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Thread: Battery Drain Protection?

  1. #1
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    Battery Drain Protection?

    My first post, but i've been doing a lot of reading to get my first pc installed.

    I have the following:

    carnetix p1900
    Acer 3610
    Liliput monitor

    I've been able to get my system working inside my house using a standard home pc supply (great idea i got from this site). I've got everything pretty much simulated outside of my car and its ready to be installed inside. Including the wiring to shutdown the acer via the shutdown controller.

    I attempted to install it this past weekend and ended up with a dead battery after a few hours. This is something i've been concerned about from day1 doing this project. After this event and reading other peoples issues, i want to kill power to the carnetix to guarantee that there is no current draw. Would really hate having to worry about this all the time.

    What is the best way to kill power to the carnetix? Do i need a relay of some sort or can i just use a standard switch?

  2. #2
    Low Bitrate
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    A switch is fine. A relay is just a remote controlled switch.

    You battery may be getting old if it died that quickly. A good battery (if you live in the U.S.) for a heavily used electrical system is the Sears Platinum, which is a rebadged Odyssey.

  3. #3
    FLAC
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    this is a circuit i designed a while ago for the same reason, i wanted the battery to be saved enough to start the car in any weird event that the computer ends up trying to drain it.

    edit- i redesigned the relay so it latches until the alarm trips it back off. at least i think this will work. im going to show some other people and make sure.


  4. #4
    Raw Wave
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    Why the 4 series 0.1F hence providing 0.025F? (Bottom center.)

    There is also the MW728 low voltage disconnect (battery protector) for ~$20 which can switch 10A else switch a heavier relay, but it doesn't have the same warning, and it trips out at 11.2V (and back on at 12.5V).

  5. #5
    FLAC
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    oh yeah... those caps were supposed to be in parallel. thanks. changed to just a single cap. i dont even know how much you would want there, because you want enough to hold the device on for say 4 seconds, but too much capacitance there might hold the relay open after the circuit shuts off. like i said, it will probably just be a trial and error thing.

    and thats the problem with most voltage cutout devices/chips. they shut off around 11v, and that is FAR too low for your battery to be able to crank an engine over. all they do is stop your battery from being damaged, which is nice but you still are stranded at 11.2v.

  6. #6
    FLAC
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    this is also a modification i was thinking about to give myself a hardware shutdown controller based on voltage (much like laptops do with software).


  7. #7
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    Quote Originally Posted by trader007 View Post
    and thats the problem with most voltage cutout devices/chips. they shut off around 11v, and that is FAR too low for your battery to be able to crank an engine over. all they do is stop your battery from being damaged, which is nice but you still are stranded at 11.2v.
    Yeah - tell me.... The there are hysteresis problems as I had a while ago - a fully charged battery (not used since its terminal vapourised) with MW728 between it and a ~5A fridge. Cycles on off on off with only the MW728s delays and time it took for the battery to self recover from 11.2V to 12.5V (~10 seconds). Problem solved after a few minutes charging off the alternator (ie, a charger with real Amps to blow off the cobwebs (ie, >20A). (And I dare I mention similar problems with smart battery isolators - which do not occur with a relay off the charge light??)

    But many sensors can be tricked into higher voltages by adding diodes. Typically the MW728 can switch off at 11.8V or 12.4V by adding 1 or 2 silicon diodes. (Then it doesn't switch on until 0.6V or 1.2V higher than 12.5V, but they can be switched out.)
    Of course, those sensors no longer switch the load, but instead switch relays that power the loads. And those relays can be wired to latch, or with delays, or with manual bypass or off.

    Nothing like the old UPS handshaking.... batteries getting low; x-minutes to power off; PC starts graceful shutdown (and can signal UPS to turn off now etc).


    But I still think a dual battery setup is worthwhile. If the only intent is cranking power, then - assuming you have a charge light - it's merely the cost of a relay and an AGM battery (say a $5 relay & $35 12V-7AH AGM). You can run on & flatten the 2nd battery without effecting your original/cranking battery.
    Then add the smarts for battery#2 protection. (After all, how far can you flatten the main battery? Do you trust your thresholds for all battery conditions & temperatures? And if the 2nd battery is big enough (7AH, 15AH or larger), it can be an emergency jumper battery for cranking.)

    Picking voltage thresholds is not easy - except for those that think 12.7V is full and 11.3-11.6V is dead flat when a battery is under load.

  8. #8
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    Thanks guys. Well, my battery turned out to be dead and took it to walmart for a replacement. After putting in the new battery everything worked fine. Display is working computer turns on and i'm getting audio out of my stereo. Long weekend trying to get everything up and running in the car.

    Thought i had everything working okay until i took the computer out to install software and update some things. Strange thing is, i can't get the darn thing to power up inside my house. Its not responding to the push button. I've checked the voltage getting to it and everything seems fine (19v)

    If i put it in the car everything boots up fine (whether i do it through turning the key or manually pushing the button). The other strange thing is it doesn't need the ACPI wires connected for the computer to turn on. As long as the power supply is connected to the computer, it turns on as soon as the ignition switches.

    Any ideas?

  9. #9
    FLAC
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    Quote Originally Posted by OldSpark View Post
    Yeah - tell me.... The there are hysteresis problems as I had a while ago - a fully charged battery (not used since its terminal vapourised) with MW728 between it and a ~5A fridge. Cycles on off on off with only the MW728s delays and time it took for the battery to self recover from 11.2V to 12.5V (~10 seconds). Problem solved after a few minutes charging off the alternator (ie, a charger with real Amps to blow off the cobwebs (ie, >20A). (And I dare I mention similar problems with smart battery isolators - which do not occur with a relay off the charge light??)

    But many sensors can be tricked into higher voltages by adding diodes. Typically the MW728 can switch off at 11.8V or 12.4V by adding 1 or 2 silicon diodes. (Then it doesn't switch on until 0.6V or 1.2V higher than 12.5V, but they can be switched out.)
    Of course, those sensors no longer switch the load, but instead switch relays that power the loads. And those relays can be wired to latch, or with delays, or with manual bypass or off.

    Nothing like the old UPS handshaking.... batteries getting low; x-minutes to power off; PC starts graceful shutdown (and can signal UPS to turn off now etc).


    But I still think a dual battery setup is worthwhile. If the only intent is cranking power, then - assuming you have a charge light - it's merely the cost of a relay and an AGM battery (say a $5 relay & $35 12V-7AH AGM). You can run on & flatten the 2nd battery without effecting your original/cranking battery.
    Then add the smarts for battery#2 protection. (After all, how far can you flatten the main battery? Do you trust your thresholds for all battery conditions & temperatures? And if the 2nd battery is big enough (7AH, 15AH or larger), it can be an emergency jumper battery for cranking.)

    Picking voltage thresholds is not easy - except for those that think 12.7V is full and 11.3-11.6V is dead flat when a battery is under load.

    that is a valid point, the battery does have a lot of fluctuation with the voltage which doesnt always immediately reflect the real amperage left.

    this is for a very specific purpose though, the pc stays on so the battery voltage drop is consistent. and if in the case that it clearly does trip the alarm too early (like if i crank the music for a few seconds while the engine is off) all i would have to do is hit that momentary switch and it would stay on. ill have a 2 minute warning at least to do this... a flashing light on the dash and the push button right next to it.

    i might even be able to design a circuit that would auto-reset the one i have if the voltage rises above a certain point, but like you are saying that might not even be practical unless i make it 14v so it always just resets with the engine on.

    ps. the part about adding diodes to normal battery protection devices... thats pretty much a crapshoot isnt it?. if there is a diode that you can turn its voltage drop up and down then it could probably work, as you could fine tune it easily.. i dont even know those exist though. i do agree though, if you want to spend the money on a 2nd car or motorcycle battery then go for it because that is the best way.

  10. #10
    Raw Wave
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    Quote Originally Posted by trader007 View Post
    the part about adding diodes to normal battery protection devices... thats pretty much a crapshoot isnt it?. if there is a diode that you can turn its voltage drop up and down then it could probably work, as you could fine tune it easily.. i dont even know those exist though.
    Does crapshoot mean crap, or unstable etc?

    Either is false. It is simple - say a device turns off when it senses 11.2V but you want it to turn off at 11.8V.
    Add a diode to its input which drops 0.6V.
    When the supply hits 11.8V, the device sees 11.2V and turns off (its load).
    Simple!
    Use whatever combination of 0.2V-0.7V diodes you need. It is also possible to use resistors, but diodes are moire consistent.

    Be aware however that whereas normally such a "low voltage cutout" (LVCO - eg, MW728) ) device would itself be switching the load direct, in this mode, the LVCO is merely turning a relay on/off. (That relay controls power the load.)
    Therefore the extra voltage dropping diodes etc see a more constant load - ie, the LVCO will its relay on on off (eg, 10mA sensing current with or without (say) 100mA for its relay) as opposed to a 10mA to 10A range with the end load connected.
    It is that former load (say 100+10mA) that you select your diodes (or resistors) for. (But make sure hysteresis isn't a problem - if so, add a latching "off" mechanism.)

    Or you could get an adjustable device. I like a kit from Oatley (Sydney, Australia) that sells for under $25, uses an 80A latching relay, and have reasonable adjustment range and can be used for over-voltage or under-voltage by changing one resistor. (I used the same kit as my original "smart battery isolator" to connect batt #2 whilst charging, and then as LVCO to protect the 2nd battery from discharge. Later I replaced the "smart isolator" with the far superior (and cheaper!) charge-lamp & relay system.

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