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Old 08-01-2006, 09:18 PM   #21
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Originally Posted by hydravien
why not run them in parallel? this increases their ability to deliver current, and reduces the voltage drop under load.
Yes, but...

The State of Charge (SOC) of NiMH (and NiCd) cell chemstry is not nearly as well tied to cell voltage as, say, Lithium Ion or Lead Acid which both work well in parallel.

If you take a look at the charge/discharge voltage curves you will see what I mean. The curves (especially for good cells with low internal resistance) are very flat through most of the charge or discharge. This is also the fundamental reason why the SOC of these cells can't be reliably determined by measuring cell voltage and why charge termination is not determined by voltage, but by voltage inflection.

In other words, you can't guarantee one parallel cell or group of cells is at the same SOC as the other. Cell imbalance is difficult to detect and manage.

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Old 08-02-2006, 11:28 AM   #22
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KANs or Sanyo or GPs have always been good for me. will build you a pack to your specs (you choose cells, wires. connectors). Someone once posted a Canadian source for cheap batteries, but I've lost track of it. sells 2 2000 mAh packs for $14...
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but weasels don't get sucked into jet engines.
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