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Author Topic: Portable station w/ 706 Mk2G  (Read 2563 times)
KE7KPY
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Posts: 4




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« on: March 27, 2009, 10:44:30 PM »

I am building a portable station to run QRP(no more than 10 watts)and am wondering if this battery/solar combo should fit my needs:

http://www.ctsolar.com/index.asp?PageAction=VIEWPROD&ProdID=5

http://www.replacementupsbattery.com/ub1280.html

The battery is an 8A gellcell @ 12V and the solar panel is a 10.4 watt @ .75A

As long as I don't run over 10W of power , I should be fine right?
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KC9ATJ
Member

Posts: 88




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« Reply #1 on: March 29, 2009, 06:27:13 AM »

how long are you planning on running portable for?  I did the math, and with just having the radio on, you will only be able to use it for about 20 hours, assuming you have plenty of sunlight during the entire time.

With the battery, to figure out how long you can use it for, you take the number of Ah and multiply by three (I think that number is right, hopefuly someone will come by and confirm it for us).  8x3=24

I then looked up how much power the mk2g used. It said that it used 1.8-2.0 A.  Subtract the power from the solar system that your planning on using and we come up with 1.05-1.25 A.

Now we divide 24 by the number of amps that we are using:

24/1.25=19.2 hours
24/1.05=22.9 hours

And remember this is assuming that you have full sunlight for the entire period.  So realisticlly, we are looking at 14 hours at best.  This isn't even taking into consideration any transmitting that you will be doing.

Also, you want to take into account your duty cycle and how much power you plan on using.  You said max 10 watts, which is definately good, we have a starting point.  You also need to figure out how long in an hour you plan on transmitting.  Listening for 45 minutes and transmitting for 15 is usually what your average op will use when planning on using battery power (3:1).

Let's assume that it takes 3 amps to transmit at 10 watts.  since we are assuming a 3:1 ratio we take (2A x 3) + (3A x 1) = 9

We then divide the 9 by the 4 parts to get an average for the hour

9/4=2.25A

If we then take the solar panel into the equation, it brings it down to 2A an hour.

24/2=12 hours of maximum operating time.

Remember, this is mostly just assumptions.  I'm not completly sure on the power drain that the mk2g has when transmitting.  Also, if you have any cloud cover during the day, that will help to drain that battery quicker.

I would recomend that you either get a bigger battery, a bigger solar panel, or a different radio that uses less power to operate.

If you have anymore questions, please feel free to ask.  Their are many knowledgable people on here.

Joel
KC9ATJ
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KC9ATJ
Member

Posts: 88




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« Reply #2 on: March 29, 2009, 06:30:47 AM »

Also, I just did the math, you can use full power and you will have a little less then 4 hours with the battery and solar panel that you are using.  Just so that you know that you can use full power for a little bit, and possibly the entire time if you aren't planning on being out for long.

KC9ATJ
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AA4PB
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Posts: 15022




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« Reply #3 on: March 29, 2009, 11:16:21 AM »

You need to be very careful about connecting a solar panel without a charge controller. A 10W solar panel (which has an open-circuit output voltage of 18-20V) can cook an 8A gel cell battery in a relatively short time if left connected to a fully charged battery. You can monitor charge current and voltage manually but its better to let an inexpensive charge controller do it for you.

The issue with the 706 for QRP is that the receive current is 1.8-2A or about 27W of continuous power draw from the battery. A 10W transmitter's average power (given the Tx/Rx duty cycle) is probably considerably less. The lower receive current is a major benefit of most of the radios designed for QRP operation. Of course if you have the 706 then you use what you have.
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Bob  AA4PB
Garrisonville, VA
KD4LLA
Member

Posts: 509




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« Reply #4 on: April 05, 2009, 08:29:02 AM »

I have a working solar system now.  I would buy the battery first and see if it will accomplish on its own what you want it to do.  Then when you have a baseline of what the battery will handle you can calculate what you need for a recharging it.  You will also need to remember that after the battery drops below about 10.5 volts your 706 will not work.  Hence the solar panel you intend to buy will not provide enough amps to charge and operate the radio.  I have a 60 watt solar panel, charge controller, and deepcycle battery working at my shack now.

Mike
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AA4PB
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Posts: 15022




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« Reply #5 on: April 05, 2009, 11:49:13 AM »

My IC-706Mk2G drops out at about 11.5V.
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Bob  AA4PB
Garrisonville, VA
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