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Thread: Why did I wait so long

  1. #1
    Jesus Freak antimatter's Avatar
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    Why did I wait so long

    So i finally got standby running in the car.

    I installed one of these
    http://www.powerstream.com/battery-i...olid-state.htm

    It seemed like the best of both worlds

    Anyhow now i can leave the carpc in in sleep mode and not worry about the main battery draining and it takes like 5 seconds to come back from sleep. I don't know why in the world i waited so long to do this.

    It seems the battery i put in (17Ah lead acid 12v) is enough to last for several days on standby

    Happy Happy Joy Joy
    -Jesus- King of Kings Lord of Lords

  2. #2
    Raw Wave
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    THANK YOU!!!!

    For those that have a charge lamp and want to save money, use a relay that is energised from the alternator's charge lamp circuit - ie, "D+" else "L".
    The relay-chargeLamp version has no timing delays (they are not needed) and no over- or under-voltage protection (nor does your main battery and charging system) but for that it's probably better fitting a low-voltage cutout or a battery/load protector on the PC end.

  3. #3
    Jesus Freak antimatter's Avatar
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    Quote Originally Posted by OldSpark View Post
    THANK YOU!!!!

    For those that have a charge lamp and want to save money, use a relay that is energised from the alternator's charge lamp circuit - ie, "D+" else "L".
    The relay-chargeLamp version has no timing delays (they are not needed) and no over- or under-voltage protection (nor does your main battery and charging system) but for that it's probably better fitting a low-voltage cutout or a battery/load protector on the PC end.
    Your welcome
    -Jesus- King of Kings Lord of Lords

  4. #4
    Constant Bitrate utd09bry's Avatar
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    I never really gave any thought to a secondary battery, but your post sparked my interest.

    I purchased an SLA battery and a high current relay and will give it a shot. I'm not sure that the extra circuitry is really all that necessary but I guess we'll find out. I was able to get a 26Ah battery and an 80A relay for $80 total.

    Being able to boot from standby has always been a major "want" in my system. Thanks for posting this

    edit: after some more thought/research ill prob need to rig up something to engage the relay only after the car has started (wouldn't want the aux battery to assist cranking the car). Other than that, I don't think charging will be an issue.. they are supposed to be pretty forgiving

  5. #5
    Raw Wave
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    The "extra circuit" is simply connecting the relay to the charge light.
    And for that, you not only have post-start actuation, but also overcome parallel battery issues and flattening your main battery.
    (Mind you, there is some lively discussion about no issues with paralleling batteries over at the12volt-121521-page2 LOL!)


    The major concerns are a suitable charge-lamp circuit from the alternator that can drive the relay's solenoid (usually up to 1 Amp is not a problem), and the desire for latching thereafter until turned off by push-button or Ignition Off or Low Voltage (as opposed to an engine stall or charging failure).
    And circuit breaker (preferable, else fuses) at each end...
    But these have been covered elsewhere (in mp3car) by some old Fart.

  6. #6
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    it really is a night/day difference having a second battery isnt it. Not only when startup times (which is darn near instant with hybrid sleep), but also when testing/toying around and not have to worry about the engine running. Its a great investment
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  7. #7
    Jesus Freak antimatter's Avatar
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    Quote Originally Posted by Sonicxtacy02 View Post
    it really is a night/day difference having a second battery isnt it. Not only when startup times (which is darn near instant with hybrid sleep), but also when testing/toying around and not have to worry about the engine running. Its a great investment
    Absolutely... I couldn't have been happier that i did this.

    80 dollars seems like a nominal cost. If i could have a nickle for everytime i has annoyed over the past 5 years because coming out of hibernation was taking too long i would be rich!!!

    I don't know if the extra circuitry was necissary but i liked the fact that it was an all enclosed unit and there has been so much debate about relay's vs diodes it seemed to make sense that a hybrid was actually the slicker solution.
    -Jesus- King of Kings Lord of Lords

  8. #8
    Constant Bitrate utd09bry's Avatar
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    Quote Originally Posted by antimatter View Post
    If i could have a nickle for everytime i has annoyed over the past 5 years because coming out of hibernation was taking too long i would be rich!!!



    I agree that the controller you found sounds like a pretty slick little device. I'm going to try using the relay and a timer/delay circuit (~3sec from ACC power). I think that should do the trick.

    I was also wondering, does anyone have experience with the charge time for the sealed lead acid batteries? Got to thinking... if your car sits for a few days and manages to run your secondary battery down pretty low, how much driving do you need to do to charge it back up to a reasonable level? I'd prefer not to have a solar panel on the roof :-p

  9. #9
    Raw Wave
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    Hybrid? You make it sound as if it is a relay-diode hybrid.
    For the benefit of others, they refer to this hybrid as being a relay and FET combination. (Not a diode isolator with relays - which I can't imagine anyhow....)


    Without the relay, it is simply a solid-state "smart" isolator - ie, it uses FETs (MOSFETs) instead of relays.
    They have no moving parts, but that's at the expense of higher contact resistance and limited through current, and often greater sensitivity to voltage spikes or other bad electrical things (leading to failure).
    So they introduce a relay to ruggedise it. (Many have similar controllers control a relay instead of the load, or as well as a load, ie, in parallel to the controller.)

    Sensing isolators require "monitoring" power which is usually in the uA region (say 4-400uA).
    Because this uses a microprocessor, its sensing (idle) current is higher, namely 15mA - the equivalent of a LED, or about 1/10th of a 2W bulb (as opposed to 0 for an alternator charge-lamp controlled relay).

    They also refer to a "high resistance with a diode drop (0.5V)" feed-through from the output to the input (unlike relays) but that should not be a problem.

    I saw nothing about reverse polarity protection. Reverse polarity won't effect a plain relay circuit - except probably blowing its contacts if the two batteries are inversely connected (hopefully that - or fuses blow - before any battery explosion or lead-melts hot & shrapnel!).


    I like the idea of a hybrid unit as the FET prevents arcing of the relay contacts whilst the relay takes the load of the FET. And the FET is quick to react (not that that is an issue - it is not a UPS system!)

    And this has the advantages that a smart isolator should have - namely undervoltage and overvoltage sensing. And the timing required for the undervoltage sensing (so that it doesn't toggle between on-off-on-off too quickly under borderline or load induced voltage drops).

    The charge-lamp control does not require any timing, but it does not have under-voltage sensing (but do you want disconnection if it goes under-voltage whilst charging?) and hence no toggling issues.
    Nor does it have over-voltage sensing, but I'd rather protect the whole vehicle than just the 2nd battery's load.

    I use a charge-lamp controlled relay because I can make it any capacity I want (140A typical; but extend to 1,000's of Amps with a 2nd relay/contactor switch via the first relay). ($5-$10 for relay)
    Then a add a low-voltage cut-out to the load off the 2nd battery to protect the battery (eg MW728 ~$20; 90mA on current). (That's not provided with battery isolators.)

    The relay is less sensitive to temperature - our engine bay and boot temperatures way exceed 50C whilst external temperatures can come close. And I don't think people want battery isolators in airconditioned cabins.
    In any case, a blown relay is cheap and easy to replace. And the optional low-voltage cut-out is a reasonably common commercial item available in many auto & electrical stores (often re-labelled MW728s).

    Oh well, my clarification led to a pros & cons comparison.
    Each system has their drawbacks. I haven't mentioned many - just those that are typical or common occurrences.

    I originally had a voltage-sensing isolator. Its advantage was its simple "add on" to the battery - I just provided the inter-battery cable and the fuses/breakers at each end.
    Later I switched to the smaller, simpler relay. It was easy to tap into the alternator's output. (Not that that can be done with modern DP alternators; but for those with LS or D+ types, no problems!) And I can upgrade or replace etc easily.
    I still keep a low voltage cutout on the rear/2nd battery but that's a separate function. (FYI - the same circuit as the original front isolator - it's merely the tweaking of one resistor. I use the MW728 as a fallback.)

    I'm one for simplicity, reliability, redundancy (or easy & fast replacement) etc, so I now use the chargeLamp controlled relay wherever possible.
    But for DP regulators/alternators and stator alternators, it has to be some sensing isolator like the one linked above.

    And I'm glad to see the linked isolator is cheaper than diode isolators - not that diode isolators IMO are the way to isolate hi-current circuits - use a proper isolator (definitely for big audio and similar dual-battery set ups!)

  10. #10
    Raw Wave
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    Must be some xmit delays lol!

    Why a timer on Acc? No second battery I presume - just a load (PC etc?)

    Quote Originally Posted by utd09bry View Post
    does anyone have experience with the charge time for the sealed lead acid batteries?
    It's usually about 5 times longer than its AH rate (C10 or C20) divided by the amount discharged - if you have the current available.

    As with any battery, you need to refer to your batteries specs; know how fast it is being recharged; how much you have to recharge it; and hope your battery matches its specs.


    You only need a solar panel if the battery discharges below its optimal discharge level or does not have enough power to crank & start.

    The solar panel should be sized to replace the power being extracted from the battery (ie, power drained plus maybe 30% recharge inefficiency), then it will last forever (subject to battery and solar etc lifecyles).

    As to recharging, a normal vehicle recovers most of its cranking charge within a few minutes if the alternator is around 14.2V - 14.4V. It may take more minutes to replace 90-95% of the cranking discharge.

    When I completely flatten my cranking battery (it's NOT a deep cycle), I can restart the car after a few minutes of running. But to fully recharge? I'd assume at least 30 minutes for ~95% capacity.???? (Albeit probably at a slightly reduced capacity due to the previous flattening.)

    Even with specifics like alternator voltage and its current output in excess to the other load demands; the AH capacity and resistance etc of the battery; and the amount of charge needing replacing etc etc, it is very difficult to provide an answer - there are lots of other variables....

    Generally only guestimates are made (aka estimates to within -50% +100% etc).
    Even with solar panels that have a known efficiency, it is difficult estimating their output.

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