Open source STM32 soldering station isolation

[blazini36]

I came across this project a while ago, I'm just getting around to digging into it since I need a new soldering setup anyway. https://www.hackster.io/sfrwmaker/soldering-and-rework-station-for-t12-and-jbc-tips-ec2c44#overview

The author mentions using an external transformer to isolate the power rails from ground as he's just using a non-isolated Meanwell 300w switching supply. I'm planning on using a Meanwell PID-250B which is a dual isolated power supply. That also gets rid of the onboard 5v DC-DC converter module by just adding a 5v connector from the PSU.

I started converting the main-board to KiCAD since there were a few things I didn't like, like the use of too many different styles of connectors, etc and I don't know EasyEDA very well. I wound up entirely re-doing the main PCB (haven't really looked at the others yet). As I was going through it I found the 5v converter section a little odd. He uses an MP1584 DC-DC converter module to get 5v from the 24v input which is fine, then uses a B0505S 5v isolated module before the 3.3v LDO. The input and output ground/commons are tied together on the B0505S as the op-amp section can't be isolated from the input the way it's done. I suppose the B0505S is cleaning up the 5v a bit but I'm not really sure that this has much use since it's common with the input that drives the irons etc...

I'm keeping the footprints for the MP1584 and B0505S on my PCB but not using them since I can bring 5v in from my PSU. I have a fairly lousy understanding of analog stuff, op-amps, etc, but I'm wondering if it would be worth the effort to isolate the 5v/3.3v grounds from the 24v ground. The OP amp section is the only thing that really makes it a problem to isolate both rails. Not sure what to do about it or if I should even bother. Any thoughts?

[Doctorandus_P]

I like the MP1584 boards in general, I once tested one, both shorted it and put an too high voltage on it's output and it did not damage it. They are quite nice small supplies, but that was years ago, the chinese probably do have fake version too now.

The B0505 is just silly in this application. It's either put there by someone not knowing any better, or it was simply forgotten to be taken out during some revision of the schematic. There are a bunch of different brands of the B0505. Mornsun recently got a slap on it's fingers for delivering stuff to Vladimir Vampirovitch Puta.

What does a "non-isolated Meanwell 300W switching supply" mean? I find it hard to believe Meanwell makes non-isolated supplies in that category.

[blazini36]

What does a "non-isolated Meanwell 300W switching supply" mean? I find it hard to believe Meanwell makes non-isolated supplies in that category.

So far as I know none of the common switching power supplies from Meanwell are fully isolated from earth ground unless they're medical grade, etc. The author uses an EPP-300 which is not. I'm using a PID-250B which is.

[Doctorandus_P]

What does a "non-isolated Meanwell 300W switching supply" mean? I find it hard to believe Meanwell makes non-isolated supplies in that category.

So far as I know none of the common switching power supplies from Meanwell are fully isolated from earth ground unless they're medical grade, etc. The author uses an EPP-300 which is not. I'm using a PID-250B which is.

https://www.meanwell.com/productPdf.aspx?i=715

Well then, what does this mean:
WITHSTAND VOLTAGEI/P-O/P:3KVAC     I/P-FG:2KVAC     O/P-FG:0.5KVAC
ISOLATION RESISTANCE I/P-O/P, I/P-FG, O/P-FG:100M Ohms / 500VDC / 25°C/ 70% RH

Sure, medical grade power supplies are designed for more stringent factors, but they will still have capacitive coupling between primary and secondary. So in the end it boils down to your personal definition of "fully isolated".

In high power antenna masts (100kW transmitters and such), the whole mast is often energized. They use special transformers to couple in low frequency mains power for powering warning lights and stuff.  Those are "quite well isolated" transformers with can have an isolation air gap between the primary and secondary windings of over 100mm. Capacitive coupling will be pretty low for those. It's a bit of a missed opportunity that Marco Reps did not include one of those in his quest for his 0.0001pF coupling.

[blazini36]

I'm still trying to figure out why people on forums go through such great lengths to derail a thread 

The EPP-300 IS isolated from FG. Thinking the EPP was not isolated is mostly due to the author of the projects own comments

The only disadvantage is thet this power supply is not isolated one. The JBC tips have feature that the termo-couple is connected to the tip body, so using switching power supply the 'Line' terminal from AC outlet goes to the body of the tip.

None of that has anything to do with the ACTUAL question posted about isolating the DC rails (and their grounds) from each other. I'm not using an EPP-300, I don't care whether it's isolated or not.....it wasn't the question.