[RE-wrenches] AGM battery charging, more details

Hugh hugh at scoraigwind.co.uk
Fri Apr 29 01:22:34 PDT 2011


At 14:52 -0700 28/4/11, Starlight Solar, Larry Crutcher wrote:
>...."Until now"?.....
>For proper VRLA battery charging, once it is full, you MUST reduce 
>the voltage. It does not matter that you are opportunity charging. 
>What if your turbine is making power 24/7? The voltage will still 
>need to be reduced after a few hours or have a fixed voltage 
>setting. I don't think you are ungrateful but again I encourage you 
>to re-read this thread and the manufacturers instructions. It's all 
>there.
>

OK thanks for driving that home.  My previous message was maybe a bit 
provocative, trying to get to the key issues.  The manufacturers 
instructions are a bit confusing in places "The charger can maintain 
the current I1 indefinitely or until the charger is shut off or 
unplugged. This stage is ideal to maintain battery state of 
charge...."(Rolls FAQ)  The Fullriver instructions offer two methods 
where the final voltage is either below or above the absorb level. 
In both methods there are criteria that are unusual for small system 
charge controllers.

It's not going to be possible to follow these instructions accurately 
with opportunity charging.  For example the initial charge will 
likely be outwith (below) the specified range of currents.  It is 
unlikely that there will be a shunt to measure current, or a system 
to monitor dV/dt to determine the transition points between stages in 
the process.  Nothing will be constant  (except for a programmable 
voltage limit, given adequate wind/sun) and there is no assurance 
that the battery will be fully charged or discharged to any known 
level.

  You state that "Once you have programmed the 2512iX charge 
controller from the IPN Pro, the controller retains the information 
and can be installed as a stand-alone unit"  However this does not 
come with a battery shunt that I can see.  And it's primarily a MPPT 
solar controller, with some sort of load control that may or may not 
be suitable for wind diversion (which can be done with the 'duo' I 
know).  The Tristar offers simple diversion load control suitable for 
both wind and solar inputs, with a float setting that takes over (by 
default) after one hour of absorb time.  Whist this is not likely to 
fit the manufacturers curves exactly it does seem likely to do a 
reasonable job of charging the battery whilst preventing the balloon 
of gas in your dramatic photo.

I will read the document that you reference (about thermal runaway) 
carefully.  I am sorry if I seem a slow learner.  This list is an 
invaluable resource for the industry.  I like to ask naive questions 
and I get a deeper understanding as a result. Thanks to all.
-- 
Hugh Piggott

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