Category Archives: PSU

SG90 9G Servo is no wimp

This litle Servo about 3 x 3cm is far from a wimp as far at current usage goes. A single Servo have no problem dragging a 10A PSU down – actually I think it’s the current regulation that is predictive, meaning it drops out because current raise is to fast – but, anyway – the only PSU I have that can manage this is a 80A battery.

I connecting 4 of these to my ESP32 Utility Driver and some of my dodgy wires burned up.

Looking at the scope I observe a small Voltage drop as the Signals pulse in. As I add servo’s it become worse. I think I need to alter my algorithm a little to spread the pulses out in time and avoid 12 servos that pulse at the exact same time. I also think I need to buy a 6V battery and ditch the 12V to 5V regulator as it most likely is this that dip a bit.

The ESP32 Utility Deriver does however work well. I am a bit puzled over my DPS5005 PSU’s. They seem to use a predictive aproach to regulating current.

Adding Wifi to DPS5005

The DPS5005 contains a USB/RS485 interface so both PSU’s can be remotely controlled. I want to use this option to create a Wifi based PSU. ESP-Wroom-32 do have 3 UART’s, so we can still keep UART0 for programming and use UART1 & 2 for each board. I do however notice on the original USB board that the vendor used photo couplers and I think that is a good idea. I would otherwise struggle with ground between the two PSU units that needs to remain isolated from each other.

The only concern here is that the opto coupler’s have limited data rates, but DPS5005 comes pre-programmed with a fixed baudrate anyway. The schematics above is just one I found and modified in Powerpoint of all things. I am not sure ESP32 is capable of driving an opto-coupler directly, so we might need transistors. I obviously also need a separate PSU as I can’t feed from any of the main ones. The signal from DPS5005 include a 5V PSU to feed that side, so we will be using 3 separate PSU’s on this board.

Dual 0-35V/0-5A Variable Lab PSU – Assembled

This shows the assembled PSU. Only one of the DPS5005 modules are mounted as I am still waiting on the 2nd. You can see the driver stage mounted inside. The black painted front turned out quite nice.

This is the back side with the mains connector, fuse and switch. I have to wait a few weeks for the 2nd module, but I am quite happy with this PSU. Actual max voltage out is 34.75V as input is 35.75V. Current limit is +/- 0.005A according to the build in meter.

Dual 0-35V/0-5A Variable Lab PSU

I recently bought a DPS5005 which is a 5A variant of the larger 20A DSP5020 I wrote about earlier. This module can deliver 0-50V/0-5A and have all the electronics inside the display module. Testing of this proves to be very good and it’s a good match for the 36V/5A driver module. As it all also fit well within a low-cost metal cabin I decided to build a dual Lab PSU.

The picture above is the HMI module. The larger DPS5020 have a separate regulator board while the smaller DPS5005 have the regulator board inside this module which makes it very size optional. Both modules are with USB. Basically I just wanted the RX/TX and Modbus in place so I can expland the Lab PSU later.

One of the things I really like with this HMI is that turning the knob by accident changes nothing. You actually have to press A or V first. You also get to adjust out power before setting it out. In fact the HMI does not look like much, but it is very impressive and clever design.

This picture show the 230VAC to 36V/5A driver module available for ca 10.- USD. DPS5005 can deliver 50V out, but as this module is limited to 36V it delivers only 35V out. This is however more than sufficient for basic needs.

This is the 17.- USD box that I use. The plates are steel, so it’s a bit of a job drilling holes etc. But, it is sufficient room for fuses and mains connection, 2 x driver modules, 2 x displays and 2 x PSU connectors. Making the holes went a bit messy. Basically the plate ended up bent around my drill, so I I had to hammer it back out and decided to change color. Was not too found of the blue in the first place.

This shows the all-in-one mains connector, fuse and on/off switch. The only drawback is that I end up with the on/off switch on the back, but I can live with that.

The last component is this female banaa plugs in front, one for each PSU. The table below show the BOM and the ca total cost of the PSU. All these parts are avaiable on www.aliexpress.com

2 DPS5005 32.- USD 64.- USD
2 Drivers 36V/5A 12.- USD 24.- USD
2 Banana connectors 2.- USD 4.- USD
1 Mains connector 4.- USD 4.- USD
1 Cabinet 18.- USD 18.- USD
Total 114.- USD

A single PSU 0-30V/0-5A is usually around 100.- USD with P&P. A dual PSU (cheap) would be ca 150.- USD++. This is a programmable, dual PSU. It will cost me anoth 50.- USD to add the ESP32 and HMI later, but once that is done you have a PSU that normally cost several times more.

PSU Ripple

The LMR14206 ripple was a bit much for my taste. It worked, I had 12V out, 3V3 out and the MCU ticked. But, it’s not a design I can live with. For now I continue on a different board and avoid mounting the DC/DC because I also realized that I could not really bypass it they way I had set up the jumpers. I decided for a 78M05 in TO252 format that gives 0,5A. But, for now I will use 12V directly.

This will work for now. I will return to DC/DC later, but looking at other peoples postings and the lack of LMR14206 popularity I get the picture.

The supercap in the schematics works well, but I probably need to add a bit of circuitry like I did on on PLC Com module. I use a 0.33F due to the size.

LMR14206 PSU Ripple

LMR14206 with 12V output to a LM1117 3.3V regulator. This is the 3.3V – 350mV ripple – not good. I need to work on that a bit. This is from my Motor Controller with MCU ticking.

I probably need to add another coil on the 3.3V, but that add a lot of space, so I am starting to think that a 7812/317 regulator is a better shoice. Will see how much is needed to fix this.

Regardless a bit impressed over my DS1054 Rigol Oscilloscope. I have an expensive Techtronics at work and to be honest I would gladly replace it with my Rigol costing only 10% of the price for a Techtronics.

DPS5020 Review 3

I was finally able to test this on a pro lab with full 20A throughput. The small Fan started moving at ca 10A, but was still silent at 20A. We shorted and let the module take a bit of beating with no effect – it continued to behave. This turns out to be a very good programmable Lab PSU module. Well done.

A minor comment is that the module lack a calibration option. Both Voltage and Current are close, but we noticed a 0.3V difference to calibrated instruments. This could easily have been calibrated in software.

PSU 36V / 5V

I purchased this for < 12.- USD and tried it as a driver stage for DPS5020. It works fine. It is small and perfect for a 0-35V / 0-6A “bread & butter” lab PSU. The DPS5020 have a cut-off setting that I set to 6A. It cut’s the PSU if you by mistake allow more than 6A out to protect the driver stage. The driver is also short-cut protected.

  • Driver PSU : 12.- USD
  • DPS5005: 25.- USD
  • Box : 17.- USD
  • Mix: 10.- USD

That is 64.- USD for a single 0-35V / 0-5A and 101.- USD for a dual. And this Lab PSU will have far better spec than any of the “cheap” ones. Also keep in mind that DPS5005 is much smaller than DPS5020 as it hide the PSU inside the HMI unit.I notice that Input Voltage to DPS5020 variates with +/- 0.05 as I use the Driver at 5A. I will put a oscilloscope to see if I have ripple later.

I had to abort the test yesterday after ca 10 minutes because my load started to melt 🙂 – we have some awesome Lab PSU’s coming up. DPS5020 do have a small fan, but it has been silent so far.

Adjusting Voltage/Current on these modules are a joy- Just select V or A and turn the knob. Push the knob to change digit you adjust. With a MCU using ADC’s we have an accuracy on ca 0.02ich – which is pretty good compared to analogue PSU’s.

What we have not discussed so far is output filtering. With some of these giving 50V – 20A we will be giving 1KW out. That is 1KW that will spike back as 1000V with 1KW energy if we have coils/motors connected. We need to ensure that the PSU can protect both itself and the equipment we are testing.

DPS5020 Review 2

The interface on the UART is Modbus RTU. I managed to translate the document from Chinese to English yesterday, so it is uploaded on the download page. Running the top-side app was straight forward on Windows 10. I had a bit of issues with antivirus installing it, so had to switch that off. The graphs are cool, but the window scale is a bit short and it only update once a second. Testing current under load was however a beauty. Using 36V in (3 x 12V/10) I had no problems with 10A out – or more correctly my load and test wires did get hot.

DPS5020 Protocol Specification 1.2 can be found on the download pages here.

Using UART/Modbus as interface it will be straight forward to create a custom HMI module to add buttons and display graphs on the box without a PC.

PSU Driver

The diagram above show the minimum needed for any mains PSU. We need a On/Off switch and a fuse. This can be purchased as a single unit. The 2nd is the PSU itself that is available in numbers on the net in nice modules.

A 12V/10A module cost < 10.- USD and they can be connected to create more current or higher voltages. Using 5 modules you can create 60V/10A at a cost of < 50.- USD. Using multiple modules like this can save some cost, but it usually require more space. As illustrated in an earlier entry the Driver stage is actually more expensive than the DPS5020.

Please check the regulations of your country before connecting anything to the mains.