OT: Can CMOS battery on PC motherboard be hot-swapped?

Folks,

Got a Dell Vostro 200 mini tower with XP on there that seems to be a bit
off in the realtime clock lately. Around five years old so needs a new
3V coin cell on the mobo.

In order not to lose all the setup stuff, can those CR2032 coin cells be
hot-swapped while the PC is running?

Of course using ESD straps, being careful and all that.

-- 
Regards, Joerg

http://www.analogconsultants.com/

On Sun, 24 Feb 2013 10:02:48 -0800, Joerg <invalid@invalid.invalid>
wrote:

>Folks,
>
>Got a Dell Vostro 200 mini tower with XP on there that seems to be a bit
>off in the realtime clock lately. Around five years old so needs a new
>3V coin cell on the mobo.
>
>In order not to lose all the setup stuff, can those CR2032 coin cells be
>hot-swapped while the PC is running?
>
>Of course using ESD straps, being careful and all that.


  the BIOS flash update utility has a backup feature which keeps settings
as well.
  you back it up, swap the battery, and then re-apply the backed up flash
image.

  And yes, you CAN apply an external 3V source to the MOBO.  Just
remember that you will be fighting the very low internal resistance of a
dead battery for the few seconds you are under power as you remove it,
and for the few seconds you re under external power as you install the
new one.
  
  Be very careful about polarity, and do not exceed 3 volts so you do not
begin "feeding" the battery.

  As a side note, many modern motherboards have enough capacitance at
that sub-circuit location to retain things long enough for you to swap
the battery.  I do not know if yours is such a design.

  another side note is that RTCs in PCs are not very accurate with the
original Pc deign and crystal.  Newwer designs may use more accurate
clock sources, but most do not, and your most accurate clock possible is
your cell phone, or iPad or other cell system connected or GPS enabled
device.  Always bet to keep your PC's clock referenced to such a more
accurate source.

  Internet updates are prone to latency errors , so do not expect better
than  plus or minus about 1.5 seconds in that realm.

   The phone or GPS device is the clear winner, and a good modern wrist
watch usually tracks those pretty well once set.  Usually within mere
seconds per year.  The phones are ALWAYS accurate as they are ALWAYS
constantly updated.

On Sunday, February 24, 2013 10:02:48 AM UTC-8, Joerg wrote:

> Got a Dell Vostro 200 mini tower with XP on there that seems to be a bit 
> off in the realtime clock lately. Around five years old so needs a new 
> 3V coin cell on the mobo. 
> 
> In order not to lose all the setup stuff, can those CR2032 coin cells be 
> hot-swapped while the PC is running?

I've done it.   The backup function of the battery means the circuitry
only draws battery power while power is OFF (and I do mean OFF,
'standby' of ATX power supplies is an ON state, even though
the computer seems powered down).

There's also a hold capacitor, usually a few seconds of power is assured while
swapping the coin cell.

SoothSayer wrote:
> On Sun, 24 Feb 2013 10:02:48 -0800, Joerg <invalid@invalid.invalid>
> wrote:
> 
>> Folks,
>>
>> Got a Dell Vostro 200 mini tower with XP on there that seems to be a bit
>> off in the realtime clock lately. Around five years old so needs a new
>> 3V coin cell on the mobo.
>>
>> In order not to lose all the setup stuff, can those CR2032 coin cells be
>> hot-swapped while the PC is running?
>>
>> Of course using ESD straps, being careful and all that.
> 
> 
>   the BIOS flash update utility has a backup feature which keeps settings
> as well.


Thanks. Now I've got to find that sort of utility, somewhere.


>   you back it up, swap the battery, and then re-apply the backed up flash
> image.
> 

If I had a flash update utlity :-)


>   And yes, you CAN apply an external 3V source to the MOBO.  Just
> remember that you will be fighting the very low internal resistance of a
> dead battery for the few seconds you are under power as you remove it,
> and for the few seconds you re under external power as you install the
> new one.
>   

So I assume even with a running PC one would still have to hook up a 3V
supply in order not to lose data?


>   Be very careful about polarity, and do not exceed 3 volts so you do not
> begin "feeding" the battery.
> 
>   As a side note, many modern motherboards have enough capacitance at
> that sub-circuit location to retain things long enough for you to swap
> the battery.  I do not know if yours is such a design.
> 

No clue, I think it's a Foxconn G33M mobo in there.


>   another side note is that RTCs in PCs are not very accurate with the
> original Pc deign and crystal.  Newwer designs may use more accurate
> clock sources, but most do not, and your most accurate clock possible is
> your cell phone, or iPad or other cell system connected or GPS enabled
> device.  Always bet to keep your PC's clock referenced to such a more
> accurate source.
> 
>   Internet updates are prone to latency errors , so do not expect better
> than  plus or minus about 1.5 seconds in that realm.
> 
>    The phone or GPS device is the clear winner, and a good modern wrist
> watch usually tracks those pretty well once set.  Usually within mere
> seconds per year.  The phones are ALWAYS accurate as they are ALWAYS
> constantly updated.


Actually, without web updates the RTC in this PC was remarkably accurate
for all those years. Well, until yesterday. I rarely had to set it.

-- 
Regards, Joerg

http://www.analogconsultants.com/

whit3rd wrote:
> On Sunday, February 24, 2013 10:02:48 AM UTC-8, Joerg wrote:
> 
>> Got a Dell Vostro 200 mini tower with XP on there that seems to be a bit 
>> off in the realtime clock lately. Around five years old so needs a new 
>> 3V coin cell on the mobo. 
>>
>> In order not to lose all the setup stuff, can those CR2032 coin cells be 
>> hot-swapped while the PC is running?
> 
> I've done it.  ...


So maybe I should just hot-swap then.


>   ... The backup function of the battery means the circuitry
> only draws battery power while power is OFF (and I do mean OFF,
> 'standby' of ATX power supplies is an ON state, even though
> the computer seems powered down).
> 

That's odd. Because the PC here is always sent to hibernate and the
power is turned off. But it remains connected to 120VAC. Still, this
morning the RTC was off again by more than five minutes from yesterday.


> There's also a hold capacitor, usually a few seconds of power is assured while
> swapping the coin cell.


And then the coin cell slips and our dog carries in to the kitchen,
"Look, ma, I found bling-bling!" :-)

-- 
Regards, Joerg

http://www.analogconsultants.com/

On Sun, 24 Feb 2013 10:02:48 -0800, Joerg <invalid@invalid.invalid>
wrote:

>Got a Dell Vostro 200 mini tower with XP on there that seems to be a bit
>off in the realtime clock lately. Around five years old so needs a new
>3V coin cell on the mobo.
>
>In order not to lose all the setup stuff, can those CR2032 coin cells be
>hot-swapped while the PC is running?

Yes, I do it all the time.  Two methods:

1.  Leave the computah plugged in and running.  On most machines, the
CMOS memory runs on computer power, instead of battery power, when
running.  Use a wood or plastic stick to remove the battery. Insert a
new battery as fast as possible.  Watch out for bending the the
negative terminal connector thing.  Don't short the battery socket or
all your settings will go away.

2.  I have a 2032 battery and holder with two clip leads.  I clip them
across the holder terminals to maintain power while the battery is
being changed.  Locating the battery connections on the motherboard is
a problem, but I can usuallly find a suitable connection by poking
around with a voltsguesser.

There are a few CMOS backup and write utilities scattered around the
web.  I've had no success with these and don't use them.  Check the
dates as many are ancient.

-- 
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Jeff Liebermann wrote:
> On Sun, 24 Feb 2013 10:02:48 -0800, Joerg <invalid@invalid.invalid>
> wrote:
> 
>> Got a Dell Vostro 200 mini tower with XP on there that seems to be a bit
>> off in the realtime clock lately. Around five years old so needs a new
>> 3V coin cell on the mobo.
>>
>> In order not to lose all the setup stuff, can those CR2032 coin cells be
>> hot-swapped while the PC is running?
> 
> Yes, I do it all the time.  Two methods:
> 
> 1.  Leave the computah plugged in and running.  On most machines, the
> CMOS memory runs on computer power, instead of battery power, when
> running.  Use a wood or plastic stick to remove the battery. Insert a
> new battery as fast as possible.  Watch out for bending the the
> negative terminal connector thing.  Don't short the battery socket or
> all your settings will go away.
> 

Done, new battery is in. Did a power-down into hibernate, came back up
like usual. The old battery still measures 3.272V but when loading it
with as light a load as 10k it collapses to 2.5V. With 1k it goes to
1.6V. So I guess the old battery was truly exhausted. It was made by
"Newsun" in Japan, never hear of that brand.

While I had the PC open I saw that I have quite a build-up of dog hair
in there, got to take it apart and clean it. Our big lab likes to curl
up down there when I am doing SPICE runs and warm air comes out. It's
amazing how tight of a space they can snuggle themselves into.


> 2.  I have a 2032 battery and holder with two clip leads.  I clip them
> across the holder terminals to maintain power while the battery is
> being changed.  Locating the battery connections on the motherboard is
> a problem, but I can usuallly find a suitable connection by poking
> around with a voltsguesser.
> 
> There are a few CMOS backup and write utilities scattered around the
> web.  I've had no success with these and don't use them.  Check the
> dates as many are ancient.
> 

Supposedly there is a Dell tool but I haven't found it yet.

Thanks for the help, Jeff.

-- 
Regards, Joerg

http://www.analogconsultants.com/

On Sun, 24 Feb 2013 13:12:20 -0800, Joerg <invalid@invalid.invalid>
wrote:

>> Watch out for bending the the
>> negative terminal connector thing.

Oops.  That should the positive terminal connector thing.

>Done, new battery is in. Did a power-down into hibernate, came back up
>like usual. The old battery still measures 3.272V but when loading it
>with as light a load as 10k it collapses to 2.5V. With 1k it goes to
>1.6V. So I guess the old battery was truly exhausted. It was made by
>"Newsun" in Japan, never hear of that brand.

It's dead.  I get about 5 years out of such batteries.  

I just tested a new 2032 battery.  3.28V with no load.  3.18V with a
10K load.  I couldn't find a 1K resistor.

>While I had the PC open I saw that I have quite a build-up of dog hair
>in there, got to take it apart and clean it. Our big lab likes to curl
>up down there when I am doing SPICE runs and warm air comes out. It's
>amazing how tight of a space they can snuggle themselves into.

Yeah, number crunching does make the machine run warm.  Suggestions:
1.  Buy the dog a heated blanket.
2.  Elevate the PC a few inches above the floor with a cardboard box,
blocks of wood, or pile of old phone books.  The air intake for the PC
is at the lower front of the machine, turning it into an effective
vacuum cleaner.  It will dutifully suck up everything within range
from the floor.  Dog hair is theoretically heavier than air and will
therefore rapidly settle onto the floor or carpet and not float
through the air much.  By elevating the machine, you'll suck in fewer
dog hairs and less dust.
3.  Build less complex SPICE models.  That will make the machine run
less hot, which will not attract the dog as much, which will not clog
the machine as much, which will make the machine run even less hot,
which will eventually reduce the need to clean out the dog hair from
the machine.

>Supposedly there is a Dell tool but I haven't found it yet.

I searched but couldn't find anything.  There are plenty of tools to
save the BIOS image (usually as part of a BIOS upgrade), but nothing I
could find that saves the settings.



-- 
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Jeff Liebermann wrote:
> On Sun, 24 Feb 2013 13:12:20 -0800, Joerg <invalid@invalid.invalid>
> wrote:
>
[...]


>> While I had the PC open I saw that I have quite a build-up of dog hair
>> in there, got to take it apart and clean it. Our big lab likes to curl
>> up down there when I am doing SPICE runs and warm air comes out. It's
>> amazing how tight of a space they can snuggle themselves into.
> 
> Yeah, number crunching does make the machine run warm.  Suggestions:
> 1.  Buy the dog a heated blanket.


It ain't the same. In his opinion :-)


> 2.  Elevate the PC a few inches above the floor with a cardboard box,
> blocks of wood, or pile of old phone books.  The air intake for the PC
> is at the lower front of the machine, turning it into an effective
> vacuum cleaner.  It will dutifully suck up everything within range
> from the floor.  Dog hair is theoretically heavier than air and will
> therefore rapidly settle onto the floor or carpet and not float
> through the air much.  By elevating the machine, you'll suck in fewer
> dog hairs and less dust.


Unfortunately on the Dells the intake is on the left side and that's
exactly where the Labrador snuggles up. Raising the PC would not help
but make it more prone to keeling over. For example when he hears the
Fedex truck and tries to travel from underneath the PC table to the
front door in milliseconds.


> 3.  Build less complex SPICE models.  That will make the machine run
> less hot, which will not attract the dog as much, which will not clog
> the machine as much, which will make the machine run even less hot,
> which will eventually reduce the need to clean out the dog hair from
> the machine.
> 

:-)

What makes it sweat is when you are almost done with a switcher and then
have to enter real xfmr coupling of 0.97 and such. Important to gauge
the dissipation in snubber parts. That really taxes a PC.


>> Supposedly there is a Dell tool but I haven't found it yet.
> 
> I searched but couldn't find anything.  There are plenty of tools to
> save the BIOS image (usually as part of a BIOS upgrade), but nothing I
> could find that saves the settings.
> 

I guess then the digital camera is the only option. Or paper and pen :-)

-- 
Regards, Joerg

http://www.analogconsultants.com/

Joerg Inscribed thus:

Don't mess about ! Do it live. Use an anti static strap. Take care not
to damage the cell holder while removing the old battery and don't let
it flip out onto the circuit board.  Make sure that you put the new
battery in the right way up, positive uppermost.

It should not take more than a few seconds to do the swap.

PS. A wood or plastic toothpic might help depending on the holder type.

HTH.

-- 
Best Regards:
                        Baron.