Thursday 7 November 2019

My build of a 30V digitally controlled, current limited bench power supply for £45

Bench power supply for <£50

Note: Some links in this article are affiliate links. This article is not sponsored in any way and all materials used were purchased privately.

I wanted to get an adjustable current-limited bench power supply however good quality retail versions are very expensive and buying a cheap power supply is always risky.

UTP1306S - see blog post

This minileaf is on a flash sale for 2 days at Banggood, only £36 for a 30V 10A <10mV ripple, 5-star rated by 97% of customers) but always comes with the risk that it will stop working and be unrepairable after a while or will arrive in bits.

Due to the problems of returning faulty products when buying from overseas suppliers, if I was going to buy a bench PSU I would buy one from Amazon for £59 as it is easier to return faulty items.

By making my own PSU from modules, it will be easy to repair just by changing the faulty module.

I was really looking for a dual supply PSU so that I could test circuits that required a positive and negative rail, but making a suitable case would present a problem. So I decided to try a single-output, isolated PSU first and then I could always purchase another if I need to add a -ve or dual supply.

I became interested in the RIDEN display\buck converter units after seeing them reviewed on an EEVblog YouTube video.

EEVBlog YouTube video

Charging batteries

Because these units can be set to a limited voltage and current output, they can also be used to charge batteries as long as you do not leave the battery on charge too long (you should see the voltage rise and then the current drop until you get to just a few mA of charging and then you can stop).

Recommended settings for battery charges are typically:
  • NiMH - 1.2V @ 0.1C  (e.g. for a 600mA cell, charge at 1.2V @ 60mA)
  • Terniary Lithium Ion - 4.2V @ 0.5C
  • Lithium Ion Phosphate - 3.6V @ 1C
  • 12V Lead acid battery - 14.4V @ 0.1C
YouTube video here. The DP and DPS units do not require you to connect a large current Schotky diode in series with the output to protect the unit from the reverse voltage from the battery.

My PSU (based on DPS3005)

This neat little mains-powered bench power supply provides 30 Volt variable output at 5 Amps and has an adjustable current limit. The extra two rear terminal posts can be connected up to supply 36V at 5 Amps (unmetered) which is the raw output from the AC-DC switching PSU. Both front and rear outputs are 'floating'' (not tied to ground). You can also attach a PC to the opto-isolated USB socket to control the PSU.

bluetooth option board (+£5) is also available which allows you to control the bench PSU from an app. However, I did not add this board to my PSU.

The RIDEN front panel module is available in various flavours:

Product ID
Difference between DP,DPS and DPH1. DPS series are updated version. Panel is different. In DPS series, we change the M1/↑and M2/↓ into V/↑and A/↓. You can press those buttons set the voltage and current fast. We add a new function “set default boot open or close output”
Others are not changed.
2. DPS5005 and DP5005 can charge the battery directly, don't need diode. When charging battery, don’t connect battery polarity reversely, otherwise, power parts will bunt.
Find the difference between DPS and DP see this video
3, DP power supply and DPS power supply are all buck (step-down) converter.  But DPH3205 is buck-boost (step-down and step-up )converter.
4, DPS3005-C and DPS5005-c are communication version. You can connect PC and use with computer
Communication functionNoNoNoNoNoNoNoNoNo
Working modeBuck modeBuck modeBuck modeBuck modeBuck modeBuck modeBuck modeBuck modeBuck mode
Input voltage4.5-23V6-35V6-55V6-55V6-40V6-40V6-55V6-40V6-60V
Output voltage0-20.0V0-32.0V0-50.00V0-50.00V0.00-32.00V0.00-32.00V0.00-50.00V0.00-32.00V0.00-50.00V
Output current0-2.00A0-3.10A0-2.000A0-5.000A0-3.000A0-5.000A0-5.000A0-12.00A0-15.00A
Output power0-40W0-99W0-100W0-250W0-96W0-160W0-250W0-384W0-750W
Voltage resolution0.1V0.1V0.01V0.01V0.01V0.01V0.01V0.01V0.01V
Current resolution0.01A0.01A0.001A0.001A0.001A0.001A0.001A0.01A0.01A
Product size79*34*26mm79*34*26mm79*34*48
79*43*48mm (display )
79*43*48mm (display )
screenLCDLCDColor LCDColor LCDColor LCDColor LCDColor LCDColor LCDColor LCD
FanNO (don’t need)YESYESNO (don’t need)NO (don’t need)NO (don’t need)NO (don’t need)YESYES
Charge the batteryNONONOYesYesYesYesYesYes
FunctionPreset  output voltage / current 
Power down storage
Store shortcut storage value
Exact shortcut storage value
Adjust LCD brightness
Open or close output
2 data groups 
Preset  output voltage / current 
Power down storage
Store shortcut storage value
Exact shortcut storage value
Adjust LCD brightness
Open or close output
2 data groups
Preset  output voltage / current(in two places by SET KEY)
Preset protection value
6 running status icons
Key lock
Data setting and store the specified data group
Store shortcut storage value
Exact shortcut M1 or M2 or specified data group
Adjust LCD brightness
Open or close output
10 data groups
Preset  output voltage / current(in two places, by V,A button and SET KEY)
Preset protection value
6 running status icons
Key lock
Data setting and store the specified data group
Store shortcut storage value
Exact shortcut M1 or M2 or specified data group
Adjust LCD brightness
Open or close output
10 data groups
Set default boot open or close output

There is also
DPH3205 - which has a buck-boost function (input 6-30V, output 0-32 5A)
DPH5005 - which has a buck-boost function (input 6-50V, output 0-50 5A) (£40)

For instance, you could use a DPH module with an old ATX PSU to get a 0-50V 5A bench supply (and still have 3.3V, 12V, -12V and 5V outputs).

DPS5015, DPS5020, DPH5005、DPS3012 and DPS3205 require the Type B case.

Download data sheets and docs from here.

A new RD6006 version + case is now available too (see below).

My PSU Features

AC Input: 110-240V 50/60Hz
DC Output voltage range: 0V-32V     
DC Output current: 0-5A
DC Output power range: 0-160W
DC Output voltage resolution: 0.01V
DC Output current resolution: 0.001A
DC Output ripple: approx 50-100mV pk-pk
DC Output Voltage accuracy: ± (0.5% + 1 digits)
DC Output Current accuracy: ± (0.5% + 2 digit)
Rear Output terminals: 36V 5A short circuit protection, over-current and over-voltage protection.
Internal 5V fan (temperature controlled).
Floating DC output (not connected to ground).
Remote USB control (optional bluetooth+app).

You can buy a similar ready-made one from Banggood (without USB\bluetooth or presets, etc.) when it is on offer for approx. £40. It has much lower noise/ripple on the output and seems to be well recommended. I don't have this one myself however and so cannot personally attest to it's quality or safety.

My shopping list

1. RIDEN steel case - I used case A for DPS3005  (£18)
2. AC-DC converter - I used a 36V 5Amp AC-DC switching PSU DC36-5. (£7)
3. RIDEN Constant current-constant voltage converter LCD voltmeter - I used the DPS3005 + USB (£21 - £26)
4. 4 off Nylon standoff pillars + 8 screws (or PCB supports) for the AC-DC power board (I found it easy to strip the threads on the nylon M3 screws I used, so I would suggest using the plastic PCB supports).
5. Metal screw + nut and tag washer for Ground connection to lower chassis.
6. Rubber grommet for mains input cable + mains cable and fused plug.
7. Various lengths wire (5A rated) + heat-shrink tubing.
8. KSD9700 (or Amazon) Temperature sensor 45 °C (wire in series with fan 5V supply).

Note the NO thermostat on top of the transformer. The PCB label says DC24 but is is actually a 36V DC unit.

The mains input - I used hot glue to ensure the two wires would always stay apart even if one of them comes loose. You can also see the small USB board.

The DC output side - both front panel and rear terminals are connected to the 36V output.

The mains lead was fitted under the rocker switch and above the USB socket!

Notes on assembly

1. Drill 4 holes in the base of the chassis to mount the AC-DC board on nylon pillars.
2. Drill one hole in the chassis near the rear for the mains earth wire connection - make sure you remove surrounding paint for good contact.
3. Drill one large hole in the rear for the rubber grommet. The size will depend on the size of your mains cable (I used a standard IEC 3-pin UK mains cable and cut off the IEC plug as I seem to have a surplus of these around). Be careful when drilling to use gentle pressure when using the drill press so as not to distort the rear panel. Tip: Smear a small amount of WD40 onto the cable to allow easy threading through the rubber grommet. Use a cable tie around the mains cable to prevent it from being pulled out, and for safety, ensure that the earth wire has more slack than the other two mains wires.
4. The AC-DC board needs to supply Vmax x 1.1 to the RIDEN converter/meter unit - e.g. if you want a 30V variable output then the AC-DC board must supply at least a 33V.
5. The rear panel fan+terminals PCB was originally intended to be used for a DC input. The PCB has a buck converter to accept approx. 12V-55V input and supply 5V to the small fan. In our case we will use the two terminals to provide a 2nd DC output. Note carefully how the wires are connected to this PCB and also note the small shorting link wire which is soldered directly across two of the pads (or you can wire the temperature sensor between these two pads instead of shorting them).
6. My AC-DC board contained a quick-blow mains fuse. If yours does not, you should consider adding one. The fuse in the mains plug can also be changed for a lower value one if you wish.
7. Use cable ties and hot glue to prevent any of the mains wiring from touching the metal case should they become loose. I also used adhesive kaptan tape to insulate the metal case lid around the mains input areas as an extra precaution.
8. You could connect the 0V output to mains earth to the 0V output if you do not need or want a floating DC output or use a 500K resistor to prevent leakage voltage appearing in the outputs (in my case the outputs could float to 90V above ground (UK mains is 230V) but at only a few uAs.
9. Check the connection from the earth pin on the plug to the chassis (find a bare metal contact point on the chassis - don't use the chassis solder tag when testing). Check there are no shorts between any of the three mains wires and that the mains rocker switch works and is wired correctly. Check for shorts on the DC side and that none of the DC output terminals are connected to mains earth (unless you connected 0V to earth). Switch on and check the AC-DC board output is correct first before connecting the front panel DC-DC/meter module.
10. I glued the Normally-Open (NO) thermostat switch on top of the transformer using a double-sided sticky foam pad. This also had the effect of holding down the AC-DC PCB when the case lid was fitted.
11. Download and test the PC app. for remote USB control.

Note that current is measured using a shunt in the 0V side (not the '+ve' side). This means that if you connect anything to the rear DC output terminals (such as another DPS unit or PSU which also measures current), then the current reading on the front panel DPS meter will be wrong (either 0A or a smaller value if the 2nd power supply also has a 0V current shunt).

My 'To Do' list
I may add an 'Earth' toggle switch to the front panel as there is not enough room to add a proper Gnd terminal post to either the front or the rear panel. My DVM measured 10-12V AC at 1uA between Gnd and the 0V terminal under load but this can float up to 90V+ with no load connected. I can sometimes feel a small tingle occasionally if the 0V output is not connected to ground at all. Some people connect a 1M or 500K resistor between Gnd and 0V to remove this floating voltage difference.

I did consider using the two rear terminals as 0V and Gnd terminals so that I could wire them together if I required an earthed 0V rail but thought having a 36V 5A output might be more useful.


If you want to go up-market, for about £100 you can make a 0-60V 6 Amp bench PSU, by combining a RIDEN 6006 module (£35) with the S06A case + wiring kit (£31) and an AC-DC Power Supply (e.g. 60V AC-DC $32 - adjusted to 67V using trim pot). It will have an IEC mains input socket at the rear and USB, WiFi and an app and probably you won't even need to get out your soldering iron or drill any holes. The official video is here. If it does go wrong, you will only have to fork out £35 or $32 to fix it.

Official video

Fit the RD6006+mains PSU into the S06A case

Dave's Eevblog video (ignore false bad noise findings - see next video!).

Note: unverified comment from Bangood feedback:

3 x 330uF 100v caps are 'permanently' connected to the output lugs?? really? I've set my output to 8v and 20 MILLIAMPERES. Turned output to ON and give power to 5watt LED! guess what?? it flashed briefly (BIG TIME FLASH) and then LED output lights at 18-20mAmps. In laymans term, the capacitor at the output will 'collect' current while there is no load. no matter HOW LOW you set current at output. yes because its a capacitor and thats what they DO! and when you connect an LED rated for 20mA, it would instantly kill it with a kick of a FEW AMPERES before 'settling' in for "20mA" god damn!!!!

I assume this is an issue with any PSU which will have large caps on the output side for smoothing??

Correct noise measurement is actually 150mV-ish pk-pk (still not brilliant though).

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