Re: [A/S] Uh-Ohh, Charger Problems?

[Jim Dunmyer <jdunmyer@xxxxxxxxxxx>]

George,
  A standard converter/charger like the UniVolt is a fixed-voltage 
affair. They're usually set to around 13.8 volts.

Now, when the battery(s) are low, they will drag the voltage down a bit 
and the charge rate (amps) will be somewhat higher for a while. As the 
batteries charge, their voltage will rise to the charger setting, 13.8 
in this case. The current will decline as the battery voltage rises, 
leveling off at something that's not *too* injurious to the batteries.

The problem with this arrangement is two-fold: to charge a battery 
properly requires more like 14.4 volts for a while. That will result in 
a high rate of charge when the battery is "low", tapering off as above. 
However, 14.4 volts is way too high to apply after the battery 
approaches 80% or so of full charge. A "smart charger" will reduce its 
output to 13.6 volts at the 80% charge condition, resulting in quite a 
low rate to finish the charge. It will then drop to 13.2 volts to 
"float" the battery and keep it fully charged, yet not cook the water 
out of it. The voltage from a regular charger/converter, staying at 13.8 
volts, will cause water loss over a period of time, especially if you're 
not using the coach and leave it plugged in.

When you think the batteries are fully charged, unplug the converter 
from shore power and let things sit for 12+ hours, then measure the 
battery voltage. It should be right at 12.6 volts. An even better 
measurement is to check the specific gravity with a hydrometer, it 
should be 1.265, IIRC, and all cells should be equal within a very small 
amount.

You might look at http://www.uuhome.de/william.darden/dcfaq.htm and 
Phred's Poop Sheets at http://www.phrannie.org for more information on 
chargers and batteries.

                             <<Jim>>