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Thread: At rest Voltages. Post start voltages on a 1999 S type 4.0 V8.

  1. #81
    Senior Member Jim_S-V6_2004's Avatar
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    Quote Originally Posted by FastEddie View Post
    The quickest fix would be to use an Optima yellow top battery , these will take 15.5v up to a case temperature of 50oC

    Leaving it on 15.3v permanently with a thermostat on the battery case that drops to the low charge rate at 30oC would be fine.

    You could even do this with a Calcium battery , switching to low rate at the closest ambient differential possible in hot weather.

    The calcium batteries in both of my ST's , regardless of load / weather sit at 15 volts all day long , both originals did 8 to 9 years.
    .
    That's a pair of good ideas Eddie, a strap-on thermal switch would be an easy mod, just break into the signal wire and the thermoswitch would make the circuit when it switches. The signal would already be down for 13.6 volts. Easy!

    Can you locate a good adjustable thermal switch since your knowledge is more "current" (hahaha ) than mine please?

  2. #82
    Senior Member Jim_S-V6_2004's Avatar
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    The thing is, an Optima Spiral AGM battery may need only 13.6 volts to charge if it's non-calcium. So we wouldn't need any mod, and that will be brilliant. The other S Types (4.2-litre and the Diesel S) have smarter systems and can detect and handle those too.

    I still can't find any confirmation of the Optima battery charging needs.

    Isn't it bluddy frustrating when even the Goddam manufacturers don't reveal their full technical info?!


    You said yellow top, which is a higher capacity than the red-top which have an 850 CA already?

    If the price is good, no problem of course.

    .
    Last edited by Jim_S-V6_2004; 10-01-19 at 22:45.

  3. #83
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    From OW... "That suggests to me that the ECM/PCM monitors the battery & only reduces the charge voltage when it has detected the battery has reached it's target voltage."!

    Is that the target voltage as set by the ECU? It has to be right? No way it could detect what the "target optimum" charging voltage might be for the battery is there?
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  4. #84
    Senior Member Jim_S-V6_2004's Avatar
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    Hah!

    Alleluyiah! Wallahi! Voilá! Eureka! etcetera!

    Finally!

    I have found a couple of articles which between them mention nearly all of the battery charging Information that I've given.

    I label them Source 1 and Source 2, and refer to them in my summary below.

    Source 1: http://www.chargingchargers.com/tutorials/charging.html

    Source 2: https://www.optimabatteries.com/en-u...ng-agm-battery

    Ok, here I'll summarise and refer to Source 1 or Source 2 for verification as appropriate...

    Battery Charging Summary...

    1. Batteries which have calcium alloy electrodes ("plates") require 14.4 volts to fully charge. Ref: Source 1.

    2 AGM batteries require 14.6 to 14.8 volts to fully charge. Ref: Source 1.

    3. Calcium and AGM Batteries can be damaged by overheating, for example due to charging them on old "dumb" battery chargers for more than a couple of hours. Ref: Source 1, Source 2.

    4. Flooded/wet cell batteries should have the electrolyte level checked and topped up if necessary, if they have removable cell caps. Ref: Source 1.

    5. Cars with fixed 13.6 or 13.8 volt charging systems cannot fully charge Calcium or AGM batteries. Ref: Source 1, Source 2.

    6. Surface charge should be removed by applying a load such as turning on the headlamps (10Amps) for 3 minutes before measuring the battery's voltage to ascertain its State of Charge. Ref: Source 1 (20Amps).

    7. State of Charge: A calcium battery showing 12.4 volts after removal of surface charge is only 75% to 80% charged. Ref: Source 1.

    .
    Last edited by Jim_S-V6_2004; 12-01-19 at 12:19.

  5. #85
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    So my calcium battery at 12.7V is fully charged yet apparently that's not possible having used 13.6V to charge it. Explain...

  6. #86
    Senior Member Jim_S-V6_2004's Avatar
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    Quote Originally Posted by 04str View Post
    So my calcium battery at 12.7V is fully charged yet apparently that's not possible having used 13.6V to charge it. Explain...
    .
    I can't.

    It certainly won't do it in a car even after many journeys.

    It will at 15.3 volts over many hours, but the 2.5 and 3.0 only maintain that for a few minutes.

    Only your STR, the 4.2 S Type and the diesel S Type can do that, with variable voltage. They don't drop below 14 volts though.

    (Actually they might if they have a "maintenance" or "float" stage when the battery is really fully charged like smart chargers do, but nobody measured for a full day or whatever it takes on one - if anyone has a recording volts monitor and a tank of fuel to burn in one non-stop journey?).

    My old 1980s or whatever it is orange Halfords dumb charger initially shows a flat battery draws up to 12 amps on the bench. Without the battery (from my Merc A160, not the S Type or the E320) connected it shows over 14+ volts on my DVM.

    Probably does go much higher, but I didn't pay much attention, some dumb chargers shoot up to 18 volts initially. But the battery holds it down and mine showed around 13 and rose to just over 14 volts when on charge, measured at the battery on the bench with my DVM. Then the battery volts drop down to under 13 volts in time once it's off charge.

    But it could overheat calcium batteries, so I only use it to start to charge dead batteries, until the smart charger doesn't trip out. Then I use my liddle LIDL "semi-smart" charger.

    The nominal charging time is 10 to 20 hours on that.

    There are warnings everywhere to not use older chargers of course, with threats of sulphation and life shortening etc.

    We know 13.6 volts won't fully charge calcium batteries, it will start to charge them until there is not enough potential difference between the battery voltage and the charging voltage to continue.

    I haven't tried charging one for 2 weeks though!

    Look at the volts each cell needs, 2.30 to 2.45. That's 13.8 minimum to 14.7 maximum depending on cell type. Old antimony only needed 13.6 to 13.8 volts. It's documented in many places, calcium plated batteries need 14.4 for "charge acceptance" to reach full charge caoacity. The voltage produced by smart chargers is fixed, 14.4, 14.7 for AGM batteries, and 15.8 volts for Desulphation and Destratification as you've seen.

    They don't supply less than 14.4.

    Your cars supply 14 to 15 volts according to the battery condition and State of Charge.

    Any guess as to why?

    To cover their arses some people say "less than 2.30" as minimum but that's just not possible since calcium resists charge until it gets 14.4 volts.

    Some people say 14.1 volts, but only a few. Again it's a question of go with the majority, or the one voice which may be the only one telling the truth.

    The manufacturers keep shtum. Why, I cannot completely understand. They would not sell as many batteries to owners whose cars produce 13.6 or 13.8 volts, maybe.

    It's probable that 13.6/13.8 volts may be OK to maintain them at full charge with no load after full charging, see explanations of "float" and "maintenance" state charging.

    The charging volts should ideally be dropped to that "maintenance" charge after the top-up charge has taken the battery to 12.7+ volts, to prevent overheating, overcharging, and sulphation and reduction of the battery's capacity. But that's only if the battery won't be used, such as in storage or when it's a standby.

    Is your charger really keeping the volts at exactly 13.6 all the time with no load on it? Over several hours, days?

    Remember it will show less than 14 volts because the battery will drag it down as it draws current.

    How long was the battery on charge?

    It's a many-spleandoured thing, is battery charging!!

    PS:- do you think it's... Female??!!

    .
    Last edited by Jim_S-V6_2004; 12-01-19 at 12:30.

  7. #87
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    Well it was on a bench PSU and I checked its voltage really was 13.6V.

    And it has charged the battery.

    I suggest many of the web sites are copying data from many other sites but some or maybe much of the data is wrong.

    People swear such things don't occur but it even happens to science text books.

    I think the sites are changing "will charge better at 14.4V" (true) into "needs 14.4V" (apparently false).

    It would explain why millions of cars which were designed to output 13.6V are fine. Most batteries apparently work OK with that. Quite possibly some of the expensive start-stop kind would not be but then you'd avoid buying one as they are 2 or 3 times the cost.

  8. #88
    Senior Member Jim_S-V6_2004's Avatar
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    No, I have proved that 3 different good calcium batteries will only reach 12.2 to 12.4 volts in my own two cars, the 2.5 litre S and my Merc E320, and other Mercedes and other marques as well as S Type owners have found the same.

    I would have to repeat your test with a regulated-voltage charger on the bench, but I don't have such a charger.

    If it takes 24+ hours to charge but can indeed fully charge to 12.7 volts then we will have proof.

    But, nobody does 24 hour runs in cars.

    .

  9. #89
    Senior Member FastEddie's Avatar
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    I can help you to a certain extent with alternator charging , standard transformer charger and modern switch mode / inverter charger differences.

    An old school 3 phase alternator with a 6 diode rectifier pack has an unsmoothed dc output , the only stabilisation comes from the accumulator , battery.
    When you are reading 14.4 for example on the battery terminals , the alternator output will be between 14.2 and 14.6 depending on the cycle / frequency.
    An old school charger will measure around 16vdc on the leads , connect a smoothing capacitor of 2200 micro-farads for example , this will then rise to 20+vdc.
    A modern automatic charger will have a smoothed output as i describe with the capacitor , 13.8vdc is what the battery will see continuously.
    The traditional charger or alternator is not a constant voltage as it is a rectifed ac voltage so will take longer to reach the charge level of a modern charger.
    The bench PSU is the same as a modern charger and is constant voltage and constant current so will charge better than rectified dc alone.

    The things you are discussing are becoming a problem on modern vehicles for split charging of a second battery for caravan / motor-homes etc.
    The euro 6 smart standard for alternator output is the magic 13.6v where possible to keep emissions lower , but makes secondary charging difficult.
    Most secondary batteries / leisure batteries are now charged with electronic inverter chargers in order to achieve a sensible and quick charge.
    The inverters operate from a wide input between 9 and 16vdc and give a switched mode output of 15vdc at up to 50 amps to bulk charge , then drop off.
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  10. #90
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    Leisure batteries are different tech as they can be deep discharged without suffering (much) as I understand them. Seems to mean they need a higher charging voltage.

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