Solar Power Lightning
many communities still have mechanical sirens, they are being
by electromechanical sirens, or state of the art
electronic sirens. The old mechanical sirens are no longer available,
but our competition still refers to them. What is available today
is electromechanical and electronic.
What is the difference between electronic and mechanical
sirens? Are there other types of sirens?
Over the past 50 years outdoor warning siren technology has
changed to meet the demands of the purpose and use of the
equipment. Sirens were originally manufactured for civil
defense purposes. During World War II, the most common use
of sirens was for signaling the threat of an air raid. Due
to the nature of this type of warning and the lack of technology
available at the time, the use of commercial power was the
most effective means of producing high-powered sound.
An electro-mechanical siren
is a fairly simple device. It consists of an electric motor
that turns a fan called
the “rotor” or "impeller",
spinning inside a slotted drum called the "stator".
However, over the years these sirens have evolved to combine
the use of electronics to control the tonality of the moving
parts in the form of timers, relays and radios thus rendering
them reliable on technology.
The first job of the rotor is as a centrifugal fan. It pulls
air into the siren axially through the intake, and blows
it out radially through the holes in the stator. The second
job of the rotor is to chop the incoming air stream into
impulsive bursts. Vanes that periodically cover and uncover
the holes in the stator segment the rotor. Each time the
rotor and stator holes align, a burst of air is forced through.
The frequency of these bursts is the pitch of the siren.
The faster the motor turns the louder the noise. The resulting
tone has a very unique sound. These devices are usually connected
to a three phase, 208, 220 or 240VAC utility service and
served their intended purpose very well but are costly to
maintain due to the high volume of moving parts and are extremely
limited in their ability to incorporate future technological
During the “Cold War Era” the threat of a nuclear
attack was at the forefront of concern. During this period,
a civil defense fund was established by the United States
Government to provide money for many cities throughout the
U.S. to purchase sirens for civil defense threats (nuclear
attack). Most cities updated their existing WWII era, air
raid sirens to a newer version of the same technology, which
is one reason that there are so many electro-mechanical sirens
still in service today. As the availability of parts began
to diminish, a new era of siren technology emerged.
In the early seventies, Whelen's engineers designed a 24-volt,
DC powered siren that had a minimal amount of moving parts
in order to provide uninterrupted siren communication in
any weather scenario without the high cost of maintenance
of its predecessor. These sirens produce their sound electronically
via a tone generator that transmits a tone or voice signal
into an amplified circuit, which passes it on to a speaker
driver configuration thus resulting in an audible signal.
These devices work exactly the same as your stereo, the more
powerful the amplifier, the louder the sound. This design
allows for both siren tones and voice announcements therefore
making it’s application much more versatile than that
of the electro-mechanical variety. The Whelen sirens have
undergone many modifications, have been constantly updated
with the latest technology and are considered to be the cutting
edge siren technology on today's market. Although our competition
has tried to embrace the technology, Whelen manufactures
and sells more electronic sirens that all of our competitors
What is the difference between high
and low frequencies?
A. The frequency of a warning
tone used in rating a siren's Sound Pressure Level is critical
in evaluating the performance of an outdoor warning siren,
where the siren's warning tones are expected to carry over
Whelen siren systems are designed to optimize the production
and projection of low frequency warning tones. It is documented
that higher frequency tones attenuate (lose power) more over
distance than low frequency tones.
A warning siren capable of producing 124 dB at 100 feet with
a 500hz warning tone will be more effective than a siren producing
124 dB at 100 feet using a 1,000hz warning tone. This factor
should be considered in planning a warning system.
Consider this example of the attenuation of higher frequency
tones that is apparent in our everyday life.As you are standing
out in your yard, your neighbor's teenage son has the stereo
in his car blasting as he is coming down the road toward
house. The earth seems to shake as the "boom, boom, boom"
of the low frequency bass notes are felt beneath your feet
and on your ears. It is not until the car is very near to
you that you can hear the high frequency acoustic guitar and
voices. As the car passes you, these high frequency tones
seem to disappear, but the pounding and thumping of the "boom,
boom, boom" bass can still be heard and felt.
This scenario clearly demonstrates that ability of the lower
frequency tones to be heard at a farther distance than the
higher frequency tones. In short, remember that not all 124
dB (at 100 feet) sirens are alike.
What should I be concerned about when using solar power as
the only source of power for a public warning siren?
Solar power is a very good solution for power in electronic
sirens due to their low consumption of power and high
battery capacity. Solar power also allows for more
freedom in system design. When designing an AC powered
system one of the criteria used in determining feasibility
of a location is whether or not a power source is available
nearby. Therefore, in some instances, optimal locations
have to be passed up for less desirable locations with
access to utilities. Solar systems have become more
and more prevalent over the past ten years as more
of the old style electro-mechanical sirens have been
replaced by electronic versions.
The most important consideration of using solar power as
a primary source of power for a public warning system is
that the combination of solar panel output and battery capacity
must handle the siren standby power requirement, while also
maintaining enough charge on the batteries to meet the run
time requirements of the siren. This requirement varies with
location, seasons and weather.
A solar powered siren depends on a properly sized battery
bank for power during bad weather such as rain, snow or fog.
Whelen sirens have a battery capacity of 230 Amp-Hours. Typical
standby current is about 50mA, therefore, after two weeks
of total darkness, only 16.8 Amp-Hours of capacity
has been drained from the batteries. There is still plenty
of capacity for a number of siren tone activations.
All Whelen sirens are equipped with a large battery bank.
The batteries actually power the siren during any warning
tone or message. Therefore, any Whelen siren will meet its
specified run time, regardless of whether it is powered by
AC or solar.
order to prevent damage to the solar panels from large, damaging
hail, a Lexan® solar
shield can be installed over the panels to allow for maximum
protection without prohibiting the amount of light reaching
What will happen during inclement weather?
A. A solar powered siren depends
on a properly sized battery bank for power during bad weather
such as rain, snow or fog. A Whelen siren has a battery capacity
of 230 Amp-Hours. Typical standby current is about 50mA,
therefore, after two weeks of total darkness, only 16.8 Amp-Hours
of capacity has been drained from the batteries. There is
still plenty of capacity for a number of siren tone activities.
How long will it take to recover to full charge?
A. Realistically, this is only
critical if the batteries have been drained significantly,
from considerable use. For example, ten activations
at 3 minutes each.
more likely scenario might be: Four activations at 3 minutes
each, with a WPS2810. This means that 44 Amp-Hours of capacity
has been used, therefore 44 Amp-Hours need to be replaced.
An SBC260 solar option will supply approximately 3.37 Amps
in good sunlight, therefore after 13 hours the batteries
will be fully recharged. Remember that even without recharging
the siren has battery capacity left for six more 3 minutes
activations, in this example.
Q. Are there any advantages to utilizing AC power as a primary
means of power?
A. Absolutely not! On the
siren systems are primarily used as warning devices for
and other emergency conditions. Due to the volatility of
high wind and lightning, which is almost always associated
with severe weather, it is no longer feasible to depend on
commercial (AC) power as a single source of power for sirens
for obvious reasons. To overcome this concern, manufacturers
of older-style (electro-mechanical) sirens redesigned their
systems to allow for 48 volt operation which can be backed
up by a 48 volt battery supply (four 12 volt batteries in
series). This system typical operates as a back up power
source whereas the primary source of power is provided by
commercial (AC) power. In the event of a loss of AC power,
the siren would switch to battery operation. As long as the
batteries are in good condition, the siren system will operate
until the batteries loose their capacity.
This capacity is the troubling part of this whole process
whereas batteries that are not exercised routinely and maintain
a constant charge have a proven tendency to loose their capacity
under load after a very short period of time. This condition
can only be diagnosed under load, as batteries will usually
show acceptable voltage values at rest if they are being
Therefore, if the system has been up and operating for several
months powered only by commercial (AC) power the battery
may show acceptable voltage. However, if a storm was to take
away the commercial (AC) power, and the system switched to
battery power, upon activation of the siren, the amperage
or capacity of the batteries may immediately drop out due
to their lack of use. Most of us who use rechargeable batteries
in our cell phones and cordless home phones have probably
experienced a similar scenario with a battery that only lasts
for a few minutes because of over charging on a routine basis.
The battery charger in the Whelen, electronic siren utilizes
a computer-controlled thermistor connected to the battery
series, which measures battery temperature, and voltage as
well as cabinet temperature and applies the proper amount
of charge accordingly. This method of charging known as “float
charging” assures optimal battery life. Furthermore,
as the electronic siren is DC only, the radios and other
standby systems are constantly drawing on the batteries as
are any tests, silent or audible. This constant drain on
the batteries exercises the system, which maintains the amperage
of the batteries. This is in stark contrast to a series of
batteries that never see any drain and maintain a constant
The most common type of battery charger used in siren systems
is known as a trickle charger. The trickle charge method
is more likely to overcharge the batteries due to constant
charging, which can cause early failure or even battery combustion
hence the use of a separate battery compartment in most electro-mechanical
The battery charger's primary use in the Whelen system is
to maintain the system battery supply to full capacity.
The Whelen siren utilizes two (2) twelve volt batteries in
series to achieve it’s required voltage of 24 volts.
These batteries are locally available, sealed and maintenance
free. DC powered systems are highly advantageous for life
safety applications due to there lack of dependence of commercial
power and regular use of batteries.
In either scenario, the batteries will have to be maintained
and changed out on a routine basis. Therefore it makes a
whole lot more sense to purchase a system that actually utilizes
it’s batteries on a daily basis and requires one-half
of the money to change out (two batteries vs. four per siren).
Are Whelen electronic sirens more susceptible to lightning than
our competitor's mechanical sirens?
A. No. Any siren sitting on a pole in
the middle of an open area is susceptible to lightning. The
key is how well the siren is protected from the inevitable strike.
How will lightning damage a siren?
A. There are two basic ways that lightning
can damage a siren. One way is from energy that is picked up
through the atmosphere by a nearby strike. This energy is often
coupled through the radio antenna or radio coax cable. The
other way is from energy that is coupled onto the AC power
lines, in the form of a voltage transient. In either case,
the siren must be protected from the inevitable.
Will lightning damage Whelen's non-metallic speakers more than
a conductive, metal speaker?
A. No. Whelen's omni speakers are made
of fiberglass reinforced Lexan® and Whelen's directional
speakers are fiberglass.
In either case this is a non- conductive
material. Lightning will seek the path of least resistance,
which is the steel pole mounting bracket and its associated
ground wire. The pole top mounting bracket is a nice lightning
How does Whelen protect its sirens from lightning strikes?
engineers stress the importance of proper grounding to insure
system protection. This ground system is not intended as a way
of trying to prevent lighting strikes, but rather creates the
perfect ground rod providing a path of low resistance.
Most siren arrays are made of a metal substance, which is obviously conductive.
As the Whelen speaker array is made of Fiberglass and Lexan, a non-conductive
substance, it is isolated from ground. Ben Franklin's experiments taught us that
lighting follows the path of least resistance. As fiberglass and Lexan are both
highly resistant materials, the speaker array becomes a "Faraday Cage".
Examples of a "Faraday Cage" are
birds on a high-tension wire, a flying airplane or a vehicle with rubber tires.
All of these things are isolated from an earth ground therefore preventing discharge.
Whelen’s grounding system creates the perfect lighting rod by using the
metal speaker bracket connected to ground by a four gauge solid copper wire.
Whelen also utilizes bleed resistors to dissipate any electrical charge lingering
along cable paths. This in no way implies that the Whelen siren will withstand
every direct lighting strike without failure, but is meant to instill confidence
in the sophisticated design, engineering and long-term useful life that is built
in to every Whelen siren. Lighting protection also includes the installation
of a Delta Lighting Arrestor at the AC service disconnect which utilizes a totally
separate ground wire and rod to filter out any stray voltage or static energy
residing on the electrical service input.