Update mainboard.md

docs/hardware/mainboard.md

@@ -156,7 +156,7 @@ This neat solution is called ["Kobra Unleashed"](https://github.com/anjomro/kobr
 
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-### MOD: Different Mainboard 
+## MOD: Different Mainboard 
 Generally speaking, it's possible to replace the stock mainboard with a different type of board, like e.g. a board from BigTreeTech (BTT) for being able to use Klipper (for example).  
 You just have to pay attention that it uses and provides 24V DC as well, as the PSU and the components like the fans etc. are running on 24V.  
 
@@ -177,8 +177,81 @@ The following picture shows the mounting direction of the fan.
 
 ![MCU fan mounting direction](../assets/images/mainboard_K2Pro_fan-mounting-direction_web.jpg)  
 
+---
+
+## MOD: Add An External MOSFET  
+
+It's advisable to add an external MOSFET for driving the heated bed (if you like, you can also add one for the heater cartridge as well of course). Even though the MOSFET on the mainboard is sufficient, it's an upgrade worth doing as it not only leads to the fact that the bed will be heated up slightly faster, but it also increases the security of the hole printer.  
+The MOSFET of the mainboard doesn't have a heatsink and it *may* caused by overheating due to an excessive amount of current being drawn, especially when using higher bed temperatures. Due to the low clearance between the fan of the moainboard and the ground the printer stands on, the cooling isn't the best as well. When using an enclosure which then heats up as well, cooling gets even worse.  
+If the board's MOSTFET dies, you most likely have to get a whole new mainboard then. Even though it's possible to solder a new one onto the board (if you're skilled to do that), additional components might have been harmed.  
+To avoid that, it's therefore adviseable to add an external MOSFET which then takes the load - the one on the mainboard only acts as a signal for the external one to switch.  
+
+The 24V DC of the PSU will be connected to the belonging connector of the external MOSFET. The 24V DC line from the heated bed screw terminals will be connected with the belonging connector of the external MOSFET and the 24V DC wires of the heated bed will then be connected to the outlet of the external MOSFET. When the mainboard switches the onboard MOSFET, it will then trigger the external one to switch and lead the current to the heated bed.  
+There are a few external MOSFETs on the market, most of them only have a "signal" connector. When using a mainboard with a dedicated 'signal' connector for this, it's then connected to that one. When using a mainboard that doesn't have this 'signal' connector like the one being used at these printers, then it's said to connect the 24V from the bed's connector of the mainboard to that.  
+
+I personally prefer a certain type of MOSFET which also offers a dedicated connector for the 24V line besides the 'signal' connector as shown in the following picture.  
+
+![MOSFET HW-300](../assets/images/MOSFET-HW300_web.jpg)  
+
+The PSU and the wiring of the bedplate are connected to the belonging connectors shown in the following picture: 24V from the PSU belongs to the connector labeled as "Power", the 24V for the wiring of the bedplate belongs to the connector "Hotbed".  
+
+![MOSFET PSU & bed connectors](../assets/images/MOSFET_connectors2_web.jpg)  
+
+The 24V of the bed's connector of the mainboard will then be connected to the belonging connector "Bed" at the MOSFET (positioned next to the connector labeled as "Sig").  
+
+![MOSFET HW-300](../assets/images/MOSFET_connectors1_web.jpg)  
+
+If you're using this kind (or a different kind) of MOSFET, you should check if the manufacturer actually added some thermal paste between the MOSFET and the heatsink - it wasn't the case at the ones I got as shown in the picture below, so that actually completely counteracts the whole installation and makes it obsolete.  
+
+![MOSFET disassembled](../assets/images/PSU_MOSFET_disassembled_web.jpg)
+
+
+!!! warning "Mind The Polarity"  
+
+    Pay attention to the polarity when connecting the components!  
+
+!!! warning "Add An Additional Fuse"
+
+    It is highly recommended to add a suitable fuse to the 24V line, right after the connector of the PSU. If your additional parts like the converter will fail, the fuse will melt - which can save you from burning down your house.  
+
+The following picture shows the MOSFET being mounted to the rear left-hand side of the frame. I made an extension wire for the thermistor wires as well. 
+
+As an additional benefit, now that it's mounted back there, the problem with the bed's wires being too short isn't given anymore.  
+
+![MOSFET mounted](../assets/images/psu_mosfet-mounted_web.jpg)  
+
+---
+
+## MOD: How To Add A Step-Down Converter For Using 12V Fans 
+
+When you want to add components which need a different voltage than the 24VDC the PSU offers, you can do so by using a step-down converter (or a step-up converter if you need a higher voltage than 24VDC). Simply connect the IN of the converter to one of the free 24VDC connectors of the PSU, dial in the voltage you need and then connect the belonging part to the OUT of the converter.  
+The following picture shows a typical "LM2596S" type step-down converter which can be used.  
+
+![Step-down](../assets/images/PSU_StepDown_web.jpg)
 
 
+However, when you want to use e.g. 12V fans which speeds are usually controlled by PWM of the mainboard, you have to connect them differently. The following drawing shows how to proceed in that case, so that the PWM will still work.  
+
+!!! warning 
+
+    The following circuit diagram about how to connect a step-down converter wasn't tested by me yet. It's assumed that the mainboard controls the PWM of the fans by switching the belonging GND of the connector.  
+
+![Step-down converter wiring diagram](../assets/images/stepdown-wiring.png)  
+
+
+!!! warning "Add An Additional Fuse"
+
+    It is highly recommended to add a suitable fuse to the 24V line, right after the connector of the PSU. If your additional parts like the converter will fail, the fuse will melt - which can save you from burning down your house. 
+
+---
+
+## MOD: Add Additional Fuses To The 24V DC Wiring 
+
+It is highly recommended to add a fuse or a fusebox to each of the 24V lines. Pay attention to choose the correct 'size' of the fuse for the belonging part (ampere rating).  
+Doing so can save you from burning down your house if components fail or if the wires somehow overheat and start to burn due to broken strands (which causes a higher resistance) or a shortcut.  
+
+(..need to add pic..)
+
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