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Author Topic: alternative power  (Read 1518 times)
VK4TJF
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« on: December 02, 2010, 03:06:59 AM »

I have an Icom 706 that i use for mobile
I was thinking of getting a 100 amp hour gel cell
and having that in the back of my pick up with
some connectors so that when i go portable for
a few hours all i have to do is disconnect the radio
from the car battery and hook it up to the gel cell
has anyone done this before and how long have you
been able to operate the Icom 706 for
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K0BG
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« Reply #1 on: December 02, 2010, 06:06:33 AM »

If you use a gel cell, you'll need to come up with a convenient way to charge it. Unlike a lead acid, you can't just connect it to the vehicle's wiring.

The best way to do this is use an AGM with a large reserve capacity like an Optima YellowTop. Even then, you'll need to be careful about how you hook it to the charging system.

If you're just switching the power to the radio, and using a wall charger to charge the gel cell, that's easy. However, it get old quickly!

There is more on the subject on my web site under Alternators & Batteries.
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WX7G
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« Reply #2 on: December 02, 2010, 07:02:46 AM »

The IC-706 draws 2 amps in receive. In key down transmit it draws 20 amps. Given the duty cycle of SSB and talking half the time the average operating current will not exceed 3 amps. Four hours on the car battery at 3 amps and you have used 12 amp-hours of charge. Do you really need a second battery?
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K0BG
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« Reply #3 on: December 02, 2010, 08:53:10 AM »

Hum, I wonder. If the fan is running, it alone draws nearly 1 full amp. It's not a stretch therefore, that the average draw could be about 5 amps depending on a lot of factors, so let's assume it does. Your average SLI battery has a C5 reserve capacity of about 200 minutes, at which time the voltage, under load, will be down to the discharge point of 10.5 volts. While some capacity recovery occurs, this point of discharge won't start your average vehicle reliably in warm weather, much less cold weather. So I'm of the opinion that a second battery is the best alternative when operating stationary mobile or portable operation.

Thinking about this a little further....

Your average 706 will shut itself down when the supply voltage drops below about 11.6 vdc. It's difficult to calculate at which point this would occur with an average SLI battery. I further suspect, that most people would use a battery booster. They're about 80% efficient, so that draw has to be considered too. Too many ifs for my money.
« Last Edit: December 02, 2010, 08:59:24 AM by Alan Applegate » Logged

K5LXP
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« Reply #4 on: December 02, 2010, 11:35:38 AM »

Anytime you start to consider the use of batteries as power sources you really need to have a clear idea of the load, in terms of currents and times.  Radios are not static loads so the average and peak draws along with duty cycle make an enormous difference.

If this is just casual operating, where you go out to a park or you operate while you're out camping for an hour or two, I wouldn't sweat the details too much.  Just connect up to the car battery and have at it.  But if this amounts to more serious operating in terms of length of time or number of outings, having a source separate from the vehicle is probably a good idea and should be selected based on the actual load you'll be using.

I've successfully used my 706 in a variety of portable operating venues, from QRP using 7Ah gels to solar to extended operating from storage batteries.  Battery life/run time can be readily modeled in a spreadsheet.


Mark K5LXP
Albuquerque, NM
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AF6WI
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« Reply #5 on: December 02, 2010, 01:41:23 PM »

I have a gel cell that's something over a hundred ampHours; see photo: http://civex.smugmug.com/Holidays/Saline-Valley-Thanksgiving/DSCF1946/253863505_uDvHV-M.jpg

It weighs 70 lbs. Be very careful how you secure your battery. You need to be concerned about it flying around during a traffic accident, and you need to be concerned about it when you're on bumpy roads - you don't want the case cracking or for it to come loose.

I only use the battery during portable operation at long campouts, and it works fine for me. I charge it at home on a trickle charger that's got a switch for gel and for regular lead-acid batteries. I recommend having a hundred+ ampHour battery for emergency use, and it's a bonus that my wife and I can use it on our camping trips and on long days at fund-raisers where we do comms. Makes the price of the battery and charger easier to support.
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K1CJS
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« Reply #6 on: December 04, 2010, 05:28:59 AM »

If you don't mind the fact that you have to watch the battery and manually connect and disconnect a charging connection, wire up an auxiliary 12 volt power socket in your vehicle and charge the gel cell with a connection to a cigarette lighter plug.  You have to watch the gel cell to make sure it doesn't overheat, but that may be the simplest way to recharge it. 

Set it up so there is an obvious indicator that would let you know the cell is connected, and unplug it when you leave the vehicle.  You could also use a toggle switch to disconnect, but there is too much of a chance that the switch may be accidently hit and be left on.  The cigarette lighter plug/socket doesn't have that danger, and a plug with an integral fuse (I use a ten amp fuse in my setup) will protect the setup from an overcurrent condition.

I've been recharging a small bank of SLA cells (4-12 volt 7 AH cells) that way for years, and I've never had a problem with them or the car wiring.
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WX7G
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« Reply #7 on: December 04, 2010, 09:20:41 AM »

Your average 706 will shut itself down when the supply voltage drops below about 11.6 vdc.

With the IC-706 shutting down at 11.6 volts there is built-in protection against discharging the vehicle battery so far that the vehicle will not start. The next step is to try the proposed operation and see if the vehicle battery will run the rig for the time desired.

Having operated 100 watt transceivers during field day using standard car batteries I can say with confidence that 5 amps is not the average current draw. 3 amps is closer to the real number.
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