[Beowulf] power usage, Intel 5160 vs. AMD 2216

[Joel Jaeggli]

Robert G. Brown wrote:
> On Fri, 13 Jul 2007, Jim Lux wrote:
> 
>>> I have never seen a NiCd last that long.  One is lucky to get a hundred
>>> power cycles out of them.
>>
>> Something is seriously wrong.
>>
>> Typical Lead Acid should take 1000 cycles (where a cycle is full
>> discharge)
>>
>> NiCds, properly charged and used, should last for tens of thousands of
>> cycles (e.g. they use them in spacecraft orbiting the earth 14 times a
>> day)
>>
>>> NiMH aren't even doing too well in my copious
>>> supply of rechargable batteries at home.  And of course a car battery
>>> that makes it to seven or eight years is more the exception than the
>>> rule.
>>
>> That's more driven by exposure to high temperatures and vibration in
>> the under-hood environment.
> 
> Yeah, well, empirically the memory effect kills the NiCds way earlier
> than that.  And I don't think anything is "wrong" -- I think that's just
> the way OTC NiCds work.

nicads can be maintained by having a charge controller that will
periodically deep cycle them. If you have a lot of them, like for
example you're powering a forklift, or for emergency aircraft systems
then charge management and physical robustness becomes a big deal.
Nicads have some attractive properties for some applications like high
current draw and heat tolerance (especially relative to lion) that make
up for their energy density and memory issues for some applications.

deep-cycle sealed gell cells or agm batteries can have service lifetimes
measured in decades if maintained at float and only discharged to some
high fraction of their capacity like 80%).

I'd refer you to:

http://www.concordebattery.com

for the cool things you can do with agm batteries.

>  Maybe the space program does it better, but
> they probably spend a few thousand dollars each on those 10Kcycle
> batteries... and their chargers.
> 
>> Just as with UPSes, they carefully design the battery charger/life to
>> not be too long (hence too expensive).  It's a sufficiently well
>> understood engineering exercise that they can draw a fairly accurate
>> graph of charge capacity vs time (with the variability of mfr and use
>> factored in).
>>
>> you get real long life in a spacecraft application because they
>> carefully hand select and match the cells, and very carefully manage
>> the charge and discharge profiles.
> 
> This I believe.
> 
>    rgb
> 
>>
>>
>> FWIW, the Mars Rovers use Lithium Ion batteries, with nominally 1000
>> cycles life. (which they've exceeded by now)
>