Wednesday, March 20, 2013

Ohm's Law and Battery Life

Remember Ohm's Law?  Tonight we are going to use it to learn a few things about battery operated radios and battery life.  In the following calculations no allowance is made for the power consumed by the radio itself.  All calculations assume the radio itself consumes no power and that all power used is converted into the transmitted radio signal.

You remember that P=V*I or Power equals voltage times current.  We will be solving for current, so the formula will become I=P/V.

First let's figure the power consumption for a radio producing 5 Watts with various batteries.

5 WATTS

VOLTS         AMPS
12V               0.42A
7.4V              0.68A
6.2V              0.81A
5.4V              0.923A

Actually, most hand held radios only produce 5 Watts when they have 12 volts coming in.  Many radios that are capable of 5 Watts and advertised as such produce only 4 Watts or less when the input voltage is less than 12 Volts.  Let's run the numbers for a 4 Watt radio.

4 WATTS

VOLTS     AMPS
12V           0.333A
7.4V          0.54A
6.2V          0.65A
5.4V          0.74A

Notice that for ANY amount of power output by the radio, the lower voltage batteries draw more current.  The lower the voltage, the greater the amps consumed.  Ohm's Law wins again!

What this means is that for any given radio at any given power setting, the lower voltage batteries are going to run out of "oomph" faster than the higher voltage batteries because of greater current drain.

Remember, a battery can sit around for weeks producing 12 volts at its terminals with no load attached.  Attach a load and the instant result is current drain.  It is that current drain that "exhausts" the battery and pulls it down into a state where it requires a recharge.

This is why you want hand held radios that have a jack on the side that will accept 12 volts.  Your 12 volt battery (with the exact same current or AmpHour rating) will last longer than the built in battery.  Add a 12 Volt battery with a much higher current rating, such as a 12 Volt 7 AmpHour Gel Cell, and you GREATLY increase your potential on air time!

How do you get this 12 volts?  Most modern radios have an optional battery replacement back that has a cord coming out of it with a cigarette lighter plug on the end.  Others have an actual 12 volt jack on the side.

If at all possible, get an emergency 12 volt source for your radio for use in emergencies.

Also, remember that your radio operates at THREE different power levels.  1) Power on but no audio, squelch is unbroken.  2) Power on and audio is being received.  3) Power on and the operator is transmitting (key down mode).  You can attach an external power source with a current meter in the circuit to find out the actual current draw for your particular radio.  It is educational.

N7OZH



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Thursday, March 07, 2013

MARA Net Mar 06 2013

You can get 12 volt 7 Ah gel cells from Amazon.  Very reasonable prices ( $16.89 with free shipping).  Check here:

http://www.amazon.com/dp/B002QGVWBW/ref=dra_a_cs_mr_hn_it_P1300_1000?tag=dradis-20

12 VDC 30A power supply
Available on eBay.  Various prices.  Best deal I found was $29.95 including shipping.  It ships from Portland, Oregon and generally arrives about 2 or 3 days after your payment clears.  Search eBay for seller richard0596022762011.
You can see his eBay ad here:
http://tinyurl.com/b5n2jsf

Sources for Wouxon, Beofang, TYT radios and QJE Power Supplies 
(as well as other ham gear.)


Universal Radio Inc.
www.universal-radio.com

Lentini Communications
www.lentinicomm.com

Austin Amateur Radio Supply
www.aaradio.com

Radio City, Inc.
www.radioinc.com

Associated Radio
www.associatedradio.com

Quicksilver Radio
www.qsradio.com

PowerWerx
www.powerwerx.com

PowerWerx is also your PRIME source for genuine Anderson Powerpole products and tools.  Some of the eBay sellers are substituting other brands which sometimes do not meet specifications.

There is some interesting Ham Radio Emergency Preparedness information here:

Here are the Emergency Preparedness suppliers who were showing their products at the recent gun show at the SouthTown Expo Center.

1st Survival Gear
867 So. Bluff St.
St. George, Utah 84770
Toll Free phone # 855-212-3816
Call them to find out where and when they are exhibiting in Salt Lake again.  They have complete first aid kits and they also sell all the supplies individually.

Ready Now Survival sells all sorts of survival gear and supplies.

Wild West Jerky sells all sorts of Jerky and other smoked meats.

Got Preparedness Supplies sells a wide variety of emergency preparedness supplies.  They are in Orem and you can reach them by phone (801-769-6181) or on the web.
============================
The next Crossroads of the West Gun Show is at the South Town Expo Center on April 13th and 14th.  More info here: http://www.crossroadsgunshows.com/calendar.php

The other gun show is the Rocky Mountain Gun Show.  Their next show is March 30 and 31 in Layton.  More info here: http://rockymountaingunshow.com/component/dtregister/?controller=event
============================

CyberGuys has TONS of items for cable management, data storage and general electronics.  They add hundreds of new items each month.  This is a fascinating web site to browse through.  You'll find tools and gadgets to solve problems you didn't even know you had!
http://www.CyberGuys.com

Here is a gadget I have purchased several of for use with ham radio and also with computers.
http://www.cyberguys.com/product-listings/?categoryid=588

SMA to BNC Adapters
SMA connectors were never intended to be used on ham radios or any other type of radios.  They break off too easily and are notorious for twisting off the center pin on your HT radio antenna.  The majority of antennas are available for BNC connectors.  The solution is to get an adapter which ads strength and also makes it easier to connect your HT to an outside antenna.  Here is the unit you want on eBay:

And here is an eBay ad showing the type of SMA to BNC connector that you NEVER want to use on your ham radio.  Using one of these is GUARANTEED to break off your antenna connector because it does not have a wide, stable base.

EComm Hamfest in Ogden April 20

Utah Amateur Radio Club

Utah VHF Society
LOTS of ham radio information on this site as well as a listing of Utah Repeaters, info on linked sytems throughout the western United States, the Utah VHF/UHF bandplan, Utah Simplex Frequencies, D-Star info and LOTS more.  A valuable and useful resource.

Here's your chance to win a free OOMA Telo and cut your home land line phone bill to just $3.73 per month.  Just go to this website and "Like" OOMA on facebook and you are entered to win.

Want to know more about OOMA?  Go here:  http://www.ooma.com/

HARBOR FREIGHT
Harbor Freight is having their GIANT parking lot sale this weekend.  Don't miss out - the savings are huge.  More info here: http://tinyurl.com/clm3xdw
At the bottom of their ad you can sign up to have coupons and news of special sales mailed to you.  This is how you get the best prices.  It is an interesting experience to be in line at the register and see someone in front of you buying the same item you have, but he is paying 75% more because he does not have the coupons that come in the mail!

Something Different
Here's something totally unrelated to anything we have discussed here tonight.  Hope you enjoy it!
http://www.youtube.com/watch?v=nvfjIY-THZE

That's enough for today - more next week.
N7OZH




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