[RE-wrenches] AGM battery charging, more details

[Hugh]

At 22:38 -0500 26/4/11, William Dorsett wrote:
>
>OK, I can see how you could input the amphr capacity of a given set 
>of new batteries, but would someone explain how a controller which 
>counts amps can adjust as the battery bank ages? As the capacity of 
>the bank drops over time, and this varies by different 
>manufacturers, it still seems that a controller which measures 
>voltage would track the SOC of the bank better than current counting.
>

Keeping track of SOC by counting Ah is a challenge in itself, but the 
battery manufacturers' instructions don't require this.  Fullriver 
and Surrette require the you make a transition between Absorption and 
Float charge regimes/stages at a certain point where the charging 
current drops to a given level (although the Rolls FAQ is puzzling in 
its wording there - suggesting that you can charge at 0.25 x C20 
indefinitely!).  Most stand alone RE system controllers do not 
possess the ability to monitor the battery current, so they cannot 
follow these instructions.  This is my concern.

At 10:54 -0700 26/4/11, Rick Cullen - Blue Sky Energy, Inc. wrote:
>There has been some discussion in the past few days regarding AGM 
>batteries and charge control switching to Float based on net battery 
>charge current matched to battery size and that our IPN-ProRemote 
>product can provide this.

Rick's Blue Sky product fits the bill but it seems expensive in the 
context of very small systems.  Phil Smith of Barden Batteries in the 
UK has told me that a correctly programmed Tristar controller will do 
a good job even though it does not 'know' the battery current.  This 
is good news.

I am still deeply puzzled about sealed batteries as I learn that you 
must not make them gas but you have to be sure to charge them well 
(like any other lead acid battery) or they will fail prematurely. 
That's why I would like to be able to fit controllers that monitor 
the battery current and use this to determine the transition to a 
float charge.

Maybe it would help if somebody told me what sort of charging would 
actually damage a sealed battery.  Then I would simply charge them as 
hard as the wind/sun allows while avoiding doing that.
-- 
Hugh Piggott

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