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Hello!
Sorry if this question is already answered somewhere, haven't found anything specific.

Just as everyone, I have a major problem with my heatbed, it hardly reaches 80-90 degrees, and if I print with fan on, the temperature drops to 55, which just destroys my adhesion. It's especially bad with PETG, which requires higher temperatures.

I know about 24V upgrade, but it requires SSR (the good one is very expensive, the cheap ones are dangerous. I like my flat, too early to burn it down).
So I want to go simple - improve my machine with stock power supply. It can be adjusted to increase the voltage, hopefully to 14-15V (haven't tried >13.5 yet), which will give a significant boost to heating. But at the same time it makes my extruder fan go crazy, it becomes extremely noisy, I don't think it's healthy for the fan as well. Looks like higher voltage is fine for motors and RAMBO board.

My idea. What if I set a DC-DC converter for the extruder fan, so it only has 10-11V (it's the noisiest part of the machine even on 12V, I want to slightly decrease the voltage), and the rest will work on 14-15V?

It will be difficult, if the fan is controlled with PWM. I've read that in theory it is, but I changed the Ext1 cooler speed setting in EEPROM, restarted the printer, but nothing changed. And this fan is always on. Is it really PWM driven? If so, can I put a huge capacitor and LM317 with a small heatsink? The current is small, shouldn't heat much.

Any potential problems? Or maybe I'm missing something and it can be done much easier?

Thank you!

Actually, another option: just a resistor in a fan circuit. Need an estimation of fan current to calculate the Ohms needed. And it might need to be quite large to dissipate enough heat, but still it's much easier, once the supply voltage and current are constant.

The heatsink fan gets a constant current, it's not under pwm control. Putting a resistor inline would be the easiest way to quiet it down. I've regularly run my rostock power supply at 14V with no problem.

Thank you! I'll measure the current for 12V and will put a resistor. Will post the results here.

I've realized that
1) The power supply for the extruder fan is not coming from the RAMBO board separately, it's just a common supply. So if I need to put a resistor there, it will have to be on the hot-end. Which sucks.
2) The extruder fan is actually not the noisiest one. The side fan, blowing air out of the base - this one is noisy. Decreasing a voltage with resistor would require 25 Ohm 0.5 W resistor, wo it will heat significantly. I've put a step-down regulator there, dropping the voltage to 9V, Plus I've added some corkwood damper, noise level is much lower now. Still bad, but better.

So the printer works on 14.3V, just finished a PID tuning, everything is fine.

Thanks for help!

For anyone else doing a similar modification, instead of a resistor I suggest you put two 1N4001 or similar silicon rectifier diodes in series with the fan. They will drop almost 1V each, bringing 13.5V-14V from the PSU back down to 12V for the fan.

Good point, dc42, but my version with step-down DC-DC converter is better - it's much more efficient, so it doesn't heat at all (maybe slightly warm on touch), and it's still cheap enough ($1-2). In-line resistor or diode, linear regulator (LM317) - they will need to dissipate 3V * 0.2A = 0.6W, which is a lot for a tiny resistor/diode/etc, so you need to cool it down somehow.
And another benefit of my approach - the output voltage is adjustable, I can tune it later if needed easily.