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  1. #1
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    Default Dual battery charging -D3 alternator voltage

    In case anyone is interested -

    After start up, with the engine idling, 14.45V on the main battery. I re-connected a Optima 55Ah AGM which had been standing off charge for 3 weeks (12.6V). Still 14.45V on the main battery, 14.22V on the 2nd battery, 3A current to 2nd battery.

    Within less than 5 minutes, both batteries were at 14.4V and the regulator dropped the voltage to 13.8V. Current to 2nd battery 1.8A.

    Use it, don't use it...
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    Todd
    2020 Ford Everest Limited bi-turbo

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    This is interesting.

    I jump started a Golf 3 last night with a dead battery (not enough power for inside light or to turn off the immobiliser). After being connected to the idling D3 for less than a minute it started on the first attempt.
    Discovery 3 TDV6 S G4 No 29 - Mine
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    Quote Originally Posted by Todd View Post
    In case anyone is interested -

    After start up, with the engine idling, 14.45V on the main battery. I re-connected a Optima 55Ah AGM which had been standing off charge for 3 weeks (12.6V). Still 14.45V on the main battery, 14.22V on the 2nd battery, 3A current to 2nd battery.

    Within less than 5 minutes, both batteries were at 14.4V and the regulator dropped the voltage to 13.8V. Current to 2nd battery 1.8A.

    Use it, don't use it...
    Completely consistent with what I would have expected.
    Cheers

    ZS5KAD - PROFFESIONAL DUMBASS
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    If you fly or drive to an anti-Fracking meeting, you have no business being there and you wont get my ear......

  4. #4
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    I suppose that means that the D3 (and 4) has some intelligence built into the alternator's regulator?

    We were very surprised when we assisted a fairly new D4 with a drained battery in the Richtersveld last year. The battery voltage rose to 14,5V within a few minutes after an assisted start.
    Eggie.

    "Do not go where the path may lead, go instead where there is no path and leave a trail."
    - Ralph Waldo Emerson.

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    Quote Originally Posted by Eggie View Post
    I suppose that means that the D3 (and 4) has some intelligence built into the alternator's regulator?
    It does.

    I would suspect that most modern vehicles have a 2 stage regulator at least.

    If it only had 1 stage, it would have to be quite low (<13.8V) to avoid overcharging the battery, which in turn would never charge the battery properly, either.
    Todd
    2020 Ford Everest Limited bi-turbo

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    Thanks Todd. I would be interested to see what the charging current to the Optima will be when it is pretty flat.

    Quite a bit of resistance there if the voltage readings are good accuracy.

    You do realise that you just told us that the batteries are pretty much fully charged. An alternator charges the batteries, how bizarre, lets keep it to ourselves!

  7. #7
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    Quote Originally Posted by Columbus View Post
    Thanks Todd. I would be interested to see what the charging current to the Optima will be when it is pretty flat.

    Quite a bit of resistance there if the voltage readings are good accuracy.

    You do realise that you just told us that the batteries are pretty much fully charged. An alternator charges the batteries, how bizarre, lets keep it to ourselves!
    According to figures presented by Todd, wiring resistance is about 0.07 ohms if the DVM's are accurate relative each other.
    Cheers

    ZS5KAD - PROFFESIONAL DUMBASS
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    If you fly or drive to an anti-Fracking meeting, you have no business being there and you wont get my ear......

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    Quote Originally Posted by Columbus View Post
    Thanks Todd. I would be interested to see what the charging current to the Optima will be when it is pretty flat.

    Quite a bit of resistance there if the voltage readings are good accuracy.

    You do realise that you just told us that the batteries are pretty much fully charged. An alternator charges the batteries, how bizarre, lets keep it to ourselves!
    Tempted as I am, I'm sitting on my hands !!
    Eggie.

    "Do not go where the path may lead, go instead where there is no path and leave a trail."
    - Ralph Waldo Emerson.

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    Quote Originally Posted by Eggie View Post
    Tempted as I am, I'm sitting on my hands !!
    Why? - I am sure is voltage readings are good accuracy.
    Cheers

    ZS5KAD - PROFFESIONAL DUMBASS
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    A V6 and an inline 4

    If you fly or drive to an anti-Fracking meeting, you have no business being there and you wont get my ear......

  10. #10
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    Quote Originally Posted by Fluffy View Post
    Why? - I am sure is voltage readings are good accuracy.
    Hahaha you two, very good. Yup 0,07ohms, wouldn't have expected it so high unless the battery is in the trailer, can't remember. Anyway doesn't matter.

    EDIT : Of course I didn't look at the photos otherwise I would have seen that the battery is in the engine bay and two different multimeters were used which explains it. Can't be such a volt drop with 3A.

  11. #11
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    Hi Guys,

    My quick method of connecting the Optima once I had checked the main battery voltage was to switch the Fluke to ammeter and stick the Fluke probes into the inline fuse 'receptacle' between the main and aux battery.

    Apart from the small diameter cable of the Fluke leads the, the round probes were not making the best contact in the spade type terminals of the fuse holder. I suspect that would be the main cause of the voltage drop.

    I am also interested to see what current is delivered to the Optima if it is discharged. I'll connect the fridge up and run till 11.5V (low voltage cut off) and do the test again.



    Todd
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    Quote Originally Posted by Todd View Post
    Hi Guys,


    My quick method of connecting the Optima once I had checked the main battery voltage was to switch the Fluke to ammeter and stick the Fluke probes into the inline fuse 'receptacle' between the main and aux battery.

    Apart from the small diameter cable of the Fluke leads the, the round probes were not making the best contact in the spade type terminals of the fuse holder. I suspect that would be the main cause of the voltage drop.

    I am also interested to see what current is delivered to the Optima if it is discharged. I'll connect the fridge up and run till 11.5V (low voltage cut off) and do the test again.


    Just make sure that the Fluke can handle the current.

    I also suspect that most of the "resistance" was due to the internal resistance of the Fluke. Internally the Fluke has to pass the current thru a know resistance and measure the volt drop and do the sums.. Thats how it measures current.
    Cheers

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    If you fly or drive to an anti-Fracking meeting, you have no business being there and you wont get my ear......

  13. #13
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    Quote Originally Posted by Fluffy View Post
    Just make sure that the Fluke can handle the current.

    I also suspect that most of the "resistance" was due to the internal resistance of the Fluke. Internally the Fluke has to pass the current thru a know resistance and measure the volt drop and do the sums.. Thats how it measures current.
    Yes, that old Fluke can only handle 10A. I will use a clamp meter which can handle much more current and won't have the voltage drop, although I am not sure how well it will work over a relatively small 6mm2 cable.
    Todd
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    This should handle it ... 1000A rated.

    Although, that big clamp on such a small cable??

    I will also check the current between the alternator and the main battery after start-up.
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    Todd
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    Quote Originally Posted by Fluffy View Post
    Just make sure that the Fluke can handle the current.

    I also suspect that most of the "resistance" was due to the internal resistance of the Fluke. Internally the Fluke has to pass the current thru a know resistance and measure the volt drop and do the sums.. Thats how it measures current.
    Spot on, the burden is about 50mV/A, you light current okes are clever. Me I'm not used to direct measurements, CTs for just about everything.

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    The wire thickness is of no relevance.

    I admit I'm also a "laaitie". But that does not stop you from knowing that the clamp devices use Hall effect to measure magnetic field and equate that to current in the conductor. Real useful meters even if not fully suitable when measuring small currents.
    Eggie.

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    Quote Originally Posted by Eggie View Post
    The wire thickness is of no relevance.

    I admit I'm also a "laaitie". But that does not stop you from knowing that the clamp devices use Hall effect to measure magnetic field and equate that to current in the conductor. Real useful meters even if not fully suitable when measuring small currents.
    Correct. Anybody playing with car size DC systems should invest in a 50mV 50A DC shunt. Or two, one for the charge side and one for the load side. Gives a direct output of 1mV per Amp.

    It will open your eyes to see what is really going on in those cables.
    Cheers

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    If you fly or drive to an anti-Fracking meeting, you have no business being there and you wont get my ear......

  18. #18
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    Yes I don't know how good the "clip on's" are for DC especially these low currents, mine needs to be zeroed all the time, absolute PITA, AC works fine. The shunts are great but obviously not good for spot measurements. How good are the more modern DC clip on's mine's more than 10 years old?

    We use Hall effect measuring heads on the DC side of large rectifiers with currents >50kA, work perfectly in this application.

  19. #19
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    Columbus, the clip-ons are most useful due their ease-of-use nature. But then you already know this. Anyone who uses a AC clamp meter would understand.

    Similarly the DC models are fine when dealing with currents above about 1A. Zeroing is a pain, but this requirement fades as you apply the meter to higher currents - say above 10A or so. Much, much more user-friendly than installing current shunts which btw can be quite expensive themselves.
    Eggie.

    "Do not go where the path may lead, go instead where there is no path and leave a trail."
    - Ralph Waldo Emerson.

  20. #20
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    Quote Originally Posted by Eggie View Post
    Columbus, the clip-ons are most useful due their ease-of-use nature. But then you already know this. Anyone who uses a AC clamp meter would understand.

    Similarly the DC models are fine when dealing with currents above about 1A. Zeroing is a pain, but this requirement fades as you apply the meter to higher currents - say above 10A or so. Much, much more user-friendly than installing current shunts which btw can be quite expensive themselves.
    Sub 100 bucks max ?

    And you get sub 100mA accuracy and resolution, so you can really see what that fridge or the camp lights are doing.
    Cheers

    ZS5KAD - PROFFESIONAL DUMBASS
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    If you fly or drive to an anti-Fracking meeting, you have no business being there and you wont get my ear......

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