# Will this MOSFET allow the heat bed to run at a different voltage than the control board

I am currently running my Tronxy X5s with a MKS Gen L board. So far I have not ran the heat bed over 50 degrees C since I have only printed with PLA so far. I plan to try PETG and/or ABS in the near future and I have a spare power supply 12V/360W laying around.

When I first got my printer I purchased this external MOSFET board after reading about X5s "upgrades", but so far have not used it.

My plan is to now run the heat bed using a separate power supply than the one running my control board using the external MOSFET to switch it. Since this power supply will only be powering the bed, I would like to bump up the voltage, via trim-pot somewhere from 12V-15V, to gain some watts per square inch on my heat bed.

Will this MOSFET isolate the heat bed circuit from my control board to allow it be ran at a higher voltage? Is it safe to run the power supply/heat bed at a higher voltage than it is rated for a significant amount of time?

Short answer YES. You can run it from a different power supply at a higher voltage. Also it has a PC817 Optical isolator (for some reason) therefore the second power supply and your main board should not be electrically connected at all.

• Where did you find the information on the PC817? – Perplexed Dipole Mar 26 '19 at 1:30
• I looked up the board online, zoomed in on the image then googled the numbers. This resulted in a link to the datasheet. – user77232 Mar 26 '19 at 14:50

Yes you can, but you should be aware that running at higher voltage implies that the current also increases. Your wiring and connectors to the heated platform have to be able to transport that extra current (e.g. the wires, the ones I got where very low quality, and connectors that came with my Anet A8 where not even rated for the standard load, let alone an even higher load). You need to properly solder the leads to the heated bed and use proper terminal clamps (C-clamps or forks) to connect the cables to the MOSFET module. Even running the basic voltage this can happen:

Let's assume the heated bed has a resistance (R) of about 1.4 Ω. A voltage (U) of 12 V would result in a current (I) of $$I=\frac{U}{R}=\frac{12}{1.4} = 8.6\ A$$ (Ampere). Running the same bed at 15 V would result in a current of $$\frac{15}{1.4} = 10.7\ A$$. The power would increase from about 102 Watt to 161, which is a 60 % increase of a 25 % increase in voltage.

• ...and so long as the thermistor is working nothing should catch fire. – user77232 Mar 26 '19 at 0:55
• @user77232 The working of the thermistor has nothing to do with that, connectors and wires could burn anyway due to not being rated for the current. There are examples where it did go wrong. – 0scar Mar 26 '19 at 6:49
• You'll have that problem no matter what voltage you run at. Bad connectors are bad at any voltage. – user77232 Mar 26 '19 at 14:58
• ... and good connectors become bad connectors when you are overpowering them. – 0scar Mar 26 '19 at 18:35