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

  1. #11
    Senior Member Jim_S-V6_2004's Avatar
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  2. #12
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    Thanks.

    I'm finding it next to impossible to believe that there are no readily-available (lead acid or whatever) batteries compatible with what those S-Types need.

    People with 3.0 cars have had batteries that are fine even if replaced within the last few years (and without using ctek-type devices). E.g. the USA people - they'd be complaining loudly and often.

  3. #13
    Senior Member Jim_S-V6_2004's Avatar
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    Well, Lead/acid are all batteries with liquid electrolyte, including modern calcium alloy batteries.

    Nobody checks their batteries as we do now.

    When they have random errors they either charge their battery or replace it.

    So the cause was only highlighted when we dug in deeper.

    The same problem appears in Mercedes and BMW forums, with different symptoms when the batteries discharge.

    To make it more difficult the battery manufacturers don't mention the "charge acceptance" voltage for any of their batteries. Varta for example says "refer to the manufacturer of the vehicle (or the battery charger)".

    The BCI (Battery Council international) which set battery standards does, as does the "battery university" and many other sites, but some have different charts from each other, such as the State of Charge, the percentage of charge represented by battery voltage, specific gravity of the electrolyte at different states of charge etcetera.

    Anyway, since we've now confirmed the charging voltages and characteristics of our different S Types' systems, we can see the cause and work with it on the models which have the problem.

    One thing I found yesterday is that one supplier of dual battery systems in Oz said that until 2006 cars produced 14.4 volts, but cars from 2006 produce lower charging voltages because of the drive to reduce emissions and improve economy. That doesn't ring true and I don't see the connection.

    Here it is, there is some other good info there:


    .

  4. #14
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    That's all great (or not) but as I posted people just aren't having the problems that ought to be occurring all the time if what you posted is all correct.

    I don't know which part(s) is/are wrong or misleading but by now we'd be seeing endless issues wouldn't we rather than the sporadic ones which then are readily fixed and stay fixed.

    Do bear in mind most of the cars are 3.0 and so vast numbers should be suffering all the time due to never having anything like a fully charged battery. They're not suffering so I think either the voltage is OK or the batteries just don't need as high a voltage as you say. Or something.

  5. #15
    Senior Member Lost it's Avatar
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    Yebbut... Conventional wisdom when I was in the trade last century was that to start a car you needed one amp per 10cc to start the car, so a 4 litre car would need 400 amps to turn a cold engine, power the electronics, overcome engine inertia. Before that we had amp hours.

    Then the manufacturers started rating batteries in CCA, which I believe is Cold Cranking Amps, an American measurement for a battery at 0 degrees temp for a 12v battery to supply amps for a set period. Probably out there on the net somewhere...

    By default we only "complain" when the cars either throw codes or won't start a car, and a battery with an 800 CCA rating even at 75-80% charge would be able to provide even the 420 amps needed to start an STR. so this kind of back ground info is actually quite important, it's telling us that even a brand new battery might only have enough reserve capacity to spin the motor a few times, or do a reasonably few short journeys before it's reserve capacity is compromised.

    Unless my logic is completely flawed?

    I guess the theory behind lower charging voltages is that the more power an alternator produces the harder it is to turn? And the pulley size can only go so low or there is a risk of over speeding the thing at high rpms. Exploding alternators when your motor hits 8,000 rpm would be novel...

    My wife is a constant reminder of this to me, she will jump in her Fiesta Mk7 to drive a few hundred yards to the local shop, with lights, heating, window defrost, a/c all running then wonders why after a week or two the battery just gives up even trying to start the car... I would walk.

    And... Now I've read the original thread I need to do the voltage checks on mine again, because I took the first reading on mine from cold with ignition off. Won't do it today, wifey might get annoyed at me.
    2001 3.0 SE Auto, Satnav, winter pack. Dark Blue, all the toys.
    2004 3.0 Sovereign Estate. Winter pack. Fixed. For Sale.
    2005 Estate X type 2.2 Sport.
    2000 V8 3.2 XJ8 LWB. "Prom" car. Lovely. Should sell this one too really...
    2005 "AllyCat", 3.0 XJ6 SE.
    2000 S type 4.0 V8. Latest toy.
    VFR800A and a VFR 800F

    Still beating cancer. Trevor 2, Cancer 0.

    Sure I took the Red pill....

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    Quote Originally Posted by Lost it View Post
    Yebbut... Conventional wisdom when I was in the trade last century was that to start a car you needed one amp per 10cc to start the car, so a 4 litre car would need 400 amps to turn a cold engine, power the electronics, overcome engine inertia. Before that we had amp hours.

    Then the manufacturers started rating batteries in CCA, which I believe is Cold Cranking Amps, an American measurement for a battery at 0 degrees temp for a 12v battery to supply amps for a set period. Probably out there on the net somewhere...

    By default we only "complain" when the cars either throw codes or won't start a car, and a battery with an 800 CCA rating even at 75-80% charge would be able to provide even the 420 amps needed to start an STR. so this kind of back ground info is actually quite important, it's telling us that even a brand new battery might only have enough reserve capacity to spin the motor a few times, or do a reasonably few short journeys before it's reserve capacity is compromised.

    Unless my logic is completely flawed?

    You are right. There is more to the story like Jim V6 already said:

    The same problem appears in
    Mercedes
    and BMW forums, with different symptoms when the
    batteries discharge
    .
    Why is this problem? Over the years more and more electronics got into the car witch all need power. But you can only add more power ( charging) when the engine is running. Looking at the Jag electrical system, when you are measuring the amps the system uses, The system keeps using a few amps after the engine is shut down and this stays this way till the car goes into sleep mode after 40 minutes. Combine this with a lower charging voltage and you can imagen that if you do a few short runs a day, the battery will never get enough charge to combat the drain. Hence the problems.

    Car manufactures want less
    fuel consumption and less pollution to meat the regulations and program there ecu/smart alternator in such's way they deliver just enough charging power with the lowest input.
    Since the battery charge voltage is controlled by the engine ecu re-programming it to let the alternator charge more would be a solution.



    I guess the theory behind lower charging voltages is that the more power an alternator produces the harder it is to turn? And the pulley size can only go so low or there is a risk of over speeding the thing at high rpms. Exploding alternators when your motor hits 8,000 rpm would be novel...
    Yes the more voltage/amps you want to get out of your alternator the more engine power you need to put into the alternator. This cause less available horsepower to the wheel and a higher fuel consumption and more pollution.

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  8. #17
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    Quote Originally Posted by 04str View Post
    That's all great (or not) but as I posted people just aren't having the problems that ought to be occurring all the time if what you posted is all correct.

    I don't know which part(s) is/are wrong or misleading but by now we'd be seeing endless issues wouldn't we rather than the sporadic ones which then are readily fixed and stay fixed.

    Do bear in mind most of the cars are 3.0 and so vast numbers should be suffering all the time due to never having anything like a fully charged battery. They're not suffering so I think either the voltage is OK or the batteries just don't need as high a voltage as you say. Or something.
    I'm with you here 04str, 12 years & over 160,000 miles with our old 3.0l & the only times it suffered from battery problems was when they were well past their expected lifespan. We bought the car at just under 7 years old, still with the original battery in place, that lasted another 3 years or so before simply giving up at the on set of winter. Perfectly ok on day, dead as the proverbial the next. Replaced with Prestige equivalent, winter 2009/10, which lasted until earlier this year before doing exactly the same. Mrs O's work commute is often less than 5 miles each way, (her work is split between two offices) so the car would often spend a month or so doing no more than 5 miles there in the morning, & 5 miles home in the evening with lights, heated screens, wipers, heater fans etc all running continuously, then standing idle all weekend & I never once had to charge it's battery, never once did it fail to start for her, & never any issues attributed to low battery voltage.
    The only time my 2.5 has suffered from a low battery was when it stood unused for months last year. Both cars charging systems have proved they are well capable of looking after their batteries & keeping them in good condition.

    Regards, OW
    1999 S Type 3.0L SE, A truly lovely old girl that's served me well. Probably the best car I've had. Now retired.
    02.5MY (X202) S Type 2.5L SE, 58,000 miles, full Jag s/h, all papers, MOT's, receipts etc from new when purchased.
    2006 X type SE 2.2 Diesel. Supposed to be Mrs O's economical commuter car.
    2004 (X202) 2.5L Sport plus, to replace the 3.0L

  9. #18
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    I remember way back then if you were a "techy" and bought a posh multimeter and used it to measure current draw with the meter placed between the earth and the terminal, the 10 amp fuse the meter had was more than adequate, old "plugs and points" rarely drew more than 7-8 amps with just the ignition on. Now they draw way more than that, in some cases you can't even turn off the interior fan to do this measurement, and my old Snap on multi meter now cannot be used for this, I've run out of the fuse links for one thing...

    Al these electronics, the alarm, the "shut down over time" systems all slowly kill the battery over time. The ideal situation would be to have a small deep cycle battery. Instead the manufacturers have been forced to supply much heavier 800 + CCA batteries so there is some reserve that still need to be lugged around all the time, and I have to wonder if any changes or "savings" made by cutting charging rate down has been lost by lugging extra mass around in the form of heavier batteries? You don't get something for nothing these days.
    2001 3.0 SE Auto, Satnav, winter pack. Dark Blue, all the toys.
    2004 3.0 Sovereign Estate. Winter pack. Fixed. For Sale.
    2005 Estate X type 2.2 Sport.
    2000 V8 3.2 XJ8 LWB. "Prom" car. Lovely. Should sell this one too really...
    2005 "AllyCat", 3.0 XJ6 SE.
    2000 S type 4.0 V8. Latest toy.
    VFR800A and a VFR 800F

    Still beating cancer. Trevor 2, Cancer 0.

    Sure I took the Red pill....

  10. #19
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    Quote Originally Posted by orsom weels View Post
    I'm with you here 04str, 12 years & over 160,000 miles with our old 3.0l & the only times it suffered from battery problems was when they were well past their expected lifespan. We bought the car at just under 7 years old, still with the original battery in place, that lasted another 3 years or so before simply giving up at the on set of winter. Perfectly ok on day, dead as the proverbial the next. Replaced with Prestige equivalent, winter 2009/10, which lasted until earlier this year before doing exactly the same. Mrs O's work commute is often less than 5 miles each way, (her work is split between two offices) so the car would often spend a month or so doing no more than 5 miles there in the morning, & 5 miles home in the evening with lights, heated screens, wipers, heater fans etc all running continuously, then standing idle all weekend & I never once had to charge it's battery, never once did it fail to start for her, & never any issues attributed to low battery voltage.
    The only time my 2.5 has suffered from a low battery was when it stood unused for months last year. Both cars charging systems have proved they are well capable of looking after their batteries & keeping them in good condition.

    Regards, OW
    My original 3.0 X type was still on it's original battery when I bought it, the car used to do 1000 miles plus a week and the only thing that killed the battery was one time it was left on a ramp for an MOT and the rather thick tester had left the a/c set at 22 degrees with the windows open and the headlights on whilst it was a very warm day, the alternator couldn't keep up, eventually the engine just stopped. then he tried to fail the car because "he wasn't able to continue with the test."

    I was less than pleased, he killed th battery stone dead and it took a lot of shouting and threats on my side to get them to replace the battery.

    Never went back there again...

    That was a Varta battery, can't remember the number on it.

    Strongly believe it's only the fact that the batteries are way larger than they need to be that keeps the cars trouble free. Depending on your age, 1990's cars came with batteries you could pull out with one hand. Now it's a handle, lift and grunt jobby. Sometimes there's two handles to lift with. A 460CCA battery would be in theory be more than adequate to keep even a 4.2 engined car going. But I'd bet it would struggle unless the car was used to do less than 10 mile journeys. I think it's also why the fail over night. They are constantly being drained and not quite refilled, thjis has to have an effect on their longevity.
    2001 3.0 SE Auto, Satnav, winter pack. Dark Blue, all the toys.
    2004 3.0 Sovereign Estate. Winter pack. Fixed. For Sale.
    2005 Estate X type 2.2 Sport.
    2000 V8 3.2 XJ8 LWB. "Prom" car. Lovely. Should sell this one too really...
    2005 "AllyCat", 3.0 XJ6 SE.
    2000 S type 4.0 V8. Latest toy.
    VFR800A and a VFR 800F

    Still beating cancer. Trevor 2, Cancer 0.

    Sure I took the Red pill....

  11. #20
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    The X type uses a different way to controle the alternator then the S type and it has less power draining electronics on board then the S type. Therefor there are less draining problems then with the S type.

    Maybe useful, from the jag repair manual:

    Battery and Charging System - General Information - Charging System
    Description and Operation
    The charging system for vehicles fitted with 2.5L or 3.0L engines consist of a 120 amp output, L3B, generator and regulator assembly.
    Vehicles fitted with 2.7L Diesel engines consist of a 150 amp output, SC2, generator and regulator assembly. Vehicles fitted with 4.2L
    engines consist of a 130 amp output, SC1, generator and regulator assembly. The generator and regulator assembly generates electrical
    power to the vehicle electrical system with electricity when the engine is running and maintain the battery in a charged state.
    The generator is belt driven by the accessory drive belt.
    For additional information, refer to: Accessory Drive (303-05 Accessory Drive, Description and Operation).
    When the engine is started, the generator begins to generate alternating current (AC) which is converted to direct current (DC) internally.
    The DC current and voltage is controlled by the voltage regulator, (located inside the generator ) and then supplied to the battery through
    the main battery positive cable.
    The 2.5L/3.0L and 2.7L Diesel generators are solidly mounted to the engine, while the 4.2L generator is pivot mounted. The generators are
    driven at approximately three times engine speed.
    Vehicles fitted with 2.5L or 3.0L engine (L3B generator)
    Vehicles fitted with manual transmission have a one way clutch fitted to the drive pulley, which reduces belt slip.
    The Engine control module (ECM) can switch the voltage regulator between two voltages to optimize the charging of the battery.
    The low voltage regulator setting is 13.6 volts and the high voltage regulator setting 15.3 volts, measured with the generator at 25 degrees
    centigrade (77 degrees fahrenheit) and charging at a rate of 5 amps. These values decrease with a rise in temperature or current flow.
    The ECM determines the output voltage setting of the generator. The high voltage setting is always selected by the ECM once the vehicle
    has started. The ECM determines the period of time that the high voltage setting is selected for.
    There are three different time periods selected by the ECM which is dependent upon the vehicle conditions when the vehicle is started:
    The longest period of time is selected if the ECM determines that the vehicle has been 'soaking' for sufficient time to allow the
    engine coolant temperature (ECT) and the air intake temperature (IAT) to fall within 6 degrees centigrade (43 degrees Fahrenheit) of
    each other.
    The intermediate time period is selected when the ECT and the IAT is below 15 degrees centigrade (59 degrees Fahrenheit).
    The shortest time period is the default time and is used to provide a short period of boost charge.
    At the end of these time periods the voltage is always set to the low voltage setting to prevent the battery from being over charged.
    The time periods are variable depending upon the temperature and battery voltage. The target voltage of the battery varies between 14
    volts and 15 volts depending upon the ambient temperature and the vehicle operating conditions. Once this target voltage has been
    achieved, providing the vehicle has been operating for at least the shortest time period, the ECM will reduce the voltage regulator to the
    minimum setting of 13.6 volts.
    Vehicles fitted with 2.7L Diesel engine (SC2 generator)
    All vehicles use a PCM (Pulse Control Modulated) generator. This allows the output voltage to be controlled between 12.5 & 16V via a signal
    from the ECM.
    This voltage is controlled between 13.5V & 15.5V. The system voltage is tailored more closely to the demands of the battery. At low
    ambient temperatures (as measured by the air conditioning ambient air sensor), the charging voltage is higher to improve charge
    acceptance. At high ambient temperatures the voltage is lower to reduce electrolyte loss and unnecessary battery self-heating. Also built
    into the strategy, is the ability to measure the battery voltage at Ignition On. A battery with low voltage at Ignition On is boost charged at
    a higher voltage for a calculated time before returning to its 'Base Characteristic' (defined by the prevailing ambient temperatures). The
    time and boost voltage depends upon the temperature and battery voltage at Ignition On.
    All vehicles have a one way clutch fitted to the drive pulley, which reduces belt slip.
    Vehicles fitted with 4.2L engine (SC1 generator)
    The battery charging voltage is determined by the temperature of the generator. In cold conditions, starting the vehicle from cold the
    battery voltage will be between 14.2 volts and 15.1 volts and will reduce as the engine warms up. In hot conditions starting the vehicle
    when the engine is already warm the battery voltage will be between 13.5 volts and 14.3 volts.
    A fault in the wiring or the connections from the generator to the ECM, will cause a fault code to be generated and stored in the ECM and
    the charge warning indicator lamp to be displayed in the instrument cluster after a short time.
    With the ignition switch in the RUN position the charge warning lamp will be displayed in the instrument cluster when the generator is not
    generating power.
    If a fault is detected with the generator a fault code will be generated and stored by the ECM. The charge warning indicator lamp will also
    be displayed in the IC. Units should be repaired as an assembly and not dismantled for repair.
    For additional information, refer to: Generator (414-02 Generator and Regulator, Description and Operation).

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