2019. december 30., hétfő

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.

2019. december 29., vasárnap

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.

2019. december 28., szombat

Hi-Fi rack - Motorized turntable shelf

I started to build a rack to my retro Akai set. I'm a small guy. When I started to plan the rack I realized that I loose space in the rack if I put the turntable on the top of it (it can't be taller than 120-130cm). If I build a 170 tall rack and put the turntable into the middle of it I still loose space, as I should open the lid somehow.
What if I build a shelf can be pulled out with the turntable? This way I not loose space. Think this a bit further: add a motor for the shelf.
Ok, but how to control the shelf?
What if I add an aluminum profile to the front of the shelf and use it as a touch sensor?
And the result:

The controlling electronics today contains an Arduino UNO, a CNC Shield, a DRV8825 motor driver and a few additional components on a breadboard.
This is not the final solution. I intend to build a specialized electronics for this. Change the motor controller to a Trinamic one because this is too loud now.