Homemade Tablet – Getting the Battery Parameters

drawt-7b

The start up voltage was higher today (10.35 volts) than it was yesterday (9.65 volts). That may point to the batteries being a little more discharged than I thought, coming out of the shipping box. If that’s the case, then I’m looking at an even better runtime on these freshly charged batteries. Vaguely, this makes sense, because of the efficiency difference between the booster and the DC-DC converter, I was indeed expecting a better runtime than four hours yesterday. So, time will tell. Literally.

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Homemade Tablet – Fun with Auxiliary batteries

eightcell6Figure 1: Working up a new battery configuration.

The new batteries arrived in a small but heavy package. I pulled the brand new Imedions out of the box, and tested them for voltage. All but one was OK out-of-box with no further charging needed. For the one, fortunately, I had kept a pre-charged spare in the battery drawer, to round out the eight battery line-up. Next, I pulled four dual “C” battery holders from the same small mail package, and arranged them on a piece of trim board (not something a person should normally do, but I did for this little test). The next little jewel that I pulled from the shipping container was the DC-DC (voltage, not frequency) down-converter. Not being patient enough to wait for the housing that I had ordered, that the batteries will ultimately reside within, I soldered a switch to a couple wires, pushed the batteries into place, connected the pack to the DC-DC converter, and threw the switch!

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Homemade Tablet – More Battery Hacking

powerswithes1

The batteries were purchased without much thought, as they were extremely inexpensive. There is high variability in NiMH cells, depending upon manufacturer. Some simple math shows that I am not extracting the full capacity of the batteries while running the Odroid. Whether this is a problem with the batteries, with the current (mA) demand, or with the “forming charge” procedure has to be determined.

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