Kerry D. Wong

We are all familiar with the I/V characteristics of a diode. The main characteristics of a typical diode is that when forward biased, it starts to conduct as the voltage applied approaches the threshold voltage of the diode and the current increases exponentially as the forward voltage increases. This behavior can be modeled by the Shockley diode equation. A question frequently asked is that what happens when the applied forward voltage is very small, say just a few millivolts? Continue reading ‘Diode Equation and Forward Current Measurement’ »

To charge the 110Ah battery bank I built, I need a power supply that can provide at least 10A at 14.6V. Since I have many old ATX power supplies lying around and the 12V rails of these power supplies are more than capable of providing 10A, I decided to modify one such power supply for using as a 4S LiFePO4 battery charger. Continue reading ‘Modifying a Computer ATX Power Supply For Higher Output Voltage’ »

The last ingredient for my backup power project is an inverter. Since the battery bank I built is a 12V 1.5kWh one, an inverter that can handle a load between 500W and 1000W would be a suitable choice. In theory, all the lights and the refrigerator in my house consume just around 500W. So the 1.5kWh battery bank should be able to power all the essentials for at least a couple of hours in the event of a power failure. Continue reading ‘Teardown and Testing of an 800W PureSine Inverter’ »

During the past couple of weeks I have been busy making a large battery bank using the eighty 32650 LiFePO4 cells I bought on eBay. The battery bank I am building is a 12V (13.2V nominal) 4S/20P one. With each cell rated at 5.5Ah the battery bank has a capacity of 110Ah, which is just under 1.5kWh. Continue reading ‘Building a 12V 110Ah Battery Bank Using 80 32650 LiFePO4 Cells’ »

For those who are following my YouTube channel, you would know that I am in the process of building a high capacity battery bank. When this project is done, I plan to use it with a 12V inverter as my backup generator in the event of a power failure. For the battery bank, I used eighty 3.2V 5.5Ah 32650 lithium iron phosphate (LiFePO4) batteries. These are arranged into 4 groups in series and each group consists of 20 cells paralleled together forming a 12.6V 110Ah battery bank. Continue reading ‘Modifying a 4S 100A LiFePO4 BMS Module’ »

I got a couple of Microsemi’s C900502 10.525 GHz X-band Doppler radar motion sensors a while ago. This batch was made in UK and had “UK patents 2243495 and/or 2253108 apply” printed on the case. I have seen a teardown of an HB100 Doppler radar module before and was wondering if I this one is any different inside. Continue reading ‘Teardown and Experiments with a Doppler Microwave Transceiver’ »

I bought six Philips dimmable LED bulbs for my dinning room chandelier last year. These are 45W incandescent equivalent (7W, 450 lm 2700K) and are supposed to provide years of trouble-free illuminations. Over the course of a year of light use however, they all exhibited the same failure mode at some point of time. Two months in, the first bulb failed. The bulb would initially turn on, but after a few minutes it would turn off by itself. If the power is recycled the light can be turned back on again but only for a short period of time, and the cycle continues. Continue reading ‘Teardown of a Philips Dimmable LED Bulb’ »

I have an old Keithley 1301 temperature probe. This probe is an accessory to the Keithley 130A/131 multimeter and is capable of measuring temperatures between -55°C to 150 °C. Since it outputs an analog voltage linearly proportional to the temperature (1mV/°C), it can be used with any multimeter that has a mV range. Continue reading ‘Converting Celsius to Fahrenheit – The Analog Way’ »

In my previous post, I did a review and teardown of a cheap BSide ACM03 Plus clamp meter and concluded that it was a surprisingly good meter despite a few minor annoyances. Continue reading ‘More Information on BSide ACM03 Plus Clamp Meter’ »

I recently purchased a BSide ACM03 Plus clamp meter so that I could do some high current measurements for my tab welder project. This meter can be bought on eBay for around $25, which makes it one of the cheapest Hall effect clamp meters on the market that is capable of measuring both AC and DC current. Continue reading ‘BSide ACM03 Plus Clamp Meter Review and Teardown’ »

I bought a Sony A6000 mirrorless digital camera last year to replace my Cannon PowerShot Elph 300 HS point and shoot camera for my YouTube videos. While its fast auto focusing capabilities is great for my teardown and project videos, the A6000 also has some drawbacks. Namely, you cannot shoot video while the camera is hooked to the charger or computer via the USB port. And because of this limitation, continuous shooting could be a challenge as the battery would be depleted rather quickly. Continue reading ‘Battery Adapter Teardown and Sony A6000 Power-Off Current Draw’ »

A flat bed scanner typically uses three rows of CCD sensors (RGB) to capture images placed directly on top of the glass bed. When the CCD array scans from one end of the image to the other, the digitized color image is formed. So with a similar approach, we could use just one photosensitive device to capture the entire image one pixel at a time via raster scanning. Now that I have an HP 7044A X-Y recorder I could use it’s X/Y servo mechanism with a suitable sensor to build a single pixel scanner. Continue reading ‘Building a Single Pixel Scanner’ »

I just bought an ESD mat for my workbench. ESD mat is great when working with sensitive electronics components as it safely dissipates any charge built-up to the ground via its dissipative surface through the attached grounding wire. Continue reading ‘ESD Mat For My Workbench’ »

I had wanted to make a spot welder for a while. Most of the DIY spot welders use a momentary switch the primary side of the microwave oven transformer (MOT). Due to the simplicity of this design, it is very simple to make. This design however, has some inherent safety issues as the momentary switch is typically within reaching distance of the operator (unless a foot switch is used) and inadequate insulation could increase electric shock risk. Further more, the current flowing through the primary winding can significantly exceed the current rating of the switch and cause the switch to fail. Due to the inductive nature of the winding, the switch can sometimes arc over and pose significant risk to the operator. Continue reading ‘Dual Purpose Spot Welder With Pulse Duration Control’ »

I recently upgraded my home phone system and thus was left with a couple of old Uniden DCT648-2 handsets. Most of the components inside are probably not salvageable but these handsets use 3×16 character LCDs, so it would be nice if I could reuse them in my other projects. Continue reading ‘Reverse Engineering a Uniden Cordlessphone LCD’ »