add power supply mod page

input/blog/2021/2021_06_25_rd_psu_mod.md

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+title: Blog
+post: Reviving a broken bench top power supply
+description: Using a chinese RD DPH-5005 buck/boost module
+date: 2021-06-25
+parent: projects
+---
+
+About two years ago, in 2019, my bench top power supply decided to give up.
+It no longer showed the correct voltage, only displaying zero, and the regulation did not seem to work anymore either.
+I noticed that when a battery I tried to charge started smoking... 😰
+
+Because of all the hassle of moving, I moved it to the healing bench where it stayed for a while.
+Some months ago, I decided to do something about it, and went to the Conrad Support.
+I originally bought it there, and they still sell it today.
+They had me send it in, but then decided they couldn't do anything about it.
+
+Some years earlier I saw [a video on the EEVblog YouTube channel about RDTech power supply modules](https://www.youtube.com/watch?v=Cw2AjcczHg4).
+So I decided to give them a go and ordered the [DPH-5005 module](https://de.aliexpress.com/item/32840324731.html).
+
+<!--%
+lightgallery([
+    [ "img/rd_psu_mod_7.jpg", "Front view of the finished PSU" ],
+    [ "img/rd_psu_mod_6.jpg", "Side view of the finished PSU" ],
+])
+%-->
+
+As you can see, I simply replaced the front panel of my existing power supply, re-using the transformer and parts for the rectifier.
+On the 3D printed replacement front, I mounted the display module as well as the buck/boost module itself.
+I also kept the original power switch, but added new output connectors.
+
+<!--%
+lightgallery([
+    [ "img/basetech_bt305_cover_2.png", "Front view of the 3D model"],
+    [ "img/basetech_bt305_cover_1.png", "Back side of the 3D model"],
+])
+%-->
+
+The rectifier of the original power supply consisted of a PCB mounted to a big heatsink in the back.
+It had some relais to switch between the different windings of the transformer, as well as the switching transistors and the rectifier.
+I desoldered the diode package and the capacitors.
+The diodes are still mounted to their original spot on the heatsink, with the leads simply soldered on.
+For the capacitors, I used a piece of strip-perf-board I had lying around, mounted with a spacer to one of the existing, now empty, holes of the heatsink.
+I used two strips of copper for each of the positive and negative poles, with a thick layer of solder on top so it can easily carry the current.
+
+<!--%
+lightgallery([
+    [ "img/rd_psu_mod_1.jpg", "Left view inside the opened device" ],
+    [ "img/rd_psu_mod_5.jpg", "Right view inside the opened device" ],
+])
+%-->
+
+Figuring out the details of the transformer was a bit of an issue.
+It seems to be a specially made transformer, just for this power supply.
+Even though it has an identifying label, it contains no usable information, and the numbers on it lead nowhere on Google.
+So I first measured the resistance / continuity (while powered off and unplugged of course!) to determine which wires are part of one coil.
+Turns out, there are two main output windings, one with only the two outer connections, and one with a bunch of center taps.
+I connected two ends of the two windings, and used the outer-most connection points, to get the maximum voltage, which is a bit less than 40V AC, or 50V DC rectified.
+
+This is also where I made an error in the selection of the DPH-5005 module.
+I specifically selected it because it can also boost the voltage up, instead of only stepping down.
+I did this because I wanted to get the full range of 50V, thinking I only had 40V input voltage.
+However, I forgot to consider that the rectified DC voltage is higher than the AC voltage.
+So I would not even need a boost module to reach the 50V output voltage.
+Of course, it still works fine that way.
+
+<!--%
+lightgallery([
+    [ "img/rd_psu_mod_2.jpg", "Closer look at the display module" ],
+    [ "img/rd_psu_mod_3.jpg", "Close up of the rectifier" ],
+    [ "img/rd_psu_mod_4.jpg", "Closer view of the connectors and the buck/boost module" ],
+])
+%-->
+
+For the output connectors, I ordered some proper [Hirschmann PKI10 A](https://www.conrad.de/de/p/sks-hirschmann-pki-10-a-au-polklemme-rot-35-a-1-st-732786.html) Polklemmen.
+The original connectors used on the power supply are of the safety-4mm-banana-plug style.
+I don't even own a cable like that, but I sometimes need to connect a bare wire, so these fit my use case much better.
+
+The DPH-5005 also has a Bluetooth or USB option.
+They both come in the form of a small extra PCB, with either a Bluetooth module or a USB-Serial chip.
+I added mounts for the Bluetooth module in my design.
+
+Supposedly ['rdserialtool' by rfinnie](https://github.com/rfinnie/rdserialtool) can be used to access the device via the serial port over USB or Bluetooth.
+I have not yet gotten this to work with Bluetooth, however, and have not tried USB.
+Also see the [sigrok wiki](https://sigrok.org/wiki/RDTech_DPS_series) for some more about the protocol and available settings.
+
+My 3D design for the replacement front [is available on my Gitea server](https://git.xythobuz.de/thomas/3d-print-designs/src/branch/master/basetech_bt305_cover.scad).