Windows 10: Question about recent power outage and PC Solved

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  1.    09 Apr 2018 #21

    Steve C said: View Post
    My PC is switched off at the mains when not in use so I'm lucky to get more than 2 years use before the CMOS battery needs changing. I've had various problems with a CMOS battery just under 3V. I fail to see how a battery at 2V would work in the motherboards I've owned. If I'm fiddling with the PC and have the case cover off, I just replace any battery CMOS battery showing under 3V.
    Yes, if you switch off the mains power most of the time then the battery is only expected to last ~3 years in the ideal case. 2V is Intel's requirement measured at the PCH. If the motherboard has other things connected to VccRTC and/or if the motherboard manufacturer used a cheap diode then there would be additional voltage losses between the battery and the PCH so the required voltage at the battery would be higher.

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  2.    09 Apr 2018 #22

    Steve C said: View Post
    My PC is switched off at the mains when not in use so I'm lucky to get more than 2 years use before the CMOS battery needs changing..
    Power on or off make no difference to a CMOS battery life expectancy. The electrical concept is called shelf life. That CMOS battery lasts just as long in a computer as it does in the original package. Because power required by the CMOS and clock is so tiny. Much more 'life expectancy' is taken by self discharge that is taken by the CMOS.

    Any battery that does not last more than five years implies a serious defect on that motherboard or inside the CMOS. And yes, we have seen some ICs that had an internal defect - caused its battery to discharge in days.
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  3.    09 Apr 2018 #23

    westom said: View Post
    Power on or off make no difference to a CMOS battery life expectancy. The electrical concept is called shelf life. That CMOS battery lasts just as long in a computer as it does in the original package. Because power required by the CMOS and clock is so tiny. Much more 'life expectancy' is taken by self discharge that is taken by the CMOS.

    Any battery that does not last more than five years implies a serious defect on that motherboard or inside the CMOS. And yes, we have seen some ICs that had an internal defect - caused its battery to discharge in days.
    Do you have a spec for a typical CMOS battery drain?
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  4.    09 Apr 2018 #24

    My laptop has a built in rechargeable battery, and one day I could not get to bios at all. I had to (carefully) short circuit the battery - I used a light bulb in short circuit to avoid doing it to fast, and eventually it discharged and I got to bios. I really do not recommend this!
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  5.    09 Apr 2018 #25

    Steve C said: View Post
    Do you have a spec for a typical CMOS battery drain?
    ICs that do this function typically consume 100 to 200 picoamps. Some will consume as much as 1 microamp.


    BTW, never short a rechargeable battery in a laptop. That can cause explosions. CMOS battery in laptops is not the rechargeable battery. Laptops often have a separate coin cell to maintain clocks and CMOS settings. Better is to remove that battery and then wait for residual charges to dissipate.
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  6.    10 Apr 2018 #26

    westom said: View Post
    ICs that do this function typically consume 100 to 200 picoamps. Some will consume as much as 1 microamp.


    BTW, never short a rechargeable battery in a laptop. That can cause explosions. CMOS battery in laptops is not the rechargeable battery. Laptops often have a separate coin cell to maintain clocks and CMOS settings. Better is to remove that battery and then wait for residual charges to dissipate.
    Assuming your spec of a typical 200pA drain and a typical c. 200mAh CR2032 battery energy capacity then this gives a battery life c. 10^9 hours = 114,000 years! That's not my experience having used various motherboards from Asus, Gigabyte & MSI where I've been lucky to get more than 3 years life with the PC mainly off at the mains. A 1 microamp drain gives a life of c. 25 years which is still far short of my practical experience.
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  7.    10 Apr 2018 #27

    Steve C said: View Post
    Assuming your spec of a typical 200pA drain and a typical c. 200mAh CR2032 battery energy capacity then this gives a battery life c. 10^9 hours = 114,000 years! That's not my experience having used various motherboards from Asus, Gigabyte & MSI where I've been lucky to get more than 3 years life with the PC mainly off at the mains. A 1 microamp drain gives a life of c. 25 years which is still far short of my practical experience.
    Intel rates the PCH drain at 6uA.

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  •    10 Apr 2018 #28

    PolarNettles said: View Post
    Intel rates the PCH drain at 6uA.

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    6 microamps would give a 3-4 year CMOS battery life which is consistent with my experience.
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  •    10 Apr 2018 #29

    Steve C said: View Post
    Assuming your spec of a typical 200pA drain and a typical c. 200mAh CR2032 battery energy capacity then this gives a battery life c. 10^9 hours = 114,000 years!
    Now read what was quoted. Picoamps is near zero - irrelevant. Shelf life provides a completely different and relevant number.
    The electrical concept is called shelf life. That CMOS battery lasts just as long in a computer as it does in the original package.
    Please read and grasp every sentence before posting.

    Making conclusions without first learning facts also explains why batteries that need not be replaced are being replaced frequently. The original batteries in the original IBM PC and batteries in a Dallas Semiconductor equivalent IC were rated at 5 years. Life expectancy numbers have substantially increased since the early 1980s.

    If a 6 microamp load defined battery life expectancy, then a 2032 cell would last over 200 years. Battery life expectancy is same whether AC power is constantly applied or not. That addresses a conclusion only based in (created by) speculation. And not based in first learning how this stuff works.

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  •    11 Apr 2018 #30

    westom said: View Post
    Now read what was quoted. Picoamps is near zero - irrelevant. Shelf life provides a completely different and relevant number.
    Please read and grasp every sentence before posting.

    Making conclusions without first learning facts also explains why batteries that need not be replaced are being replaced frequently. The original batteries in the original IBM PC and batteries in a Dallas Semiconductor equivalent IC were rated at 5 years. Life expectancy numbers have substantially increased since the early 1980s.

    If a 6 microamp load defined battery life expectancy, then a 2032 cell would last over 200 years. Battery life expectancy is same whether AC power is constantly applied or not. That addresses a conclusion only based in (created by) speculation. And not based in first learning how this stuff works.

    As a professional scientist I think I grasped your post. The shelf life of a CR2032 battery is c. 10 years which is about 3x the practical service life when you switch off the PC when not in use - see http://data.energizer.com/pdfs/lithiumcoin_appman.pdf What does your exceedingly low quoted drain of 100-200 picomaps refer to?

    Your maths is wrong. A CR3032 battery has a 240mAh capacity (above reference). A practical current drain of 6 microamps will deplete the battery in 40000 hours or 4.57 years which is consistent with my experience of around 3 years. The practical life is less than the calculated 4.57 years since this figure assumes complete depletion of the battery to 0V output whereas I've found you can start having BIOS parameter storage issues if the voltage is below c. 2.7V.

    Now check your maths and
    read and grasp all before posting.
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