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Re: Re: NiCd Battery Experts?



Larry Kayser wrote:

> IF and that might be a significant issue, but IF you have done a careful
> matching job of the cells that make up your battery then there should be
> almost NO chance of cell shorting or reversing this early in life.

Yes, we matched the cells but these were students and you can never be
sure of the quality of the results.  They were not EE's and had not seen a
voltmeter before..

> There is of course another solution to your problem.  Pick a few good hams
> spread around the world and just slam PCsat with OFF commands,

That is what we have been doing on every orbit (98+) since this got
serious about 10 March..  The low power command is only of any value if it
happens at sunrise and this is only happening now over the southern
hemisphere so we have stations on 'all' southern continents doing this.
Since the 12th we have not had one success in getting through eclipse.

>  >Before you reply, remember that all of us HAMS consider ourselves as
> experts in NiCd's, just >assume we already have more than enough opinions
> already and don't need any more... But >documentable and proven facts are
> welcome...
>
> With an opening like this I was reluctant to reply at all.

Yes, you were the kind of answer we wanted.  We just didnt have time to
filter thought hundreds of other opinions that repeat the same general
knowledge about nicads that any expereinced electrical engineer already
has...  Thanks!

Anyway, thanks for your comments.  But remember, we only have two options.
Our Sat has NO PC on board, no program, no timed events, nothing
that wouild be called a contrl system.  But we can turn on and off about
40% of our fixed load to change how much solar power is going into the
batteries by about 40%.

So GIVEN that we may possibly be deep discharging to near zero every
eclipse for the next 3 weeks and that we only have two command states that
have anything uselful to do with power budget, then the question remains:

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?

Normally the answer is to maximize your charge.  But if one took the
other Option to its extreme, that is to take the battery to zero and leave
it there, then that might be better than cycling.  But since we cannot
do that anyway, somewhere in beteeen  is a decision point where the right
answer flips from answer A to B.  I doubt the only 40% difference we can
make will make that much of a difference, but anyway, that is why we
asked.

Bob

PCsat WEB  page     http://www.ew.usna.edu/~bruninga/pcsat.html
ISS-APRS FAQ:       http://www.ew.usna.edu/~bruninga/iss-faq.html
CUBESAT Designs     http://www.ew.usna.edu/~bruninga/cubesat.html
APRS LIVE pages     http://www.ew.usna.edu/~bruninga/aprs.html
APRS SATELLITES     http://www.ew.usna.edu/~bruninga/astars.html
MIM/Mic-E/Mic-Lite  http://www.toad.net/~wclement/bruninga/mic-lite.html

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