How Much Does Emergency Power Cost?

Some folks are criticizing the ARRL for not modifying the Field Day rules in response to the Wuhan virus epidemic. Most of them are looking for a way to operate Field Day from home but still have a club score of some kind. I posted my thoughts here: Don’t Mess With The Field Day Rules.

The Field Day (FD) rules allow for a home station with commercial power to participate in FD as a Class D station. However, Class D stations cannot work other Class D stations for points. If the home station has emergency power (batteries, gasoline generator, etc.), then it is a Class E station that can work all FD stations for point credit.

Emergency Power: Too Difficult?

I’ve heard some hams argue that it is too difficult to set up emergency power for their home station. In many cases, the argument is actually that it is too expensive to do this.  I can see this point if you run out and buy a name brand gasoline generator…a Honda EU1000i costs about $950.

This raises the question of what is the lowest-cost way to equip a home station for emergency power?  Let’s consider the case of a typical 100W HF transceiver such as an IC-7300 or FT-991A. These radios require a 12 V power supply at 22 A maximum on transmit. Receive current is much lower, typically 1 to 2 A. Under FD rules, we don’t need to power our computer or other accessories from emergency power, just the radio. If we assume a 50% duty cycle, this class of radio consumes about (22+2)/2 = 12 A average current. (Yes, you could choose to operate QRP and really stretch the battery but let’s stay with the 100 W scenario.)

Get A Battery

So what is the cheapest way to get this done? Let’s take a look at using a deep-cycle battery. Walmart has an RV/Marine battery for $75, rated at 101 AH. Assuming 12 A of current, this battery would support about 8 hours of radio operating. This is going to be way short of the 24 hour operating period of FD but it might be enough to support a less intense operation.  We could also do some things to stretch out the battery life, such as reducing our transmit power. Dropping to 50 W would roughly double the operating time to 16 hours, which should be enough for a single-operator station.

Of course, another option is to double the battery capacity by using two batteries. These amp-hour ratings on batteries are always a bit idealistic and our transmit duty cycle might be more than 50%. Let’s assume we buy two batteries to give extra margin and allow us to run 100W. We will also need a simple charger, which costs about $25. So there you have it, 2 x $75 plus $25 = $175 for a decent emergency power source.  (If we decide to use only one battery, the cost drops to $100.)

Now $175 is a significant investment and only you can judge how well your ham radio budget can support this. For many people, this is affordable and the real question becomes is this how you want to spend my hard-earned cash.

This is my best shot at a low-cost emergency power source. Do you have a better idea?

73 Bob K0NR

The post How Much Does Emergency Power Cost? appeared first on The KØNR Radio Site.

Bob Witte, KØNR, is a regular contributor to AmateurRadio.com and writes from Colorado, USA. Contact him at [email protected].

One Response to “How Much Does Emergency Power Cost?”

  • Logan, KE7AZ:

    When I was active in ARES and lived in earthquake country, emergency power was a big consideration. Power Sonic has a very detailed technical manual that provides “everything your need to know” about AGM batteries. In this manual, we found out that the amp hour rating is for current draw over a 20 hour period down to a battery voltage of 10.5V. Our equipment stops operating at about 11.7v, per spec. Using the Power Sonic curves and the 11.7 v limit, 240 Ah will provide 12 hours of operation. That is only half of the desired 24 hour operating time. If you want to get down to the 10.5 v you will need a battery booster. That will get you to about 20 hrs. As Tim, “The Toolman”, Taylor might say, “More Power.”

    On the other hand, given the practicalities of Field Day, like sleeping, eating, bio breaks, etc, maybe 12 hours is enough.

    One last thing to consider is weight. Two 100 Ah batteries will weigh in at about 150 pounds. That’s a lot of lead to move.

    This year’s Field Day will be different and it should be interesting.

    Good Luck and 73
    Logan, KE7AZ

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