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  • number of days of standby (S3) time.

    I've run some numbers. I'm hoping you all can confirm or blow holes in my conclusion.

    These are probably specific to my setup.
    - My VW GTI has a 60 amp hour battery. (I assume that's the 20 hour discharge rate).
    - I configured WinXP to do suspend on power button, set my via m10000 bios to go to S3, and turned off everything I could find, so I think it's just refreshing RAM.
    - I'm using an M1-ATX, which I've set to 5sec off delay, NEVER power off. When I turn the ignition off, the m1-atx hits the mobo's power button. I intend for the carPC to be in the S3 state most of the time when I'm not in the car.


    What I really want to know is how long I could leave the car with the PC in S3 without doing killing my battery. To do that, I need to know how much the whole car (including the carPC in S3) is drawing from the battery when I've walked away and turned on the alarm.

    Here was my test:
    - I hooked up the multimeter in series between the battery negative terminal and the cable that normally attaches to the negative terminal. Is this correct?
    - I turned on the key (not the engine!!) and let the carPC power up. The fuel pump and such kick on, drawing about 9A max here when everything stablizes.

    - I turn off the key, let the carPC go to S3, get out and lock the doors. There's still some pump/fan noise on in the engine bay, drawing 1.1A here.

    - A bit later, the pump/fan noise turns off. This should be my "walk away and leave it overnight" draw, right? 470mA.

    - About 15 minutes, I check again (just to be sure), and the draw is down to 180mA! Maybe some other component in the car powers down after the long delay? I did the test twice with the same results. So I'm pretty sure this is the "walk away and leave it overnight draw".


    Here's my math to guesstimate how long my actual draw will last on my 60AH battery.
    Code:
    60AH / 20H = 3A
    3A / 0.18A = 16.67
    16.67 * 20H = ~333 hours = ~13 days
    So, I could leave my car for 13 days!?! To be safe, let's half that and round down. That gives me 6 days. That's not bad! The reality is that I want to install a kill switch that cuts the constant 12V to the PSU when I plan to leave the car for a while (more than 1 day). Also, the M1-ATX says it'll cut all power if the battery voltage drops below 11V. I don't know how long that would be for a new, healthy batter. Does this all sound reasonable or have I missed some important point?
    My worklog.
    Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

  • #2
    completely reasonable.

    do keep in mind that using all 60 amp hours leave nothing in the battery to crank the engine though

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    • #3
      If you halve your figures, that'd be 6 days to get your battery half drained. If you can start your car off of even 7V, I'd ask what scientist you had setup your electrical system. Your car will not start if it goes below ~10V. I'd say you'd be lucky if you could go 2 days and be able to start the car. Keep in mind the stress you'll be putting on your battery though with the constant discharge. You most certainly will want to get a deep cycle battery if that is your plan.

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      • #4
        Originally posted by StrataG
        If you halve your figures, that'd be 6 days to get your battery half drained. If you can start your car off of even 7V, I'd ask what scientist you had setup your electrical system. Your car will not start if it goes below ~10V. I'd say you'd be lucky if you could go 2 days and be able to start the car. Keep in mind the stress you'll be putting on your battery though with the constant discharge. You most certainly will want to get a deep cycle battery if that is your plan.

        wrong!


        battery capacity to voltage relationship is not linear

        drain a battery halfway and it drops about a volt

        drain it the other half and it drops a lot more

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        • #5
          Originally posted by greenman100
          wrong!


          battery capacity to voltage relationship is not linear

          drain a battery halfway and it drops about a volt

          drain it the other half and it drops a lot more
          So please explain to me how long his system will last. If he is even close to correct, why aren't more people doing it? Why do so many people end up with dead batteries who try this? I'd love to be able to use standby, but from what I understood, it was not viable for people who do not drive their car everyday.

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          • #6
            I have left my system for a week several times on standby without any problems. Although, once i left it for over 2 weeks and my car started normally but the computer did not resume form standby, it seems the opus cut the 5vsb line when it sensed the battery level was too low, i have a pentium m micro atx setup. For the people that end up with dead batteries, i don't think their motherboards cut power to their usb ports which puts a lot more drain on their battery.

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            • #7
              Originally posted by Kalt
              I have left my system for a week several times on standby without any problems. Although, once i left it for over 2 weeks and my car started normally but the computer did not resume form standby, it seems the opus cut the 5vsb line when it sensed the battery level was too low, i have a pentium m micro atx setup. I think the people that end up with dead batteries motherboards don't cut power to their usb ports which puts a lot more drain on their battery
              Have you ever tested your amperage? I'd love to be able to do that, but my question is, if that is the case, why aren't more people doing it? Everyone complains about startup/resume times and coming out of standby is typically a lot quicker. If you have any further info, lmk. thanks in advance.

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              • #8
                Well, I have an M10k, with a lot of USB devices, that are still power after the pc goes into standby or powers off. I keep mine in standby, and when the battery was new, and not so cold outside, it would hang on for about 5-6 days. Now, I'm really really lucky if the car starts the third day...
                Renault Megane...the OEM look

                The Lost in Europe Ford Escort

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                • #9
                  Originally posted by Cris
                  Well, I have an M10k, with a lot of USB devices, that are still power after the pc goes into standby or powers off. I keep mine in standby, and when the battery was new, and not so cold outside, it would hang on for about 5-6 days. Now, I'm really really lucky if the car starts the third day...
                  How old is your setup? I felt what happened to you is what typically happens. Any battery, even deep cycle will lose it's ability to hold a charge a lot faster if it's constantly drained. Obviously you are not completely draining it, but I know the lifecycle of a battery is longer if the discharges are very small and vice versa. If I needed to replace my battery every few years, it wouldn't be a big deal. If I'd have to replace it every year though, it would have me avoid this type of setup.

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                  • #10
                    I tested my amperage a while back, it was low enough that i was comfortable enough to try it but i don't remember the exact number. I know they are a few other members doing this too, but from what i have seen majority of mobos usb ports stay active durring and some mobos dont turn off the cpu fan durring s3. I'm sure this stops a lot of members going this route, cause all their usb devises would be active. From what i understand only memory requires power in standby.

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                    • #11
                      Originally posted by StrataG
                      So please explain to me how long his system will last. If he is even close to correct, why aren't more people doing it? Why do so many people end up with dead batteries who try this? I'd love to be able to use standby, but from what I understood, it was not viable for people who do not drive their car everyday.

                      He's good for 4-7 days, depending on how cold it is outside.

                      More people aren't doing this for a couple reasons.

                      Some motherboards don't have S3.
                      Some people have a ton of USB devices that draw on standby
                      and likely the biggest factor, most people just don't know about it.

                      I have a dual xeon system, 1.6ghz chips overclocked ot 3.2ghz, each. The chips cost me $120 total. a similar pair of chips that can run 3.2ghz stock, would have cost $600. WHy don't mroe people overclock? Not many know how.

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                      • #12
                        Why don't most do it? Maybe they don't turn as much off on the mobo, maybe their car draws more than mine, who knows. Maybe 5 people posted that they drainer their battery and the rest of us just took it as gospel. Once I ran across the 60AH rating for my battery, I had to do the real test to know for sure. It's a daily driver for me, so I hope the overnight drain isn't too much. Combined with the kill switch (with relay thanks to greenman100's advice in another thread. Although I did find a 25A/12V "automotive" switch at RadioShack I might use, I'll need a relay for another thing.)

                        StrataG:
                        As for testing it yourself. I'm new to this, I just bought a multimeter a month or so ago (there's even a post about it, I needed advice), I just bought an "automotive test lead" kit a couple of nights ago. If I can figure it out, you can.

                        greenman100:
                        So, half discharge is about a volt drop, so that'll be about where the m1-atx cuts power. At 11V, can I start my car? I know constantly going to 11V would shorten the battery's life, but with my driving pattern, I don't see that happening.
                        My worklog.
                        Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

                        Comment


                        • #13
                          Originally posted by StrataG
                          How old is your setup? I felt what happened to you is what typically happens. Any battery, even deep cycle will lose it's ability to hold a charge a lot faster if it's constantly drained. Obviously you are not completely draining it, but I know the lifecycle of a battery is longer if the discharges are very small and vice versa. If I needed to replace my battery every few years, it wouldn't be a big deal. If I'd have to replace it every year though, it would have me avoid this type of setup.

                          this is true. But how many of us go a week without using their cars? I use mine every day. And if you restart every 24 hours, that's only discharging about 15%

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                          • #14
                            Originally posted by kbyrd
                            Why don't most do it? Maybe they don't turn as much off on the mobo, maybe their car draws more than mine, who knows. Maybe 5 people posted that they drainer their battery and the rest of us just took it as gospel. Once I ran across the 60AH rating for my battery, I had to do the real test to know for sure. It's a daily driver for me, so I hope the overnight drain isn't too much. Combined with the kill switch (with relay thanks to greenman100's advice in another thread. Although I did find a 25A/12V "automotive" switch at RadioShack I might use, I'll need a relay for another thing.)

                            StrataG:
                            As for testing it yourself. I'm new to this, I just bought a multimeter a month or so ago (there's even a post about it, I needed advice), I just bought an "automotive test lead" kit a couple of nights ago. If I can figure it out, you can.

                            greenman100:
                            So, half discharge is about a volt drop, so that'll be about where the m1-atx cuts power. At 11V, can I start my car? I know constantly going to 11V would shorten the battery's life, but with my driving pattern, I don't see that happening.

                            as for the 25amp switch, that'd work fine. I was worried about the 5 amp switch you'd proposed earlier.

                            half discharge is about a volt drop, yes, but this is all very rough. a lead acid battery is actually naturally at about 12.5v, fully charged, with no load. so, a volt drop....from 12.6 or 12? I hope you see I'm making generailzations - I don't know much about your setup or environment at all.

                            11volts should be okay as long as it is not too cold out. keep in mind, the colder the engine, that harder to start AND the less the battery can put out

                            Comment


                            • #15
                              Originally posted by StrataG
                              How old is your setup? I felt what happened to you is what typically happens. Any battery, even deep cycle will lose it's ability to hold a charge a lot faster if it's constantly drained. Obviously you are not completely draining it, but I know the lifecycle of a battery is longer if the discharges are very small and vice versa. If I needed to replace my battery every few years, it wouldn't be a big deal. If I'd have to replace it every year though, it would have me avoid this type of setup.


                              The battery is almost a year old, as is the system. It's a chep battery I bought for something else, when my stock battery died, so it was a quik replacement. I never thought it would last this long.
                              I figure with a quality battery one should have no problem leaving the car for 6 days.
                              Renault Megane...the OEM look

                              The Lost in Europe Ford Escort

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