I mentioned earlier that manufacturer claims are overly generous. Whatever performance you get on Day One, it will only go down from there. There is also the rule of diminishing returns: From the moment a battery is placed into service, its abilities begin to degrade. Even identical batteries can yield different results due to small inconsistencies in the manufacturing process. Keeping your duty cycle low ( ie, don’t run your mouth on the air too much) will stretch battery life.īattery performance varies greatly depending on the temperature, age of the battery, and internal characteristics. If your duty cycle is 50%, that means you split your radio time equally between talking and listening. Duty cycle and why it matters.ĭuty cycle is expressed as a percentage and is the term used to describe the ratio of transmit to receive. In fact, the radio will draw continuous peak power only when transmitting in the AM mode, which is seldom used anyway. A modulated signal will cause the current to swing up and down, hitting the peaks only momentarily. Under most conditions an amateur will be transmitting only part of the time, and even then, the radio will not continuously pull maximum amperage. As we’ll find out soon, these estimates are way overstated.īut first let’s deconstruct this. In the receive only mode, assuming an average of 1 amp, the battery will go for 35 hours. Following the math, the 35 amp-hour battery should push James’ 22 amp transmitter for a little over ninety minutes. The 0.5C-rate (or c/2) would be 17.5 amps for two hours, and so on. So what can he realistically expect from this setup?Ī 35 amp hour battery can provide 35 amps for one hour. He plans on adding a solar panel at a later time. James wants to run his radio with a 35 amp hour AGM battery and charge it with a 2 amp plug in charger. The official Yaesu specifications state that this radio consumes maximum 22 amps/304 watts on transmit, and 0.55-1.5 amps/8-21 watts on receive depending on the audio level (these numbers are rounded). Off Grid Ham reader James (whose question was the inspiration for this article) asked about going off grid with his Yaesu FT-450 radio. Before you can know how much battery you “need”, first find out how much power all your stuff consumes and what you plan on doing with it in the real world. It certainly does not help that many of the answers floating around the internet are based on guessing, hypothetical conditions, and overly generous manufacturer data. Before asking the question, provide some answers. The question is too open ended and comes with too many variables to give a definitive answer, but there are some basic battery concepts that will help you sort through this confusing topic. It’s always some variation of “How big of a battery do I need to run my (fill in the blank) radio?” It comes up a lot, not just in my email but also on the various forums and blogs I visit.
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