i heard the cmos battery isn't even used unless the tower is unplugged since there is always power to the tower when plugged in (even when powered down). is this true? it goes against everything i have heard.
cmos battery actually doesn't kick in unless you unplug the pc??
- Thread starter carolinaboy
- Start date
With AT, power off meant power off. Battery in use when turned off.
WIth ATX, there's power all over the place. Finally convinced me to start pulling cords after all these years. Whether your CMOS will clear on shutdown with a dead battery probably depends on the motherboard though.
WIth ATX, there's power all over the place. Finally convinced me to start pulling cords after all these years. Whether your CMOS will clear on shutdown with a dead battery probably depends on the motherboard though.
lore
i thought the cmos battery kept power to the chip when the system was powered down. someone mentioned that the cmos battery isn't used even when the system is powered down; it is only used when the system is unplugged, thus removing all power from the tower.
i thought the cmos battery kept power to the chip when the system was powered down. someone mentioned that the cmos battery isn't used even when the system is powered down; it is only used when the system is unplugged, thus removing all power from the tower.
the battery supplies power when there is no power. with atx, there is always power since it is soft-off, which means a 5VDC line is always going to the mobo unless your ps is off (some atx pses come with a real off switch). it's that 5vdc signal that allows us to turn on the computer with the keyboard. it is also the reason why some optical mice stay on if the ps2 port is used as a connection since the mouse can also be set to turn on the computer.
i've also recently started physically unplugging the computer when i work on it....ever since i installed a pci card that happened to make the computer turn on when i put it in (scary stuff!) i don't just "shut down" the computer anymore.
plus, i like how most new mobo's have LED's on them, reminding you "hey, i'm still live here"
plus, i like how most new mobo's have LED's on them, reminding you "hey, i'm still live here"
the following article shows that one can change the cmos battery WHILE THE COMPUTER IS ON "and if youre fast enough", not loose the settings. This implies that the tiny charge is necessary all the time as a separate circuit independent from the PSU. The ATX constant trickle charge (to capacitors)is for speed up of boot up only.
Text
and the above can easily be tested.
Simply turn on your computer, go into windows, then remove the battery from mobo. Use the computer for ten minutes (enough to discharge cmos memory IF it only runs off battery) and put battery back in while computer is still on. Then shutdown and reboot. Id say your cmos info is lost. Supposedly, for those who think that the mobo juice also keeps cmos going, and the battery is only backup, the power supply should keep cmos charged and info secure while battery is out. Right?
It's obvious you never tried your so called test. The only reason you have a CMOS battery is to save the settings when you power completely down. I have seen old AT's that would stay running for weeks with no battery at all and there was no trouble until you had a power failure or something, then the settings would be lost. All you had to do was redo everything and remember not to turn it off and you were good to go again. A lot of the old batteries were rechargeables like little ni-cads that were recharged by the same current source that made the battery redundant as long as you didn't turn off the machine. A diode separates the CMOS circuit from the rest of the 5 volt system when powered down so the battery won't try to backfeed the rest of the system. Sometimes if you short the CMOS system accidently it takes out the diode which has sacrificed itself like a fuse and the system acts like it has a dead battery. If your motherboard acts like the battery is dead but changing it does no good, look for the blown diode which can easily be replaced..
<<<< I have seen old AT's that would stay running for weeks with no battery at all and there was no trouble until you had a power failure or something, then the settings would be lost.>>>>>
The above statement is irrelevant to the question posted. The CMOS info is for boot up purposes only. ANY computer will run indefinitely with no battery if not turned off. The CMOS is not in play. The only issue here is whether the mobo voltage is mainly used for cmos retention or is it the battery only. Rechargeable batts adds another separate complicating factor. Shutting off the computer with the battery out, is not the same as taking the battery out of a booted system and putting it back in that booted system five minutes later. By your statements, nothing should be lost.
Edit: To try and further clarify: if the battery is only used for "backup" in a no juice shutdown condition, then that means the mobo voltage is the main source of charge all the time EXCEPT for shutdown.
SOMETHING has to supply voltage to the cmos at all times.
Therefore, if a computer is on, the cmos is being charged and the battery is not necessary to retain settings DURING THIS TIME. And if you put back in the battery before shutdown, it should take over as needed, nothing should change.
The above statement is irrelevant to the question posted. The CMOS info is for boot up purposes only. ANY computer will run indefinitely with no battery if not turned off. The CMOS is not in play. The only issue here is whether the mobo voltage is mainly used for cmos retention or is it the battery only. Rechargeable batts adds another separate complicating factor. Shutting off the computer with the battery out, is not the same as taking the battery out of a booted system and putting it back in that booted system five minutes later. By your statements, nothing should be lost.
Edit: To try and further clarify: if the battery is only used for "backup" in a no juice shutdown condition, then that means the mobo voltage is the main source of charge all the time EXCEPT for shutdown.
SOMETHING has to supply voltage to the cmos at all times.
Therefore, if a computer is on, the cmos is being charged and the battery is not necessary to retain settings DURING THIS TIME. And if you put back in the battery before shutdown, it should take over as needed, nothing should change.
well, i just did "my test"
i booted up, removed the battery for 5 min, replaced it, booted down
guess what: no cmos settings lost
so i can now safely assume that the mobo does indeed supply juice to cmos chip, and battery is only necessary under total no power situation.
(live and learn)
Edit: and that article referred to above on PCMechanic about hurrying in battery replacement to retain settings has no relation to reality, there is no hurry involved. What were they thinking?
i booted up, removed the battery for 5 min, replaced it, booted down
guess what: no cmos settings lost
so i can now safely assume that the mobo does indeed supply juice to cmos chip, and battery is only necessary under total no power situation.
(live and learn)
Edit: and that article referred to above on PCMechanic about hurrying in battery replacement to retain settings has no relation to reality, there is no hurry involved. What were they thinking?
Oh I'm sorry about what I said - I didn't mean it as a blanket statement.
The battery is used when there is no power going through the board at all. And yes, in ATX systems that means pulling the power cord out of the power supply.
The battery is used when there is no power going through the board at all. And yes, in ATX systems that means pulling the power cord out of the power supply.
How long do these batteries last then. I live in Florida so during the summer you better pull the plug from the wall because surge protectors arent fast enough to save your comp from a close lightning strike. So i always unplug mine if i know i wont be home in the afternoons. And i had one motherboard for like 2 yrs without having to replace the battery. Guess it dont matter not like they cost a lot
most cmos lithium batteries i've seen dead are 3-5 years old...which isn't too bad of a lifetime at all.
usually only 3-5 bucks to replace
usually only 3-5 bucks to replace
CMOS batterys are only used when the system is not recieving any power. The CMOS battery provides a source of power to keep the information in your bios such as system time, and POST data.
Hea MDAY;
Could you expand on this turning the computer ON with the keyboard?? I've never seen this option or trick yet......but maybe my generic 101 board doesn't have this feature.
lassie
Could you expand on this turning the computer ON with the keyboard?? I've never seen this option or trick yet......but maybe my generic 101 board doesn't have this feature.
lassie
Not all mobo have the power by KB option. Check the manual and it should refer you to a jumper or a bios settings if there's any.
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