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From: terryS on 24 Jan 2010 13:54
Have just replaced watch button battery from a package of five bought
yesterday.
The replacement cells are SR60W 1.55 volts. (Diam 6.8mm, depth
2.15mm.)

Measured the removed battery (several years old now) open circuit,
using a high input impedance DMM, at 1.486v. Doesn't seem that low?
But that's off-load and it obviously run down because it doesn't make
the cheap 'quartz' watch tick!.

The first replacement cell was not functional at 0.948 volts. The
second replacement at around 1.5v seems to work fine.

Having introduced the topic/question can anybody comment on how much
current these button type cells provide in a typical watch? Probably
of the order of micro-amps?

Nothing important but having now got involved one wonders!

TIA. Cheers.
From: John Fields on 24 Jan 2010 15:47
On Sun, 24 Jan 2010 10:54:08 -0800 (PST), terryS
<tsanford(a)nf.sympatico.ca> wrote:

>Have just replaced watch button battery from a package of five bought
>yesterday.
>The replacement cells are SR60W 1.55 volts. (Diam 6.8mm, depth
>2.15mm.)
>
>Measured the removed battery (several years old now) open circuit,
>using a high input impedance DMM, at 1.486v. Doesn't seem that low?
>But that's off-load and it obviously run down because it doesn't make
>the cheap 'quartz' watch tick!.
>
>The first replacement cell was not functional at 0.948 volts. The
>second replacement at around 1.5v seems to work fine.
>
>Having introduced the topic/question can anybody comment on how much
>current these button type cells provide in a typical watch? Probably
>of the order of micro-amps?

---
The SR60W is a 1.55V 60mAH silver oxide cell.

If it lasted "several" (3) years, then since 3 years is equal to:

24 hr * 365.25 days * 3 yr
t = ---------------------------- = 26,298 hours
1 yr

and the capacity of the battery is equal to 60 mAH,

the current supplied for 3 years will be:

C 6E-2 A H
I = --- = ------------ ~ 2.28e-6 A - 2.28 microamperes.
t 2.6298e4 H


JF
From: terryS on 24 Jan 2010 23:54
On Jan 24, 5:47 pm, John Fields <jfie...(a)austininstruments.com> wrote:
> On Sun, 24 Jan 2010 10:54:08 -0800 (PST), terryS
>
>
>
>
>
> <tsanf...(a)nf.sympatico.ca> wrote:
> >Have just replaced watch button battery from a package of five bought
> >yesterday.
> >The replacement cells are SR60W 1.55 volts. (Diam 6.8mm, depth
> >2.15mm.)
>
> >Measured the removed battery (several years old now) open circuit,
> >using a high input impedance DMM, at 1.486v. Doesn't seem that low?
> >But that's off-load and it obviously run down because it doesn't make
> >the cheap 'quartz' watch tick!.
>
> >The first replacement cell was not functional at 0.948 volts. The
> >second replacement at around 1.5v seems to work fine.
>
> >Having introduced the topic/question can anybody comment on how much
> >current these button type cells provide in a typical watch? Probably
> >of the order of micro-amps?
>
> ---
> The SR60W is a 1.55V 60mAH silver oxide cell.
>
> If it lasted "several" (3) years, then since 3 years is equal to:
>
>          24 hr * 365.25 days * 3 yr                
>     t = ---------------------------- = 26,298 hours      
>                   1 yr
>
> and the capacity of the battery is equal to 60 mAH,
>
> the current supplied for 3 years will be:
>
>          C      6E-2 A H
>     I = --- = ------------ ~ 2.28e-6 A - 2.28 microamperes.
>          t     2.6298e4 H
>
> JF- Hide quoted text -
>
> - Show quoted text -

Thanks for the info John:
That's what I was missing; the ampere hour capacity of the button
cell. Amazing something with that small a volume can be 60ma/hr. Guess
that is what the '60' in SR60W means!
And yes; if 3 years that's (60 x 10to minus 3)Ah./24 x 365 x 3 = Of
the order of 2.28 x 10to minus 6.Amps.
Cheers.
From: Phil Allison on 25 Jan 2010 09:02

"terryS"

Thanks for the info John:
That's what I was missing; the ampere hour capacity of the button
cell. Amazing something with that small a volume can be 60ma/hr. Guess
that is what the '60' in SR60W means!
And yes; if 3 years that's (60 x 10to minus 3)Ah./24 x 365 x 3 = Of
the order of 2.28 x 10to minus 6.Amps.


** Shame that JF failed to say the calc gives only the AVERAGE current
drawn.

The *peak current* draw at the moment of each "tick" is up to 100 times
higher.

Has a big effect on the life span of the cell and what kind of cell ESR
value is tolerable.



.... Phil


From: Paul E. Schoen on 25 Jan 2010 14:20

"Phil Allison" <phil_a(a)tpg.com.au> wrote in message
news:7s5mkgFeu3U1(a)mid.individual.net...
>
> "terryS"
>
> Thanks for the info John:
> That's what I was missing; the ampere hour capacity of the button
> cell. Amazing something with that small a volume can be 60ma/hr. Guess
> that is what the '60' in SR60W means!
> And yes; if 3 years that's (60 x 10to minus 3)Ah./24 x 365 x 3 = Of
> the order of 2.28 x 10to minus 6.Amps.
>
>
> ** Shame that JF failed to say the calc gives only the AVERAGE current
> drawn.
>
> The *peak current* draw at the moment of each "tick" is up to 100 times
> higher.
>
> Has a big effect on the life span of the cell and what kind of cell ESR
> value is tolerable.

I suppose there might be a capacitor in there to handle the peaks.

Paul


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