Battery

Cells and Batteries

AF5NP Battery, Cell, Emergency Communications (EmComm), Power, Primary, Rechargeable

Batteries are quite important to radio amateurs, especially when working portable or when using handheld transceivers.  There are a number of US license exam questions on the subject and hams should have a fair understanding of batteries and how they are used in amateur radio.

Figure T-1
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Let’s start with some terminology.  A battery is a collection of electrochemical (galvanic) cells connected in series (greater voltage) or parallel (more current) for a given application. The schematic symbol above hints that there is more than one cell in series to represent a generic battery. More on cells vs batteries at the end of this post.

There are various battery types and many battery sizes but for all applications–not just ham radio–there are two basic kinds of battery: Primary and Secondary.

Primary batteries are used once, then disposed of (non-rechargeable). Years ago these were mainly carbon-zinc composition but today we find alkaline and lithium give better performance and are more commonly used, along with smaller coin cell silver oxide and mercury compositions. The advantages of primary batteries or cells over secondary ones are higher energy per unit, longer storage times, and instant readiness.

Secondary batteries are rechargeable, which is their only real advantage over primary batteries. The most common rechargeable battery technologies today are lead-acid, Nickel-Cadmium, Nickel-Metal Hydride and Lithium-ion, and all are used in ham radio.

What does this really mean for hams?

Many years ago, radios used vacuum tubes (electron valves) and required multiple high voltages. Two or three different dry cell batteries were used, often wired in series, and they had to be replaced frequently. Be glad those days are long gone.

Nowadays modern ham radio gear runs off 12V DC power or lower, and there are occasions to use either primary or secondary batteries. Generally, secondary (rechargeable) batteries are preferred most of the time. The typical handheld transceiver (HT) comes with a rechargeable battery pack. Working portable HF or VHF/UHF with no AC power requires a battery, and this is almost always a secondary unit (lead-acid or Lithium-ion brick).

One instance where non-rechargeable (primary) batteries is smart is when using a HT in an emergency situation where there is no power or facility to recharge the unit. You can buy accessory primary battery packs for many HTs. It’s a good idea to keep one of these available along with spare alkaline or lithium cells in your go-kit for a real-life EmComm scenario. AA cells can almost always be purchased or scrounged in an emergency.

HT with stock rechargeable battery (7.2V) on right, AA pack (6×1.5=9V) on left

The lead-acid battery is still a primary reference in ham radio, largely because it is a vehicle’s power source for starting engines and powering on-board electronics (including mobile ham radio equipment). In fact, the 12V power standard for most modern ham gear derives from the car battery and is really 12.6V nominal with 13.6V standard level as when a car’s alternator is running to charge the lead-acid battery. That’s why ham radio 12V DC power supplies typically run around 13.5 to 13.8V; our equipment is designed for in-vehicle operation with a running engine.

12V lead-acid batteries for non-vehicle use often are sealed (SLA) with a gel electrolyte instead of liquid, making them less hazardous to handle and store. Absorbent glass mat (AGM) batteries are a similar variant of the lead-acid battery. All of these tend to deplete at around 10.5V. Draining the battery below this level may compromise its ability to fully re-charge, and possibly damage the battery.

The main advantages of lead-acid batteries are that they are relatively simple, inexpensive, durable, dependable, with low self-discharge rates yet capable of high discharge rates. Disadvantages of SLA or AGM batteries include bulk and weight (very heavy), limited number of full discharge cycles, limited discharge (not deep-cycle), and environmental concerns (hazardous waste).

Lithium-ion polymer (LiPo) technology is relatively new but is perhaps the best performing rechargeable battery as of this writing, and is relatively light weight, making it ideal for radio amateur portable use; very popular today. One manufacturer has ham-specific lithium ion phosphate (LiFePO4) products and even has equipment operating charts to help select an appropriate battery. A bit expensive but worth it to portable operators or those looking for emergency backup power.

One advantage of Nickel-Cadmium (NiCd or NiCad) batteries over other rechargeable types is low internal resistance, meaning you can suck a lot of energy out of them quickly (high-drain), so are popular with the radio control (RC) model crowd, despite their inferiority in other ways (including the “memory effect“).

As mentioned earlier, cells and batteries are not exactly the same thing, even though the term battery is quite often used for individual cells. A battery consists of one or more cells, most always connected in series to reach a desired voltage.

Continue reading →

Series and Parallel Circuits

AF5NP Battery, Capacitor, Circuit, Component, Electronic, Impedance, Inductor, Parallel, Resistor, Series

jumblecircuit

All hams should have at least a limited understanding of basic circuits, and this means being able to differentiate between series and parallel components.

Besides numerous license exam questions (dozens below in green boxes; knowing helps you pass the exams), some technical discussions in ham radio will throw the terms around so let’s explore the matter here.  In addition to our own presentation, some excellent web references are given at the end for further (and often more interesting) information.

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Before jumping into circuits, let’s discuss series and parallel connections.  Visualizing this will help us understand series and parallel circuits.

As the name suggests, series connections are lined up end-to-end.

series res

We’re demonstrating with resistors but the principle applies to any two-terminal component: capacitors,  inductors, diodes, cells/batteries, and light bulbs can all be wired in series with two or more of each (or a mix of different parts).  Lining them up terminal to terminal makes a series connection.

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Schematically, 3 parts in series looks like this:

Series schem

From this simple schematic we intuitively see that the current flowing through a series string has to be the same though the chain; there is nowhere else for electrons to flow (current).

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Equal current is one way of defining a series circuit.

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Also as the term suggests, parallel connections are side-by-side.

parallel res

Again, demonstrating with resistors and again, the principle applies to any two terminal component.  Arranging components across each other makes a parallel connection.

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Schematically, 3 parts in parallel looks like this:

Parallel schem

From this simple schematic we intuitively see that the voltage across parallel components must be the same.

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Equal voltage is one way of defining a parallel circuit.

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We just learned that current is the same through components in series, and voltage is the same across components in parallel.  What about  the voltage across series components, and current through parallel components? Continue reading →

Electrical Hazards

AF5NP Battery, Capacitor, Circuit, Circuit Breaker, Electrical, Fuse, GFCI, Hazard, Protection, Safety

Safety is an important topic in ham radio.  There are 11 questions on electrical hazards in the USA Technician class license exam pool, 13 questions on tower safety and associated grounding, and 13 questions on radio frequency (RF) hazards.

Several of these have been used by us previously but in retrospect we should have given the safety topic more airtime, pun intended.  New hams are unlikely to have antenna towers so we don’t plan to discuss tower safety much.  That leaves electrical and RF hazards to cover.

This post will address general electrical hazards and related safety; a future post will focus on RF hazards.

Radios and accessories are electrical devices so let’s start with the most obvious hazard: electric shock, which is caused by current flowing through a human body.  Current is useful in electronics but harmful when flowing through a person.  Current can disrupt heart and lung function at even low levels.  It can also cause unwanted muscle movement, or prevent it (can’t let go).  At higher levels, electric current will damage skin and internal organs.

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There are many factors in electric shock and there are other electrical hazards.  But this is a big one and you should avoid touching live circuits.

Fire is another electrical hazard.  When too much current flows in conductors, the wires can get very hot and ignite combustible material.  In fact, the US National Electrical Code is actually a document of the National Fire Protection Association (NFPA), not a government agency.

To limit the risk of fire and other damage, every power circuit needs some form of  protection.  Fuses are quite common; their internal metal melts at a pre-determined current to disconnect power.

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Also, a smaller (amp rating) fuse can safely be inserted in a protective circuit but one should never put in a larger one.  A fuse is sized to the circuit requirements and wiring  is sized to the fuse.  So a higher-ampacity fuse will not properly protect the wires or the circuit and serious overheating may occur in both AC and DC power circuits.

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In addition to one-time use fuses, circuit breakers are another popular form of circuit protection; these may be reset and are often used as an on/off switch.

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While fuses and circuit breakers do not directly provide shock protection, they may do so Continue reading →