*** Testing and Inspection of Batteries ***

From:	 Ed Harris [Ed.Harris@p3006.f120.n109.z1.fidonet.org]
Sent:	 Monday, October 19, 1998 10:26 AM
To:	 sarinfo@mindlink.net
Subject: Testing and Inspection of Batteries

The following short article is a follow-on to the previous item
entitled "Introduction to Auxiliary Power Systems for Emergency
Communications" and is intended to address questions on inspection
and test of batteries donated for re-use by amateur radio or other
volunteer emergency response organizations.

        Inspection and Test of Donated, Used Batteries

C. Ed Harris, KE4SKY, AEC, Fairfax County ARES

Power packs such as Quantum are excellent for powering hand-held
transceivers, but are expensive. You can make your own by using Yuasa
NP2-12 or similar 12-volt sealed lead-acid (SLA) batteries obtained
from local hospitals. The 2ah size fits in a coat pocket and powers a
5 watt handheld radio all day. Two or more connected in parallel and
taped together power the handi-talkie, a palmtop computer such as the
HP 100LX or HP-200 and a terminal node controller such as the Kantronics
KPC-3 as a portable digi-peter for high-speed, error-free data retransmit.

Sealed lead-acid (SLA) batteries used are used to power medical diagnostic
instruments, alarm systems or uninteruptiple power supplies (UPS) and
are usually replaced on a fixed schedule before they are worn out. Because
they require disposal as hazardous waste unless recycled or reused, a
hospital's "donation" to your RACES, ARES or CAP group reduces their
disposal cost. Emergency Coordinators may write to local hospitals,
explain how gel batteries they discard are useful to provide power for
emergency communications activity. It is likely you may obtain a quantity
free for the asking, with no more trouble than signing a receipt to
satisfy the environmental officer and writing a "thank you" to the
hospital administrator.

A suburban hospital discards from 50 to 100 pounds of SLA batteries
monthly. Handling the logistics of collection, testing and distribution
should be shared by group of individuals trained for the job. After
having made initial contact through our hospital's Environmental Officer,
the Engineering supervisor now calls whenever our shelf in Material
Management is "full." I use a hand truck to collect the batteries we
distribute to amateur radio operators throughout Virginia District Two,
which covers five counties.

Donated SLA batteries must be inspected, recharged if necessary and then
tested before reissue. We check open circuit voltage to sort out batteries
which may be load tested and distributed immediately. Any 12V batteries
having an open circuit voltage (Voc) of 12.8V or greater are ready for
load testing. Those with Voc less than 12.8V are charged by connecting
in parallel across a regulated 13.8V power supply. Any batteries not
accepting charge after 4 hours are discarded. Batteries are initially
charged for 4 hours and any that require more time are checked every 2
hours, but exercising care that total charge time and current for a
depleted battery does not exceed 140% of capacity.

Typical 12-volt SLAs have an open circuit voltage of about 13 volts when
fully charged and 11 volts when fully discharged. Most amp-hour ratings
of batteries are based upon a discharge rate at 1/20 of capacity,
expressed as "C over 20," for a rate of discharge, typically 25% for gel
cells. More rapid discharge, such as using a marginally sized battery for
the load, reduce the available capacity and the number of charge-
discharge cycles that a battery will provide.

Because our VHF and UHF communication equipment doesn't operate properly
below about 11.5 volts, you can't exceed the depth of discharge which at
which the battery voltage under load decays to below that figure.

Batteries which accept charge to Voc greater than or equal to 12.8V must
still be load tested after recharging. An easy quick check is to apply a
load in amperes which approximates battery capacity in amp-hours, for 10
seconds, monitoring the voltage drop. In a "good" battery voltage drops,
but quickly stabilizes after a few seconds, does not continue to fall and
recovers within a few seconds after the load is removed. We have gotten
reliable service from 12V batteries that don't drop below 11.7V after
subjecting to a "C" load for 10 seconds.

If you have a small number of batteries and more time, a better test is
to approximate a continuous equipment load for at least a full minute.
We test 12V batteries up to 2ah, such as used to power hand held
transceivers, with an 8w florescent light at 0.6A load. Larger ones up to
10ah can use a 12V, 50w incandescent lamp at 4A load.

For larger batteries, connect the test battery to the intended transmitter,
such as a 50w VHF mobile or 100w HF-SSB. The transmitter feed line should
be connected to a non-radiating dummy load, then monitor the voltage drop
during a minute of full-power key-down. Accept for reissue batteries which
no exhibit more than 0.5V voltage drop at normal work load and duty cycle.
In our experience one in ten donated batteries is rejected and taken to
the County household hazardous waste disposal site for recycling.

When you subject a battery to a current load which exceeds "C over 5" or
1/5 of its amp-hour capacity, expect a 25% reduction in its delivered
capacity. At lower temperatures available capacity is further reduced.
Lead-acid batteries typically lose 50% of their capacity at 32oF!

A rule of thumb for adequate battery capacity to approximate C20 discharge
is one amp-hour per watt of peak envelope power at the transmitter. This
is adequate to provide 24 hours of SSB operation or 12 hours of FM
carrier, CW or digital modes at a typical operating duty cycle.

Lead-acid batteries at normal ambient temperature should be charged at a
current of from 1/10 to 1/20 of their capacity. Any sealed battery will
vent if overcharged to the point of excessive gassing, because the valves
are designed to purge extreme pressure building up inside the battery case.

Marine or automotive chargers intended for flooded batteries must not be
used to charge gel cells unless they are equipped with voltage limiting
circuitry to preclude their exceeding 14V peak during charging.

73 de KE4SKY
--... ...-- -.. . -.- . ....- ... -.- -.--
Asst. Emerg. Coordinator, Fairfax Co. ARES

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