[RE-wrenches] AGM battery charging, more details

[William Dorsett]

Hugh, .25 x C20 would be a C80 rate, and with flooded batteries, C100 was
the cutoff point at which you could do without a controller. All controllers
that I've ever worked with make adjustments in current to meet the
transitions between bulk-absorption-float. PWM controllers do it by
adjusting the width of the current pulse - but by basing the point of
transition on reading voltage instead of counting current.  I agree that a
$450 controller is a lot to add into a small system bid. I've generally
steered clear of sealed batteries, believing that the trade-off between
maintenance and the fragility of plates made with calcium instead of
antimony favors adding water occasionally. 

 

Bill Dorsett

Sunwrights

Manhattan, KS

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Hugh
Sent: Thursday, April 28, 2011 12:59 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] AGM battery charging, more details

 

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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