Module 13 - Power Supplies & Batteries
- Reading Assignment
- Power Supplies
- Power Supply RATINGS
- Mobile Installation
- Quiz 13
- Recommended Reading
Read Chapter 5, Pages 5-14 to 5-16 in your text before you continue.
Mains - Shore Power - Household Power, no matter what you call it is the power supplied by your local utility. In our country the voltage is standardized at approximately 115 Volts AC. It is referred to as 110 VAC to 120 VAC. The frequency is 60 Hz or Hertz (Cycles).
Actual power supplied to most households is 240 VAC 60 Hz
It comes from a transformer with a 240 VAC secondary that is center tapped. That center tap is tied to ground potential and called the neutral. The wires are called L1, L2 & Neutral. If you were to measure from the neutral to either L1 or L2 you would measure 120 VAC. If you measure across L1 & L2 you would see 240 VAC.
Older radios usually worked directly from 120 VAC and had transformers and power supplies that supplied filament voltage for tubes and high voltage DC power for the plate voltages. Today such an arrangement is rare and not necessary, for the radios are mostly transistorized and use much lower voltages.
The reason I mentioned the 240 VAC supply is so that you might understand utility supplied power. Also, some power amplifiers require the higher voltage of 240 VAC as an input voltage. The reason for this is the high current required by the amplifer.
Most modern radios actually use 12vdc (13.8 VCD) directly and there is no need for any power supply in mobile operation or when the base station is powered by batteries or solar power.
In fact now, when one mentions a power supply, you are usually referring to a supply that converts 120 VAC to 13.8 VDC which the radio uses.
Like the nominal 115 VAC power, 13.8 VDC is often referred to as 12 VDC, why? That is really unknown. The radios are designed to operate from 12 VDC to about 14.2 VDC/
The U.S. frequency is 60 Hz, while much of the rest of the world is only 50 Hz.
120 VAC to 12 VDC power supplies come in two general types: Linear & Switching.
Linear Powers Supplies
Linear power supplies have a bulky steel or iron laminated transformer. It provides a safety barrier between for the high voltage AC input and the low voltage DC output. The transformer also reduces and the AC input from typically 115 VAC or 230 VAC to a much lower voltage, perhaps around 30 VAC. The lower voltage AC is then rectified by two or four diodes and smoothed into low voltage DC by large electrolytic capacitors. That low voltage DC is then regulated into the output voltage by dropping the difference in voltage across a transistor or IC (the shunt regulator).
The Linear Power Supply has low noise and very little ripple along with good regulation.
The cost and weight of the Linear Power Supply is high by comparison to the other type. The efficiency of the Linear Power Supply is only about 60 % and the loss is dissipated as heat.
The Linear Powers Supply has a very limited range of input voltage compared to its rated input. It also is frequency sensitive and usually a 60 HZ power supply will overheat with 50 Hz supply voltage.
Switching Power Supplies
Switch-mode supplies are a lot more complicated. The 115 VAC or 230 VAC voltage is rectified and smoothed by diodes and capacitors resulting in a high voltage DC. That DC is then converted into a safe, low voltage, high frequency (typically switching at 200 KHz to 500 KHz) voltage using a much smaller ferrite transformer and FETs or transistors. That voltage is then converted into the DC output voltage of choice by another set of diodes, capacitors and inductors. Corrections to the output voltage due to load or input changes are achieved by adjusting the pulse width of the high frequency waveform.
The Switching Power Supply will take quite a range of input frequencies and still supply rated power. It also is not so sensitive to input frequency. So, it will work well from 90 to 240 VAC 50 - 60 Hz, which makes it ideal for traveling to foreign countries.
However the Switching Power Supply is noisier and has more ripple than the Linear Power Supply
POWER SUPPLY RATINGS
Powers supplies are rated by several criteria. First the power supply is rated by input voltage, output voltage and current output. A typical rating for a power supply would be 120 VAC 60 Hz input, 13.8 VDC @ 10 Amps output.
This means you have to plug it in nominal 120 VAC 60 Hz. The power supply has an output of 13.8 VDC at up to 10 amps. You can hook up equipment that requires much less than 10 amps with no problem. However is you hook up equipment needing in excess of 10 amps, it would overheat and possibly blow its protection fuses.
An other rating consideration is the regulation of the power supply. The regulation is the ratio of the no-load voltage (nothing drawing current) to the full-load voltage (drawing maximum current). In addition to producing a clean DC voltage, a power supply employs a regulator circuit. The regulator circuit controls the amount of voltage from a power supply. The better the regulation the more stable the output voltage. This is a good thing for the equipment using the power supply, as it prevents voltage fluctuations from reaching sensitive circuits and causing damage.
Power supply wise, the mobile installation is easy. Radios are designed to operate on nominal 12 VDC, so it is just a matter of connecting the radio to the vehicle electrical system.
We need to discuss the rest of the physical installation in a mobile vehicle since many of us will have a mobile installation.
In addition to the radio features, it has to be able to be mounted in your vehicle. Some models have a detachable faceplate. This allows for remote mounting of the radio. This way you only need a small amount of dash or operator compartment space.
However, if you remote mount the radio itself, you will probably have a hard time hearing the speaker. I would recommend mounting a small external speaker, preferably on the post next to your left ear.
You need mounting space for the mike. The mike needs to be accessible for you, but also needs to protect the mike from being bounced around.
The control head or faceplate of the radio needs to be where you can glance at it and tell what frequency or channel you are on.
Power connections. Some will tell you to mount the power connection directly to the battery terminals. The reason for this is less alternator noise etc. is introduced to the radio through the power lead. The alternator can be a source of a high-pitched whine. This whine is easily identified by varying the speed of the engine. As the speed increases the whine will increase. A properly working alternator in a system with a good battery will produce little whine. A good battery when properly charged acts as a filter or large capacitor and filters out the small amount of whine produced by the alternator.
Alternator whine can become so severe that you will also hear it on the transmitted signal.
DON'T HOOK UP THE POWER DIRECTLY TO THE TERMINALS NO, NO, NO!
However, the answer the exam wants is to make the negative power connection at the battery or engine block ground strap. Select that answer, but always use the engine block ground strap in actual practice
I have decades of experience in the 2-way mobile business and have installed and serviced more mobiles than most people have even seen in their lifetimes. If you mount the leads directly to the battery terminals they will corrode and fall off. Most vehicles have a very short positive lead that connects to a large terminal bolt. This is where you attach the power lead. It is very close to the battery and will do the same thing as attaching to the terminals directly, but will not be a maintenance problem.
The negative lead is best connected to the same spot the negative battery cable is connected. Usually the engine block.
A coating of no-ox is a good idea. No-ox is available at your local hardware store.
Fuse protect both the positive and negative leads.
Now you must remember to turn off your radio when you are not using it or it will run the battery down. Some people hook the positive lead to an accessory position on the ignition switch so the radio goes off when the key is off.
Pros and Cons of this. Radio is not available when key is off. That's right, that is both a pro and a con. You need to ensure the radio is not used by unlicensed personnel when you are not present. But if you want to operate the radio without the key on, you won't be able to do so.
Personally I hook up the radio through an interposing relay. That just means the power lead goes close to the battery but through a relay contact. The relay is then controlled by a concealed switch that allows operation at any time regardless of the ignition switch position, but is still not available to unauthorized people, and it is connected close to the battery for noise reduction.
Batteries come in three major categories:Disposable - One time use and then disposed, Rechargeable - can be recharged numerous times & Storage - used for long term storage or powering remote equipment such as a mountain top repeater. Also used to provide backup power in case of a power outage.
I am not going to list all the kinds of batteries because they are listed along with pictures on page 5-16 of the text book in Table 5-2 & Figure 5-14.
The text covers much about batteries, so I will try not to repeat that information, but to amplify the material.
Please dispose of all used batteries in a green manner. There are recycling centers everywhere. Batteries can harm the environment if not disposed of properly.
Storage batteries have a large capacity (rated in ampere-hours) and can supply a large amount of current in a very short period of time. Be careful with tools around storage batteries because shorting out the battery or a single cell of the battery can cause a large spark and enormous amount of heat. Storage batteries vent flammable gas and even more so if being discharged quickly. The combination of a spark and the flammable gas can result in explosion, fire and toxic gas.
Equipment should be fused for protection against shorts causing fire and damage to equipment.
Never defeat the fuse or protection devices of a battery supply bank. You are just asking for trouble. The fuse or circuit breaker would not have blown in a properly fused supply.
Batteries for hand-held radios are generally several cells packaged together and designed for the radio. Three popular types of rechargeable battery are NiCad (Nickel-Cadmimum), NiMH (Nickel-Metal Hydride) & Li-ion (Litium-ion). There are advantages and disadvantages-advantages of each of these types.
NiCad advantages: long life cycles, performs in cold temperatures, lower self-discharge level than NiMH (shelf life), maintains voltage near discharged levels. Disadvantages, they are heavy, making it harder to use for longer periods of time. They suffer from 'Memory Effect' constantly discharged half-way and then recharged.
NiMH advantages: The are lighter than NiCad, have 2- 3 times capacity compared to equal size NiCad. Disadvantages: They have fewer life cycles compared to NiCad, have a shorter run time & perform poorly in cold temperatures.
Li-Ion advantages: They perform well in cold weather, light weight. They have a better life cycles over NiCad and NiMH, so it keeps going past other batteries. They charge more rapidly. They do not self discharge on the shelf. So you can store them without having to freshen the charge often like the NiCad or NiMh batteries. The main disadvantage is the higher cost.
You must be cautious when charging batteries for portables. Drop in battery chargers must be matched to the batteries they are recharging. Some chargers are not made for some type batteries. Also some chargers have a higher rate of charge than the battery charge rating. Read your owner's manual and consult an expert if changing battery types in your portable radios.
You might not have utility power available all the time, in fact, during ARRL Field Day, hams go out into the field and operate from alternative power in a contest environment.
You can receive your alternative power various ways: A hand crank generator charging a storage battery. Solar panels charging a storage battery. A gasoline or diesel powered portable generator.
Portable generators produce various types of power: 120 VAC, 220 VAC & 13.8 VDC are common. Some generators will only produce 120 VAC.
That might not meet our needs. Sure you can plug power supply into a 120 VAC generator to produce nominal 12 VDC to power your transceiver, but remember power supplies are only 80% efficient at best.
Sometimes we might need to make ac from dc or dc from ac. There are devices available to do that. Remember this memory peg. IDA the CAD. OK, so IDA is a CAD, so what? Well this is how you remember what these devices are called. An Invertor makes DC into AC (IDA, get it). A Convertor makes AC into DC (CAD).
Generators actually create power using mechanical energy and magnetic lines of flux cutting windings. Even though generators are called generators, technically they don't always use a generator to actually do the job.
Years ago, automobiles used true generators to create DC voltage. Actually the voltage starts out as AC but is connected to a split-ring commutator. Voltage pickup brushes run on the split-ring commutator and the output is more pulsating DC, which is then smoothed out by the automotive battery.
Modern automobiles use an alternator to generate the DC voltage. Now there is no commutator rather slip rings that the brushes run on. There is no break in the slip ring and the output is AC. This AC is applied to a rectifer bridge which changes the AC into a rather smooth AC voltage. There is usually a built in regulator module inside the alternator to regulate the output voltage.
Back to the portable generator. It may be a generator or an alternator that is actually making the voltage, it generally is still called a generator.
An important consideration in selecting a portable generator or any power unit for that matter is the current or wattage rating. The generator must be able to supply enough current or power to supply all the units that are hooked up to the generator.
Less expensive generators may not have good regulation. One way to alleviate problems from the generator fluctuations is to use the generator to run a battery charger to charge a storage battery and then run the radio from the battery. Battery chargers are plentiful and inexpensive, while radios and even power supplies are not.
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Power supplies are important to radios, whether they are DC supplies or batteries. Treat your power sources with caution and care.
View the complete Technician Question Pool in Chapter 11 of your Ham Radio License Manual.
Review the complete Technician Question Pool with Hints to help you to remember the answers for the test available by clicking the last item on the left hand select menu.
More information on rechargable batteries is available here.
There are always videos on You Tube.
Lots more care and feeding of storage batteries from US Bureau of Reclaimation. Click Here
Review the Term Glossary in Chapter 10 of your Ham Radio License Manual
Practice Exams are available at www.arrl.org/exam-practice and there are links to many other test practice sites also.