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Recelling, Take Two.

NeXT

Veteran Member
Joined
Oct 22, 2008
Messages
7,221
Location
Kamloops, BC, Canada
So as we learned with the TransNote around a year and a half ago (Which I would like to point out, a year after that rebuild, three of the four chinese cells had completely failed and gassed up so along with being rated for the use the cells were defective from the factory), cheap batteries are often not something you can be assured will work out of the mail packet.

So here I am again with yet another instance where a battery pack is far more economical to rebuild then replace. For a number of years I've owned a Canon EOS 1D MK I. It's a 4 megapixel DSLR but in comparison to my T3i which I more regularly use, it uses Compact Flash media and it is almost a full-frame camera (a crop factor of 1.3x which can visibly make a difference.) It is worth it to attempt a rebuild. Canon's battery pack consists of ten Ni-MH AA cells with tabs spot welded on. Pretty easy and cheap to source on ebay. Originally I planned to rebuild both cells I have but through an error I bought 16 cells instead of 20.
A month later they all arrived and the rebuild began.The process is fairly straightforward and I was done in less than an hour.

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At this point I plugged it into the charger and let it run a full discharge and recharge. Curiously it completed the entire cycle in 30 minutes. I immediately grew suspicious. I carefully slid the partly assembled pack back into the camera and took a couple of test shots. Sure enough after barely half a dozen photos the camera shut down do the a low battery.

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I knew what was up this time around. Recharging the battery and then monitoring it afterwards revealed that while it started off fine at 13.6v (roughly the average of all ten cells wired in series on a full charge) after a period of time the voltage had dropped to a more concerning 12.8v. Putting it back in the camera and taking a few more photos dragged it all the way down to the cutoff and after leaving it for a week the pack had almost completely discharged on its own. Not good.
With the lithium cells in the TransNote I had no easy or safe method of individually charging and discharging the cells. With Ni-MH I did. A conventional AA battery charger will do two cells at a time without me having to completely dismantle the pack. All ten cells were individually recharged by disconnecting one end of each cell and using alligator clipped leads to connect it to a cheap battery charger. Once charged I grabbed a stopwatch, a notepad, the mutimeter and two 1/4 watt 22 ohm resistors wound in parallel, giving me a 1/2 watt 11 ohm resistor to use as a load. The voltage of the cell to be tested had its initial voltage logged, then after the load was attached, every ten minutes and for the next 40 minutes the voltage was recorded.

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This took a massive amount of time. In reality I recommend if you can to use a timed measuring system so you don't need to attend to the logging. You miss a check interval and your results will be thrown off. It took several days in my spare time to complete all ten, plus the six additional cells. The resulting data was then entered into a spreadsheet and graphed.

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Three cells in particular were discharging far faster then they should. Cell 2 in particular dropped below 1.2v so soon that there was no point continuing to monitor it after the 20 minute mark. One cell in the spared was dead after 15 minutes! The cells were removed and three cells from the spares that tested the best after testing were added in. Again the rebuilt pack was fully cycled using the REFRESH button on my Canon built charger and an hour and a half later it was finished. After installing the pack into the camera I was delighted to find that my shutter count before the battery started to get tired could run into the hundreds. The rebuild this time was successful.
So we have learned an interesting method to test cells for exactly how healthy they are BEFORE the back is completely reassembled. While it may take a longer period of time to complete the task it is presumably this step that is omitted from the chinese manufacturing process, thus allowing me to buy these cells for as little as $1 each. I will have to keep this in mind. My next task will be to build a more suitable charging and discharging assembly for Lithium-Ion cells. That TransNote beckons to see some field use.
 
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