Motherboard backup battery usage

patrik · 2014-04-12, 16:03

Is less power used from the motherboard backup battery when the computer is attached to standby power as compared to when power is switched off completely?

The reason I ask is that I just bought a remote power switch, and I have two ways of using it:

1) Having each computer's BIOS set to turn computer on when power is applied. This way I can shut down the computers by software and then turn the power off. And later turn them on when I want to.

2) Having the BIOS set to last state when power returns. This way I can only use the remote switch to power-cycle the computers if they get to hot and hang. (Or turn them off until I return home.)

There is also a variant of 1), shutting it down by software, but not turning the power off. Then it would turn on again after a power loss (unless I redefine the behaviour for each outlet (to stay off after power loss) each time I turn its computer off, and redefine it again when I turn it on).

tServo · 2014-04-18, 00:54

Quote:

Originally Posted by patrik

Is less power used from the motherboard backup battery

Are you referring to the small, coin size battery on the motherboard? If so, I think the power draw from it so SO INFINITESIMAL that it hardly matters. I say this because I have seen many computers taken out of storage after YEARS of not being plugged in and have yet to see one with all the power drained from those batteries. I'm not sure we're talking about the same battery, tho.

LaurV · 2014-04-18, 04:19

And additional, the power withdrawn from that battery is the same per unit of time, no matter if the computer is on, or off, plugged in the wall, or not, sleeping, gaming, or crunching prime numbers. [edit: the battery is not rechargeable, the energy is always slowly consumed out of it, no matter what your computer is doing; the goal of that battery is only to maintain alive a small cmos memory (small as physical dimension, not as capacity), and to run the RTC (real time clock) small integrated circuit, which altogether take less than 4-6 microampers at 3 volts; you will have to change that battery after 5-8-10 years no matter what you are doing with your computer, store it or use it]. However, I don't think he is talking about that battery.

TheMawn · 2014-04-18, 04:42

I've never heard of a motherboard backup battery. I've always seen a computer turn off literally the second power is cut (some hard drives are at risk of not having enough juice to finish some operation if the PSU is bad) so I don't know either.

I didn't know the CMOS battery wasn't rechargeable though. The things you know...

LaurV · 2014-04-18, 05:22

Quote:

Originally Posted by TheMawn

I've never heard of a motherboard backup battery.

Me neither

We call it CMOS battery, or RTC battery. But some other guys do call it backup battery. However, I can't believe the OP was talking about that :D

Some systems have real backup batteries, who maintain the ram refresh in sleeping mode, (like for laptops). Usually, when I think about "backup" (power, not information), I am thinking about something like an UPS. That is also called "backup battery", just is external.

Xyzzy · 2014-04-18, 06:52

Quote:

I've always seen a computer turn off literally the second power is cut (some hard drives are at risk of not having enough juice to finish some operation if the PSU is bad) so I don't know either.

On our computer, if we cut the power with the PSU switch or by unplugging the cord, there are several lights on the motherboard that take up to two minutes to go out. (We assume some capacitors are involved.)

Xyzzy · 2014-04-18, 06:59

Quote:

Some systems have real backup batteries, who maintain the ram refresh in sleeping mode, (like for laptops).

This isn't really related to your quote, but your quote reminded us about an interesting computer we played with once, which was the original "portable" Mac. It had static RAM.

http://en.wikipedia.org/wiki/Macintosh_Portable
http://en.wikipedia.org/wiki/Static_..._access_memory

Xyzzy · 2014-04-18, 07:14

Another interesting data point WRT CMOS/RTC batteries: We once worked on a pretty large (boat anchor) Compaq or Dell server that had 2×AA NiCd cells in a little shrink-wrapped holder wired up as the CMOS/RTC battery, and it would charge continuously, at a very very low maH rate. Unfortunately, over (a long) time, the NiCd cells lost their ability to hold a charge and failed.

Since we had piles of Sanyo Sub-C NiCd cells for our remote control cars we just slapped two together with shrink-wrap and some wire and used double-sided sticky tape to secure it in the chassis.

Up until that point the organization was going to scrap the server (!) because nobody could figure out why the clock would slew continuously. (And there was no facility in the OS to compensate for the slew.) The BIOS defaults were enough for it to boot. (It was a real simple BIOS and we think it had to be accessed via a serial port.)

So we were a hero for a day.

LaurV · 2014-04-18, 08:31

Haha, we also did such tricks with AA (AAA) batteries, wires, scotch tape, or even with accumulators and soldering a diode (or substituting the one on board with a resistor, there is one which protects the battery when the power is applied to the RTC integrated circuit) for charging, etc., in the very far past, but since a cr32 battery can be bought here in every minimart or 7-eleven, for less than a dollar (~60 to 80 cents, in fact) and holds over 2 years, well... it does not really worth the effort.

P.S. Sinclair Spectrum (our first computer ever that we build by ourselves, we could write programs for it, and own it, in the same time) also had static RAM, the very huge amount of 16 kilo bytes! Some of the flavors came even with a RAM "backup" battery, I don't remember which, but still have a ram PCB at home in Ro, with 16k (8 integrated circuits, each with the tremendous amount of 2 kilo bytes of RAM) and small button cell on it.

xilman · 2014-04-18, 08:49

Quote:

Originally Posted by tServo

Are you referring to the small, coin size battery on the motherboard? If so, I think the power draw from it so SO INFINITESIMAL that it hardly matters. I say this because I have seen many computers taken out of storage after YEARS of not being plugged in and have yet to see one with all the power drained from those batteries. I'm not sure we're talking about the same battery, tho.

I inherited a Sun workstation whose mobo battery had drained completely. Can't remember seeing any others. However, there are so many geriatric computers stored in my attic that it seems quite likely that some are up there.

patrik · 2014-04-19, 19:32

Quote:

Originally Posted by tServo

Are you referring to the small, coin size battery on the motherboard? If so, I think the power draw from it so SO INFINITESIMAL that it hardly matters. I say this because I have seen many computers taken out of storage after YEARS of not being plugged in and have yet to see one with all the power drained from those batteries. I'm not sure we're talking about the same battery, tho.

This is indeed the battery I'm talking about. No need to worry then, how I set it up?

But speak of the devil. When I unplugged my oldest computer "nu" (bought in August 2007) for routing the power through the switch, all BIOS settings were lost. I'll have to replace that battery. (And of course, it had to be the innermost computer (see photo).)

2014-04-12, 16:03	#1
patrik "Patrik Johansson" Aug 2002 Uppsala, Sweden 5²×17 Posts	Motherboard backup battery usage Is less power used from the motherboard backup battery when the computer is attached to standby power as compared to when power is switched off completely? The reason I ask is that I just bought a remote power switch, and I have two ways of using it: 1) Having each computer's BIOS set to turn computer on when power is applied. This way I can shut down the computers by software and then turn the power off. And later turn them on when I want to. 2) Having the BIOS set to last state when power returns. This way I can only use the remote switch to power-cycle the computers if they get to hot and hang. (Or turn them off until I return home.) There is also a variant of 1), shutting it down by software, but not turning the power off. Then it would turn on again after a power loss (unless I redefine the behaviour for each outlet (to stay off after power loss) each time I turn its computer off, and redefine it again when I turn it on). Attached Thumbnails

2014-04-18, 04:19	#3
LaurV Romulan Interpreter Jun 2011 Thailand 7²·197 Posts	And additional, the power withdrawn from that battery is the same per unit of time, no matter if the computer is on, or off, plugged in the wall, or not, sleeping, gaming, or crunching prime numbers. [edit: the battery is not rechargeable, the energy is always slowly consumed out of it, no matter what your computer is doing; the goal of that battery is only to maintain alive a small cmos memory (small as physical dimension, not as capacity), and to run the RTC (real time clock) small integrated circuit, which altogether take less than 4-6 microampers at 3 volts; you will have to change that battery after 5-8-10 years no matter what you are doing with your computer, store it or use it]. However, I don't think he is talking about that battery. Last fiddled with by LaurV on 2014-04-18 at 04:22

2014-04-18, 08:31	#9
LaurV Romulan Interpreter Jun 2011 Thailand 10010110110101₂ Posts	Haha, we also did such tricks with AA (AAA) batteries, wires, scotch tape, or even with accumulators and soldering a diode (or substituting the one on board with a resistor, there is one which protects the battery when the power is applied to the RTC integrated circuit) for charging, etc., in the very far past, but since a cr32 battery can be bought here in every minimart or 7-eleven, for less than a dollar (~60 to 80 cents, in fact) and holds over 2 years, well... it does not really worth the effort. P.S. Sinclair Spectrum (our first computer ever that we build by ourselves, we could write programs for it, and own it, in the same time) also had static RAM, the very huge amount of 16 kilo bytes! Some of the flavors came even with a RAM "backup" battery, I don't remember which, but still have a ram PCB at home in Ro, with 16k (8 integrated circuits, each with the tremendous amount of 2 kilo bytes of RAM) and small button cell on it. Last fiddled with by LaurV on 2014-04-18 at 08:45 Reason: links

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2014-04-18, 04:42	#4
TheMawn May 2013 East. Always East. 3277₈ Posts	I've never heard of a motherboard backup battery. I've always seen a computer turn off literally the second power is cut (some hard drives are at risk of not having enough juice to finish some operation if the PSU is bad) so I don't know either. I didn't know the CMOS battery wasn't rechargeable though. The things you know...

2014-04-18, 07:14	#8
Xyzzy "Mike" Aug 2002 202A₁₆ Posts	Another interesting data point WRT CMOS/RTC batteries: We once worked on a pretty large (boat anchor) Compaq or Dell server that had 2×AA NiCd cells in a little shrink-wrapped holder wired up as the CMOS/RTC battery, and it would charge continuously, at a very very low maH rate. Unfortunately, over (a long) time, the NiCd cells lost their ability to hold a charge and failed. Since we had piles of Sanyo Sub-C NiCd cells for our remote control cars we just slapped two together with shrink-wrap and some wire and used double-sided sticky tape to secure it in the chassis. Up until that point the organization was going to scrap the server (!) because nobody could figure out why the clock would slew continuously. (And there was no facility in the OS to compensate for the slew.) The BIOS defaults were enough for it to boot. (It was a real simple BIOS and we think it had to be accessed via a serial port.) So we were a hero for a day.