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Re: Re: NiCd Battery Experts?



On Sun, 24 Mar 2002, Larry Kayser wrote:

> >Given that we have two charge rates A and B and A is only 40% higher than
> >B, and NEITHER is sufficient to keep the battery above 1.0 volts even half
> >of the way through eclipse, then is it better to charge at A and cycle a
> >greater chemical process or charge B, a lesser chemical process, given
> >that we are going to end up at the same deep discharge state towards the
> >end of eclipse anyway?
>
> sheets of paper.  I have a strong feeling that these "options" are maybe at
> best something that you can only influence to a certain degree...
> ... keep the battery as cold as possible.  NiCd cells have very limited
> enthusiasm to do  anything when they are cold... The real issue is what
> is the  temperature of the battery in PCsat please?

Per orbit, they cycle maybe 5 degrees from about 3 to 8 deg C now. With
the LOWER temp being when they will see the deep cycle... (that sounds
like thats good news)... During full sun orbits (last one was 2 weeks in
January) they are at about 20 to 25 C)  We put them on a plate thermally
connected to all sides of the cube so they would experience the least
thermal cycling.

> [cold for a NiCd in my terms is 5c and below, hot is above 25c.

Wow, sounds like we nailed it!

> >I doubt the only 40% difference in charge rate options we have will
> >make that much of a difference, but anyway, that is why we asked.
>
> Yes, I tried to say that above, it wont make much difference which option
> you choose at this point.  You already know your not in a good position so
> my recommendation is to focus on minimizing the range of voltage change and
> do what ever it takes to keep the battery as cold as possible.  It is
> little known but you can keep NiCd cells at zero voltage, ie shorted, and
> in cold storage refrigerator or freezer for decades with no measurable
> degradation in performance.
>
> Bob, in closing, you may in fact already realize that you are facing a
> binary decision that must be made with a distinct lack (i.e. a minimum) of
> perfect information.  You alone have to cut this one, I offer that keeping
> things cold and minimizing the range of voltage swings are the things to
> focus on.

Yep, I had that suspicion as well.  Since it goes against the
first order conventional wisdom, that is why I wanted a second opinion as
well from a true expert in the field.  And sinec we only have a small
range (say 40%) of control anyway, it probably wont make much difference,
but might just be worthwhile sinec there is nothing else we can do but
wait for more sun..

> Good Luck to you in your deliberations. I regret of course that
> I am not able to offer you a magic solution, in fact maybe just recognizing
> and stating the obvious, the binary decision to be taken with imperfect
> information, might be the greatest value I can offer.
> Larry, VA3LK.

Yep, thank goodness it is only a binary decision, since weighing even a
few more control options (if such were available) maes for LOTS and LOTS
of more possibilities and all with imprefect infomration.... <grin>

THANKS!  Perfec answers!

Bob, WB4APR

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