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Thread: Fully 100% automatic battery charger

  1. #11
    FLAC
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    Quote Originally Posted by vull View Post
    i need one too :s
    then i could bring the sound system into the house in the winter and still enjoy tha baassss?
    A charger won't run the sound system, unless you're planning on using a battery and a charger to power the system.

    You shouldn't charge a battery while draining it though or else you'll overcharge it. Unless you know that the constant load is more than what the charger puts out.

    Doing something with like a 1 amp load and a 20 amp charger connected will make most chargers think the battery isn't fully charged and overcharge the thing.
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  2. #12
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    Quote Originally Posted by PaulF View Post
    Well, looking at the Optima website, the suggested charge rate is 10 amps
    And yet they also say "No current limit as long as battery temperature remains below 125F (51.7C)" for both Rapid (15.6V) and Cyclic (14.7V) charging.
    And I recall seeing recommendations to charge them at much higher rates (eg, 40A).

    I presume that in the linked Schumacher Battery Maintainer, "fully automatic" means it switches to 13.8V etc once fully charged.


    Quote Originally Posted by PaulF View Post
    You shouldn't charge a battery while draining it though or else you'll overcharge it
    Sorry Paul, that's incorrect.
    It is done all the time - eg, vehicles, planes etc.

    A vehicle's charging system is effectively a constant voltage charger - it tries to maintain a certain voltage (eg, 13.8V, 14.4V max etc).

    However CHEAP chargers often output above 14.4V.
    This is often true for trickle chargers (to quote.. "because they are only 1-2A, what damage can they do?". LOL! bang!)
    Bigger chargers should have a 14.4V limit or cutoff but usually don't.
    And once full, the charger should reduce to below 13.8V anyhow....


    Batteries - so simple - a true Scientific Art.

  3. #13
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    I understand that it's done all the time, but it hasn't worked for me at all. The problem is most chargers don't recognize the battery as full when there is a load. I killed two optima batteries at this point by failing to recognize this. It appears the chargers use current monitoring to sense when the battery is full and they would never sense it being full and overcharge it.

    Also, often it's quite possible that 125F is the ambient temp in the trunk, so that could be an issue too. My new setup cuts the load off of the battery and runs it off a 12 volt supply while charging. Faster charging and it gives me peace of mind that I'm not going to kill another.
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  4. #14
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    No - incorrect. A battery's charging is based on voltage.

    The only time current play a part is (1) if current limiting is required, & (2) that a battery will always have a minimum current draw even when full - ie "float current" (typically 2A for car batteries; less for AGM).
    The latter may be a method for some "smart" or automatic chargers to detect when to drop voltage to float level, but they shouldn't be above 14.4V anyhow....


    When you have a load connected to the battery, the charger has no way of knowing what is going to the battery and what is going to the load.

    It doesn't matter anyhow - the charger (alternator) should output up to 14.4V and that should not wreck the battery(s). Whether 10A of this is going to the battery, or 9A to load and 1A to battery etc etc doesn't matter.


    However, if you are saying that Optima batteries cannot handle (say) 14.4V when full....


    But I suspect you have a charger that goes overvoltage.
    Strange that it goes over-voltage WITH a load, and not without, but that suggest a switching load that is confusing the charger's voltage sensing - ie, a low quality charger.

    Think about it - car batteries are connected and charged with a load. My car batteries last 8 years - and they are not Optimas!
    If what you said was generally true, all Optimas in cars would be wrecked...


    But temperatures - yes - lower voltages for higher temperatures.
    No if you battery were at boot ambient temperature, you;d be fine with an Optima - they specify 14.7V is ok with no current limit as long as battery temperature remains below 125F (51.7C).
    But the battery will be warmer than ambient, so you'd have to get more specs from Optima - is 14.4V ok at 135F or 145F etc.
    But IMO that's not hot - our engine bays are much hotter.


    We can get in to temp & voltage sensing the battery; or each battery. But hey - most people see to prefer a single-wire (D+) alternator because more than that is "too complicated". If I dare suggest extending the Sense wire to the boot battery, or that alternators should have external temp sensors (mounted on the battery)...


    FYI:
    A 30C increase in cell temperature means a ~0.1V/cell DROP in charging voltage - ie, ~0.6V for a 12V battery.
    So from 13.8V to 13.2V, or 14.4V to 13.7V f temp increases from 70F/20C to 125F/50C.
    OTR, if a 100% charged AGM is 12.80V@80F/25C, it should be about 12.815V@125F/50C - about a 0.1% change.

  5. #15
    FLAC
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    cars only run for a few hours at a time, thats why they dont overcharge the battery. when the battery is outside its normal vehicle environment, it needs a charger that can tell when full is full.

  6. #16
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    Cars and other vehicles can run much longer than a few hours - that is not the reason.

    The reason for overcharging is "unregulated" chargers that exceed their voltage limits.

    End of story.


    But yes - if you want maximum life, you can install current monitoring and temp sensors for the battery - and then you pay for it.
    But how may automotive system have that - yet their batteries still last for years. Even taxis and trucks that run almost full time.
    Even my ute that tends to sit for days unused, then do high-speed trips of several hours.


    Limit the voltage to 14.4V if you want fast charging and max audio and halogen power, or limit it to 13.8V if you want to maximise battery life.
    And compensate for temperature.
    It is that simple.

  7. #17
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    I just looked at the black and decker charger I was using. It charged at up to 26 amps. Nice thing about it is it has an LCD on it that tells you the voltage, and the amperage. It usually read 14.4 volts on the screen. Sometimes 14.6 tops. Car-off load requires about 1.5 amps. I normally would plug in the charger in at night and it would go to town at 26 amps. Then in the morning it would read 2.3 amps which is in fact the charger's float current.

    Heres something a little strange though. The second you hit charge on the charger, it goes to work at 26 amps. Stays that way for around a minute, stops for a couple of seconds and then proceeds to charge at a (usually) lower rate. But what's odd is if a battery is fully charged, it shouldn't be accepting 26 amps. .. unless the charger is over voltage. But it is only at 14.4 volts...


    Regardless of what was happening before, I like the new system where the always-on electronics in the car draw off their own supply when plugged in and that way the battery gets a chance to "relax." I'm sure this will extend the life of the battery. Also, I'm sure that the slower charger will help the battery life too. So if this works out now, then I'll be happy.
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  8. #18
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    Paul - EXCELLENT!

    I feel like you have endorsed much of what I know.... (more later...)

    And I too thought that I agree about the initial 26A... they must be fudging (hi volts etc)...
    But then I thought that could be normal....

    VIZ - the battery changes state (??) - it can be idling, charging, or discharging.
    Each state has its own chemical process.
    Each chemical process take time to initiate.

    This stuff is really scratching my memory - I'm so used to talking about simple battery things (like paralleling, oversized current, etc) and haven't discussed real technicals for decades. (Though recently I did go through dynamic analysis of audio systems with caps versus batteries - it's nice having gurus do the Laplace & Fourier transforms....)
    But there are graphs etc that show the response times for the state/phase changes.
    We are taking milli-seconds or seconds - not minutes etc....
    But f.ex (and from my memory) - a battery changing from charge to discharge dips from its high-voltage (maybe ~14.4V capacitive charge or ~13.8V surface charge or 12.7V etc) to BELOW its steady-state voltage before returning to its steady-state voltage (say 12.7V assuming low current for negligible internal-resistance voltage drop).

    So I'm thinking the 26A (which is probably the most your charger puts out) is what the battery can/does accept until that dip voltage recovers.
    That's something I cannot recall ever considering.... the voltage dip magnitude & time yes, but not what current is involved. I'll add that to my list of tuits (maybe the next guru meeting next decade, or century?)

    And being a digital display, it will have a certain refresh rate so that if dip time & 26 Amps is only there for 100mS, the LCD will display it for longer....

    But you say it is there for a minute.....
    Hmmm - seconds I'd expect...
    By comparison, after cranking, my vehicle's 40AH battery (a Yuasa UXH38 AGM UPS battery) takes about 40A (from a 70A alternator) but this drops to ~20-30A in ~30 seconds, and under 10A after a minute. (That's at 14.4-14.6V.)
    Now that's close to 26A for 1 minute - but that is after a discharge (~140A starter for 5 seconds etc).
    Maybe your battery is old? It would be interesting comparing a few batteries....



    But congrats on your charger....
    My gurus advise that after storage or a flattery (battery flattening), car batteries need at least 20A to blow off the cobwebs etc (sulfation?).
    I reckon voltmeters should be digital - there can be a big difference between 14.4V & 14.5V. (I recall rejecting 8-bit batery voltage samplers because they just weren't enough - at least 10-bits was required - ie, 0.01% resolution. Not to be confused with only displaying 3 digits in a vehicle voltmeter - ie, 13.8V not 13.84V.)
    And though ammeters are generally only need to be indicative, accurate-ish float currents are useful! (A good check on battery condition and self discharge perhaps.)


    Paul - thanks for giving me something to think about - as in a real challenge to think about. Damn you!!!! (LOL!)
    Then again, who cares?



    PS - as to your last paragraph....
    Probably the biggest shock (strain) to a vehicle battery is cranking; 200A to 400A is typical. Not many loads come anywhere near that - even high-beams are say 40A maximum (4x100W).
    But in general - yes, the less the strain/shock, the longer the battery life. Hence less discharge meaning slower rate and to lower depth, and usually slower recharge.
    But sometimes more is better - eg, the HIGH charge current to reverse sulfation (which occurs as soon as the battery is "not full" - ie, begins infinitesamally small as soon as removed from charging and below (say) 12.8V) and increase with dropping voltage).

    Some say occasional exercise is good too, but I'm shaky on this. I know the "memory effect" in untrue (even for NiCads - that was a misunderstanding), but that is different to an occasional deep or heavy discharge. And much has changed in recent years. (When UPS systems began using AGMs, the theory was "constant current" charging. Luckily that too has become constant voltage charging! And exercise - never - except to exercise/test circuits, switches & breakers, and as a reserve-capacity test.)

    But added to that - the car battery is an amazing piece of equipment. It's cranking current is extreme, and then to ask it to operate for years in a hot vibrating G-force environment. (I was once going to specify them for a UPS system...)
    As a general rule, there is little that effects their life. Okay, over-voltage wrecks them as may under-voltage, EXTREME temperatures, and long-term storage (full or especially when discharged), but the minor things like distilled versus tap water, daily usage profiles etc seem to have little effect.
    Having said that however, I get at least 6 years out of my plain old "semi-sealed" 2-year warranty wet lead acids; as does my mum. I'm rough on mine (goat tracks, headlights left on) whereas she had occasional intermittent flattenings and still deserts her car for 6 month per year.

  9. #19
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    That initial inrush of 26A is actually what is bringing the battery up to 14.4Volts. It takes quite a lot of energy to do so, and that energy is not getting 'stored' chemically. It's more like charging a capacitor at that point. The current will decay as the voltage difference between the charger and the battery decreases.
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  10. #20
    Raw Wave
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    That fits the "battery is a capacitor" behaviour (which I only touched on).
    But if that's 10's of Amps for a minute - that is a HUGE cap! A few kilo-Farads perhaps?

    But whatever you do - don't tell that to anyone that reckons capacitors are essential or useful to combat voltage dips (and peaks) - you could ruin many livlihoods!
    It's bad enough simply referring to surface charge.
    But they know they are defeated one the cap gets below 12.7V.....


    (I may have given apparent pro-cap arguments in what I wrote earlier, but that's probably from a simplistic view - like one that refers to a cap's low ESR. And there are times when a cap is needed, but I reckon few know why & when. Based on how and why I see caps used, I am generally very anti-cap. I merely state this in case I confuse people on that stance.)

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