Alkaline AAA batteries as memory backup??

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#1
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Hello buddies!

I was thinking if it's possible to use two AAA batteries to replace a lithium coin backup cell.

It's not a new design, but a "cost cut" in an old design that needs to start going again.

The device in question draws 10uA from the battery for backup purposes, which should fall well below the self discharge characteristic of the AAA cell.

I'm asking this question here because there were low (10's of mA) to high (100's of mA to 1' of A) discharge curve characterizations of those cells, but not uA in the many battery datasheets that I've found in the net

There is no battery leaking concern, nor size, nor space. They will be glued to a part of the enclosure and attached with wires.

What really matters is what backup time may I expect for AAA carbon alkaline cells with a 10uA load

cheers
Nachus

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A Good AAA alkaline has about 1000mAH
and last at least 5 years.
So with 10uA it's 100000 hours = 11 years.

So I guess you are good for at least 5 years.

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Hello Sparrow:

I think that for even a 300mAh cell the discharge is negligible, but the problem is not the remaining capacity but if voltage curve is more or less flat for that (10uA) current and for a good period of time (2-3 yr).

Also it would be good to know what I should expect for this arrangement

thank you anyway!
nachus

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There's been a memory chip backed up on my desk for the last two years on a couple of duracel AA. I'm told it's over eight years old...

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What can your design live with 2V 2.5V 3V ?

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Hello sparrow:
Supposedly yes, but I'm not sure. I have to test that

nachus

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official a alkaline's voltages drop fast, but that is with a "normal" load, with this low load it will be higher than the load graphs will show.
But are you sure that 2 two good alkaline (no leak etc) with mounts, are cheaper than a cheap coin cell and a clips.

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OP wrote:
AAA carbon alkaline cells

What is a "carbon alkaline cell"?

No RSTDISBL, no fun!

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sparrow2 wrote:
official a alkaline's voltages drop fast, but that is with a "normal" load, with this low load it will be higher than the load graphs will show.
But are you sure that 2 two good alkaline (no leak etc) with mounts, are cheaper than a cheap coin cell and a clips.

Hello sparrow. Alkalines are not the best for a design using it as backup. problems are leaking, size, discharge curve (depending on the chip you're backing up) Those are the best option for price/endurance in MY situation and with THAT equipment. Maybe not the case of anyone else.

I just tested the equipment with a 2 cell arrangement and a pot to see at which voltage level the memory got corrupted and found that from 3,2 to 1,2v the bakup worked well (no corruption)

Below 1.1v the memory may or may not get corrupted, but with the previous voltage headroom I think the solution will be very useful

Brutte wrote:

What is a "carbon alkaline cell"?

I refer to the common alkaline cell (carbon zinc?) and not fancy chemistry cells (lithium non rechargeable, silver oxide, etc) that are also alkaline

nachus

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nachus001 wrote:
Brutte wrote:

What is a "carbon alkaline cell"?
I refer to the common alkaline cell (carbon zinc?)

Zinc-Carbon is distinct from "Alkaline" - in fact, they have an acidic electrolyte!

http://en.wikipedia.org/wiki/Alk...

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