cooling.
Only thing is the traces on the controller board. I don’t know what current they can take without damage.
[quote=“ichbinsnur”]Yep, the onboard FET should be able to handle up to 15A easily even without cooling.
Only thing is the traces on the controller board. I don’t know what current they can take without damage.[/quote]
The traces are very short, so even though they’re not very wide, their resistance is low and your I2R losses therefore low. You’re not going to get much heat. You can pull a remarkable amount of current through short traces, even if they’re narrow.
[quote=“Paul Compton”]Some of us have been using the on-board MOSFET as a low side switch and supplying the high side of the bed with an external supply for a long time.
It’s been documented several time on the forum. Well within the FET’s ratings.
I went one stage further and cut the track between the power connectors and used both; 24v on the barrel connector (actually changed to a screw terminal) and 12V on the screw terminal (giving the onboard regulator an easier life).[/quote]
I have been running my heat bed on a 24VDC power supply and using the stock controller for hundreds of hours without any problems. The heat bed ON LED is still working fine too.