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Thread: Dual-battery setup with a smaller battery?

  1. #11
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    never mind man i gotta learn how to read ahead

  2. #12
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    kbyrd,

    Have you looked into this more? I'm thinking I'd like to add a second battery and run in standby when the car is off, all of the time.

    I have an Opus, so cranking isn't an issue with me either.

    This seems like the best way to hook it up:

    http://mp3car.com/vbulletin/showpost...9&postcount=12

    Just curious if you maybe tried this out, or if anyone had any other input.
    '03 Intensa Blue Pearl Lexus IS300

    Specs: Xenarc 700TS, Opus 150W PSU, CarCPU Case, 2.0 GHz Celeron D, DFI PS-35-BL, SB Audigy2 NX, Centrafuse 1.4

    Progress: Car PC up and running!
    To Do: Navigation, WiFi, AM/FM Radio, DVD

  3. #13
    FLAC arebelspy's Avatar
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    I've got this tank circuit and battery:
    http://carpc.kyferez.com/Products/products.php?id=10
    http://carpc.kyferez.com/Products/products.php?id=13

    They also have a slightly bigger battery. Only lasts a few hours
    but is sufficient for my needs and works great.

    -arebelspy
    See my trades here! My For Sale/Trade Thread. Email joe at eipse.com

    Quote Originally Posted by xdjxklusivex
    i think every thread is now a whoreing thread

  4. #14
    Maximum Bitrate kbyrd's Avatar
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    azzuro: I haven't looked at this any more, I did compute my draw in S3, about 180mA. On my current (OEM main cranking) battery, that's many days if I'm willing to drain it. I installed a kill switch so I can cut all power if I leave the care a few days. But, constant drain isn't good for these starter batteries. So, I've been thinking of replacing my main batter with an Optima Yellow Top (or anything that will start the car but be more tolerant of a 180mA constant drain)

    arebelspy: The smallest one there is 7AH (usually over 20 hours). For my draw, that's 7AH/0.18A = 38.8 hours. So I could leave my computer in standby for a little more than a day. That's not much, I'd like it to survive the weekend. For the 12AH battery, it's 12/.018 = 66H, a little over two days. That's more what I'm looking for. You said you have this tank circuit, are you using it to survive crank or to do what I'm asking (power the PC when car is off, but be recharged when the car is on?) How does the tank circuit do that? Finally, are these deep cycle batteries? How will they handle being discharged 80% every weekend?
    My worklog.
    Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

  5. #15
    FLAC arebelspy's Avatar
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    Quote Originally Posted by kbyrd
    arebelspy: 1The smallest one there is 7AH (usually over 20 hours). For my draw, that's 7AH/0.18A = 38.8 hours. So I could leave my computer in standby for a little more than a day. That's not much, I'd like it to survive the weekend. For the 12AH battery, it's 12/.018 = 66H, a little over two days. That's more what I'm looking for. 2You said you have this tank circuit, are you using it to survive crank or to do what I'm asking (power the PC when car is off, but be recharged when the car is on?) 3How does the tank circuit do that? 4Finally, are these deep cycle batteries? How will they handle being discharged 80% every weekend?
    Labeled your thing with numbers to make a reply easier (you can reply to mine with the same numbers for simplicity's sake):

    1) The 7AH one is the one I have. Sounds like the 12AH one would work for your needs, assuming you measured the draw correctly and such.. Out of curiosity do you know how many AH an average car battery is, or where to find specific info on a certain car model's battery?

    2) I'm doing both, actually. I have the carputer hibernate so normally when I start my car the car starts with it and doesn't need to survive crank, but I have a switch in the front I can flip so the carputer stays on (or turns on if off) when the car is off. In that case the battery is powering the carputer when the car is off, and then when I start the car (assuming I don't flip the switch to hibernate again and exit the car) I use it to survive crank. I obviously don't standby like you're planning, but I have used it to power the carputer when the car is off, then charge up when the car is on.

    3) Uhh, I have no idea. I attached the wires, and it does it.. ask a more electrical person if you really want the details if it matters

    It was seriously plug and play.. I had the wires running straight to my PSU, instead attached them to this then the PSU, took me around 5-10 minutes max to set up and it worked first try. the easiest thing in my whole carputer insteall, literally.

    4) Again, not sure. I'm not planning on deep cycling mine much, just for use to survive crank or when I go to the gas station I flip the switch to keep the comp on, gas up my car, and start the car again so the battery 1) kept the comp on while car was off for music, saved boot time, etc and 2) let it survive crank. Email the people at the site I linked to, they should know if deep cycling them is okay.

    -arebelspy
    See my trades here! My For Sale/Trade Thread. Email joe at eipse.com

    Quote Originally Posted by xdjxklusivex
    i think every thread is now a whoreing thread

  6. #16
    FLAC arebelspy's Avatar
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    Under "features" of the batteries, they say "long service life":
    "Under normal operating conditions, four or five years of dependable service life can be expected in stand-by applications, or between 200 and 1000 charge/discharge cycles depending on the average depth of discharge."

    Soulds like it might work for your purposes. It says depending on avg depth of discharge we'll assume your full discharge = limits the life, so we'll say the minimum of their quote, 200.

    So every 200 weekends you'd need to replace it.. 52 weeks a year, so that's every 4 years? Sounds good to me. I'd still email them and ask (And they'll prolly just say generic statement abut how that's not good for the battery and limits its life), but I don't see why it wouldn't work. $35 for the battery every few years (so under $1/month, even if you assumed only 3 years, not 4) isn't bad IMO for faster boot times.

    -arebelspy
    See my trades here! My For Sale/Trade Thread. Email joe at eipse.com

    Quote Originally Posted by xdjxklusivex
    i think every thread is now a whoreing thread

  7. #17
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    Quote Originally Posted by kbyrd
    azzuro: I haven't looked at this any more, I did compute my draw in S3, about 180mA. On my current (OEM main cranking) battery, that's many days if I'm willing to drain it. I installed a kill switch so I can cut all power if I leave the care a few days. But, constant drain isn't good for these starter batteries. So, I've been thinking of replacing my main batter with an Optima Yellow Top (or anything that will start the car but be more tolerant of a 180mA constant drain)
    I think that any parasitic drain is bad for a starter, period. Right now the Opus turns the PC off with ignition, but I still have my USB devices powered and the ATX PSU is still sucking a bit of power. This leaves me uneasy enough... leaving the computer is standby is even worse.

    I can see my car deciding not to start at the worst possible time.

    If I do this second battery, I can leave my computer in standby all the time, and not worry about anything.

    arebelspy, thanks for the links.

    I don't think that I would need the tank circuit though. I see no reason why I can't just wire it with a relay, such that the 2nd battery is connected in parallel to the 1st battery only when the car is on, otherwise the 2nd battery is all on its own. This is remarkably simple to wire up (just one relay).

    That 12 AHr battery is pretty small, which is nice.

    Here are the Optima YellowTop specs: http://www.optimabatteries.com/publi...cal_specs.html

    They are all pretty big, which probably won't work for me.

    The only thing I'm not sure about is if it is proper to charge using the car battery when it's on. What if the car is on but the engine isn't running? (i.e. in ACC)
    '03 Intensa Blue Pearl Lexus IS300

    Specs: Xenarc 700TS, Opus 150W PSU, CarCPU Case, 2.0 GHz Celeron D, DFI PS-35-BL, SB Audigy2 NX, Centrafuse 1.4

    Progress: Car PC up and running!
    To Do: Navigation, WiFi, AM/FM Radio, DVD

  8. #18
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    Also, don't need to worry about the Opus deciding not to shut off for whatever reason. I know some people have had problems with their PSUs not turning off in rare situations.
    '03 Intensa Blue Pearl Lexus IS300

    Specs: Xenarc 700TS, Opus 150W PSU, CarCPU Case, 2.0 GHz Celeron D, DFI PS-35-BL, SB Audigy2 NX, Centrafuse 1.4

    Progress: Car PC up and running!
    To Do: Navigation, WiFi, AM/FM Radio, DVD

  9. #19
    Maximum Bitrate kbyrd's Avatar
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    arebelspy: The numbers are a good idea:

    1) The 12AH is the minimum I would consider. I measured my draw with a multimer in series with the battery. I've done the test several times to confirm. It's right. There is no "average" AH rating. Some cars have bigger batteries, some smaller. My VW says 60AH right on the battery. But, pulling all 60AH out of the battery would destroy it. Also that 60AH is the 20 hour rate. Meaning you get 3 amps for 20 hours. If you draw more than 3 amps, you'd get less than 60AH total (so, you'd less than 15 hours using 4amps), but if you draw less than 3 amps you get more than 60AH total.



    2 & 3 & 4) I'm not sure the tank circuit is the right choice for what you're doing. There are problems with dual battery setups that supposedly only a well designed battery isolator will solve. I don't think the tank does it.
    My worklog.
    Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

  10. #20
    FLAC arebelspy's Avatar
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    1) 60AH for VW, that's what I was looking for, thanks. Yeah, if you're leaving it in standby for a long time you'd definitely want a bigger battery. I wonder if there are any power settings to drop a computer from standby to hibernate after X amount of time. There obviously is for laptops, but I wonder about regular desktops. If so you could always use the 12AH battery and then drop it from standyby to hibernate after a day or something.. your boot will then be slower (Still hibernate so not too bad) that one time at the start of the week after not having used the car for the weekend, but when using it al through the week (only 12 hours aftr you last shut it off or whatever) it'll be coming out of standby.

    Latter numbers: I'm not sure why you think this, it's working perfectly. More reasoning/links to other thoughts or suggestions?

    -arebelspy
    See my trades here! My For Sale/Trade Thread. Email joe at eipse.com

    Quote Originally Posted by xdjxklusivex
    i think every thread is now a whoreing thread

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