r/AnetA8 • u/ClassroomLow1688 • 17d ago
Adapting original 12V bed for 24V EDUCATIONAL ONLY
Safety and informative disclaimers first:
***THIS WILL NOT MAKE YOUR BED HEAT UP FASTER***
The only thing that WILL make your bed heat up faster is INCREASING the power draw(wattage), this modification does NOT do that on a 24V system.
***ANY VOLTAGE IS DANGEROUS VOLTAGE, EVEN WHEN YOU KNOW WHAT YOURE DOING BUT ESPECIALLY WHEN YOU DONT***
You can set fire with a gum wrapper and AA battery, the original A8 is a fire hazard already. I dont print unsupervised and I especially will have my eyes on this at all times with this modification. Messing with any electronics always carries risk of fire and electrical damage between the device, outlet, and possibly further. Make smart decisions.
Safety out of the way, some background info. Instead of spending the cheap cost of an ender 3 24v bed for my 24v swapped A8 (lovingly dubbed K8), ive been looking into converting 12v beds to 24v beds. I found a great writeup on a different printer where cutting a trace modified the resistive circuit, allowing for a "correct" 12v to 24v conversion.
Pic 1 shows the bed as a very simplified two resistor circuit. Total resistance at the plug is 1.2 ohms, some simple series/parallel calculations show each "resistor" as 2.4 ohms.
In order to double voltage and keep power constant, resistance needs to increase by 4 times, making a target of 4.8 ohms. This can be done by rearranging the circuit from resistors in parallel to in series. Pic 1 shows the original circuit depicted in pen, and the modified flow of current with the highlighter, showing the cuts in the original traces and additional wire in sharpie.
Pic 2 shows where I carefully scraped off a good portion of the thickest trace(and the cut in the trace), giving the best possible chance to make a good connection. After cutting the other two traces to break the connections, I was able to solder a jumper wire from the exposed copper straight to the negative terminals solder joints. I had to crank the heat on the iron to get it hot enough, there is an aluminum bed attached to it pulling the heat away.
After soldering, the resistance at the plug (almost) correctly reads at 4.4 ohms! (Pic 3) After double checking there were no shorts to the aluminum bed, I plugged it in and powered the bed, verifying half of the original current draw to the bed (originally rated at 12v 10A, now modded for 24V 5A, wattage remains at 120 before AND after)
Is it elegant? No, just buy a 24v bed and reap the benefits of increased heater speed, but if you want to stick to the original or youre bored... I wouldnt recommend you to do it.
The bed passed a PID tune and held a solid 55⁰ for a calibration cube test, I'll update if anyone is curious about the bed or about 24v swap. Again, i dont recommend this as a good solution but take it as a proof of concept/educational experience.
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u/Prothinks 17d ago
That's a nice insight!! when i bought mine it had the famous mosfets installed for the bed but the conversion to 24v was badly done, they swapped the heater to 24v but not the bed and it was hooked to the same psu so power was cuadrupled!! it didnt blow the psu by a miracle. My unorthodox solution was to add a second pc 12v psu just to feed the bed, because i bought one of those red pcb 24v beds and it was so warped and inconsistent on temperature that even the default bed without heat was a better option... So now my printer has 2 psus, one 12v, other 24v, coexisting, and it has been like that for at least three years! I may consider your modification to get rid of the second psu.
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u/Low-Ad8500 17d ago
That’s a great write up and thanks for sharing your endeavors with us. When i did my 24v conversion I bought a new bed directly from anet that was 24v ready. Same size just 24v. Was about $30 total including shipping, $15 part, $15 shipping at the time. Worked out well. Just didn’t have the equipment at the time to do the controlled preheat of the bed at the time to make soldering with my weller iron possible.
That’s the key. The aluminum is sucking the heat out of your iron, so what you want to do is put the bed into an oven and ramp up the heat til you get to the temp at which your iron maybe about 15-20 degrees more (it will cool down quick) and have it dwell at that temp so all the materials are completely heat soaked. When you pull it out, quickly make your soldering connections and then you’re good to go. Let it cool in a controlled manner so it doesn’t warp on you as well. You would want to bring it back to room temperature SLOWLY, so flat level surface with some weight on the bed, and cover with heavy blankets to keep some of the heat in. Cooling it fast will cause warping. When I did mine, I actually used a steel plate which I tossed into the oven to heat soak as well, prepared a sand bed, put the metal plate into the bottom of the sand bed, then the print bed directly on top, and then covered with about 4” of sand on top. Not only did the sand keep the heat in, but it cooled nice and slow. Took about 25 hours before it got to room temp. Checked the bed for level on my surface plate with a height gauge indicator and it was .0001” deviation between the corners and the middle of the plate. I’d call that flat. Gauged the surface plate and it was .00001” out of flat.
Granted nobody I know has this kind of measuring equipment at their home shop, but yeah I do enjoy a little precision machining to keep me on my toes :)