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Nov 24, 2012, 11:48 PM
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NiMH secrets

The quest for powering the 580EX II revealed only 1 of its 4 lithium cells actually died. Testing the voltage of all of them instead of just 1 revealed 1 cell had 1.3V while the others had 1.4V. But the new trick was measuring current. The 1.3V cell had 0 current. Didn't measure the 1.4V cells. Not sure how much a fully charged lithium cell would generate.

The 580EX II was powered by a single set of NiMH's ever since it arrived in April 2008. It very quickly showed it wouldn't work with anything but brand new batteries, yet new & old batteries showed the same voltage. The same 4 NiMH's made the only photographs of M.M. in 2010 & suddenly stopped working with the flash in Sep 2012.

The Fluke 87V finally revealed why. Their ability to provide current decreases with age. Fully shorting a new NiMH gives 7A while a 4 year old NiMH only gives 1A. The flash needs 7A while a mouse can get by on only 1A. Don't try this with a Lipo. There are ways of doing it with a resistor.
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