[RE-wrenches] AGM battery charging, more details

[Hugh]

At 15:30 -0600 24/4/11, Allan Sindelar wrote:
>The Solar Boost products actually used an external shunt option, 
>tying to the Kelvin terminals on the shunt to measure current and 
>allow compensatory current; a dip switch controlled 
>internal/external sensing. Modern digital controllers apparently 
>rely solely on voltage variations.

Thanks Allan,

So most modern controllers cannot sense the battery current and 
therefore cannot use this as a cue to switch to floating the battery. 
I confess that I had never heard of the Solar Boost external shunt 
but since most of my systems have an element of wind and/or hydro 
this would not be an option for me.  Without this external shunt, a 
controller is not going to know the charging current (since part of 
the current will be going to the load).  Without knowing the current, 
how can you do a proper job of switching to float and avoiding drying 
out the battery?

I don't understand how people can use sealed batteries successfully 
on RE systems.  I avoid them when I can and I usually set the 
absorption voltage too low, for safety, if I do have to.  But I am 
keen to learn about a successful approach that does charge the 
battery properly without drying it out.
-- 
Hugh Piggott

Scoraig
http://www.scoraigwind.co.uk