Monday, Aug 04, 2003 at 19:21
Bruce,
I see where you're coming from, but trying to get that battery charged in 15 mins every few days on your boat is asking a bit much of the battery. The only way you will push in the amps, as you say, is to raise the voltage (hence the reason for bypassing the regulator), but in so doing, you could raise the volts to unacceptable levels, both for the battery, and for any electricals on the boat/vehicle.
In addition, lead acid batteries do not like fast recharges in the way that sealed Ni-Cd or Ni-MH batteries do. Sure, you might get the battery up fast, but at what cost? (as a lad, I used to charge my 6v motor bike battery up by putting it across a 12v battery - it charged in a few minutes, but didn't last long)
True, some solar regulators initially take the battery up to 15v following a deep discharge, but that is to initiate gassing to prevent stratification of the electrolyte, and then it is only for a short period and a moderate charge current before reverting to a max voltage of about 14.2.
The other issue is that even if you do monitor the charge (I'm not sure what your criterea are), how do you take into account load changes (eg fridge cutting in/out). This is what a regulator is for. An unregulated alternator can put out 50-100v (true!!) - is it worth the risk?
The 13.8v you quote sounds a bit on the low side for flooded cells, but is probably more than enough if you are running gel cells. While charge current will drop off as the battery charges, lead resistance from the alternator to the battery could be a factor in limiting your charge current. Some alternators have a separate sense lead from the battery back to the alternator regulator (my Patrol does), which takes into account the voltage drop between the two and corrects it; this will improve the charge current without running the battery over-volts.
rgds, Gerry
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