Tuesday, Apr 13, 2004 at 10:38
Done some research here....
Tried recharging a Marine Battery from the vehicle's alternator. Voltage before charging was 11.91 V
In the first minute of charging, the battery was drawing over 20A of current. As the voltage of the battery rose, the current tapers off so after 10 minutes, the current was 16.5 A and after 15 min, 14.5A.
I believe a flooded cell 12V battery is only 75% efficient at charging. ie. 25% of the current going in is wasted in heat etc.
So, after 30 minutes of charging, I estimate only 5.56 A had actually been stored in the battery. After 60 minutes, this had tapered to 8.89A.
Within reason, I think the size of the alternator is irrellevant (unless you are running big spotties at the same time). A 12V battery will only accept a high current for a short period of time before this tapers off to around 10A. Aparently deep cycle batteries will accept less current and AGM batteries more. No experience here.
Therefore, I doubt you will come close to recharging a battery significantly in an hour.
From memory, the doco with my Rotronics Isolating DB setup recommends 4-5 hours to charge a battery. To complicate matters even more, I believe a standard alternator will not charge a battery beyond 70% anyway.
Interested to hear others findings ...
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