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#1
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Alert! System battery voltage is low. message
Now this might sound really stupid, but I'm getting this message frequently
when I boot up (Dell Dimension 8300 I think), the PC is probably a couple of years old - but I thought the motherboard battery would recharge when you have the power on? I do have my PC on for up to 20 hours per day most days Is this an easy/safe thing to change - I've put together my own PC a couple of times but believe it or not, have never had to fiddle with the motherboard (I assume by "system battery" that's what it means) battery It still allows me to continue booting with F1 (or setup on F2) but is this harming my system or just running slower than normal? Do I need a generic battery or one specifically obtained via DELL? thanks in advance LeeH |
#3
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Alert! System battery voltage is low. message
In article , "Lee Harris"
wrote: Now this might sound really stupid, but I'm getting this message frequently when I boot up (Dell Dimension 8300 I think), the PC is probably a couple of years old - but I thought the motherboard battery would recharge when you have the power on? I do have my PC on for up to 20 hours per day most days Is this an easy/safe thing to change - I've put together my own PC a couple of times but believe it or not, have never had to fiddle with the motherboard (I assume by "system battery" that's what it means) battery It still allows me to continue booting with F1 (or setup on F2) but is this harming my system or just running slower than normal? Do I need a generic battery or one specifically obtained via DELL? thanks in advance LeeH This is what a typical CMOS powering circuit looks like. The lower diode prevents the battery from being charged. Current can only flow out of the battery, not back in. The battery is never called on to provide a large current, and that is why they can get away with the 1K ohm resistor in series with the battery. * * * * * * * * * * * *|\ | * *3.3V_standby -----------------| \|-------+ * *reg from 5vsb * * * |/ | * * * | * * * * * * * * * * * * * * * * * * * * * * | * * * * * * * * * * * 1K ohm * * |\ | * * * | * * * *To Southbridge * *Battery * * *----/\ */\ *-----| \|-------+-----+---------- * *CR2032 * * * * * * \/ *\/ * * |/ | * * * * * * | * *Lithium * * * * * *resistor * diode * * * * * --- 1uF * *3.0V nom, * * * * * * * * * * * * * * * * --- filter * *min about 1.4V * | *cap * *by spec ICH5 * * * ** * * * * * * | * *plus diode drop * * * * * * * * * * * __+__ * * * * * * * * * * * * * * * * * * * * * * * * *___ *GND * * * * * * * * * * * * * * * * * * * * * * * * * _ The purpose of the two diodes, it to implement an "either-or" scheme. When you switch off the computer via the switch on the back, or unplug the computer, the upper power source is off. Then, the battery provides a tiny current through the lower diode. When the computer is plugged in, and the switch on the back is ON, then the upper power source is engaged. If that power source has a slightly higher output voltage, the current flow from the battery is cut off. In other words, it is possible no battery current is used while your computer is running for its 20 hours a day - and neither would the battery be used if the computer is in a sleep state. Only killing power via the switch on the back, puts the motherboard back onto battery power. If the upper voltage was weak for some reason, then a tiny bit of current could be drawn from the battery. The CR2032 battery is common to a lot of ATX motherboards, so should be readily available, even at places like Radio Shack. If you have a multimeter, you can measure the battery, and if it is ~3.0V, then leave it alone, as it is fine. The spec sheet for the ICH5 says it has a 1.0V minimum, but you have to add a diode drop, which at the low current involved, might be on the order of an additional 0.4V. So, if the voltage at the battery drops below about 1.5V, then the voltage point after the diodes will drop below the minimum needed by the Southbridge. The result in that case, would be the CMOS clock could stop, or thing stored in the small CMOS RAM logic block inside the Southbridge could be erased. You can enter the BIOS and write down your settings before changing the battery. A Dell might not have that much in the way of custom settings, but you might have a look anyway. Based on user accounts, if you are not too slow in removing the old battery, and putting the new one in place, the "filter cap" on the right can hold enough energy to run the CMOS clock for a short period of time. On a digital watcn, the current to run a 32768 Hz oscillator is about 2 microamps, so the Southbridge shouldn't gobble up the charge on that capacitor too fast (the ICH5 spec sheet says the battery current is 6 microamps). Consult your manual, to see if there is a recommended procedure for battery replacement. If it was my machine, it would be shut off and unplugged, before opening the side of the case. Remember to bring your body to the same potential as the computer case, by touching the case before touching the motherboard. That will remove any large electrostatic charges that could flow if you just touch a component on the motherboard first, without discharging yourself to the case first. I like to handle batteries like that with a soft cloth or tissue, so no fingerprints all over the nice shiny battery :-) In the above circuit, even if the battery is flipped upside- down by accident, the diode should prevent the reverse bias from damaging the Southbridge. Current should only flow if the (+) of the battery is connected to the 1K ohm resistor. So, the dual diodes can do three things: 1) Prevent battery discharge, as long as +5VSB is powered from the ATX PSU. 2) Prevent the battery from being charged, which I understand can have explosive consequences. No, I don't want to test that hypothesis :-) http://www.duracell.com/procell/safety/pdf/2032_3c.pdf 3) Prevent damage to the motherboard, if the battery is flipped over by accident. A reverse biased diode will not conduct. HTH, Paul |
#4
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Alert! System battery voltage is low. message
"Lee Harris" wrote in message ... Now this might sound really stupid, but I'm getting this message frequently when I boot up (Dell Dimension 8300 I think), the PC is probably a couple of years old - but I thought the motherboard battery would recharge when you have the power on? I do have my PC on for up to 20 hours per day most days snip the cmos battery is not rechargeable but it should only take you a few minutes to replace |
#5
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Alert! System battery voltage is low. message
On Wed, 23 Nov 2005 08:27:08 GMT, "Lee Harris"
wrote: Now this might sound really stupid, but I'm getting this message frequently when I boot up (Dell Dimension 8300 I think), the PC is probably a couple of years old - but I thought the motherboard battery would recharge when you have the power on? I do have my PC on for up to 20 hours per day most days No, the typical motherboard battery does not recharge. They generally last up to 7 years, sometimes far less, sometimes a little more. Is this an easy/safe thing to change - I've put together my own PC a couple of times but believe it or not, have never had to fiddle with the motherboard (I assume by "system battery" that's what it means) battery Yes very easy. Unless there are cards or cables in the way it should be visible, silver coin shaped object in a (usually) holder with a spring or plastic tab on the edge. Gently pry the tab away from the corner of the battery and it should pop out. The Dell System documentation usually covers basic items like this, http://support.dell.com/support/edoc...sm/battery.htm Usually it's a "CR2032", a very common size even at stores that only carry misc. button cell batteries but no PC parts. It should be stamped on the original battery too. It still allows me to continue booting with F1 (or setup on F2) but is this harming my system or just running slower than normal? Could be running at same speed as always if your system configuration didn't need any of the bios defaults changed. Do I need a generic battery or one specifically obtained via DELL? No you do not need to get it from Dell. Check a local drugstore or wherever you buy watch, hearing aid, camera or other misc small batteries. Of course there are myriad places online to buy one too, but since they're only $1 or 2 the shipping cost is a high overhead compared to buying it locally. |
#6
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Alert! System battery voltage is low. message
"Lee Harris" wrote in message ... Now this might sound really stupid, but I'm getting this message frequently when I boot up (Dell Dimension 8300 I think), the PC is probably a couple of years old - but I thought the motherboard battery would recharge when you have the power on? I do have my PC on for up to 20 hours per day most days Is this an easy/safe thing to change - I've put together my own PC a couple of times but believe it or not, have never had to fiddle with the motherboard (I assume by "system battery" that's what it means) battery It still allows me to continue booting with F1 (or setup on F2) but is this harming my system or just running slower than normal? Do I need a generic battery or one specifically obtained via DELL? thanks in advance LeeH Many thanks to everyone who helped with this issue. I'll save the BIOS settings, whip it out and pop a new one in :-) |
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