*Minimum* charge current?

 

Hey group,

Long time no post.

Been contemplating a battery bank upgrade lately. One candidate is
Global batteries, and I note with some concern that the charging guide
says:

"Minimum Charging Requirements -The ideal charging current, which
would be applied to recharge your battery, is 10% of the 20 hour rated
capacity of the battery. For example a 1065 amp/hour battery (85T-17 @
72 hour rate) will require an initial start up rate of 85 amps (850
amp/hours @ 20 hours) to be supplied by the selected battery charger. A
combination of charging sources such as generator/PV array can be used
to achieve the initial charge."

The model I was looking at has a C20 capacity of 650Ahr, implying that
I require an initial charge current of 65A to properly charge this
battery. In turn this implies an array of over 2kW, if PV is the sole
source of charge current.

If this is for real, and applies not just to the initial (time of
installation) charge but to day-to-day charging, this would mean that
my modest array (600+W) would be woefully inadequate, and that I'd only
be able to properly charge the batteries with my generator,
irrespective of how little energy I'm using on a daily basis. Also
there is no mention of temperature compensation in the guide, which is
odd. In any case, the dealer sells the exact bank I am contemplating in
a package along with a 700W array, so I'm obviously missing something
here. I've asked him to explain the conflicting information, but in the
meantime I was curious to know what rules of thumb, other
manufacturer's recommendations, or experience y'all might have had with
the issue of minimum charge current.

The guide may be written based on information assuming a motive
application for the batteries, where significant discharge is expected
on a regular basis, whereas I am looking to extend my days of autonomy,
and would be withdrawing only about 10% of capacity on a daily basis.
But I'm not keen to second-guess the manufacturer's instructions,
especially when they make a point of saying that these are
product-specific and do not necessarily jibe with recommendations for
other lead-acid batteries.

-=s

 



solarscooter wrote:


What battery technology is this ?

Graham

 


Eeyore wrote:

Sorry, where are my manners?

Lead-acid in general - though as you may know there are various breeds
of lead-acid chemistry. These have nifty tubular plates and stuff.

Here's a link to the manufacturer's FAQ page from which the information
is drawn.

http://www.davidsonbattery.com/faqs/

A summary of comment from the dealer will be added in a follow-up to my
original post.
-=s

 



The general rule of thumb I've run across (in the Outback
Power Systems user forum) is 5% of 20h capacity recommended,
and 3% the absolute minimum. The battery mfr is not tuned
into the lower power of a PV system, but that doesn't mean
it won't work. The MAX charge rate is around C/8 (one eighth
the 20h capacity), and the mfr wants you to get it charged
as quickly as possible.

-K

 


ken wrote:

I'd just make the minimum by that rule.


Who doesn't? :-)

More in a follow-up to my original msg.

-=s