On Fri, 01 Aug 2008 11:58:05 -0400, John Popelish
wrote:

ian field wrote:

Yuasa publish a "Little red battery book" which recommends supplying a
sulphated battery with 29V current limited to 1/3 of the Ah capacity,
assuming the sulphation starts to break down the terminal voltage will pull
down to the deep discharge value ( about 10.8V for a 12V battery) A
comparator should be arranged to detect this event and switch the charger
over to constant voltage charging (about 13.8 to 14.4V).

Down loadable in PDF form at:
http://www.yuasa-battery.co.uk/indus...downloads.html

The 29 volts is a standard level from a 24 volt battery charger, and
reality they were saying, use a constant current supply. They now
seem to have changed to 1/10 of the amp-hour capacity, and not 1/3 .

Their present recommendation reads:-
Depending on the degree of sulphation, a battery may be recovered
from this condition by constant current charging at a higher voltage
with the current limited to one tenth of the battery capacity for a
maximum of 12 hours.
Note: The applied voltage will exceed the normal recommendation
and so the battery must be monitored (not left unattended) and
removed from charge if excess heat is dissipated. The voltage
required to “force” this maximum current into the battery will reduce
as the battery recovers until normal charging can take place.
In extreme circumstances a battery may never fully recover from
sulphation and must therefore be replaced.

Peter