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Re: [OM] NiMH Batteries +Nicads and 310 flash.

Subject: Re: [OM] NiMH Batteries +Nicads and 310 flash.
From: HI100@xxxxxxx
Date: Tue, 15 Jun 1999 04:03:40 EDT
        Jan Steinman and Frank van Lindert debated the merits of various 
battery options and Jan enthused about rechargeable alkaline cells:  he 
really liked using them and they had good cost performance in relation to 
conventional alkalines.  

        From an economy point of view the rechargeable alkalines are not as 
good as might first appear because they have a substantially lower capacity 
per cycle than the capacity of a normal alkaline. The consumer report tests 
some years back showed something like a 1/4 of the capacity of a conventional 
alkaline. Thus the breakeven point may be more like 12-16 charges rather than 
the 4 calculated on the previous report. I seem to remember that the internal 
resistance is higher especially after a few cycles  so that the energy 
extraction is lower too for a high current application like a flash. Also as 
Jan mentioned it is quite important not to extract too much capacity per 
cycle so this means rather frequent charging which may be why the 
manufacturer now specifies a much  large number of "cycles". Consumer reports 
was not very enthusiastic about the rechargeable "Renewal" cells from a cost 
per energy or an environmental point of view so it is interesting that Jan 
finds them so effective.

        Testing primary cells is actually quite difficult since small changes 
in the exact rest between discharge cycles makes a huge difference in 
performance. 
Thus when using your flash with any type of alkaline you may double your 
capacity if you switch off periodically to allow the cells to rest. 
Temperature makes a large difference too so keep your cells under your jacket 
before using them under cold conditions. Even going from 20-30C ambient can 
increase capacity something like 20%.

        There was also some discussion on being careful to avoid using Nicads 
with the 310 flash because the lower internal battery resistance will blow 
the transistors in the flash. This was common in many flashes of that era. 
Normal AA alkalines will produce short circuit currents of the order of 1.5A 
which translates to about 1-1.5 Ohms internal resistance. In contrast Nicads 
can produce 10 times that current. If you are environmentaly conscious and 
really want to use Nicads in a 310 you can just add a 5 Ohms,1.5W resistor in 
series with one of the leads to the battery holder. I did that years ago with 
a C*n*n flash with good results although the cycle time gets rather long if 
you go back to alkalines.

        Interestingly older compact flashes that included rechargeable Nicads 
like the old Metz's used a different type of Nicad from the AA cells now 
commonly used. These were internally dry (no electrolyte) similar to the 
button style cells used internally in one of Olympus packs for the motor 
drive. These have much slower self discharge rate than the more common "wet" 
cells, so work much better when stored for a while between use.

Tim Hughes
Hi100@xxxxxxx

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