Using 40W adapter on 30W heater cartridge?

Question

Recently, I accidentally shorted out my heater cartridge when trying to do my first nozzle swap on my Prusa MK3S+. I just ordered a new E3D v6 Hotend with 30 W Heater Cartridge and it will be here in a few days. I just cut the wire from my heater cartridge to my heat block (long story short, I can't remove it from the block). I'm not sure I understand exactly the wattage though. The heater cartridge that came with my Prusa MK3S+ is 40 W. Does that mean the actual cartridge or the plug into the board? Also, can I just solder the existing 40 W wires to the new 30 W cartridge? If so, does it need to be a precise solder (I'm not very good at precise soldering) Finally, can I just wrap the connection in electrical tape? Sorry for so many questions; this is my first time trying to understand the electrical component of 3D Printing. Any help would be appreciated.

I can't replace my individual heater cartridge because the screw was melted in. I checked my mainboard fuses and they are fine. My printer still powers on, all the motors work fine, and even the bed heater works. I cut the wires at the heater cartridge and left them in the air not touching, and now it thinks it's heating up, so I think that I can deduce that the wires were touching the heater cartridge, and I wasn't able to separate them. Unfortunately, I don't have a wire crimper and am trying to keep this fix as simple as possible.

Note:

After using a 30 W heater on my MK3S+ for a while, I started getting thermal runaway problems somehow, and I have switched over to E3D Revo Six for the safer PTC heating element.

Answer 1

There's a lot going on in this question, and I think you would have done better to ask first before ordering anything how to fix your printer. It's not even clear what part is damaged. A heater cartridge itself can't be damaged by shorting, as that's basically the normal mode of operation for it. However, if you shorted the leads going into it to one another, bypassing the heater, those wires or more likely your mainboard could be toast. Or you might just have broken a wire.

Moreover, it doesn't make sense why you ordered a whole replacement hotend, much less one that's a downgrade for your printer. The E3D V6 is woefully underpowered at 30W. 40W is a bare minimum nowadays.

To answer your specific question points, normally heater cartridges and preassembled hotends come with wires long enough, and proper gauge, to go all the way to the terminals on the mainboard. Some, however, have short wires and some sort of connector. If it has long wires, it's best to just run them all the way to the mainboard as intended rather than splicing. If you do need to splice wire or add a connector, wiring that was made for a higher current will be fine for lower current (as long as it's undamaged). Solder joints are generally not a good idea, though, as they will undergo wear when the wire moves with the toolhead. My understanding is that it's better to use some sort of crimp splice.

And of course, before you do any of this, try to determine whether your controller board is what's damaged. If so, which I think is fairly likely, then you need to either repair or replace it, not the hotend. Connecting a multimeter (in voltage mode) or light bulb of the appropriate voltage to the heater terminal on the board and trying to run the heater would tell you immediately if it's bad (no output) but won't necessarily tell you that it's good.