Just how good are those used, sealed lead-acid batteries? [RE-wrenches]
Bob Clark
bclark at solar-wind.us
Fri Oct 20 23:48:14 PDT 2006
Thanks, Jeff. Note, however, that, because these are sealed batteries, I will be unable to measure SG.
Bob Clark
SolarWind Energy Systems, LLC
bclark at solar-wind.us<mailto:bclark at solar-wind.us>
----- Original Message -----
From: Jeff Clearwater<mailto:clrwater at earthlink.net>
To: RE-wrenches at topica.com<mailto:RE-wrenches at topica.com>
Sent: Friday, October 20, 2006 8:59 PM
Subject: Re: Just how good are those used, sealed lead-acid batteries? [RE-wrenches]
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<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<http://www.villagepower.com/>
gosolar at villagepower.com<mailto: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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