THE MANATEE AMATEUR RADIO CLUB, INC.
October 2016
RADIOWAVES
MARCI Newsletter
FROM THE PRESIDENT:
Your BOD continues to work on the plans for the
Holiday party on December 6th. More details will be given at the October meeting. In
addition, we will discuss upcoming events such as JOTA and Winter Field Day. The
program for the meeting will be given by our Radio Waves editor Geoff, N1GY. ,subject
to be ARRL benefits and programs. Hope to see you all there. 73, George,,K4AWA
The Hurricane Season is not quite over yet, so don’t let your
guard down. The Hamfest season is starting up again, so count up all those pennies and get
ready for all the local and regional hamfests that will be starting up soon.
FROM THE EDITOR:
Tech-Talk
Part 21
Welcome to part 21 of our series.
We've been talking about DC Power. When we're home, we generally use
power supplies that convert house current (nominally 110V AC in the US) to
the nominal 12V DC that our radios require. But when we're operating
portable, whether for fun, emergency and public service communications, or
even "at-home portable" when the lights go out, we turn to battery
power. Let's find out a little more about batteries.
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Safety First, Second, and Third!
Batteries can deliver a tremendous
amount of current in a very brief
time. Never short the battery
terminals. Never place the battery where
metal can accidentally contact the
terminals. Always fuse the positive wire
as close as possible to the battery.
Batteries fall into two broad categories. "Primary" cells are designed for onetime use. When they can no longer deliver sufficient current -- that is, the
voltage is too low to power the load -- we consider them dead and must
replace them. Typical examples are the D, C, AA, AAA, and 9-volt sizes that
we're all familiar with. They're handy for running small devices like flashlights,
but not too practical for most Ham Radio applications.
So we turn to the other choice -- "secondary" or rechargeable batteries. They
start our cars, and power our cell phones, tablets, and laptops. When they go
dead, we plug them in, charge them up, and we're back in business.
Rechargeables come in a wide variety of types, differentiated by their
"chemistry" -- the types of material that make them up. All of them rely on
some type of chemical reaction to generate useful electricity. The simplest,
and oldest, type is the lead-acid battery. Car batteries and so-called gel-cells
are typical examples. Early battery packs for hand held devices were NickelCadmium (NiCad) cells. Later, Nickel-Metal Hydride largely replaced NiCads,
and in turn were supplanted by even better refinements like Lithium-Ion and
Lithium-Polymer. Even more exotic technologies exist and will almost
certainly work their way into mainstream products in the coming years.
So what makes each advance in battery technology "better"? To oversimplify,
it's an increase in Power Density. Let's take a look at that concept.
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A common way to measure battery capacity is in Amp-Hours, abbreviated as
AH. Smaller batteries are often rated in Milliamp-Hours, or mAH. In essence,
this means the battery's ability to deliver a specified level of current for a
specified amount of time before its voltage drops to a specified level. For
example, in theory a common 7AH battery should be able to power a load of 1
amp for 7 hours; a load of 500 milliamps for 14 hours, or a load of 2 amps for
3.5 hours. In practice, most batteries will exhibit higher capacity when
powering smaller loads, and lower capacity at higher loads -- in our example,
the 500 mA load is likely to run for longer than 14 hours, but the 2 amp load
will stop at something less than 3.5 hours.
Power Density is -- again, oversimplifying -- a
measure of Amp-Hours per pound, or Amp-Hours
per cubic inch. At left are three common sizes of
sealed lead acid gel cells. In front is a 7AH
battery. It weighs about 5 lbs. These are often
used in alarm systems and emergency lighting
units. In the middle is a 35AH version. This one is
referred to as a "Group U1" size, and weighs about
22 lbs. And at back is a "Group 24" size -- similar
to many car batteries. It's rated at 79 AH and
weighs a hefty 50 lbs or so. In contrast, a modern
Lithium-Ion battery of similar capacity would weigh
about 1/3 as much as the lead acid cells. But as I'm sure you've guessed,
there are trade-offs. First off, Lithium batteries are much, MUCH! more
expensive per Amp Hour of capacity. In addition, they require specialized
charging circuits, which add to the cost and complexity of use. Due to both
factors, they are not generally available in standard sizes like the ones at left.
Now, battery capacity may seem like a pretty straightforward idea. But things
get slippery quickly. As a fully charged battery delivers power to its load, its
voltage drops. A "dead" battery is not necessarily (in fact is probably not) at
zero volts. It simply can no longer supply sufficient power to the load. It
follows, then, that to accurately specify a battery's capacity in Amp-Hours, a
manufacturer must also specify a lower limit to the voltage. Specifying a lower
voltage will make one battery seem to have a higher capacity than
another. Surprisingly <g> some manufacturers use this trick to hype their
product over their competitors' products. And here's "surprising" trick #2.
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As we noted above, batteries will exhibit somewhat higher capacity with
smaller loads. In our example, a 7AH battery with a 500 milliamp load lasts
longer than 14 hours. If, say, it powers the load for 18 hours, then some
vendors will claim it's a 9AH battery!
A related issue is recharging cycles. Let's take a brand new 7AH
battery. Well, after it's discharged and recharged, it may be a 6.999 AH
battery (note that I'm just making up numbers to illustrate the point). After the
second discharge/charge cycle, it may be 6.998 AH, and so on. When we say
a battery doesn't hold a charge, we mean it has effectively become a zero AH
battery. You've no doubt seen this yourself as your gadgets gradually operate
for less time between charges.
Now by altering the physical construction of the battery, it's possible to make it
with a higher initial capacity. But here's the catch -- what they don't tell you is
that the capacity drops off at a steeper rate, so you get fewer charge
cycles. Therefore, you'll need to shell out for a new battery sooner and more
often. Caveat Emptor! As always, your best bet is to purchase your battery
from a reputable vendor. Just remember -- if it seems too good to be true, it
probably is.
That's it for this one, gang. Next time, we'll continue looking at portable
power, and try to answer the #1 question -- what size battery do you need?
73 for now
John Bee, N1GNV
Quicksilver Radio Products
SWAP / TRADE / SELL
VHF and UHF Antennas: Made with 3/32” welding rod and SO-239 connector easy to
assemble and mount on ¾” PVC pipe. $10.00 each Call Geoff at 941-447-8579
Headsets with adapters for many rigs $25 Fits FT-7800 through 8900, Ft817, 857, 897.
Also IC-703 and 706 all models, 7000, may fit 7100 as well. Call Geoff at 941-447-8579
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Microphone selector boxes. Keep the hand mic and the headset connected at all times.
Switch from one to the other with the turn of a knob. $25 Call Geoff at 941-447-8579.
PowerPole Power Distribution Blocks in 4+1, 6+1, and 8+1 sizes $15, $20, $25 each
respectively Call Geoff at 941-447-8579
Club Meetings
Monthly Regular Meeting Oct. 4, 2016 LWR Red Cross Malachite Drive 7 PM
Monthly Board Meeting Oct. 18, 2016 LWR Red Cross Malachite Drive 7 PM
Monthly ARES Meeting Oct 25, 2016 LWR Red Cross Malachite Drive 7 PM
Club and Other Nets:
MARCI Info Net Sunday 7:00 PM 146.820 – 100 Hz.
ARES Net
Monday 7:00PM 147.195 + 103.5 Hz.
Manatee Skywarn Net
Thursday 7:00 PM 147.195 + 103.5
WCF ARES & INFO Net Monday 7:30 PM 145.430 – or 442.950 + 100Hz.
WCF Eagle NTS Net Nightly 8:30 PM
145.430 – or 442.950 + 100Hz.
WCF Skywarn Net Tuesday 9:00 PM
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WCF Technical Net Thursday 9:00 PM
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If anyone in the club (or out of the club) has built any gear for the
furtherance of their enjoyment of the radio hobby, please write it up and
send it to your editor. The newsletter needs articles to fill the pages. If none
are coming forward, this newsletter will be getting shorter in the future.
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