Just how good are those used, sealed lead-acid batteries? [RE-wrenches]

[Jeff Clearwater]

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HI Bob,

Here's how you do it.

First understand lead acid chemistry thoroughly by reading "Battery 
Book One" by Curtis instruments or some such book.

Then do the following procedure.

1) Set up a charging station for each battery separately (not in any 
series and/or parallel arrangement).

2)  Bring each battery to a good equalize charge state.  For sealed 
lead acid you want a "constant current, constant voltage, constant 
current" type of 3 stage charge that is carefully regulated not to go 
past the 14.4 volt or whatever the battery manufacturer recommends 
for those batteries.

3)  Set up a load station - use a resistance element like those used 
for dump loads.  This should be on the order of a C/10 discharge 
rate. (i.e. if a 100 amphour battery - a 10 amp load)

4)  Now here's the tricky part that requires attention and time. 
Discharge each battery with the load and note the start time and 
amperage and take careful voltage and amperage and specific gravity 
readings periodically - perhaps every 30 minutes or hour - record 
these readings in a spreadsheet like Excel or equivalent.  Record the 
time and voltage and amperage and SG.

5) Discharge until the battery shows about 1.90-1.95 volts/cell at 
the C/10 rate.  (11.4 - 11.7 volta for a 12 volt battery.

6)  Graph the discharge curve you obtained - graph the voltage the 
amperage and the specific gravity on the same graph.  Let the battery 
sit discharged for an hour or so and take SG and voltage readings 
again.

7)  Now you can analyze this data quick and dirty or you can analyze 
it with sophisticated analysis.  Quick and dirty is just to take the 
total time until you reached the state you reached times the amperage 
during that time (rough average) and that will give you rough 
amphours that the battery delivered to that theoretical state of 
charge.  You can obtain State of Charge vs SG readings for  your 
particular battery from the manufacturer.  By comparing the 
theoretical new battery graph to yours you can roughly determine how 
much capacity yours has.  This will also give you the relative health 
of each battery.

A more sophisticated analysis might involve you integrating the area 
of the time vs amperage or time vs. SG curve and determining exact 
amphours.  But you can tell alot if you just compare your curves to 
that of a new battery or the manufacturer's curves or even just to 
each other.

Oh yea - then charge the batteries back up - don't let them sit discharged!

You may have to do this procedure a few times - especially if the 
batteries have been sitting around - they may need "working" to get 
to accept a fuller charge.

AND you need to assess whether all this labor is worth the price of 
these batteries!  Most VRLA batteries don't last more than 200-300 
cycles max.

Hope that helps!

Best,

Jeff Clearwater
Village Power Design


>Wrenches:
>
>I can quite easily measure the voltage of a sealed battery by using 
>a meter, but how do I know how "good" a used, sealed battery is? 
>That is, if the sealed, lead-acid battery has been in use for 2 to 3 
>years, how do I determine its condition (and capacity to hold a 
>charge) if I do not know its use history?  I need to determine how 
>"good" each of 20 of these batteries are (I have reason to believe 
>that the condition of these batteries varies widely).  I would hate 
>to have to haul them somewhere (except to recycle them if they are 
>no good) to be tested.
>
>Bob Clark
>SolarWind Energy Systems, LLC
>bclark at solar-wind.us<mailto:bclark at solar-wind.us>
>[Non-text portions of this message have been removed]
>
>
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-- 
~~~~~~~~~~~~~
Jeff Clearwater
Village Power Design
Sustainable Energy & Water Solutions for Home & Village
http://www.villagepower.com
gosolar at villagepower.com
NABCEP (tm) Certified Solar PV Installer

530-470-9166
877-SOLARVillage
877-765-2784
65 Schoolhouse Rd
Amherst, MA 01002
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`~


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