[KYHAM] KEN Training for Nov. 4: Intro to Auxiliary Power Systems For E-Comm Part 7

[Ron Dodson]

As this is going to be a busy weekend, here's next week's
material a little early.

Intro to Auxiliary Power Systems For E-Comm Part 7
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.
---------------------------------------

To test the no-load, open circuit voltage an accurate DC
voltmeter is required.  Operate the loads from the batteries
for five minutes to remove any surface charge the battery
plates may have.  Turn off the loads and disconnect the
batteries from the rest of the system.  Now measure the
voltage across the terminals of every battery.  Open circuit
voltage without any load is a good preliminary indicator of 
the state of charge.  The open circuit voltage of a fully
charged 12-volt battery is over 12.72 volts, whereas it is
about 12.6 at 75%, 12.48 at 50%, and 12.12 at 25%.   

To perform a load test, after recording no-load voltage,
reconnect the system, but leaving float chargers, charge
controllers or solar arrays disconnected.  Operate equipment
at normal duty cycle for an hour, disconnect the batteries
and measure the battery voltages again.  If any battery
indicates a voltage of 10 percent higher or lower than
others, it should be serviced or replaced.  An automotive
load tester can be used, although you must be aware that
this places a large artificial load on the batteries for a
short time rather than waiting for a small load to slowly
discharge the batteries.  Because available capacity is
reduced at faster rates of discharge, this test is not as
reliable for communication use as a load test done at the
normal system duty cycle and rate of discharge.

Accurate trouble shooting requires that all batteries in a
bank and individual cells of unsealed, wet-type batteries
be  numbered.  Recording a system history identifies
patterns and trends and is a great time saver for others who
may  service your system in an emergency, because they  can
focus first on the most frequent problems and can anticipate
the proper tools and materials to bring.   Battery systems
not used on a regular basis must be checked in the spring
and fall, at minimum.  Monthly is recommended.

First disconnect all loads.  If battery tops are wet or
dirty, remember that fluid on top of the battery is highly
acid electrolyte! Clean battery tops with a cloth or brush
and a baking soda and water solution.  Rinse with clean
water and dry with a clean cloth.  Remove the caps from all
cells, check the electrolyte level of every cell in every
battery and add distilled water to the fill line on the
battery, or 2" above the top of the plates.  Determine the
battery's state of charge with a hydrometer.  Discolored,
odorous electrolyte indicates contamination caused by adding
other than  distilled water, which results in battery
failure.  Inadequate charging without adding water can
result in lead sulfate shorts between the plates, cracked
partitions between cells and leakage which require the
battery to be replaced.

NEVER hammer cable connections onto terminal posts! This
breaks fragile spot welds between terminal posts and plates,
causing shorts, which could cause a spark and ignite free
hydrogen gas, causing an explosion!   Inspect all caps for
sound good condition, replace and tighten securely by hand
only.   Tighten battery tie-downs securely, but not so tight
as to distort the case. 

Batteries that will not accept a charge may be rejuvenated
for a short time by adding a conditioner available from
marine and auto stores, but this  is only an emergency
measure until they can be replaced.  They may have had their
electrolyte boiled off from prolonged overcharging, or
become sulphated by being left at a low state of charge for
too long or have suffered  physical damage and should be
replaced.  Inspect and repair any corroded, loose or burnt
connections and blown fuses.  Cartridge fuses donut look
different when they are blown, so remove them and check
continuity with an ohmmeter. A blown fuse shows an infi-nite
reading, a zero reading means it is still intact. 
 Always determine why a fuse blew before replacing it.
Proceed logically, check the most obvious things, such as  r
excessive voltage drop at the load. Knowing what failed is
necessary to avoid repeating the condition causing the
failure.  If the same fuse blows again, don't consider the
system operational until everything has been checked out.