Every amateur radio operator ought to have a go-bag. That is, a bag that the amateur can pick up on a moment’s notice, go out into the field with it, and begin transmitting after setting up his or her station.
One of the elements of a go-bag is an energy source. But what should you get? While much of that will depend on details of what the likely application is to be, this blog post will discuss the considerations of different technologies and will address the energy required to be running a mobile station in the field (i.e. 50 Watts).
The first consideration is to address what capacity is required. To do this we have to estimate the duty-cycle. That is, how long will the battery be in operation until it can be recharged. Then the amateur will want to estimate the expected ratio of transmit to receive time. With heavy transmitter use, a viable ratio might be 50%. But perhaps the station will be primarily in receive mode with an estimated use ratio of 5%.
What energy will be demanded by the transceiver? You might want to allow for full power operation of the transceiver. To address this question, it is easier to define an energy capacity question in terms of current. You will want to consult the owner’s manual specifications page for your transceiver to see what current it demands given the transmit power setting. Battery capacities are commonly defined in terms of Ampere-hours. That is, the battery will supply so many Amperes current for so many hours. Multiply the duty-cycle figure (hours between recharge) by the transmit ratio. Suppose a transceiver is specified to demand 13 Amperes and your time to required recharge is 10 hours and the transmit ratio is 0.2. Multiply 13A by 10H by 0.2 for an Ah specification of 26 Ampere-hours. Your battery will need to be specified to have a capacity of 26Ah.
But what battery technology should you get. Many times a personal budget defines what technology to get (the cheapest) simplifying things. Because this is for a go-bag application, we want to minimize weight. Therefore an energy density figure is helpful to know. There are three Lithium-Ion technologies commonly used and among these, Lithium-Ion Phosphate is among those having the largest density (Wh/kg). It also will recharge more than the others before collapsing its current delivery capability–typically 2,000 cycles.
One thing to be particularly aware of is that you cannot parallel all Lithium-Ion batteries for increased capacity. Any battery that you buy will clearly state on the box not to parallel the battery if that is the case. This may seem like an odd requirement but this is the case for those batteries having a BMS (battery management system). A BMS is very beneficial in that it protects the battery from you. For example, when the battery state-of-charge reaches a low level, the BMS will shut off current flow to protect the battery from going into a deep discharge which shortens its life.
Another consideration is weight. This was partially addressed above with a density consideration. You want to pack the biggest punch in the smallest (and lightest) package.
One thing to be particularly aware of is to protect the battery from hazardous shorting conditions. These things cause first that you cannot put out! It is highly recommended that you get a carry bag roughly fitting your battery that will ONLY hold the battery.
It is also recommended that you use Powerpoles for all of your equipment electrical hookup needs. Configure the leads in such a way that they are easy to deploy while safe to pack up in the battery carry bag.
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