2 Lithium Manganese Dioxide cells in parallel. ?

[N_Cook]

Well nearly , the 2 negatives joined and 2 epitaxial diodes (avoiding mutual
discharge possibility) from the positives commoned and then on to the
memory, is there some circuitwise reason? Both cells are from the same batch
, so not as though "all your eggs in one basket" circumvention.
Is the chemistry of this type of cell odd? 3V cells originally , could be 20
years, but removed from the pcb and out of circuit still 3V. Put 150K across
either cell and it drops in voltage to 2.9V or so compared to just DVM
loading. Remove and immediately recovers to 3V.
Tried 5K6 over for 12 hours , dropped to 2.6V , measured a few minutes ago,
removed the R and immediately recovered to 2.9V, I expect when I get back to
it , it will be back to 3V with just DVM load

 

[William Sommerwerck]

I'm not sure what your question is. Or if you have a question.

3V lithium coin cells are commonly used to back up memory, including 5V
systems. They can last for years; I've never seen two used to add capacity.

I have no idea why such a light load (150K) would cause the voltage to
immediately drop by 3%.

 

[N_Cook]

I'm not sure what your question is. Or if you have a question.

3V lithium coin cells are commonly used to back up memory, including 5V
systems. They can last for years; I've never seen two used to add capacity.

I have no idea why such a light load (150K) would cause the voltage to
immediately drop by 3%.

I've only ever seen a single cell or if multiple ones, then in series. On
first confronting , much confusion. Realised they were tied together but not
realised in parallel.
Each one measured 3V , in turn, but put the DVM over the other 2 ends then
near enough 0V, scatching head.
Put DVM on resistance scale and measured a varying low resistance of 20 to
60 ohms , varying slowly like across a large C capacitor , but no large
capacitors present. The approximately 0 ohms between 2 nearly equal 3V cells
was being interpreted as low ohms.

When I get replacement cell/cells? (why spend out on 2 ?) I'll try the 5K6
over night and see what effect on a known good cell , or at least new from
the supplier. These cells were 1/2AA size Sanyo CR14250SE if that is
relevant, ie not the usual PC large button cells

 

[N_Cook]

We had to use CapStore RAM in the equipment we built for NASA. No
lithium batteries were allowed into space.

Maybe they wanted to be able to replace the batteries one at a time,
without losing what was stored in the RAM.

For the same reason that Boeing should have stopped them being incorporated
on their recent product fiasco?

Both batteries are tanged and would require desoldering/soldering to replace
either. If designed to allow one failure then I'd expect at least for them
to be from different batches if not different suppliers, both same make and
batch number here

 

[William Sommerwerck]

I'm taking about lithium coin cells used in battery-backed

RAM and real-time clock modules. NASA said that if they
failed, lithium could contaminate the atmosphere.

NASA was "nuts" about such things. It was worried about outgassing from the
rubber feet on HP calculators. These were removed.

 

[Cydrome Leader]

I am taking about tiny coin cell sized lithium batteries that were
used in battery backed RAM and Real Time Clock modules. NASA stated
that if they failed, Lithium could contaminate the atmosphere inside the
ISS.

burst lithium cells do smell truly awful.

those things are up there in space though, so maybe nasa has exceptions,
or just doesn't care about all of them.

 

[Cydrome Leader]

NASA was "nuts" about such things. It was worried about outgassing from the
rubber feet on HP calculators. These were removed.

well, rubber does outgas, crappier types more than others, but how do you
know which is which? It seems like an odd but sensible thing to do.