[KYHAM] KEN Training for Oct. 28: Intro to Auxiliary Power Systems For E-Comm Part 6

Ron Dodson [email protected]
Fri, 25 Oct 2002 18:37:16 -0400


Intro to Auxiliary Power Systems For E-Comm Part 6
Virginia RACES gratefully acknowledges materials provided by
the Battery Council International,   Naval Facilities
Engineering Command, Sandia National Laboratories and the 
U.S. Army Construction Engineering Research Laboratory, used
in this compilation 
Edited by C. Ed Harris, KE4SKY and John Bartone, K4KXK, MSEE
Used here with permission.
---------------------------------------

Most battery problems are caused by oversized loads or
equipment operating at excessive duty cycle for too long. 
When batteries remain in a low  state of charge, check the
load as well as the batteries and charging system! 

 The four ways to determine the charge state of lead-acid
batteries, in declining order of accuracy are:

     1     hydrometer/refractometer
     2     actual equipment load test
     3     artificial load test
     4     open circuit voltage

When using a hydrometer you are working with strong acid. 
Wear eye and face protection and rubber gloves.  Have baking
soda and plenty of fresh water ready to neutralize spills. 
To use a hydrometer, squeeze the bulb while the inlet tube
is still above the electrolyte level.  Then lower the
hydrometer into the electrolyte and slowly release the bulb
to draw in the electrolyte.  At the first cell being
checked, fill and drain the hydrometer three times before
removing a sample.  This brings the hydrometer to the same
temperature as the electrolyte.  Take a sample and allow the
bulb to fully expand.  The sample must be large enough to
completely support the float. 

Hold the hydrometer straight up and down, so that the float
does not touch the sides, top or bottom of the tube.  Look
straight across the electrolyte level to read the float. 
Ignore the curve of the electrolyte on the sides of the
hydrometer.  Be careful not to drop the hydrometer or allow
acid to drip out of it. After reading the hydrometer, to
empty it slowly squeeze the bulb again with the inlet inside
the cell, but just above the electrolyte level to reduce
risk of spills.  Record the Sg of each cell on a work
sheet.  After use, rinse the hydrometer with fresh water at
least five times to flush out any acid.  Allow it to dry
completely before using it again.

Temperature compensation is required for batteries not at 80
degs. F.   Use an accurate glass thermometer and immerse
only the thermometer bulb into the acid, leave it for 5
minutes, read it and then rinse in clear water.  For every
10 degs. F above 80 degs. F, a factor of 0.004 must be
added.  Subtract the same factor for each 10 degs. below 80
degs. F.  As an example, if a battery at 30 degs. F has an
Sg of 1.240, the battery is 50 degs. below the standard, so
the compensation is subtracted from the specific gravity. 
The compensation to be subtracted is .004 x 5 = .020; so
1.24 - .020 = 1.220.  A refractometer is the most accurate
way to measure electrolyte Sg, requires only a small amount
of fluid and is automatically temperature corrected. 
Refractometers are compact, rugged and recommended for
ongoing maintenance of large auxiliary power systems.