You may have seen the Ruideng range of programmable power supply modules from China: small and relatively inexpensive switch-mode buck converters, with microprocessor control and a front panel featuring a large colour OLED screen. Given 30 volts or so they can supply any lower voltage with the extra bonus of current limiting. They’ve been so successful over the several years they’ve been available that they’ve even spawned their own Chinese clones, and countless hacker projects, for instance on the DPS300X and DPS500X models.
Late last year a new module came from Ruideng, the Riden-branded RD6006 combines the basic idea of the previous modules with an extremely flexible front panel with full keypad and rotary encoder, creating something like the front panel to a decent bench power supply but without the accompanying power supply. I ordered one, waited for it to clear customs, took it to my bench, and reviewed it.
What Does Fifty Dollars Get You As A Power Supply?
It’s well packed in a sturdy box with a foam inner shell, and additionally includes a plug-in temperature sensor, a set of crimp spade terminals, and a spare fuse. I’d ordered the slightly more expensive “W” version with WiFi connectivity, so my £38 ($49) also netted a small plug-in PCB holding an ESP8266 module.
There isn’t a paper manual. Instead there’s a card directing the user to a PDF download on the Ruideng website that yields a document in both Chinese and English which is well written and easy to follow.
The unit itself is a grey rectangular plastic box around 165 mm x 81 mm (6.5″ x 3.2″) on its front panel, and about 50 mm (2″) deep. The front panel has the complement of buttons and encoder, a 6.25 mm (2.5″) diagonal OLED screen, and a set of output terminals. It’s designed to be a module that sits in a piece of equipment rather than a standalone device, so the rear is not covered and the printed circuit boards are fully accessible. Sockets for temperature sensor and WiFi module are on the left-hand side, and these were easily installed.
Power input is via a set of pluggable screw terminal blocks that can take anything between 6 V and 70 V. I lack a handy 70 V supply, but as will many people with a junk box, I do have a power supply from an HP printer that supplies 32 V at 1.5 A. I hooked it up, and then powered up the unit with its on-off switch.
The basic interface will be familiar to anyone who has used one of the previous Ruideng modules. There are three main displays of output voltage, current, and power, and to the right of them a set of smaller displays showing the parameters of the system. Input voltage, output voltage and current limit, and over voltage and current settings are all there, while along the bottom is a temperature display and a set of status flags. To set values there are a set of buttons for selecting which to change, and then a numerical keypad or the rotary encoder to select a value. There is also a battery-backed clock.
What’s It Like In Use?
Beyond the basics the device supports up to nine memory settings for frequently used voltages, and most interestingly, a graphing display option that provides a view of current and voltage over time. The graph can be the default screen, and when it is enabled the input and output voltage and current displays are relegated to the right hand side in a smaller font. It has a flaw though in that it does not appear to automatically update its axes, making it difficult to follow small currents. There did not appear to be a menu option to disable this.
Power output comes from three 4 mm socket/screw terminal combos as you’ll expect from other power supplies. There are the usual positive and negative terminals, with a third terminal between them for a lead-acid battery charging function.
At first glance it’s a capable and easy to use little power supply. Press “V-set” or “I-set” and key in a value, and it’s ready to go. There’s an “On/off” button below the encoder that enables the output; pressing this makes the juice flow. I tested the supply with a variety of loads, from big wirewound resistors to motors, other pieces of electronics, and even shorting a 4 mm cable across it to test the current limiter. As a straight DC power supply in this way it performed faultlessly, never missing a beat and providing measured voltages and currents exactly as it claimed.
There’s a little more to a DC power supply than just DC though, because only the idealised DC from a textbook page is really DC in the frequency domain. All power supplies contain some noise, even batteries, and since the Riden is a switch-mode supply there’s a chance that some of its switching frequency might find its way onto its output terminals. With cheap switch-mode supplies, such as dollar-store phone chargers, this can soemtimes even be visible as a high-frequency ripple on a normal oscilloscope. In the case of the Riden there is no such ripple to be seen.
How do you characterise the noise output of a power supply? In this case I think rather than overall noise we should be interested in looking for any peaks at particular frequencies , for example at harmonic multiples of its switching frequency. The only suitable instrument I have is my oscilloscope with its FFT function enabled. It’s a mediocre substitute for a spectrum analyser, but it will quite happily display the harmonics of a square wave used for calibration, so it will serve our purpose here. Hooking the Riden up to a wirewound heating element as a load and applying some volts with my trusty Rigol 1054z attached, I was able to pull up a spectrum of its output. As I would expect there was a broad spectrum of noise but not significantly higher than when connected to a linear supply, and I was pleased to see that there were no obvious peaks even up into the HF range. It seems they’ve done a good job of regulation and filtering, but without better test equipment that’s about as far as we can go.
But This Is The W Version, What’s That All About?
There’s one final part of this review: the WiFi module. It looks suspiciously like an ESP8266-to-serial module that plugs into the main PCB, but how do you use it? In essence it provides connectivity to either an iOS or an Android app. There is an option to enable WiFi connectivity, and then the supply should be restarted in proximity to the mobile phone running the Riden app. At a guess it sets up an access point that the app connects to, you are asked for the credentials of your wireless network, and that’s pretty much it. You can then connect to your power supply with your phone.
At first sight it simply replicates some of the front panel controls, handy should you ever need to change your current limit from your armchair, but on further inspection there’s a little bit more to it. The graphing function in the app is far superior to that on the device, with axes that scale to the readings in question, and there is the option to save a log of readings. This turns the phone into a powerful extension to the unit, and is in my opinion worth the extra few quid. It’s worth pointing out that in addition to the WiFi there is a USB serial port on the front panel, I’d be extremely disappointed if someone in our wider community doesn’t reverse engineer the APIs involved and produce some open-source software to do more with this facility.
In conclusion, the Riden RD6006(W) seems to follow on from the quality established with the previous Riden modules, and provides a very useful power supply for the price, with plenty of features to keep you occupied. It doesn’t have a mains power supply of its own, so factor that into the price. However, as I found out, there are plenty of readily available supplies that can be used even if they don’t provide the full range of what the unit is capable of. This is well worth considering when you are in search of a power supply.