Here is a true recycling project — turning a laptop’s internal CPU cooling fan into a general-purpose portable air-cooling fan/blower for an electronics hobby workbench. Frankly speaking, major-level repairing of a laptop is often tricky because you need expensive hardware tools or the components are too customized to do anything fruitful with them. The introduction of high-density circuit boards and unhelpful labeling of components make the identification of circuitry and individual parts extremely difficult. As an after-effect, you may be forced to throw away your laptop as an “electronic scrap.” But hey, you are an electronics hobbyist, so pull the laptop out from the garbage and get ready to discover an opportunity (like me) to breathe new life into some discarded devices that had been condemned to oblivion!
A recent treasure hunt in my junkyard finally gave me the opportunity to properly play with one laptop’s internal CPU cooling fan. The rugged CPU cooling fan, dismantled from a Toshiba laptop, is a 400-mA/DC 5-V brushless fan from Delta Electronics Inc. It is a three-fan (as usual) with red (+5 V), black (0 V), and yellow (tach/pulse) connection leads. The model number of the fan (as printed on its label) is KSB06105HA.
First, the two power supply wires (red and black) were hooked up to my lab power supply. The fan immediately turned on and began to render a strong current of air through its rectangular vent. The current consumption at DC 5 V measured about 580 mA (0.58 A)!
After the child’s play, the fan stayed in a corner of my workbench — a useless device. What use did I have for it? Without any firm ideas, I stored it in my junk box. A few days later, I reconsidered the fan, and it quickly became clear that I could do something useful with it. Yes, I had an insight. What about a USB-powered cooling fan/blower unit or a portable air-cooling fan/blower system?
What I learned from an old piece of documentation (Analog Dialogue 38-02, February 2004) is that a three-wire fan can also be controlled using the same kind of drive as for two-wire fans — fixed/variable DC or low-frequency pulse-width modulation. A three-wire fan has an additional techometric (tach) output for closed-loop speed control, which provides a signal with frequency proportional to speed. The tach signal (available through the third wire) indicates whether the fan is running and its rate of speed. However, I just wanted to play with only two wires because the tach signal was not essential for my initial concept.
I got my hands on a defunct China power bank weeks ago. It was given to me at no charge, and after a spry disassembly, I was left with only one relatively healthy 18650 (3.7 V/2,000 mAh) lithium-ion battery. Although it seemed like a good starting point, I wasn’t lucky enough to have another vital component on hand to realize my initial concept. So I ordered a set of two from eBay, and after a few days, I had finished the fabrication of my prototype (the model is still in its infancy, so no pictures yet).
In fact, my initial circuitry was built around a handful of discrete components, and it worked well. Later, I chose a ready-made eBay module (USB 18650 battery power bank module — see next figure) because it’s more compact and perfect for my idea (my basic design has a lot more components).
Below is the tried and tested hardware diagram of the “retooled” portable cooling fan/blower with a built-in rechargeable battery, battery charger, and optional USB power port.
Right now, there is only one very simple mode of operation: Set the system live and the connected cooling fan will keep running. I haven’t put it to much use yet; I still have some ideas on how to expand its functionality. However, it seems to work quite well this way!
As you might have noticed, at the heart of the power bank module is an eight-pin chip HT4928S from HOTCHIP. It’s undoubtedly a very clever design (see the original circuit of the module inside the shaded area of my schematic)!
Have you ever made a similar device? I would love to see it, post it in the comments below!