[Icom] Running 725 on a battery

[Dana Hoggatt]

On Jun 9, 11:31pm, "Dean Wooldridge" wrote:
} 
} I want to take my 725 portable to Boy Scout Camp this summer 
} and need some pointers on operating with a battery.
} 
} I have questions like . . .


1.  12.8 volts is great.

2.  When the voltage drops too low, most rigs will simply stop
    working.  There's no direct evidence that this harms the
    rig, however, prudence dictates that you'll want to limit
    how often you do it.

    The high current depands of transmitting tends to drop the
    voltage slightly.  Thus, you'll first encounter the shutdown
    while transmitting.  As soon as you stop transmitting,
    the voltage rises again and the rig will operate normally.
    If you're not paying attention, you might not notice.

    As the voltage drops, your RF output power (and your power
    consuption) will drop as well.  This is good as its sort-of
    like a built-in power saving mode.

    When you attempt to transmit at full power with reduced
    voltage, most rigs experience increased IMD and splatter.
    The threshold and severity of the effect varies, of course.

3.  As you guessed, your power requirements will depend upon
    how you intend to use the rig.  The best I can do here
    is to illustrate my own power budget for the upcoming
    field day.  You can use that as a starting point for your
    own calculations.

    In these, I've assumed that I'll spend 75% of my time
    receiving and 25% of my time transmitting.  I've also
    assumed that I'll be running at half power (50w).


Light (15w, 12Vdc flourescent)
     Avg Current         1.2 a   (measured)
     Hours Operation      10 hr  (only needed at night)
     --------------------------------------------------------
     Total                12 amp-hrs


Tuner Meter Light
     Avg Current         0.2 a   (specs)
     Hours Operation      10 hr  (only needed at night)
     --------------------------------------------------------
     Total                 2 amp-hrs


Transceiver (IC-746)
     Receive current       2 a   (from rig specs)
     Transmit current     10 a   (measured at half power, 50w)
     Duty cycle            4:1   (transmit 15 sec out of every 60)
     Avg Current           4 a   (  (45x2A + 15x10A) / 60  )
     Hours Operation      25 hr  (includes some setup time)
     --------------------------------------------------------
     Total               100 amp-hrs


Notebook Computer
     Power Rating         60 w   (wall-wart rating)
     Inverter Efficiency  75%    (conservative estimate)
     Avg Current          6.7 a  (  (60w / 75%) / 12V  )
     Hours Operation      25 hr  (includes some setup time)
     --------------------------------------------------------
     Total               167 amp-hrs


That's about 281 amp-hrs.  I've arranged for three 100Ah
batteries.

I hope that helps.

Dana, KB9SSS