Join Date: Apr 2006
Thanked 175 Times in 172 Posts
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"1st stage bulk - max current supplied to batteries. This is limited by the wiring and batteries. The voltage is not important but not "
I spent some quality time asking questions to a couple of battery mfr techs about charging in this past year. Each seems to contribute one more nugget. Each said, specifically, that during the bulk phase BOTH amperage and voltage have specific maximums, and that exceeding either one can damage the battery. They go hand and hand, and as a practical matter of keeping things simple enough for the mass market consumer, the mfrs only give you the one figure (voltage) and tell you not to exceed that. HOWEVER, there is a much wider range of both voltage and amperage and it really is a matter of not exceeding some combinations of the two.
In that one specific case, the AGM mfr told me 13.5-14.4 volts at no more than 10 amps, for a 75AH rated deep cycle battery. So even at a conservative 13.5V, if I supplied a 15A charge I could damage the battery.
OK, you have 14.57 and want to cut that down probably to 14.3-14.4, right? Buy an isolator, any isolator, and wire up one diode to your alternator output. It should reduce peak voltage by possibly 0.7V at high current rates, to a more typical 0.3V at lower current rates. (Or, browser some component houses, you can find specific high-power diodes with specific 0.3V drops, sometimes under $10 at surplus houses.)
OR, you may be able to trick the alternator even more simply. Assuming (rashly!) that it has a sense lead, where is that sense lead conected to? If it is conected at the batteries, you can temporarily disconect it there, and bring it back closer to the alternator--even to the alternator output post directly. Some "one wire" alternator installations are actually designed that way. What happens now is that the sense lead is reading "full" output, but the cables to the batteries are providing some drop, often 0.3V or thereabouts. So the alternator folds back a little sooner than what the batteries are really getting--compensating for the extra voltage you're seeing.
It is possible that someone, sometime, set the rig up "a little hot" in order to overcome cable losses in the system. You know the saying? "It seemed like a good idea at the time." ?