ZK-4KX power supply module
Cheap but handy DC/DC converter module.
Pros:
- price (less than $10)
- independent output voltage and current control with pretty good resolution
- nice form factor, ready to be mounted on the panel
- decent user interface: LCD display with backlight, rotary encoder, two extra buttons
- multiple protections
- energy, power, time display for battery charging
- no assembly required
Cons:
- high capacitance at the output = no proper current limiting
- radiator is held only by a single screw (mine got loose after time and required disassembling)
Two latches on the sides for mounting on the panel.
Module has two stacked PCB, connected by two 5-pin headers. The "bottom" one (the one with radiator) is the actual DC/DC
converter, the "top" one contains control unit with display.
Bottom board is held by some thermal glue, top one by latches.
Microcontroller: Nuvaton N76E003. Relatively new part (announced in 2017), 8051 core with 18 kB FLASH and 1 kB SRAM, internal RC oscillators,
8 channels of 12-bit ADC 300 kSps.
TM1621B LCD driver.
UART and probably programming (IAP) interfaces.
LM358 operational amplifiers.
FP5139 DC/DC converter controller.
I was using this module for about two years without proper enclosure until finally commiting to create more permanent setup.
Initial layout plan.
For a power source I've used switching
mode power supply from old Lexmark printer, 30V/1A, with a grounded output (important for me).
As I've pretty often used this power supply for charging multiple USB devices, I've added three double USB sockets.
With this power supply charging current can be limited (potentially extending battery life) and it is also possible
to determine charging state and battery condition.
Two part metal enclosure was made of scrap metal sheet from old PC cases. I do have only rudimentary tools
and bending was made by hand after cutting the groove. Not too clean, but still acceptable in my opinion.
If I would be doing this again, I probably would made it slightly smaller - there is a little bit too much empty space inside.
So far I've opted for self-adhesive feet. Time would tell if this is durable.
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