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Author Topic: HF Battery Life  (Read 2084 times)
N7GCO
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Posts: 142




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« on: July 15, 2013, 06:14:56 PM »

I am wanting to use my Icom 706 portable for an upcoming contest. I will be operating from my truck and not using the truck batteries, I plan to buy a AGM battery. I found one today that is rated for 75 amp hours. Can some one tell me how long a can anticipate operating at 100 watts before I will need to charge the battery?

Thanks
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N3HFS
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« Reply #1 on: July 15, 2013, 07:28:53 PM »

From my experience running a TS-440 on a 105 amp-hour lead acid battery some years ago, you stand a chance of making it through 24 hours - but it depends very heavily on how much you'll be transmitting.  Even small details like using compression on SSB can make a cumulative difference in your power consumption.  Even if you only listen for 24 hours, you'll draw a lot (between a quarter and a half) of the battery's capacity. That's if your radio draws just 1.0 amps or 12 watts, which I think is about right for the IC-706 series.

Perhaps you might plan on monitoring your voltage and cutting down your output if/as needed in the later hours of the event?

Also, have you had ample opportunity to "shake out" your power system to ensure that your particular battery is willing to deliver the necessary 20 amps or so for as long as you need for your transmissions? Some battery designs are better at delivering the amps at the minimum required voltage for minutes instead of just seconds (you'll be drawing as much as 0.25C or 1/4 of the full battery amp-hour capacity, that's pretty hard work).

Best of luck on your contest!
« Last Edit: July 15, 2013, 07:31:57 PM by N3HFS » Logged
K5LXP
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« Reply #2 on: July 16, 2013, 11:01:09 AM »

Running the numbers for my own 706, at a 50% TX/RX cycle running CW at 100W will require 3.105Ah.  Divide 75Ah by that and you get about 24.15 hours of operating.

Now, at high power it will not be possible to extract all the amp hours out of the battery due to terminal voltage drop as the battery discharges, so your effective battery capacity will be less than the 75Ah spec'd.  Reduce your power a bit or more accurately predict and control your duty cycle (TX-RX and mode) over my assumed values and you can get there from here.  Characterizing the exact radio and battery for currents and capacity ahead of time will help make the predictions more accurate.


Mark K5LXP
Albuquerque, NM
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AA4PB
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« Reply #3 on: July 16, 2013, 11:17:46 AM »

When a mfg specifies a 12V battery for 75AH that includes operating down to a terminal voltage of 10VDC. The problem is that most transceivers quit at about 11.5VDC, well before the battery reaches its terminal voltage. The result is that you get somewhat less than the rated capacity from the battery in that application. You should probably plan on getting about 60AH out of a 75AH battery with a typical transceiver.

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KC7YE
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« Reply #4 on: July 16, 2013, 04:24:19 PM »

I operate /m as live in condo. Using about same setup. Blemish deep cycle battery, IC 706 or IC718, CW. get 7 - 8 hours or more. More then can sit in car ! Charge from aux plug while under way. First outing was 2012 Washington Salmon Run, never ran out of battery, just steam. Couple other WA's did same, we covered the SE corner of WA. Go for it.
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AC4RD
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« Reply #5 on: July 16, 2013, 04:30:53 PM »

James, I've done some operating from the 706 in my car, just sitting with the engine off, over the years.  (I've had the same 706mk2g for around 10 years now--it's been in four different cars so far.)  ;-)   I don't have specifics, but you should get lots of operating out of a 75AH battery.  And if you have an isolator of some kind, so you can run the engine every hour or so, for 10-20 minutes charging both the car battery and your HF battery, you should have NO problems, I think.  A dozen times over the years, I've operated from the car for an afternoon.  Run the engine for 10-20 minutes every hour and I've always been fine.

Have fun, OM!  There can be a bunch of fun in operating like that!  73!  --ken
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KB4QAA
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« Reply #6 on: July 16, 2013, 04:56:19 PM »

I use a 32Ah AGM battery with a 706 and get 6-7 hours from mostly rx ops.  I would estimate that you would get about 12 hours from your battery.

Remember, you can only get the full amp-hour rating out of a battery once!  Smiley
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N7GCO
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« Reply #7 on: July 16, 2013, 10:45:13 PM »

Thanks everyone for the feedback. Got what I needed to move ahead.
Mel
N7GCO
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