Additional power supply for heatbed

many thanks… now it is clear :wink:

For the timer Elko C1 ( 47uF ) it is better to use with a 100-220 uF. Except it does not bother you that again and again the lights go out in the first layers. By Hotend Heatbed in the range of the temperature sensor is heated to the extent that the Heatbed heater must not be partially activities for 2-3 minutes.

Hi guys,

Thank you for the information. I followed the first several pages, bought IRLR8743PBF and made a circuit. Then I realized that there exists a better solution. IRLR8743PBF only allows 30V which is too close to 24V. But the onboard MOSFET can go up to 70V. And I don’t feel good hangling wires and circuits around. So I changed to the following solution.

First I soldered one wire and two female connector to one 4-pin male connector.

Then I plugin the connector to the board. The heatbed goes to the new connector. The red wire goes to 24V+. The black wire goes from the PCB ground to 24V ground. That’s it. Simple and reliable.

It takes one to two minutes to heat up from 15C to 50C using 24V. The 24V 15A power supply I bought can adjust voltage from 20V to 30V. 24V gives the bed 90W power and probably 10W to the factory wires. The factory wires remain cold when heating up the bed. But I will replace them and boost the voltage to 30V, which will give the bed 150W power. Also I feel the need to increase the voltage of extruder. It’s too slow now.

The heatbed LED lights up using 15V power not the 24V power.

Be carefull not to burn your bed!! Heating too fast can cause the temperature sensor to react too slow so the temperature of the print lanes becomes too high, which could result in coming loose after some time., your solution does seem very cunning. The 24v part I think I understand. But unless I misunderstood you didn’t explain the 15v side, is this done as normal? In the pic there is not a red wire powering the board via the usual connection. It looks a bit like you have some extra red wires, one seems to be coming in and is attached to the board, another seems to join parts of the board, perhaps that is part of another change you have made? I’m very interested, as this seems easier and cleaner than the other solution documented here. Thanks!

Please take a look on my post.
I also made a additional Powersupply for Headtbed.

Kind regards,

Yes, 15v is done as normal. I didn’t use the blue factory power termial block because it’s cheap and wires kept falling out of it. I was using the black female Jack DC Power Adapter on the right side when taking the picture. But it’s only experimental. The idea is that you can have many different voltage. For example, 12V for the fan, 18V? for extruder, 24V for the heatbed. All the ground connected together. Each connector’s minus pin (drain pin of BUK6215-75C) still connects to the fan, extruder or heatbed. The other wire from fan, extruder or heatbed connects to the new power source.

When using a much powerful power source (I’m using 24V 15A), make sure to install a fuse along the wire. The blue factory power termial is too weak to be trusted. The best way is to remove it and solder stronger wires on to the board directly. Currently I’m using a male and a female 4 pin molex connector for the connection. I hope to change it to MSTBA and MSTBT which is much eaiser to connect and disconnect.

The extra wires in the picture has nothing to do with the heatbed. I burnt two pins of the microcontroller when replacing the heatbed using a connected soldering iron. So I remapped them to other pins and jump wires around the board.


The 7805 on the board is generating too much heat. My burnt controller uses 115mA current. A Mega2560 board I recently bought uses 80mA current. That’s means the 7805 is consuming (15-5)*0.08=0.8W. So I bought 5pc DC-DC LM2596 Power Supply Step Down Adjustable Converter Module1.3V-35V from ebay (only for $6.23!). They can convert down the voltage and convert up the current (up to 3A). I’m using one of them to provide 5V to the microcontroller. I plan to add another two to provide 12V for the fan and 18V for the extruder. Then I can connect only one 24V power to the controller to power up the heatbed and step motors.

Thanks for reminding me. MK2 PCB uses 12V 10A. So I assume that any PCB can take up to 120W without a problem. And this increased power is only for the initial heat up from 15C to 50C. After that there is no difference between 24V and 15V. But maybe 120W is the upper bound for the PCB. I’m thinking about the possibility of mounting a 1200W heatgun on the back right side to speed up for fast prints. For large parts which takes a long time 24V is already more than adequate.

The bed temperature for ABS is 125-140. The bed should be fine if overheated from 50C to maybe 140C. If it’s actually burnt, then it’s time to try Alu-Heatbed MK3 :slight_smile:

Hi dannyoneill,

I realized that there is a even simpler method. Just cut the positive wires of heatbed and connect it to 24V+ then connect 24V GND and 15V GND together.

The + pin of heatbed is directly connected to 15V+. The - pin of heatbed is connected to the drain pin of MOSFET. Make sure the headbed is connected between the drain pin of MOSFET and 24V+. If a wrong wire is used, then it’s possible to connect the heatbed between 15V+ and 24V+, or short 24V+ with 15V+, or short 24V+ with the drain pin, which will be extremely bad.


Are you sure the FET can handle the higher current well enough without becoming too hot?

Hi laserguy,

well, personally I would feel the need to add a heatsink and/or forced cooling (i.e. fan) to the MOSFET for this. However, the guys from Italy seem to be very confident about their design:

[cite from]
Let’s talk about the MOSFET driver used to power the heaters and the fan: they are all BUK6215-75C, manufactured by NXP, with N-enhancement mode channel, capable of a drain current that reaches 57A and capable to bear with a Vds in lock state, of 75 V; their very low Rdson (15 milliohms max with a drain current of 15A) is used to minimize the power dissipation and therefore being able to solder them directly to the PCB track (which acts as a heat sink). The case is a SOT428, for surface mount, and allows to do this.

In our case the MOSFETs are used with small currents, because we are in the order of 2 to 2.5 A for the heater extruder (which must be connected to HEATER1) and 5 to 6 A for the heated plate (to be connected to HEATER2), which is why there is no need to equip them with the heat sink and they cool just thanks to the dissipative effect of the slopes where the foil collector is welded.

So, 6 A even without heatsink - someone willing to try?

Since my board as of today seems to be broken anyways, I would “donate” it and test the MOSFET, as long as Velleman still send me a replacement :wink:


Hi Kurasuu,

thanks for the information.

Yes, I’m willing to test it but of course as your board is dead, I will have to connect the gate manually so it will be visible that something happened to the PCB and you could lose your warranty. So before that I think it is advisable that I will contact Velleman to talk about this and see if we can agree that it is ok to do the experiment. In that case, you could send your board to me (Belgium, is cheap by post from Germany), I do the test and share the results (IR heat photo included), I’ll test your board and if it really is defective, I’ll arrange the swap at Velleman’s and I’ll send the new one to you.
Is that ok for you?

Hi laserguy,

sure enough, I’ll contact Velleman to check the warranty before rewiring. More afterwards.


Hi Kurasuu,

do mention that Guy from Alfa Parts - Vael will do it and that he will be very carefull and that he will share the information with them ;).

I’m not sure how long should we expect to wait for the result. A CPU running at 70C probably will die in several years. A CPU running at 30C probably can last for ever. But no body is willing to run that kind of experiment. Because no body will use the same CPU when the experiment finished. But it is certain that for any kind of circuits, the cooler the better. When the temperature raises, more electrons will jump through the gate and generate more heat. All heat will slowly melt the circuit to a point where the circuit is not usable. It doesn’t matter what the document said. Use heatsink and fan to any circuit which generates heat if you plan to use it forever.

The resistance of the bed is 5Ohm. The resistance of the wires is 1Ohm. With BUK6215 we can only go up to 75V 15A at most. At 15A the bed should be able to heat up to 50C within several second. Not sure if anybody has a 1200W 75V power to run the experiment. It’s probably achievable by charging a super cap first then release all energy to the bed instantly. It will be nice to see how many degrees the bed can raise within a second.

My bed is using 24V 4A with stock controller, wires and pcb. Not a problem at all. But I do have a 120mm fan blowing the controller.

@edirol, please bare this greenhorn question now: in your schematic you have several components connected to ground. I am confused how I should do this in practice on the PCB. Do I use the 24v DC return line as ground or do I need to use a separate (third) line for ground?

Anyone else who knows the answer feel free :slight_smile:


Every GND connection on the schematic has to be connected together on your PCB. This GND only belongs to the 24V part. It is my intention to have no electrical connection to the controller board, so you must not connect the grounds from the heatbed and the controller board.


OK, I think I understand now. This concerns only the 24V part o the PCB (right hand side of the optocoupler). The grounded parts will be going to the same line for ground and this will be connected to the X2-2 (-) connector of the 24V power supply.

Powering the heatbed with 24 Volts works rather well. After 30 minutes, the FET has a temperature of about 40 degrees and this does not change further. Tested with the board of Kuraasu. As this FET can withstand very high temperatures according to the datasheet, it looks safe.

@koke: Yes, thats correct

@laserguy: What board/FET are you referring to?