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

Started by Joerg February 24, 2013
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.