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Author Topic: Emergency Power  (Read 1100 times)
KB9ZDD
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Posts: 2




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« on: May 24, 2004, 01:07:22 AM »

Here is a question that I am sure has been answered many times, but I am going to ask it anyway.

I have aquired several lead acid deep cycle batteries in good condition. I have built an vented enclosure for them and have enough 00 welding cable to run to the shack. (about 10 feet)
what I would like to do, is to run the 12volt equipment in my shack from the batteries, and use a charger to maintain the batts. That way, if the power goes out, there is no switching nessarey. (I am somtimes the net control station for the local Skywarn net. losing power in the middle would be bad.)

Several Questions.

Does anyone have a design for a charger that can maintain several 12volt battries? I would like one that could put out several amps, but that will not overcharge the batts. I would really like to build this myself, both because I am cheap, and because I like to build things.  

How do I prevent the charger from trying to provide too much current when the radios are transmitting. I could see if the radios are pulling 10amps from the batts, the charger going up in smoke if it tries to provide it, rather than letting the batts.

How do I figure out how long the batteries will last?
I know that the only way to be sure is to disconnect the charger and try it, but I would like a rough estimate.

sorry for the poor spelling.

Thanks
Mike
KB9ZDD
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KI4BUM
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Posts: 59


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« Reply #1 on: May 24, 2004, 01:47:16 PM »

> Does anyone have a design for a charger that can
> maintain several 12volt battries? I would like one
> that could put out several amps, but that will not
> overcharge the batts. I would really like to build
> this myself, both because I am cheap, and because I
> like to build things.

Not built this myself but here's a link to get you started. It's a solar charger but it should give you an idea on how to do it.

http://www.redrok.com/electron.htm#charger


> How do I prevent the charger from trying to provide
> too much current when the radios are transmitting.

Commercial chargers have a limit to the amount of current they will provide. Mine has a trickle, 5amp and 15amp setting.


> How do I figure out how long the batteries will
> last? I know that the only way to be sure is to
> disconnect the charger and try it, but I would like
> a rough estimate.

First you have to figure out your average drain. Check the Emergency Communication section for various estimates based on receive vs transmit ratio, or Im sure someone will post the math.

I have a link in my bookmarks at home (currently at work) to a website where you can type in your usage and battery backup size and it will tell you expected run time. I'll post it when I get home.
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KI4BUM
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Posts: 59


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« Reply #2 on: May 24, 2004, 03:04:54 PM »

http://www.voltageconverters.com/faq.htm#15

Link to "how long can I run" tool
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KC8VWM
Member

Posts: 3121




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« Reply #3 on: May 25, 2004, 11:20:57 PM »

>>Does anyone have a design for a charger that can maintain several 12volt battries? <<<

Ahhh.. my favorite subject I have an entire website dedicated to the subject of emergency backup power.

http://www.angelfire.com/on/cbushell/solar/solar1.html

Enjoy,

Charles - KC8VWM
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KD5JFT
Member

Posts: 82




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« Reply #4 on: May 29, 2004, 02:13:36 AM »

I have a 128AmpHr battery bank with a Guest three stage charger.  The battery bank is wired in parallel (diode isolated) with an Astron RS-70M power supply.  When the AC is on, the Astron supplies the power.  When the AC is down, the battery bank supplies the power.  I have been transmitting when the AC went poof, and the radio didn't even notice.  The batteries will power the radios, computer, etc for several days of normal usage.  If you want to try something like this, let me know.  I am planning to re-build all of this and can supply diagrams, notes, etc, that might help you.

KD5JFT
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W0IPL
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Posts: 410


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« Reply #5 on: May 29, 2004, 03:21:46 PM »

One item I don't see in your question: How well do your radios do on 12 Volts? There are many radios that will work on 12V but at a noticable reduction in output power (IC-706 is one of them). Those will do VERY well on 13.8 volts but as noted above not do too sooper on 12.

I run an Astron N2412-24 regulator. It takes two 12V batteries in series to deliver the 24 volts but produces regulated (spec's are .01 volt variation from no load to 20 amps) 13.8 output (24 amp momentary max current).

Just a thought.

C Ya
 Pat
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AA4PB
Member

Posts: 13032




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« Reply #6 on: June 04, 2004, 02:40:17 PM »

I just found this web page. http://www.powerstream.com
They have a 700W peak, 20A continuous output 12V to 12V converter. It takes 10VDC to 15VDC input and provides a regulated 13.8VDC output. Efficiency is >85% and cost is $114. Not bad!
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CROOKIE
Member

Posts: 41




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« Reply #7 on: June 05, 2004, 01:13:48 PM »

In VHF/UHF mobile radios, what brands (models?) run well (at/near full output) at 12.0V +/- vs. what ones want to be nearer 13.8V? Also how about absolute shutdown voltage vs brands (models?), as sooner or later the batteries will run down below 12V?

For the ones that have trouble, is it just drop off of output power (and what percentage typically), or is receive sensitivity/selectivity/etc. also compromised.
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K2GW
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Posts: 535


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« Reply #8 on: August 26, 2004, 10:48:25 PM »

For a simple way to float gel cells for emergency power, see the September 2004 QST Hints & Kinks column.  

73

Gary, K2GW
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