center tap and SC voltage converter [RE-wrenches]

Darryl Thayer daryl_solar at yahoo.com
Sun Jul 23 05:52:58 PDT 2006


Hi to All, Jeff, Allan and others.
First I enjoyed meeting several wrenches at the recent
ASES (American Solar Energy Society) conference in
Denver.

My experience with battery equalizers and DC to DC
converters, is limited BUT The battery equalizer
approach has been 100% failure, where as the DC to DC
has been 100% success (except for a three year life on
one unit). 

I think the battery equalizer approach has to fail
because the equalizer can not tell state of charge of
the batteries.  My experience is what Jeff explained,
it is not possible to balance, unless all draws and
recharges were the same.  If you draw power from a
battery The voltage must drop, when you charge it must
rise. When you draw current in excess of the equalizer
the the battery is drained, but when the draw is over
the equalizer raises the voltage above quiescent and
"thinks" the battery is full. 

The DC to DC converter l;eaves the battery set to self
balance (with of course periodic equalization) and
provides the load from the higher batter voltage.  The
DC-DC converter must have a low no load energy draw
and be able to meet the surges.  On one case where the
surges were large I used a separate 12 volt battery
and used the converter to maintain the battery at
float, again this requires homeowner monitoring
battery SOC.
Darryl
 

--- Jeff Wongstrom <thirstylake at interbel.net> wrote:
> Allan,
> 
> I have installed three Solar Converter EQ 12/24 20's
> as battery equalizers.
> All three required initial adjustment for equal
> balancing.  On follow up
> visits two of the equalizers were imbalancing the
> battery halves and
> required readjusting.  One I readjusted on several
> different occasions
> because it repeatedly wandered.  I have since
> changed all three to
> converting to 12 volts for the loads instead of
> balancing.  This is
> applicable since there are no surge loads (i.e.
> fridge) to consider.
> 
> I do not know what was happening or if I am missing
> something or wiring up
> something wrong.  Has anyone else been checking
> battery halves after
> installing equalizers and found imbalanced (tenths
> of a volt or more)
> batteries ?
> 
> 
> Jeff Wongstrom
> NABCEP Certified Solar Installer
> Thirsty Lake Solar
> 406-889-5324 


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