I just noticed, the FP16-3000 transformer is labelled as 48VA, 3A, 16V. NOT the 18Vac you have on your diagram. I don't think it makes a big difference, but wanted to make sure I am not misunderstanding something. The only significant change that makes is that point C will not be 24VDC, but more like 21VDC. The only thing that changes is the maximum output on the variable voltage setting.

I do have a second transformer of 40VA, 24VAC and 1.7A. Since I am designing mine to have as many as all 4 outputs (3.3, 5, 12, var) in use at the same time, I thought sticking with the 3A transformer was the better choice.

Thoughts?

I am unsure of the specs of the meter, it seems to say it works with a voltage of 4-30V to drive not measure. If that is true, instead of using the unregulated 24VDC, I could use regulated 12VDC since I could easily leave that 'on' all the time. I am not planning a switch.

I have question about the volt/amp meter.  I have been reading thru some materials and watching some videos on the volt/amp meter -- particularly regarding the use of an independent vs a shared power supply.  As I understand what I have read/watched, it seems that a shared power supply can be used provided that the voltage fed into the meter from that supply is between 4 and 30 volts. 

Since the PSU in the tutorial has a max voltage of 20 volts, could the volt/amp meter be wired to share the same power supply as the load?   In other words, in the case of the PSU in the tutorial, does it make a difference if the meter shares a power supply with the load or has its own power supply?

Duh!  It says right in the article that you used a 1K trim pot!  And the 100 ohm resister is a good idea, and I'll add it to my schematic that is the beginnings of the PCB.

Right now my 3D printer is chugging away at printing a template I'm going to use to layout the front panel of the project box.  I could have laid it out in thin card board and gotten done much, much faster, but somehow that just isn't as much fun as messing around with Fusion 360 to design the template.  Then exporting an STL file, slicing that and producing the g-code for the 3D printer.  And then watching a 2 hour print job!  I'll post some pics of the finished products when I'm done.

Find out exactly what you are dealing with. 

We all want to see you back again.  :-)

M

My point ..a good Transformer is becoming hard to find....

M

I confess I skipped your Linear DC Power Supplies presentation since I got it drilled into me in Trade School back in the 80s.

I would really love to build a proper Old School power supply but the availability of "big grunt"  transformers seems to be dwindling and they are becoming ever more (very) expensive.

I have seen projects involving Trashed Microwave Ovens and re purposing those transformers to do crazy stuff like spot welders.

I know it seems dippy but would it be possible to employ the same scrounging methodology but put a few more turns into the core to get thirty some volts? The rest of the circuitry would just be "plain sailing" but am I dreaming?

The practicality of winding such a machine makes my head hurt. The applications I have seen repurposed involve big fat copper of several turns at most, and very low voltage.

Microwave ovens grow like mushrooms on the kerb side trash collection.

Kindest Regards

M

I used a 1k, and I actually put a 100 ohm resistor in series with it so that the value never got down to zero.

The fuse is a 5x20mm, it fits in the power entry module. I used a slo-blo fuse in case of power surges.

And the perfboard I used was 9x15cm.

Hope that helps!

😎

Bill

Was that 4th trim pot, to replace the 560 ohm resistor from your schematic, still a 10K like the other three, or did you use a 1K?  Seems like the 1K wouldn't need as many turns to dial it into the right value.

And is the fuse phyisical size for the AC 5x20mm?

One more question.  What are the dimensions of your perf board.  Have ordered the chassis from Jameco, but have started the Kicad layout.  I would like the PCB I'm working on to be about the same size as your perf board.

Thanks! 🤠 

Switch mode power has it's place in modern design. 

Ham radio operators use linear for low noise because  high freg. artifacts may inter their IF. 

I like your design..

JS