I've always figure the discharge of a lead-acid car battery at 50% of its
rating. Example: 150 AH battery at 50% is 75AH. Now to draw 10 amps
average, we must consider transmit at some 22 amps and receive at some 2
amps average for about 50% of the time. Now, 75/10 = 7.5 hours. If you
have a "hot shot" CW operator that runs 30 to 50 WPM then the duty cycle
goes up and so does the average current. Therefore 10 amps may be a bit low
for an average figure. If the bands are dead and you spend 95% of the time
listening then the average goes down.
In a 100% receive mode theoretically the battery would last, 75/2 or 37.5
hours. The 2 amps is with min audio so expect the real current drain to be
a bit higher. So we will take a more realistic approach and say 75/3 = 25
hours.
Other factors one must consider is the internal IR drop of the battery. New
batteries are lower, old batteries are higher and deep cycle batteries tend
to produce a higher voltage longer but at the expense of less current.
Keep in mind that this radio is not going to like a voltage below about 12.8
to 13 volts. It is rated at 13.8 VDC. A lead-acid battery open terminal
voltage not under charge will likely be 12.8 to 13.5 depending electrolyte
temperature. That takes a HOT battery, one that is very new and preferably a
deep cycle marine battery. Therefore, a car battery is not the battery of
choice as it is designed to be a "high current" device and that is not the
application here. Based on this scenario, one could not expect a battery to
provide much more than 25% of its rated AH value and thus for a 150 AH
battery we now have 37.5 AH available. Again using our example, 37.5/10 is
3.75 hours of use time before required re-charge or a radio and associated
internal processors getting flakey.
OK, so one says we'll have two batteries, one to run on and one to charge.
Not so fast on the draw cowboy. The correct charge rate should equal 2X to
3X the discharge time so 5 to 7.5 hrs will be required to restore the
battery to full charge. Oh, one can do a fast charge but this raises the
electrolyte temperature, plates and spaces expand and the capacity of the
battery in terms of AH decreases. This gets us to the point that we need 3
to 4 batteries to support the operation.
In other words, the Orion II is a power hog and not really suitable for
Field Day battery operation.
One solution, use a good fresh marine deep cycle battery to power the radio,
keep a charger attached and power the charger off of the generator. Using
this method, the radio will have lots of current when needed, the battery
acts as a big filter capacitor so humm from the charger is not a concern,
and the battery acts as a voltage regulator to protect the radio from surges
and generators as they "do their thing with changing loads", and when the
generator dies or is down for refueling {you do shut it down don't you?} you
can continue operating the station.
73
Bob, K4TAX
A connoisseur of fine radios
----- Original Message -----
From: "Larry DiGioia" <listacct@longwire.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Thursday, March 30, 2006 5:56 PM
Subject: [TenTec] battery life
I am looking for guesses as to how long an O2 would run, connected to a
reasonable large, fully-charged car battery, while operating CW for
Field Day...?
--
Larry N8KU
w w w . l o n g w i r e . c o m
100% CW 100% HF
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