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Ammeter readings

Discussion in '365 GT4 2+2/400/412' started by 365GT4 2+2, Aug 22, 2019.

  1. 365GT4 2+2

    365GT4 2+2 Karting

    Jan 1, 2016
    51
    Essex, England
    Full Name:
    Justin R
    Looking for guidance, my 365 ammeter seems to think it's a tachometer ! At 2000rpm it shows 20amps, 30 amps at 3000rpm and 40 amps at 4000rpm, all with no lights/fans running and this is after running for at least 20minutes, battery is new, alternator "overhauled" recently. Does this indicator a regulator fault or alternator ?

    Thanks in advance.
     
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  3. Al Campbell

    Al Campbell Formula Junior
    Silver Subscribed Owner

    Nov 22, 2013
    479
    Australia
    I would start by measuring the battery voltage with engine off, at idle & at higher revs. This should let you know if it is overcharging or not & then go from there.
     
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  4. raemin

    raemin Formula Junior

    Jan 16, 2007
    696
    Lyon (FR)
    Full Name:
    R. Emin
    #3 raemin, Aug 22, 2019
    Last edited: Aug 22, 2019
    The ammeter tells you the flow of current between the battery and the whole system. So on one side of the shunt you've got the battery (and only the battery), and the whole electric system on the other side. In other words the alternator(s) and battery are on the opposite side of the shunt (that feeds the ammeter). So negative reading means the battery is providing current (i.e alternator do not provide enough current to the system), positive reading means the battery is drawing current (recharging).

    Under normal circumstances, the ammeter should be close to zero (battery is charged and alternators are giving enough juice to the system) or positive (alternator do provide enough energy to the system and even a bit more to recharge the battery). If your car is one of the earlier model with a single alternator, charging a fully depleted 70A/h battery could take up to 2 hours. With a single alternator, investing in a small CTEK (or equivalent) charger is a safe bet.

    It is only when the engine is off that the ammeter tells you the consumption of the system as the alternator are not providing energy and all current is provided by the battery.

    Based on your explanation I would say that maybe you sucked up lots of current in order to crank the engine and the alternators are now trying to recharge the battery? In order to validate this hypothesis, just turn the engine off when you notice such high consumption and check the battery voltage. if it is significantly lower than 13.8v it is normal that the alternators are making their best to "top it".
     
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  5. 365GT4 2+2

    365GT4 2+2 Karting

    Jan 1, 2016
    51
    Essex, England
    Full Name:
    Justin R
    Thanks for this comprehensive response. I will check this out at the weekend. It just seemed surprising to see such a high amperage and increasing with revs.


    Sent from my iPhone using Tapatalk
     
  6. raemin

    raemin Formula Junior

    Jan 16, 2007
    696
    Lyon (FR)
    Full Name:
    R. Emin
    As a side note, your battery could be the "culprit". A bad battery has a high internal resistance, so whenever the alternator applies some current, the voltage raises rapidly (remember Voltage = Resistance x Amps: a battery is not a resistor but the Ohm law applies somehow). In this circumstances, the voltage regulator reduces the output so has to maintain the voltage below 13.8v (and battery takes forever to fully charge). By contrast if you've got a good battery with low internal resistance, the alternator can send a massive Amp draw to the battery until it is fully recharged to 13.8v . A "perfect battery" is just capable of accepting whatever the alternator can provides, which can be quite a lot when the engine (and alternator) reaches high RPM.

    All in all It seems quite logical to see higher Amp draw when a new battery is fitted. For peace of mind, given that the alternator was also overhauled, you could do as per Al Campbell recommendation and validate that the alternator is not overcharging the battery. AGM batteries (for Stop & Go) do require higher voltage (2.465v per cell in winter, i.e 14,8v for the whole battery) in order to be properly de-sulfated, by contrast our regular batteries degrades rapidly above 13.8v, so an "AGM voltage regulator" with regular battery is a big no-no (but highly unlikely) . So, yes, for peace of mind just check the voltage, but the most probable scenario is that you just treated yourself with a very good battery...
     
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