Should I install external MOSFETs?

Should I install one or more external MOSFETs in my Anycubic Mega?

My answer to this:

As long as you don't replace the bed with something more powerful, you don't need an external MOSFET at all. Neither for bed nor for hotend.

The original ones on the board don't even get lukewarm and are designed for much higher currents. The clamps are perfectly fine too. The little electricity that goes through there is switched loosely. We're only talking about a MOSFET here. This is a "switch that turns a heater on and off". And only as well as the main processor controls. No more and no less. Just on and off.

And seriously: I've seen defective external MOSFETs more often than anything else. And then they roast the power supply. The self-made cabling is also often not the best thing.

So what's the point? Correct. It feels like "tuning". But it is not.

Anyone who installs an external MOSFET likes to argue that this takes the load off the board and that the board could burn out. - But it can't. Several fuses are soldered there. It doesn't get hot at all ... just touch it. And then the insane costs in case the boad breaks? ... Uh ... 30 euros including shipping for a trigorilla? A set of external MOSFETs + fuses costs more.

The argument that ABS and ASA need higher temperatures and therefore "more power" on the heating bed is often made. Umm ... The bed is only switched ON or OFF. Always with the same output, because that is determined by the resistance of the heating bed. It makes absolutely no difference whether you leave it on a little longer until it is at 90°C, or switch it off and pulse so that it stays at 60°C.

This is all nonsense to me.

For those who install a larger/hotter bed + new power supply, it may make sense ... for everyone else, it's like a rear spoiler on the VW Polo. Looks good, but it's useless.

After being asked again and again which MOSFET is good, I looked at different ones. Unfortunately, the manufacturers of the circuit boards are silent about the actual components. It just says something like "Max 30A" or "Hotbed <150W" almost everywhere ... Has anyone ever looked at what is installed on the Anycubic Trigorilla Board? A VS40200ATD.

Here is the data sheet: https://datasheetspdf.com/pdf/1281879/VanguardSemiconductor/VS40200ATD/1

So let's assume you want to install a thicker heating bed and then consider using an external MOSFET .... yes then I won't buy anything that is worse than what is already on my board anyway !

Back to the subject of "security":

1. An external MOSFET protects against nothing. If the heating cartridge is down, it will burn out. The inside is cast in with ceramic. It doesn't make a short circuit. Even if there is, there is still a fuse on the board. Same with the heating bed. In the event of a short circuit, the fuse blows. However, the bed never burns out during normal operation.

2. If one of these external MOSFETs dies, which are easily clamped directly to the power supply unit and are also sold without a fuse, then the power supply unit or the thin cables will burn off.

3. In most cases, an external MOSFET can withstand much less and can switch lower currents than the original on the mainboard.

4. The external MOSFETs are still switched via the internal MOSFETs on the board. When the external ones are really gone, then the ones on the board are short-circuited as well. Has anyone ever looked at the supply lines that are included with most of them? The board is still pushing full power out of the output. Which will light up first? The 25A fuse or the thin cable to the external one? Correct. The thin "control line" of the external MOSFET, which is now totally pissed off. Your mainboard now thinks that a heating bed would be attached to it;)

5. Better alternative solution: A real upgrade in terms of security is that you cut off the tip-soldered leads to the board one centimeter (so that the solder is off and the strands are free again) and instead a real cable lug (wire sleeve) with the appropriate crimping pliers crimps.

Background: Soldered cables in any type of screwed terminal pose a danger. The soldered ends are "hard" and the screw can be tightened firmly. But it doesn't stay that way the longer you are connected. The more current flows, the faster the solder / solder will soften and contract under the screw.

The result: the screw is loose, the contact is poor and heat is generated due to the high contact resistance. -> The clamp burns down! ... and yes, that is a realistic scenario that has occurred several times.

Cheap solution: Shorten the cable with the side cutter and strip it again. Then twist the strands and screw them into the elevator clamps.

Better solution: As described above, crimp a wire sleeve firmly onto it. This prevents the strands from "dangling around" and prevents possible short circuits.