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Re: NiCd Battery Experts?



Bob:

Two different friends have emailed me about your survival problem.  I have 
no idea if I am a qualified expert in your opinion or not - I did send 
about 5 million commands to OSCAR VI to keep it going for over 5 years 
along with another chap who sent an additional 5 million over the same 
total period.  Secondly I am the guy who put in 10 years of work examining 
NiCd cells to see how they worked - this work led to the creation of the 
battery here in Canada for AMSAT OSCAR 11/UOSAT 2 which has been running 
nearly 18 years and 70,000 plus orbits with that battery and both are still 
working excellently I am told.  After 70,000 charge and discharge cycles I 
feel somewhat qualified to have a few opinions....

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.  I have 
some interest if you have the list of matching priorities (such as terminal 
voltage at several charge and discharge rates, temperatures of the cells 
[assuming you put a few of them in a calorimeter for some thermal cycle 
tests] and the voltage curves during at least a 20C [yes I said a real 20C 
discharge - seriously] discharge) and the sigma values you achieved in the 
matching they might tell me a bit more about your battery.

If the battery is made up of cells that are closely matched well enough you 
can do almost anything to it, including taking it to zero volts and keeping 
in that way for months at a time.

If however you did not do a good matching and selection process as has been 
well documented and easily available for the last 15 years or so, then of 
course all bets are off.  What I learned in my ten year look at NiCd cells 
is that when cells are randomly picked and put in a battery (as a group of 
cells) the differences tend to pull against each other, in other words they 
start an accelerated death spiral upon assembly and use.  Statistically 
even a random selection process will occasionally create an excellent long 
performing battery - it just does not happen very often.

The battery in OSCAR 11 has had on occasion terrible treatment, it was out 
of control from several months early in its life and was subjected to 
brutal discharge levels.  It survived as noted above.  I expected it 
would.  I would of course give a good chunk of my left arm to get it back 
now and have a good look at that battery, I bet we could learn a lot more 
about these things - but that is not going to happen with the Shuttle 
getting such high marks for fixing Hubble up hi.

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, so every 
time it sticks its nose over any of the command facilities horizon PCsat is 
commanding it OFF.   This actually works, we used that process to keep 
OSCAR VI going and then we implemented a rigorous tight management program 
and every 70 milliseconds that OSCAR VI was within my radio horizon I 
either put it ON or OFF as the algorithm for management called for.  Within 
a few months we had it performing fairly reliable - this is trivial task 
today with PC hardware, I did it with 8 level paper tape (miles of the 
stuff) and it was not easy but I was very happy when I got it running with 
my first micro and Intel 4004.....

I don't know your orbital parameters but if your in a high inclination 
orbit, a KL7 or a GM etc. might get a good short at it every polar pass and 
slam it OFF.  This would be easy to co-ordinate over the Internet today.  I 
was able to get at OSCAR VI over the pole for all but 2 or 3 orbits every 
day, that made a big difference in keeping it under control.

 From your email....

 >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.

Oh yes, I also remind you that I also built the batteries for AO 14, 15, 
16, 17, 18, and 19 over 12 years ago and I am told that some of them are 
still running as well.

Good Luck to you.  If you have any questions I will try my best to answer them.

Larry
VA3LK

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