The Tech Blog

9V Battery Teardown

Posted under Hacks, Product Design, Teardown on May 23rd, 2021 by Amaldev

I was looking for a thin cylindrical battery for a project and thought of tearing down a 9V battery to repurpose its internal battery. To my surprise, I found a different stack inside it. I always thought (had opened one before) that these were made from six 1.5V cylindrical cells. This one seems to be a stack of six plastic pouches in series. A bit of googling helped me find that these are zinc-carbon battery pouches with a Zinc plate being the negative electrode, and the black brick (mixture of carbon + manganese oxide) being the positive electrode. Seems that manufacturers like Duracell go with the cylindrical cells and most others go with the pouch design. Learned something new today.

For those of you who do not know, most higher voltages in batteries are made by connecting smaller cells in series. Except for Lithium electrode batteries (which give cell voltages from 3V to 3.7V) most other known cell voltages range from 1.2V to 2V with usually 1.5V being the common one. This fundamental idea of increasing the overall battery voltage (by connecting in series) and increasing the battery capacity (by connecting in parallel) is the fundamental principle by which all batteries are made, ranging from the one powering your TV remote to the one in electric cars.

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Back to Basics: Photoresistors

Posted under Back to Basics, Educational, Technology on May 16th, 2021 by Amaldev

These are light-sensitive devices whose resistance decreases when more light falls on them. They usually have a resistance range specified based on the amount of light falling on the surface. Light Dependent Resistors(LDR) are usually made from cadmium sulfide(the squiggly line) with plated metal electrodes on both sides. It has a weird snake-like track of cadmium sulfide(CdS), to maximise the area of contact with the metal and also to increase the area of sensitive material exposed to light. When light falls on it, photons excite the electrons from the valence band to the conduction band which in turn can carry current(Hence the resistance drop). The CdS material is designed to sense light in the 400-700nm(Visible light) range.

They are very cheap and are used in a lot of devices that need to be triggered whenever there is a change in light irradiation. They come in different size diameters and are epoxy coated. Larger the diameter, the better its resistance variation to small changes in light intensity.

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