K1JAW / qrp

A "Primary" battery is your disposable battery, and a "Secondary" battery is a rechargeable. Choosing the best battery is not always the easiest. Gel cells are financially efficient. That means they are easy to obtain, they can be "timed" charged at a rate of C/10. (This means that you look at the capacity of the battery, 8 amps for example, and charge it with a charger that is capable of .8 amps or 800 ma for 12 - 15 hours max). This should not be done with other chemistry batteries except in a pinch!. If you do not discharge them below 11 volts, and you keep them charged, they will last a long time. They are heavy. NiCads are old technology so save your money; and NiMH are becoming reasonably priced although a good charger is required. I keep a set of Duracel "primary" batteries with me, up to last year (2009) I used 8 Ah Gel cell chemistry; and this year I have converted over to 3.6 Ah NiMH to work with my solar panel. There are also other options which you will find with the link below. For the record, I am not a proponent of "Deep Cycle" batteries.

2. CHARGING

Every battery chemistry is different and so are the methods of charging them. If you want your batteries to last a long time, then learn the correct method for charging, use, and storage. The three worst processes that you can do is overcharge the battery, deplete the battery totally, and use the wrong charging method. You should not use a NiCad charger on a NiMH, or a automobile charger on a gel cell. Once you choose a battery type, study the specifications, and follow the manufacturer's recommendations. Your batteries will last a long time if you follow proper maintenance procedure. Here is a good "in English" source for all batteries: Powerstream Battery FAQ.

3. HOW MUCH BATTERY POWER DO I NEED

1. Knowing your operating habits -

Easy – right? Lets start by saying that your operating habits are totally different for contest, and for casual operating.

During a full week of hill topping, I turned the radio on at 1000, and off at 1400 for a total of 4 hours per day. (This kept me out of hot water with the family.) After turning the radio on, I got a cup of coffee, organized myself, tuned the antenna, and called a station at 1020 and spoke for 20 minutes on CW. After that I got another cup of coffee, a snack, and at 1040 I made my second contact. This continued until lunch when I stopped for 30 minutes then started a similar process until 1400. Typically, I talk as much as I listen. This translates to the radio is on for 4 hours (240 minutes); I only operate for 100 minutes of which 50 minutes is talking;

Therefore, my transmitting operating duty cycle is 50/240 = .21

2. Knowing the duty cycle of SSB, CW, FM, PSK etc.

Here is where I am going to get into trouble so – lets KISS. If you use CW or SSB, consider that your duty cycle is 50% (0.50). For all others, consider 100%(1.0). To be honest, there are many modes that I am not familiar with and may be surprised by, but this is not suppose to be a tutorial, just a primer.

<Remember the two underlined decimals above> ( RED)

Keeping the values the same (Ugh!) Watts = P = E I = Volts x Current

Batteries are in Amp hours, transmitters are in Watts, fuses are in amps, and volts are doing the work for the ride. Lets start by looking at the your manual’s specification and find the “no-signal” current draw. This is the amount of power that your radio will consume for each hour of operation. In my case, my K1 draws <100 milliamps (1/10 amp) x 12 volts (1.20 watts). That was easy! Now, using the ammeter on my DVM, I measured my current draw during key down into a dummy load and found that my K1 draws <1000 milliamps (1 amp). <I have rounded numbers for simplicity>

Amps X Volts = Watts or, (Transmit) 1 amp x 12 volts = 12.00 Watts (transmit on for and hour)

Total Xmit duty cycle in watts (per hour)

.21 (above) x ..50 (CW) = .105 x 12 watts = 1.26 watts for my hourly transmit power usage

Plus Receive (last paragraph) 1/10amp x 12 volts = 1.20 watts

Total Watts used per Hour is 2.46 watts

3. Almost there – Sizing the Battery

I know that I want to operate four hours a day for five days so:

4 hours x 5 days x 2.46 watts = 49.2 watt hours is required at 12 volts

49.2 / 12 = 4.1 amp hours x 1.25 battery (in)-efficiency = 5.12 Amp Hour battery required.

Therefore, I should (and can) be able to operate for the full week with a 8 Amp Hour battery. I have a 8AH gel cell that fits into my backpack and it never hiccupped! Hope this made sense! 73’s

WARNING – If you are not using a regulator / battery disconnect, pay attention to your voltage and do not go under 11.5 volts as it is bad for the battery, and will put some radios into oscillation.

This page was last updated on 07/06/10.