Homemade Tablet – External Battery Case


Posted 08-01-2015:

The batteries were pretty exposed, lying on the kitchen table with their wires all hanging out. I had to fix that situation. Today, the mailman brought the clear top box I’d been waiting for, and that helped to put the batteries in a better home. I was happy I managed to find the exact same color for the case, in spite of the fact that I ordered it from a different manufacturer. I thought the photo came out pretty well. The red on the display is reflecting off of my bedroom walls. The case shows six of the eight cells. Two cells are hidden by the angle, but there really are eight cells in there

Figure 2: The items all fit into my leather laptop case for a trip to the deep woods. The battery case itself is only 7 x 4.5 inches. Again, the photo angle is not showing all the cells, but there are eight.

Figure 3: Running on the external pack.

Figure 5: The battery switch can be seen on the side of the external battery pack. For transients, I’ll strap a 5.6V zener diode across the switch.

So, I’ll have nickel metal hydride batteries inside the plastic encased homemade tablet, as well as an extra external battery pack of the same capacity. Each should be good for over five hours, giving me a total of ~ eleven hours of run time. I recharged the batteries in a charger, and inserted them into the external pack, to put them to work. The initial charge on the battery bank, as indirectly measured with the voltmeter, was 11.5 volts, meaning they were probably charged to the fullest extent. Some circuitry embedded in the case along with the batteries converts the 11.2VDC to 5VDC, while some other circuitry protects against over-current and short circuits and the like. We’ll see how it goes …

To be continued …

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Note: the author does not have a recent, applicable background in circuit building, or battery related issues, so this is presented as the work of a hobbyist, and is not meant for duplication by others. Readers should look elsewhere for design advice and info.


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