2kW Bench Power Supply 2.

Please don't look for the first part under the title above! It was published as Few stories ...
It took a while to go further with this project.
I built and tested the my delay circuit mentioned here.

Works as expected.
Done all of the cabling, mechanical work, needed for the assembly.

I was choosing a C20 connector instead of the regular C14. The two power supplies can consume maximum 3kW, so I felt that a bigger connector is needed.
After almost of a year skip, I restarted my 3D printer. So I created a 3D printed back panel:

I made a short video shot to show how the delayed startup of the two supplies works:

So, this unit is working now. The only thing is missing, the computer control.
The two units originally has two separate optically isolated USB to Serial units. I wanted to solve this with one USB port. So, I ordered a dual channel FTDI module, what unfortunately not yet arrived.
The USB port already assembled to the back, it just waits for the module and an optoisolator board design from me. This will be the second phase of this project.

Two problems - one solution

As usual I'm building several things in parallel.
In my last post I was writing about the switch on problem of my dual power supply. This is the first thing need a solution.
A few month ago I bought a 1,5kW variac for a bargain price (€50 what is a joke if I add that this unit even has isolated primary and secondary winding).

When I tried to use it, realized, that it immediately switch of the circuit breaker. Too much inrush current (huge iron core).
For the first problem I need a timed switch circuit, what can be controlled by a low current switch circuit. For the second problem I need a classic soft start unit.
If we dig a bit into the operation of the circuits we will find that those are similar. In the first we need to switch on the high power side after a certain amount of time. In the second the system will be switched on immediately just through a pack of power resistors, what will be shorted after a certain amount of time.
So If I separate the the switch of the controlling power supply from the high power side with a switch, I'm ready.
In the delay switch unit I'll left out the power resistors and control the small PSU from the front panel switch. In the soft start unit I'll populate the power resistors and shorting the small PSU to the high power circuit (and add an external, high current capable mains switch).
During the design of the circuit I went a bit further. Added two of the units above to a single PCB. Those can be used either in master-slave mode (adding only one mains input, one power on switch, one low power PSU but two different delays with two relays) or it can be used as two fully functional units if we cut the PCBs two side.
So, the whole design is complette now. I'll order the PCB in a few days (I've a few other things in my head and I want to pay only a single shipment cost from the manufacturer).
The schematic diagram:

The PCB design:

The 3D model of the board:

This is first of my designs what have a complete 3D model. I was able to use the OpenSCAD -> scad -> FreeCAD -> step workflow for creating models for my own part designs easily.

Few stories - Build something on it.

I'm building something. As usual.
I'm telling a few stories about things - unusual? I don't know.

1. I'm fundamentally an IT guy. Most of my life I worked in various companies fulfilling various IT jobs. This dates back when I was head of the IT plus sysadmin at a company called "Láng Holding".
This was before the internet era (just to understand, the internet was existing way before some of the younger or not core IT people thinks). So it dated to 1998-1999 (Before the dotnet boom).
We acted as a usual holding company. Mainly working as financial/legal entity. One of the biggest IT challenge at those days was to have the countries laws, the country wide corporate registry available electronically for our employees. At that time this information was not available on the just starting web.
There were a company who provided this information on subscription based CDROMs.
A usual computer has only one CDROM drive (mostly non today), but I needed more, centrally on the server. So I bought a nice SCSI box with four drive bays and four SCSI CDROMs for the task.
Those days passed. We finally closed this company, and the box above landed in my loft (together with many old IT things).

2. A few weeks ago I ordered two identical 60V/1500W DC power supply modules from China. As I didn't wanted to pay the higher shipping cost of DHL, I ordered them separately. It costs $99 each.
This was a good test of the local post, how they handle the customs. I can tell: randomly.
The first one I ordered landed at customs, and still didn't arrived to me. The second one I ordered landed in my house without customs handling.

3. Back in 2017, I ordered a Ruideng DPS5020 power supply module from Banggood. After a few month it become clear, that it will never arrive. So I complained, they resent it, and after a while both arrived. I agreed with them to keep both instead of sending one back.

As you may realized by now I want to build a dual channel 0-50V/20A power supply to my lab. This is in my mind since 2017.
As I have both the lab supply modules and the huge mains power supply for it, I started to think, what would be the best possible enclosure for it. All the ones I found at the local suppliers and the online sources were too big and too costly. Then come into my mind the forgotten SCSI box from the loft:

Removed everything from inside:

Built two power modules from the Ruideng controller and the 1,5kW PSUs added some aluminum profiles:

Mounted it into the box above:

Here come a few problems:
1. I started to think. The box has 3kW PSU inside. I think, the original power switch will never be able to handle around 15A current.
2. I don't want to switch those PSU simultaneously on, because the mains fuse will not handle the inrush current
3. I want to control the PSUs from a PC, but on a single USB port. So I need to change the USB/RS232 adapter came with the units to something else.

As you see the build almost finished, I just need to address those issues. Especially to first two. Those will come in a later article.

High Voltage DC Power Supply 4. - The phase switching module

!!!DANGER!!!

The circuit described bellow is dangerous. Using it improperly will kill you. On the other side I may also made mistakes during the design and built. I'll take absolutely no responsibility for it. If you want to build it, please don't ask for circuit board or help. I won't help you.

In my previous posts about the high voltage supply I already wrote about the small electronics able to keep the GND of the DC side on earth potential without isolation.

No this is not voodoo. It just a simple circuit.

The theory:

The protective earth connection in the mains connector is connected to the mains null somewhere in your system. Probably somewhere around the utility meter. So if we measure the voltage between the Line and Earth, it will be the full mains voltage. If we measure the voltage between the Null and the Earth, it will be zero. To be able to work with, I draw the following circuit:

This is just two simple zener regulator, what provide the necessary sense signals for the further processing.

I designed a complete circuit around this, with an MCU, a 5V power supply, MOSFETs for driving relays and two DPDT relay.

The board design:

Based on this design I ordered the boards from allpcb. Actually I made a mistake around the design. I bought my relays after I sent the board for manufacturing. The result is that I connected the switched circuit on wrong direction. This means if I build the circuit the relays create a short circuit to the mains.
Throw away the boards (without even soldering a single component), ordered a new batch.
It also arrived within a few days:

The finished board:

I wrote a small arduino code to run the board. It has an ATTINY84 in it. Actually the code would fit in an ATTINY24 easily.
Assembled the whole thing into it's final place:

I connected the final thing to the mains. Switched on the power switch. Everything looked fine, until I pressed the output button.
The main circuit breaker in my house went off. Shitt.
Few more tries. The result get even worst. It killed the mains even switching on the power switch and not the output button.
Removed the phase switching board. Measured. It looked like both of the relays killed. There was a short circuit between the line and the neutral on the board.
Here is when Murphy comes into the picture. How many components buy I usually for my circuits? Way more than needed. Except this case. I had only those two relays on the board. Weekend. I should wait until Monday, to replace the relays.
In the meantime I removed the relays from the board - I hate the THT desoldering.
Removed the cap from one of the relays to be able to make a picture of the burnt contacts:

The surprise come here. No burned contact. Even I made a picture with my microscope. The result is the same:

Nothing, the contacts are intact. Measured the second desoldered relay, what still has it's cap. the result is the same, no sign of the failure anymore.
Just my guess that the heat and mechanical torture of removing the relays of the board resolved the temporal latch-up of the contacts.
Now back to the basics. As I can't find out the source of the problem (didn't wanted to play this game with new relays). I just guessed that the inrush current of the capacitors causing the problem (as I wrote earlier, I had problem with it already). So I hacked a solution. Together with the new relays I bought some inrush protector NTCs. It isn't an ideal solution, but hopefully will be sufficient. Hacked a PDU board to accommodate the NTCs. I've a few spare anyways:

The relays replaced. The whole thing works as expected.
I'm still thinking about the proper solution. The device is a tool and not a target for me. So it may not worth the effort to build a second version.

High Voltage DC Power Supply 3.

!!!DANGER!!!

The circuit described bellow is dangerous. Using it improperly will kill you. On the other side I may also made mistakes during the design and built. I'll take absolutely no responsibility for it. If you want to build it, please don't ask for circuit board or help. I won't help you.

So, I continued to work on the issues from the previous post.
"Mill a hole for the mains socket and the circuit breaker to the backpanel"
done
"Mill the holes for the banana jacks to the front panel"
Actually it was much simpler than I meant originally. My step drills eventually arrived. Sooner than expected. Never used such tool previously. On the first try I was able to drill the holes in no time.
"Finish the wiring"
done

"Set the correct decimal dots"
It wasn't easy to remove those solder blobs, but done
"build a dummy load to be able to test the current measurement"
Actually a professional DC electronic load what is able to work above 300V isn't cheap. So I decided to pick a 100W 1K resistor and screwed onto an old s478 heathsink. The question is if the fan have to be used. Finally it worked without it.

"Calibrate"
done
"Paint the front panel"
done

Actually I had serious problem with assembling the panel meters into the front panel. Most of the fixing clamps are broken of (because of the material aging or bad construction, who knows)

I hate that hot snore glue, but I had no other option here, to keep the panel meters in its place:

"Build the phase switching electronics (not mandatory, maybe after finish)"
Actually I've quite a progress with it, but it will be the subject of an other post. Not finished yet, so it is not assembled into the unit yet.

"Create the console for the caps"
This was funny. I don't know why I completely forgot that the outside (and therefore of the mounting screw also) of those large cans are the negative pole of the capacitor. building two caps with different potential on the same conductive (aluminum) mount is not a best idea of the world:

Luckily I realized this before switching on, and exchanged the mounting plate to a plastic one (unused etched FR4):

As I'm at the end of the todo points. The project is almost finished (just the phase switching electronics missing):

What's next:
I'll finish the phase switching electronics and install it.
The PSU itself has some room for improvement. Like cold start current limiting and proper capacitor draining. I'm not quite sure, that those improvements will be done in the near future. The usability of the equipment will tell.

High Voltage DC Power Supply 2.

!!!DANGER!!!

The circuit described bellow is dangerous. Using it improperly will kill you. On the other side I may also made mistakes during the design and built. I'll take absolutely no responsibility for it. If you want to build it, please don't ask for circuit board or help. I won't help you.

As the other PCBs are arrived for the supply, I continued the build.

Finished the separated isolated supplies for the panel meters (these are nothing else just a simple dual 7809 based linear supplies):

Also added the power distributor and some wiring for the backpanel:

Connected the panel meters and, milled parts of the front panel (manually as my CNC mill is still broken)
How the whole thing looks like today:

And its working, partially:

As you see the decimal dot is on the bad place (it is more likely 330V than 33V)
In addition I took a picture of the board on thermal camera. You can clearly see that the two capacitor draining resistors getting warm:

So I can tell, it is progressing, but quite few things still ahead of me:

• Mill a hole for the mains socket and the circuit breaker to the backpanel
• Mill the holes for the banana jacks to the front panel
• Finish the wiring
• Set the correct decimal dots
• build a dummy load to be able to test the current measurement
• Calibrate
• Paint the front panel
• Build the phase switching electronics (not mandatory, maybe after finish)
• Create the console for the caps

continue...

High Voltage DC Power Supply 1.

!!!DANGER!!!

The circuit described bellow is dangerous. Using it improperly will kill you. On the other side I may also made mistakes during the design and built. I'll take absolutely no responsibility for it. If you want to build it, please don't ask for circuit board or help. I won't help you.

I've many ideas in my had, what to build, what to experiment with.
A few of them involve using mains voltage directly. Some of this need to rectify and clean the input before using.
My lab power supplies are able to produce 60V DC maximum, what is clearly not enough for those experiments. A cost of a proper high voltage variable DC supply is enormous, and I don't need most of the features of it right now:

• Not need to be variable. My built circuits will have rectifications on its own. The input comes from mains anyways so this is the only voltage I need.
• Not need to be stabilized. Same concept as above.
• Not need to be isolated. I know, at this point the real professionals start to scream: IDIOT!!!! Let me explain why I'm not:
  1. I've built a proper isolation transformer in the past. I can use it, when it is necessary.
  2. My negligence: two way rectified mains after filtering in my country is around 650V DC. It is lethal anyways. If you make a mistake, it will kill you. It can't kill you twice because of the missing isolation.

So the plan:
Build a simple two way rectified supply with large can electrolytic capacitors (I bought 3300uF/500V ones for a good price. These puppies are huge).
Add necessary circuits for small panel meters to be able to measure, what is coming out from the circuit.
Add necessary circuit to discharge the capacitors. If they left unattended, they can still kill you after long time.
Add a special circuit I designed for it. It has two functions:

1. Test if the equipment grounded to the protective earth (it is not a proper grounding test, but if your lab is properly grounded, it will tell you if you have cabling problems)
2. Test the polarity of the incoming supply and change it if necessary. So the 0V output line of the equipment is always connected to the Null and never to the Line.

This circuit is still under development, so I don't know if it will work or not, but it isn't absolutely necessary for my power supply design. It adds some protection to the circuit, but nothing substitute the extreme care and the proper isolation.

I started to design this something like two weeks ago. Ordered the circuit board on the last Saturday. Actually it is already in my hands since Thursday, thanks to the extremely cheap, fast and high quality PCB manufacturer I found recently: ALLPCB (10 pcs 100x100 two sided boards for $5.49 delivered in 5-6 days - insane):

Yesterday I had some time to populate the board:

Those cans are huge, I told you.

Let see some measurement:

I've an isolation transformer, as I told before.
Ouch! My Fluke 117 unable to measure the output voltage.  According to the specification it is able to measure until 600V. In fact it was working until 650V, but the supply is above this. Lets change to a 1000V rated tool:

So, the PSU works now. My first impression, that the 100k/5W resistors I connected in parallel with the capacitors are improper for draining them. It take quite a long time (several minutes) to do their job, and generating some (not to much) heat during the operation (the 3W consumption on the display of the isolation transformer). It is sufficient  now, but I'm thinking to replace them to some active solution. (an AC Relay with some lower value/higher power resistors maybe).
This is it for now. Next is building into the enclosure, adding and calibrating the panel meters.

The surgery succeeded, the patient is dead

I got two fairly dead Electrodragon relay module from a friend to try to repair it.
The first looked like maybe repairable:

The second is completely dead:

From this wanted to salvage the terminal blocks from the secondary side to repair the first module, and the ESP module to put onto one of my dev boards.

Removed the blocks and the ESP from the board.
Created a new dev module from it:

The build succeeded perfectly (I'm getting better in SMD soldering),
but when I connected it to the programmer even the programmer felt out from the USB bus.
So the surgery succeeded, but the patient died.
I also repaired the first module, but as is it mains connected I don't want to try out without some precautions. I don't have more time for this right now.
Continue... 

Electronics - New projects cont...

How the Saturday boards are standing today:

I should write soon, not just taking pictures. :-)

CNC Motor Driver 5.

I planed to build the new motor driver during the weekend, what unfortunately doesn't happened. It took an additional week. What I want to mention here, that together with the motor driver I also designed a new measurement circuit. This one is able to measure not just the rotational speed but the current (it was also in the previous but untested) and the voltage of the motor. In addition I included the necessary protection diodes what was left out from the previous one, and a configurable fifth order low pass filter to test the filter for the final design.

Here is the schematic diagram:

And the PCB design:

The first weekend achievement - etching the boards and collecting the parts:

A week later - the boards cut, populated:

The next things to come (not necessarily in this order):

• Test this two boards
• Design a home made pcb for MCU+Display
• Add additional filtering into the adjustable DC
• Design and build the last missing piece - the high voltage input 3.3V PSU
• Test and tune the PID controller code
• Move to the final PSU from the lab supply
• Put everything together - write the code for the rpm setting from G-Code
• Write the code for the voltage/current/power measurement
• Design and order the final boards
• Build everything into the original controller box