[KYHAM] KEN Training for Nov. 11: Intro to Auxiliary Power Systems For E-Comm Part 8

[Ron Dodson]

Intro to Auxiliary Power Systems For E-Comm Part 8
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.
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Portable Generator Basics And Safety

If you can't recharge your batteries when the grid is
down after a disaster, they are useless.  Generators
frequently come to mind, but are not the only answer. 
If you don't know what you are doing, stay away from
generators, because a screw up may kill you! 

NEVER connect a portable generator to house wiring unless a
transfer switch has been hard-wired into the breaker panel
to disconnect the house wiring from the AC mains to prevent
back-feed when they come back up.   Installing one is a job
for a licensed electrician.  Ensure adequate earth ground
for your personal safety.  Never run a generator in standing
water or work on the generator or feed lines while standing
on wet ground.

Never run a generator inside an enclosed building because it
is impossible to adequately ventilate carbon monoxide and
fumes.  Use only UL-listed 3-wire extension cords.  Always
plug cords into equipment first before connecting them to
the generator feed.  Medical devices and computers require
clean power and should never be run direct from
unconditioned generator feeds.  

Gasoline generators produce about 600w at 120 volts AC for
each engine horsepower.  A typical HF transceiver requires
about 1200 AC watts at 120 volts.  Generator capacity must
be sized to not only the running wattages of the equipment,
but also the starting loads.  For low-loads such as furnace
fans multiply running wattages x 2, for  pumps or
compressors multiply the running wattages x 7. 

A  3.5 HP generator is about the minimum recommended for
RACES use.  It can be carried by one person, uses 5 gallons
of gas every 24 hours and produces about 2 kW.  It can power
a modest station, such as a barefoot 100w-SSB or dual-band
FM mobile, laptop, TNC, a couple small nicad chargers, an
automotive battery charger and limited emergency lighting. 
Don't expect it to also power your 180-watt VHF amp,
refrigerator, hot plate and coffee pot!  Light-duty
recreational generators are not rated for continuous duty,
may quit and not restart when hot, under prolonged disaster
conditions.  They should be limited to intermittent use for
battery chargers, emergency lighting, cooking and limited
use of power tools. 

The minimum generator to power an average house or an
emergency command post is 5kW.   A  commercial grade,
continuous-duty generator of this size has an 8 HP engine,
weighs 200 lbs., produces 32A at 120 volts and runs 8 to 10
hours on 5 gallons of gas and uses a 55-gal drum of gas
every three days.  A large generator is practical only if
you have a reliable source of clean fuel. 

It is unsafe to store more than one Jerry can of gasoline in
your barn or garden shed.  Stored gasoline goes bad in a few
months unless treated with a fuel stabilizer, available at
Walmart or West Marine.  Store extra Jerry cans empty.  When
a hurricane "Watch" changes to a "Warning", fill your
cans while there is still power to run the pumps, then store
them under cover, but tied down outside!  Once the generator
is started, use a wooden dip-stick to check fuel level
every  2 hours and "top off" tanks before they run out.

Photovoltaics Make Sense

Photovoltaics produce DC electricity from sunlight and are
ideal for maintaining battery banks against self-discharge
during extended periods of non-use.  Properly designed solar
arrays can provide sufficient current to run communications
equipment directly or to maintain battery  banks at
operating capacity during periods of heavy load.  

A photovoltaic panel producing a current of from 1% to 12% 
of battery capacity is recommended to compensate for
self-discharge in storage batteries and can maintain them on
float indefinitely.  No charge controller is required 
because maximum current doesn't reach the threshold to
evaporate electrolyte after full charge is reached.  A diode
is wired in series with the panel to prevent battery
discharge at night when panel voltage drops below battery
voltage.  This method of float charging is recommended for
storing vehicles or equipment which are not used at least
monthly.  

Additional panels may be added to the system to replace
energy consumed daily by the loads and to compensate for
energy used by charge controllers, etc.  To avoid
over-charging the batteries during periods of non-use, a
charge controller is required to disconnect the panels from
the batteries when they reach a fully charged state.  

While voltage is nearly constant, the charging current
produced is dependent upon incident light in watts per
square meter under operating conditions. Under ideal
conditions (full sun perpendicular to the panel in clear sky
at 20 degs. C) this figure is about 800w/m2.   A 50w panel
produce 1,500+watt /hours of energy weekly under full sun 
or more under ideal laboratory conditions, but only a
fourth as much during a cloudy mid-Atlantic winter. To
properly size a photovoltaic system adequate to operate
continuously, total all loads in watts, multiply by the
average daily use in hours, plus a 30% allowance for DC line
losses.  Subtract the average daily energy produced by
back-up generators and divide the total by the product of
the module power rating times the Area Factor which
compensates for local sun conditions (A4" in the
mid-Atlantic states) to yield the number of panels required.
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This concludes this series on Aux. Power.  I hope you found
it useful.

Next week, we start a 3 part unit on some radio choices for
E-Comm.
73 and Happy Veterans Day!

Ron