Regulated benchtop power supplies can be expensive. Fortunately, the market is full of affordable DC-DC converter modules that function as adjustable DC power supplies. The ZK-4KX DC-DC Buck Boost Converter is one such model that is highly popular in the DIY community. It is not a particularly high-power device with a “normal” power rating of 35W. You can technically increase it to 50W but I will discuss the problem with that later in this review of the ZK-4KX Module.
I have seen some users building a DIY Bench Power Supply using the ZK-4KX Module and a computer PSU. Initially, I thought of doing something similar (using a 12V SMPS instead of a PC PSU). Since the absolute maximum current that ZK-4KX can handle is only 4A, I decided to go with the USB-PD route.
In this ZK-4KX DC-DC Buck Boost Converter Review, I would like to share my experiences of using this module as a mini regulated power supply as well as a battery charger. I will also share the details of the case that I built to pair it with a 100W USB-PD Adapter (through a USB-PD Trigger Module).
I already reviewed a much powerful DC-DC Converter: the XY5008L Buck Converter (a much better choice).
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What’s in the Box?
The unboxing experience is rather simple. The module came in a small cardboard box that has some basic specifications printed on it (Vin, Vout, and Iout). Opening the box, we get the main module in a bubble wrap.
There is nothing else in the box. As far as the user manual is concerned, there is none in the box. You have to look for manuals online.
Design of ZK-4KX DC-DC Converter
The ZK-4KX module is quite small measuring around 80mm×43mm×26mm at its maximum. On the front, there is a small custom LCD. To its right, there is a rotary encoder with a push function. We have a couple of push buttons on the left of the LCD (with labels SW and U/I). Above the LCD, there are two LED indicators, one is for the output status (Output ON – Green LED, Output OFF – LED Off) and the other to indicate Constant Current (CC) operation. I will explain more about the user interface i.e., the LCD, push buttons, and the rotary encoder in the next section.
If you flip the device to its back, you can see four screw terminals for input and output connections (OUT+, OUT-,VIN+, and VIN-). While we are on the rear, you can see the heat sink, main inductor, and a lot of passive components. I thought of disassembling the entire unit but as you can see, there are two blobs of glue (I think). I didn’t want to risk pulling out any tiny components under those blobs. Looks like there are two PCBs: one has the control unit (main controller, LCD, Rotary Encoder, Push Buttons, LEDs, etc.) while the other is for all the Buck-Boost conversion.
Seems like this style of vertical stacking of PCBs to make the entire module fit in a tiny space is pretty common with such DC-DC converters (the XY5008L DC-DC Converter Module also has a similar design approach).
How to Power the ZK-4KX Module? (USB-PD Trigger)
Before proceeding further, I would like to talk about how I planned on using the ZK-4KX Buck-Boost Converter Module. As I said before, my plan was to use a USB-PD Power Adapter (a 65W one) with ZK-4KX as its main source of power. However, in order to use that, we need a USB-PD Trigger Module to negotiate 20V from the USB-PD Adapter and deliver it to the device. I have a bunch of USB-PD triggers but the issue was picking the right one and also selecting a suitable case that fits both ZK-4KX and the USB-PD Trigger.
After some searching, I found a 3D case design on Thingiverse by BromBarium (I don’t have much experience in 3D Modelling). This particular design uses one of the simplest types of USB-PD Triggers with CH224K IC.
Using the DIP switches, you can negotiate the output voltage from a USB-PD Adapter (5V, 9V, 12V, 15V, and 20V). I immediately ordered a 3D print for the case and it arrived in just a couple of days.
ZK-4KX 3D-Printed Case
Here’s a quick look at the ZK-4KX case. It has the main box where the ZK-4KX module goes as well as a couple of holes to insert banana connectors at the bottom. The rear of the box/unit has a slot to slide the USB-PD Trigger Board and a separate bracket holds this board in place.
The back cover has a cut-in slot for the USB-C Port of the USB-Trigger board along with four holes for screws. Speaking of screws, the designer went for brass inserts instead of a threaded design (I am grateful for the design but had to purchase some M3 inserts). Also, an angled front would have been nice so that we can easily see the display.
After preparing some wires, I finished assembling the ZK-4KX into the case along with the USB-PD trigger in under 10 minutes.
Overall, happy with the outcome. Both the modules (ZK-4KX and USB-PD Trigger) fit perfectly in the case and the best thing is, I could power it with a USB-PD Adapter with ease.
User Interface and Controls
I plugged in a USB-C cable to the USB-PD Trigger and the ZK-4KX unit powered on immediately. We have to use a combination of rotary encoder, SW button, and U/I button to operate the device. Let me take you through the basic controls, parameter adjustment (output voltage and current), and the settings interface of ZK-4KX. I have been using this module for some time and made some adjustments to the settings. Sadly, I don’t remember how the first boot looks like (if there is a way to factory reset the module, do let me know).
Basic Adjustments
With the power on, the first thing that the LCD shows is OUT but the values of voltage and current are 0s. The output is off as indicated (or rather the lack of any indication) by the ON LED. To turn the output on, short press the rotary encoder button. The ON LED turns green and the LCD shows output voltage on the top and current at the bottom. Alternatively, if the output is on, the rotary encoder button will turn it off.
While the output is on, short press the ‘SW’ button to toggle the bottom part of the LCD between Current (A), Power (W), Capacity (Ah), and run time (h).
You can long press (press and hold for a couple of seconds) the ‘SW’ button to switch the top part of the display between output voltage, input voltage, and on-board temperature.
How to set the output voltage and current limit? With the output off, short press the U/I button. First, the voltage adjustment begins (as indicated by the blinking digit and display of the SET option). You can use the rotary encoder wheel to adjust the voltage and click its button to switch between digits. If there is no input from the user for about 10s, the displayed value will be set as the output voltage.
While setting the voltage, if you press the U/I button, the control will move to current adjustment. Again, use the encoder wheel to set the current limit and rotary encoder button to switch between digits. After setting the current limit value, either wait for 10s to automatically save and exit or click the U/I button to manually save the values and exit.
These are the basic operations for setting voltage and current limit.
Settings
Long press the U/I button to enter the Settings interface/menu, starting with the power on state. By default, the output of the ZK-4KX is off after you power it up. However, there is an option to change this i.e., the output turns on as soon as you power on the device. This might be useful to some industrial users but for regular users who intend to use it as a bench power supply, you should always be in control when the output becomes active.
The first parameter in the Settings menu, ‘OPEN’ sets the power on state. Use the rotary encoder button (long press) to switch between OFF and ON states. You can immediately exit the settings page by long pressing the U/I button or click the SW button to move to the next parameter.
The next seven parameters are a bunch of software protection mechanisms. Here’s a quick overview:
- LVP (Input Low Voltage Protection), default is 4.8V.
- OVP (Output Over Voltage Protection), default value is 31V.
- OCP (Overcurrent Protection), default is 4.1A.
- OPP (Over Power Protection), default is 50W.
- OAP (Maximum Capacity in Ah), default is off. Long press the encoder button to activate and rotate the encoder wheel to set a value (up to 60Ah). To disable, long press the encoder button until the message OFF is displayed.
- OHP (Maximum Running Time), default is off i.e., counts the time up. If set (same as previous), the device will work in countdown mode (shuts down output when reaches 0). You can set up to 99 hours and 59 minutes.
- OTP (Over Temperature Protection), default is 110℃.
After these basic parameters, we get a bunch of ‘Advanced’ settings in the form of calibration.
Calibration
At the OTP (Over Temperature Protection) parameter, if you click the ‘SW’ button, you will enter the calibration settings. If you are a beginner, I would recommend you not to mess with these settings. However, if you feel the values displayed on the ZK-4KX module’s LCD are slightly offset, you can make necessary changes here.
The first value is the input voltage. Use the encoder wheel to adjust the value and once set, long press the encoder button until the digit stops flashing (as an indication that the calibration value is saved).
You can similarly adjust output voltage and current values. The manufacturer recommends a minimum voltage of 12V (at both input and output) and a current of 1A for proper calibration.
You can switch between parameters in the Settings menu by clicking the ‘SW’ button and exit the Settings interface by long pressing the U/I button at any time.
Performance
Now that I have discussed almost all the important parameters, adjustments, and settings of the ZK-4KX DC-DC Converter, let us see how it performs in practical situations.
Regulated Power Supply
The main application of the ZK-4KX Module is using it as an alternative for a bench power supply (at least for students and beginners). As I have already mentioned how to set the output voltage and current limits, using ZK-4KX is simple and straightforward.
To check the accuracy of the values displayed on the LCD, I connected a 10Ω 10W power resistor as the load. In the following two images, you can see the output voltage on the LCD of ZK-4KX as well as a multimeter. The lack of resolution is a factor but I have to say that the values are pretty accurate.
The same is true even for the current values. There is about 2-3mA difference at lower currents (below 800mA) but as the current values increase, the accuracy is spot on.
As this is a Buck-Boost converter, the input voltage (and current for that matter) is very important. As per the manual, you need to supply at least 8V as input to get the full range of voltages at the output (focus on the power rating of the input supply you are using). Since my operation is purely based on a USB-PD Adapter (100W with 20V 5A), I might not have issues using this either as a buck or boost converter. But there are some concerning problems with this device, which I will mention in the next section.
I don’t have a scope to check it but the notes from the manufacturer says that the output ripple is very low and they used a Pi filter (that helps in minimizing the AC ripple on the output). You can see the Pi filter in the image of the rear side (left to the screw terminals).
ZK-4KX Battery Charger
If you are a regular reader of my blog, you might know that I love 18650 batteries and use them frequently in a lot of projects. I have been testing a new 3S BMS that is capable of handling up to 10A charge and discharge current. To test ZK-4KX as battery charger, I charged some 3S 18650 battery packs with different charge currents (1A, 1.5A, 2A, and 2.5A).
I am happy to say that the ZK-4KX is perfectly capable of charging most lithium-ion batteries (with proper BMS). The Constant Current (CC) mode activates as soon as I connect a battery and turn the output on.
While the BMS shuts off charging after the battery is full, you should always keep an eye on the battery pack if you plan to charge batteries using ZK-4KX Module (or other similar DC-DC converters). You don’t want to move the 18650 (or any lithium ion batteries) into float charge mode.
There is reverse polarity protection for both input and output terminals (hardware protection).
Problems with ZK-4KX Buck-Boost Converter Module
The ZK-4KX Buck Boost Converter Module is a very useful device to have around (especially if you are on a budget). However, there are a couple of serious problems with it.
Output Voltage Adjustment
When the output is on, you can adjust the output voltage on the fly by engaging the encoder wheel. This is okay as you can see the output voltage on the LCD as you rotate the rotary encoder.
The problem is when you turn the output off. As soon as you turn off the output, the LCD shows 0V and 0A. During this time, if you rotate the encoder wheel, you are actually adjusting the output voltage but since the output is off, the unit is not showing that. When you once again turn the output on, the output voltage this time will be whatever you set by rotating the encoder and not the value when you turned it off.
You have to be extremely careful while using ZK-4KX (especially if you want to power sensitive devices like LEDs or charge batteries). There is no way to lock the UI.
Thermal Performance
The next biggest concern is the power limit and thermal performance. On paper, the ZK-4KX is capable of delivering 35W without any additional cooling. They say we have to enhance cooling (by adding a cooling fan) if we want to increase the power limit to 50W.
For the first test, I set the output voltage to 10V and the current limit to 3.5A. I then connected the output of ZK-4KX to an electronic load and started pulling about 3.4A (output power around 34W).
In less than 3 minutes, the on-board temperature hit 80℃ (I set the Over Temperature Protection OTP to 80℃) and the unit shut off. When I captured the thermal image of the rear side of the unit, the heat sink and the rest of the components were at an okay temperature (heat sink was around 42℃, while the rest of them hovered between 60-65℃).
I mentioned a couple of blobs covering some components on the ‘power supply’ PCB. A transistor below one of the blobs was at 95℃.
Maybe 34-35W is too much. So, I dialed it down to 30W (10V, 3A). Even in this case, the device ran only for 5 minutes before OTP kicked in.
While the manufacturer says to add a cooling fan to improve heat dissipation (when current is over 3A or power is over 35W), there is no direct provision for it on the PCB. In case you plan to add a fan, you have to power it externally (not worth the hassle in my opinion).
Realistically, this can deliver about 30 – 34W if you limit the current to around 2A (set the output voltage between 15 and 17V).
Specifications
- Input Voltage: 5 – 30V
- Output Voltage: 0.5 – 30V
- Output Current: Only heat sink – 3A (can reach 4A with cooling fan)
- Output Power: Only heat sink – 35W (up to 50W with cooling fan)
- Voltage Display Resolution: 0.01V
- Current Display Resolution: 0.001A
- Conversion Efficiency: about 88%
- Input and Output Reverse Polarity Protection
- Input Undervoltage Protection: 4.8 – 30V (Default 4.8V)
- Output Overvoltage Protection: 0.5 – 31V (Default 31V)
- Output Overcurrent Protection: 0 – 4.1A (Default 4.1A)
- Overpower Protection: 0 – 50W (Default 50W)
- Overtemperature Protection: 80 – 110℃ (Default 110℃)
- Timeout Protection: 0 – 100h (Default off)
- Maximum Capacity Protection: 0 – 60Ah (Default off)
- Operating (Switching) Frequency: 180KHz
Price
I purchased the ZK-4KX DC-DC Buck-Boost Converter Module for around ₹1,000 ($11) from a local online electronics store. The USB-PD trigger was ₹300 ($3.5) and the 3D Case for ZK-4KX was also ₹1,000 ($11). The total cost of the full “bench power supply” using ZK-4KX with USB-PD support was around ₹2,500 (around $30). Is it worth the price?
Honestly, I don’t think so. There are much better DC-DC Converter Modules with way better specs than the ZK-4KX. The XY5008L, which I reviewed earlier, cost me only $26 and it came with a nice little metal case, it is USB-PD capable (along with few other input options), and is capable of delivering higher voltages and current.
Conclusion
So, what are my final thoughts on the ZK-4KX Buck Boost Converter? It is a compact little unit with a very small power rating. I really don’t understand its popularity as many people are using it to build a “bench power supply” with ZK-4KX and a computer PSU. That said, if you are on a very tight budget and want a decent regulated power supply, the ZK-4KX is an okay unit. I would definitely recommend the USB PD route I went with (provided you already have a decent USB-PD Adapter) instead of an ATX PSU or a laptop adapter.