[KYHAM] KEN Training for Sept. 23: Intro to Auxiliary Power Systems For E-CommPart 1

Fri, 20 Sep 2002 15:44:30 -0500

Great post Ron, I'm looking forward to the rest of the series!

73
Dan

Dan Evans N9RLA
Scottsburg, IN 47170
{EM78}
IN-Ham list administrator
QRP-l #1269
1/2 of the N9RLA /R no budget Rover Team
Check out the Rover Resource Page at:
http://www.qsl.net/n9rla

----- Original Message -----
From: Ron Dodson <[email protected]>
To: <[email protected]>; Christian Co. Emerg. Services
<[email protected]>; <[email protected]>
Sent: Friday, September 20, 2002 5:45 AM
Subject: [KYHAM] KEN Training for Sept. 23: Intro to Auxiliary Power Systems
For E-CommPart 1

> This week, we begin a 8 part series on Auxiliary power
> sources and systems.
>
> This is a broad discussion on everything from different
> types of batteries, to generators to photovoltiacs.  I hope
> you will agree that this is written in a form that is
> understandable to all levels of experience from beginners to
> old hands.  Again, I thank the author for giving permission
> for our use here.
>
> 73,
> KA4MAP
> ===========================
> Introduction to Auxiliary Power Systems For Emergency
> Communications
> 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
>
> Part 1-
>
> RACES operators  can't learn all that they need to know
> about auxiliary power for emergency communications from
> books or lectures.  Practical experience is needed to apply
> theory with common sense.  The following won't make you an
> expert, but provides basic knowledge to "keep you out of
> trouble," explain the basics of battery-based DC power
> systems, portable generators and photovoltaics to plan
> auxiliary power for your emergency communications.
>
> Batteries are only a temporary power source unless you have
> a sustainable means of recharging them, independent from AC
> mains.  Photovoltaics (PV) provide sustainable DC power at
> lower life-cycle cost than generators, when combined with a
> properly designed battery bank and charge controller.
>
> Attention to POLARITY is always important, but especially so
> in DC systems!  Whenever using battery power, the correct
> connection sequence is important to avoid sparking or damage
> to system components.  Just because a battery is lower than
> your house current does not mean it is harmless.  An arc
> caused by wiring a connection in the wrong order may ignite
> hydrogen given off by a battery, causing an explosion!  High
> current flows at low voltages can still be lethal.  Always
> disconnect all circuits before working on any power system.
>
> Always follow the correct re-connection sequence:
>
>      1     positive connection to battery
>      2     positive connection to load
>      3     negative connection to battery
>      4     negative connection to load
>
> Typical 12-volt lead acid batteries have a voltage of about
> 14 volts when fully charged and 11 volts fully discharged.
> Most amateur equipment doesn't operate properly below 11.5
> volts, so you can't exceed the depth of discharge at which
> battery voltage under load drops to below that figure.
> Battery systems are current limited and their capacity is
> finite.  Oversized loads or excessive duty cycle cause rapid
> depletion of battery capacity.  Battery systems must be
> sized to the load, or they cannot supply the current needed.
>
> Cold Cranking Amps (CCA) represent the current a starting
> battery provides continuously for 30 seconds at 0 degs. F
> before voltage is drops to 1.7 volts per cell (Vpc) which it
> is fully discharged.  For MCA or Marine Cranking Amps, the
> measurement is taken at 32 degs. F.  Cranking amps tell
> nothing about how long a battery can run your transmitter.
> Reserve capacity  is the time a starting battery can sustain
> a continuous 25 amp load before cell voltage drops to
> 1.7vpc.
>
> The performance measurements used for rating deep cycle
> batteries are their amp-hour capacity and depth of discharge
> (DoD).   Amp-hour capacity is total current available over
> time, measured at 80 degs. F.  DoD is the percentage of
> capacity available during a charge- discharge cycle.
>
> Amp-hour ratings of deep cycle batteries are based upon a
> discharge rate at 1/20 of a battery's capacity, expressed
> as AC over 20.  A marine battery rated 200ah at C20, when
> discharged continuously at 10 amps, at 80 degrees F., will
> sustain that load for 20 hrs.  Starting batteries are
> designed
> for  20% DoD, gel cells  25%, "deep cycle" batteries from
> 50% to 80% and flooded NiCds 100%.
>
> Starting batteries perform poorly for communications
> because they are designed for short periods of high load.
> Deep cycle batteries are acceptable and flooded NiCds best
> for communications because they withstand long periods of
> slow discharge.  For a typical 20% transmit duty cycle, a
> 100w VHF repeater, drawing 20 amps on transmit, requires a
> minimum 100ah battery to stay within a C20 discharge rate,
> at 80 degrees F. At lower temperatures available capacity
> is reduced. Lead-acids lose 50% of their capacity at 32
> degrees F!
>
> More rapid rates of discharge, such as using a marginally
> sized battery for the load, further reduce available
> capacity and the number of charge-discharge cycles the
> battery will provide.  A BCI Group U1 (25 lb., 31ah) gel
> cell is well balanced to power a 2-meter mobile at 25% duty
> cycle, on medium power transmit, requiring about 6A for 25w
> PEP, approximating C20 rate of discharge.  If Tx output is
> increased to 50w, current load increases to 10 amps, a
> mildly oversized load approximating C10, but enough to
> shorten the life cycle of a gel cell!  A deep-cycle, flooded
> lead-acid tolerates C10 with some loss of life cycle.  A
> portable battery pack designed for a C10 discharge rate
> should be a true "deep cycle" type rated for 50% depth of
> discharge or greater, such as AGM construction, NOT gel!
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