Dave Plowman (News) wrote:
In article ,
John Williamson wrote:
If they were *really* bad and refused to take a charge any other way, we
used to whack 'em across a heavy duty 24V start/ charge unit on flat out
for a minute or two, (About 100 amps...) then charge as normal. That
often got another week or two of use out of them. It was kill or cure,
though.

A sulphated battery will have such a high internal resistance, you'll not
'whack' high current into it with any charger. What you do need is fairly
high voltage - 30 or so - to speed up the chemical process. An old basic
charger with no regulation is likely to achieve this rather than a modern
one, unless the modern one is designed to pulse charge.

Well, our 24V jump start/ rapid charge unit was high enough voltage to
give us an indicated 60 rising to 100 amps going into a 12 volt battery.
Maximum one or two minutes, before the electrloyte started either
boiling or gassing. As I said, kill or cure, but we were doing it for a
fleet of rather tired old coaches, which *had* to be out on the road
*now*. This charger would start a vehicle with completely flat batteries
within seconds of being connected, too.

The 22 to 24 volt bit is what the modern pulse power units do, except
they don't ouptut that much current, and they're controlled by a
microprocessor and not a fitter reading a meter. They also take rather
longer to do the job.

--
Tciao for Now!

John.