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Thread: Looking for a battery saver circuit...

  1. #1
    Variable Bitrate
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    Question A battery saver circuit- Q 4 Aaron

    Does anybody know if there are any ready made (or schematics in order to build one myself) circuits that disconnect the load when the battery voltage falls under a sertain level (the kind of circuits most inverters have build in)?
    I am using an ATX DC-DC PSU with a circuit that shuts down the computer 15 mins after the accessory line is off. I would like to use my motherboard's suspend to RAM feature though in order to have faster boot times, but I am worried that even that (if I leave the car parked for many days) will eventually drain my battery and I will not be able to start the car.

    Thank you,
    Dimitris

    P.S.: I would prefer it to be "clever" enough so that it doesn't cut off when the voltage drops suddenly and shortly (for example when I crank the engine)but only when it discharges gradually.

    [ 10-09-2001: Message edited by: Dimitris1976 ]

  2. #2
    Constant Bitrate
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    Post

    Use TCA965,this is a window comparator,it means,it can monitor votlages below,in the range,or more than the range of voltage.You can set your range limits with resistors,I don't remember exactly how,search for its datasheet.I used this in my car a couple of years ago,but unfortunately I don't have any schematics...I used it with 3 LEDs to monitor car voltage(below,in range,or over the range),but you can hook its below range to transistor to activate a relay to disconnect your battery.For more information search for its datasheet on the net.
    Enjoint life!

  3. #3
    Variable Bitrate
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    Question for Aaron Cake

    Aaron,

    I would like to use that Low Voltage Alarm schematic you have in your circuits page, BUT I have to modify it a little and need your help.
    Right now when the voltage drops below threshold the circuit closes (ie sounds an alarm, lights a LED). Is it possible to reverse this function and have the circuit normaly closed and open when voltage drops below threshold? I want this in order to control a relay that will disconnect the battery from the PSU when the voltage drops, but I don't want the relay to draw current itself too at these crucial voltage levels.
    Also, do you think I could use a simple tank circuit (diode and capacitor) in parallel with this circuit in order to prevent reboots from disconnection when/if voltage drops under threshold for a while during engine starts?

  4. #4
    FLAC
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    The next shutdown controler I build will have this feature. Arg, I just have to finish it...

    Keep buggin me..
    MPEGBOX - Plexiglass Computer
    www.mpegbox.com

  5. #5
    Newbie
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    OK, Zootjeff. Consider this a strong "get off your butt, people are waiting" bug!

    Seriously, I'm waiting with baited breath for your new shutdown controller, and my wife says my breath was bad before.
    Wellfooled
    Workin' on an mp3 Sequoia

  6. #6
    Retired Admin Aaron Cake's Avatar
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    Off hand, a transistor connected to the output of the op-amp that switches a relay with normally closed contacts. When the circuit activates the alarm/relay, the contacts then open...Heh, I'll probably put on on my player now.
    Player: Pentium 166MMX, Amptron 598LMR MB w/onboard Sound, Video, LAN, 10.2 Gig Fujitsu Laptop HD, Arise 865 DC-DC Converter, Lexan Case, Custom Software w/Voice Interface, MS Access Based Playlists
    Car: 1986 Mazda RX-7 Turbo (highly modded), 1978 RX-7 Beater (Dead, parting out), 2001 Honda Insight
    "If one more body-kitted, cut-spring-lowered, farty-exhausted Civic revs on me at an intersection, I swear I'm going to get out of my car and cram their ridiculous double-decker aluminium wing firmly up their rump."

  7. #7
    Variable Bitrate
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    Aaron,

    I was wondering if we could modify this circuit to work with a relay with normaly open contacts. I wan't to use a relay that connects the PSU to the computer and consume power (at it's coil) when there is sufficient voltage (so, a relay normally open). I don't want the relay to consume power in order to keep the psu disconnected from the battery. So I need to reverse the way your low power alarm circuit is functioning.

  8. #8
    Retired Admin Aaron Cake's Avatar
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    Swap the inputs to the op-amp, or use an inverter at it's output.
    Player: Pentium 166MMX, Amptron 598LMR MB w/onboard Sound, Video, LAN, 10.2 Gig Fujitsu Laptop HD, Arise 865 DC-DC Converter, Lexan Case, Custom Software w/Voice Interface, MS Access Based Playlists
    Car: 1986 Mazda RX-7 Turbo (highly modded), 1978 RX-7 Beater (Dead, parting out), 2001 Honda Insight
    "If one more body-kitted, cut-spring-lowered, farty-exhausted Civic revs on me at an intersection, I swear I'm going to get out of my car and cram their ridiculous double-decker aluminium wing firmly up their rump."

  9. #9
    Variable Bitrate
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    I can build stuff from schematics but I am not really good at electronics... Could you please put the reversed circuit I need on your home page (with the exact part numbers I need to use)?

    Thanx
    Dimitris

  10. #10
    Retired Admin Aaron Cake's Avatar
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    There's not much more to it. Literally, you just reverse the + and - inputs to the op-amp.

    Sorry, but I don't have time to support electronics questions on my site (major reason I am no longer updating the electronics stuff).
    Player: Pentium 166MMX, Amptron 598LMR MB w/onboard Sound, Video, LAN, 10.2 Gig Fujitsu Laptop HD, Arise 865 DC-DC Converter, Lexan Case, Custom Software w/Voice Interface, MS Access Based Playlists
    Car: 1986 Mazda RX-7 Turbo (highly modded), 1978 RX-7 Beater (Dead, parting out), 2001 Honda Insight
    "If one more body-kitted, cut-spring-lowered, farty-exhausted Civic revs on me at an intersection, I swear I'm going to get out of my car and cram their ridiculous double-decker aluminium wing firmly up their rump."

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