Topics:
| 3.1 | Transceivers |
| 3.1.1 | Transmitter power output |
| 3.1.2 | Transceiver power requirements |
| 3.1.3 | Transceiver controls |
| 3.2 | Power Supplies |
| 3.2.1 | Mains supplies |
| 3.2.1.1 | Constant voltage transformers |
| 3.2.1.2 | Fail to battery |
| 3.2.2 | Generators |
| 3.2.3 | Batteries |
| 3.2.3.1 | Types |
| 3.2.3.2 | Capacity |
| 3.2.3.3 | Life expectancy |
| 3.2.3.4 | Charging |
| 3.2.3.5 | Discharging |
| 3.2.3.6 | Low Voltage Disconnect |
| 3.2.3.7 | New Battery from Old |
| 3.2.4 | Solar Battery Chargers |
| 3.2.4.1 | Available Solar Energy |
| 3.2.4.2 | Electrical Connection |
| 3.2.5 | Diodes in Solar Chargers |
| 3.2.5.1 | What is a diode? |
| 3.2.5.2 | Main diode |
| 3.2.5.3 | Blocking diode |
| 3.2.5.4 | By-pass diodes |
| 3.2.5.5 | Diodes for multiple loads |
| 3.2.6 | Solar Regulator |
| 3.2.7 | Pedal Generators |
The word transceiver is an abbreviation of transmitter-receiver and indicates that these two facilities are combined into one unit. Normally the transceiver can either transmit or receive at any one time. The transceiver will only use one aerial which is switched automatically to the transmitter or receiver portion within the transceiver. Many different types of HF Single Sideband (SSB) transceivers are manufactured. Some sets appear to be rather complex being fully synthesised and capable of being tuned to any frequency e.g. from 2 to 30 MHz, simply by typing in the frequency on a keypad. In fact the front of these sets are often covered with press buttons and indicator lights enabling a wide range of facilities to be selected. Such sets should only be selected for use if competent operators are available who would fully understand the use of all the controls and if an adequate repair facility was available for the sophisticated circuitry. There are more simple HF SSB sets available such as those with only 4 or 10 pre-selected frequencies. The number of front panel controls on these sets is usually less and their circuitry often is more easy to repair.
3.1.1. Transmitter output power
The power output of SSB transceivers is defined by its Peak Envelope Power ( PEP ) which is about 3 times the average power output. Sets are available which provide PEP in the range 25 to 150 watts. Of the 155 transceivers reported in the Questionaire, 26% had a PEP of 60 watts and below, 52% had 100 watts PEP and 22% were between 100 and 150 watts PEP. Almost all transceivers, with power outputs up to 150 watts PEP, manufactured after 1988 were completely transistorised i.e. not containing any thermionic valves. Also many of these transceivers will operate direct from a 12 volts DC power source e.g. a car battery. It is possible to calculate the theoretical transmitter power necessary to achieve highly reliable radio communications over a specified link. However there are many other incalculable factors which determine whether you will be heard and understood by the distant station. At the present time some developing countries have a very limited telecommunications infrastructure hence Government departments, commercial companies, missions etc. all have their own HF radio communication networks with the resultant crowding of the radio channels. You may experience any of the following situations:
b) Even if you have your own radio channel you can experience interference from stations operating on adjacent channels or on the other sideband e.g. you are using USB (Upper Sideband), they are using LSB (Lower Sideband).
c) In a town the transceivers of several different groups may be located close to each other e.g. within 1Km. Although the groups are using completely different frequencies the transceivers can cause interference with each other simply because of their proximity.
In an ideal interference free situation you might expect to use a 25 watt PEP transmitter for ranges up to 300 kms. with power rising up to 100 watts for 1,000 Kms. What is happening in practice is that many groups are using higher power transmitters in an effort to make themselves heard, even resorting to the illegal use of amplifiers producing 1,000 watts. This produces an increase in the level of interference for other users and the "law of the jungle" results.
The Questionaire showed that 74% of the transceivers were 100 watts and above. The only realistic conclusion that can be drawn is that unless you are sure you can operate satisfactorily with a power less than 100 watts then you should select a transceiver capable of producing this power. You may be able to reduce the power output of your 100 watt transceiver to a lower level if required but you cannot increase the power output of a 40 watt one without buying more equipment.
3.1.2. Transceiver power requirements
A rough guide of the average input power required by a transceiver, during transmission, is 2/3 of the PEP watts. For example, a 150 watt PEP transceiver would require an average power of 2/3 x 150 = 100 watts. The relation between power, voltage and current is:
Power in watts = voltage in volts x current in amps.
or Current = Power/Voltage.
Hence the current required from a 12 volt battery for a 150 watts PEP transmitter:
Current = (150x2/3)watts/12 volts = 8.3 amps average.
The transceiver will in fact be demanding a peak current for short periods and then no current. The value of this peak current can be a little above twice the average current, in this case about 18 to 20 amps. Whilst receiving the transceiver will take very little power. Typical 150 watt PEP HF SSB transceivers require 0.2 to 0.5 amps during reception.
3.1.3. Transceiver controls
The number of controls on the front of a transceiver can vary from some 5 to 25. The more common and essential are described here:
VOLUME or AUDIO.
As found on all radios, cassette players etc. it simply adjusts the loudness of sound from the loudspeaker and earphones.
Combined ON/OFF and AUDIO.
These are frequently found on ordinary radio receivers as well as transceivers. Because the action of switching off requires the knob to be turned down to zero volume each time and also up again to normal level each time you switch on there is excessive wear on this component and it is often the first item to wear out. If a separate ON/OFF switch were available then the volume control could be left in its usual position.
POWER light.
This indicates that power is being supplied to the set. It is usually a red bulb or Light Emitting Diode (LED).
TRANSMIT light.
This may be a red or orange light which flashes when you speak into the microphone of a SSB transceiver and shows that the
transmitter is generating power. The light may be labelled TRANSMIT or XMT.
R.F. GAIN and ATTENUATION.
The purpose of these controls is to adjust the amount of amplification of the incoming signal in the receiver portion of the transceiver. The RF GAIN control is operated in a similar fashion to the volume control. Alternatively there may be one or two switches labelled ATTENUATOR, with values of 5, 10 or 20 dB, which enable you to reduce the RF amplification by the number of dB switched in.
CLARIFIER or CLARIFY.
There can be a difference of several hundred cycles in the frequency of the transmitters you are listening to. So when you listen to one person speaking they may appear to have a deep bass voice whilst the next one has a high pitched and perhaps unintelligible voice. The CLARIFIER will enable you to adjust the pitch of the voice coming from the loudspeaker to your particular preference.
SQUELCH.
On some Australian transceivers this is labelled MUTE. The control can either be a variable one like the AUDIO one or an ON/OFF switch. The purpose of the SQUELCH is to prevent any noise coming from the loudspeaker unless speech is being received. Hence you could have your transceiver left switched on receive, on your office desk, without it producing continuous hisses, crackles and bangs. The effectiveness of squelch circuits varies depending on their design. Some manufacturers offer what is called SYLLABIC squelch. This looks for the syllabic rate in speech and so it is able to differentiate between speech and other noises.
CHANNEL selector.
This control selects the particular radio frequency which has been allocated to each channel. A rotary multi-position switch may be used for fixed frequency sets e.g. crystal controlled ones. Each switch position can have the full radio frequency beside it e.g. A 7305 KHz, B 5782 KHz, or the positions may simply be labelled A, B, C, etc. Synthesised transceivers are more versatile, by selecting a channel and typing in the frequency the transceiver will store this frequency so that whenever that particular channel is selected in the future it will automatically be set up to the stored frequency.
USB/LSB.
A single channel frequency can produce two usable channels. One channel is the UPPER SIDEBAND (USB) which occupies 3 KHz above the channel frequency while the LOWER SIDEBAND (LSB) occupies 3 KHz below the channel.
AM.
This stands for Amplitude Modulation and is used by broadcast transmitters on the short-wave bands. An AM facility is not found on all transceivers. AM is not used or indeed not usually permitted for speech communications as it requires twice the amount of frequency space that USB or LSB does i.e. 3 KHz above and 3 KHz below the channel frequency.
CW.
This stands for Continuous Wave and only the channel frequency is transmitted and is switched on and off to form the Morse Code
or any other kind of code.
Basically there are two types of power sources. One source which can be considered to be "interruptable" e.g. a 110 or 220 volt AC mains supplied by the local electricity authority. A failure anywhere in the generation or supply system can mean that, often without notice, you will be without power. A similar loss of power can occur when your own generator fails. So you must consider the reliability of the electricity supply which you intend to use for your radio and the effect of not always being able to transmit when you wish. Such shortcomings can be overcome by using a "uninterruptable" supply, that is to store the electricity in your own storage battery which is automatically connected to the transceiver when the mains fail. The battery will require charging and you will have to put into the battery a little more energy than you expect to get out of it.
3.2.1. Mains supplies
The availability of the mains electricity supply in some towns of the developing countries can be unreliable. The supply can disappear for hours or days with no information being available regarding when it will go off or come on. So it is as well to discover as much information about the mains supply which you intend to use before you complete the plans for your network. This information should be obtained from existing users rather than the electricity supply authority. Sometimes the authority will give you an over optimistic picture of the supply, it may well be what they hope to supply you with but not what you actually get. Some towns may have electricity for certain hours only e.g 6 pm to 10 pm.
3.2.1.1.Constant voltage transformers
Apart from interruptions your mains supply may fluctuate considerably about its nominal value e.g. 240 volts. One European standard for national voltage supply is that it shall be within +/- 6% of 240 volts. You may obtain your electricity from a locally generated supply e.g. a plantation or a hospital, which also may be unreliable and unstable. In all such situations a fast-acting constant voltage transformer i.e. one which will respond to changes within 1/50 of a second could be used to advantage. Such a constant voltage transformer may accept input voltages in the range 204 to 276 volts and provide an output in the range 236 to 254 volts.
3.2.1.2. Fail to battery
This facility is as its name describes. When the mains fail the transceiver is automatically connected to a standby battery. A mains operated relay can be used as shown in Fig.3.8. The relay contacts must be capable of carrying the maximum current required by the transceiver. Provision must be made to always keep the standby battery fully charged.
3.2.2. Generators
You may encounter a wide range of generators from 50,000 watt ones driven from 6 cylinder noisy diesel engines to 150 watt ones driven from small quiet petrol engines. If you intend to use power from an existing generator you should check the reliability of supply for both times when power is available and the constancy of the voltage. For example, does the voltage rise by 10 or 20 volts when a load is switched off or does a 230 volt supply fall to 190 on occasion? Is there a reliable fuel supply and is the generator well maintained or are there periods of days or weeks when the generator is not working ? Is there a standby generator available ? You may wish to provide your own generator. This could either provide 110 or 230 volts AC direct to your radio or 12 volt DC for charging your radio battery. Some small generators provide both 110/230 volts AC and 12 volts DC.
3.2.3. Batteries
Batteries can be divided into two groups. Primary batteries are ones which cannot be recharged and which are thrown away after use e.g. some torch batteries. Secondary batteries are ones which can be used and recharged many times. It is only secondary ones we shall deal with here. The value of secondary batteries is that they can be charged when electrical power is available i.e. when a generator is running, the energy is then stored and can be used when required. The classic example in daily use is the sun on the solar panels during the day charging the battery which will provide energy for lighting at night. The importance of battery use can be seen from the Questionaire which showed that 74% of the 176 transceivers at fixed locations n Africa used batteries recharged by various means.
3.2.3.1. Types
There are many different types of secondary or rechargeable batteries. Small capacity nickel cadmium ones are used in torches and in small transistor radios. The battery most commonly used for radio transceivers is the vented lead acid type i.e. the car battery. Now increasing use is being made of sealed lead acid batteries both for cars and radios. The sealed types are sealed for life and require no maintenance whereas the vented ones need checks on their acid level and filling up with distilled water as necessary. Note that it is important to keep the charging voltage within the manufacturers limits especially for sealed types. Care should be taken when purchasing sealed for life batteries because special PHOTOVOLTAIC batteries are now available. These are sealed for life batteries specifically designed for use in solar systems where the charge and discharge currents are usually lower than in a car. Therefore they must not be used in any vehicle for any reason not even to start one. It is suggested that their currents are calculated from the 100 hour rate in paras. 3.2.3.4. and 5. In practice the calculated values can be exceeded during peak solar charge and peak transmitter load. When one cell of a normal 12 volt battery fails the battery is of little use. It is now possible to buy a battery made up of 6 individual 2 volt cells. The advantage is when one cell fails you need only buy one new cell to restore the 12 volt supply. The cost of this arrangement is more than for a normal 12 volt battery.
3.2.3.2. Capacity
The amount of energy that can be stored in a battery is expressed in AMP HOURS (AH or Ah) i.e. Amps x hours. The working of a battery can be understood by considering a typical car battery with a capacity of 60 Ah. A fully charged 60 Ah battery will give 1 amp for 60 hours or 10 amps for 6 hours. This is an over-simplification because the efficiency of a battery decreases with higher discharge current. Efficiency is the Ah obtained from a fully charged battery during discharge compared with the Ah used to fully recharge it. Misunderstandings have occurred concerning the relationship between battery voltage and the state of charge of the battery. It has been assumed that the voltage of a fully charged battery was 12 volts and that this voltage would fall to 6 volts when the battery was half discharged. There is in fact only a small change in battery voltage. When a battery is delivering current its voltage will be about 12.6 volts when it is fully charged. When the voltage has fallen to about 11 volts some 90% of the stored energy will have been used up and the voltage will soon fall to 10.6 volts when it is fully discharged. These figures will vary slightly according to the type of battery and its condition. To calculate the Ah capacity of the battery you require see para 3.2.3.5.
3.2.3.3. Life Expectancy
The most commonly used battery for transceivers in the mid 1980s was the rechargeable lead acid type e.g. the conventional car battery. Only a few sealed types were in use. A conventional type car battery should not be stored in a discharged condition because this can drastically reduce their life expectancy. When you buy a new battery how do you know when it was manufactured and in what condition it has been stored? A good quality British made battery was purchased as new in Mbandaka in Zaire in September 1986. After 8 months in use one cell failed and the battery was no longer usable. Enquiries made to the British manufacturer showed that it was at least 5 years old when it was bought in Mbandaka. The normal storage life for that type of battery without deterioration is considered to be 1 year. You may not be able to obtain any information regarding the true age of batteries which are not manufactured in the country so if you wish to buy locally it would be best to obtain them from large trading establishments e.g. in the capital city, where there may be a rapid turnover of goods. Alternatively you could import a battery yourself preferably by air if you are able to do so. Once you have a good battery its life expectancy will be further determined by how it is used. If a battery is kept fully charged and only a 1/3 or 1/2 of the energy stored in it is used before it is recharged again a reasonably long life can be expected. The following figures indicate how many times a lead acid battery can be charged and discharged. They are for guidance only and details for any particular make of battery must be obtained from the manufacturer:
| Percentage of energy used | Number of times battery can be charged and discharged. | |
| before recharge. | Vented | Sealed |
| 30 | 1,000 | 850 -1,200 |
| 50 | 700 | 280 - 450 |
| 100 | 350 | 100 - 180 |
These figures suggest that a vented lead acid battery used each day powering a transceiver will last for 3 years if only 30% of its energy is used and it is recharged daily. However if the battery is fully discharged each day it is used then its life expectancy is less than 1 year.
3.2.3.4. Charging
The voltage of a battery will vary whilst it is being charged. The actual voltage will depend upon its type and condition and its state of charge. To ensure that charging current flows into the battery the voltage of the charger should exceed that of the battery by at least 1 volt. Regulators on many vehicles limits the maximum battery charging voltage to 13.6 volts. When solar panels were first used for battery charging the voltage of the panels was often some 14 to 15 volts but this voltage did not really require regulating. Now higher voltage panels are in use and will need regulators see para 3.2.6. When a fully discharged battery is put on charge its actual voltage may be only 11 volts so a high charging current will flow. As the battery voltage gradually rises to its maximum e.g. 14 volts the charging current will reduce.
| One recommended maximum charging rate | = | Battery capacity in Ah _____________________ 10 hours |
| For example: | 60 Ah battery ______________ 10 hours. | = | 6 amps. |
The approximate state of charge of a battery can be deduced from its voltage.
| Battery state | On charge | In use i.e. Not connected | on load |
| Fully Charged | Maximum set by charger e.g. 15V | 13.2 V. | 12.6 V. |
| Requires Charging | ___ | ___ | 11.1 V. |
| Fully Discharged | 11 to 12 V. | ___ | 10.6 V. |
Another method of determining the state of charge of a battery is with the aid of an inexpensive HYDROMETER. This sucks a small quantity of the acid from the battery into its transparent bulb and a calibrated float gives a reading of the SPECIFIC GRAVITY (S.G.) of the acid. The acid is then returned to the battery. The following table gives the relation between the S.G. and the state of charge of the battery:
| Battery state | S.G. |
| Fully charged | 1.28 |
| 3/4 charged | 1.25 |
| 1/2 charged | 1.22 |
| 1/4 charged | 1.19 |
| Fully discharged | 1.11 |
3.2.3.5. Discharging
The current demanded by the transceiver will determine the Ah battery capacity required. There are two figures to consider. First the total energy in Ah required from the battery before it is recharged each day. Take for example a transmitter requiring an average current of 8 amps. For a total transmit time of 1/2 hour Ah = 8 x 1/2 = 4 Ah. Transceiver when operated in the receive mode requires 1/2 amp. For a total receive time of 4 hours Ah = 1/2 x 4 = 2 Ah. Therefore total energy required from battery is 6 Ah. Second figure to consider is the maximum discharge rate in this case 8 amps. For continuous use the recommended rate is :
| Discharge amps | = | Battery Ah capacity ________________ 10 hours |
Or this can be written: Ah capacity = 10 hours x Discharge amps. However for intermittent demands of current, such as speech transmission, the 10 hour rate can be reduced to 5 hours. Thus: Ah capacity = 5 hours x 8 amps = 40 Ah. Of the two figures calculated for Ah, 6 and 40 in this example, the highest Ah is the one required. If the battery cannot be recharged when necessary, perhaps because a solar battery charger is used and the amount of sunshine is irregular in certain seasons or if a generator is not run at regular intervals, then a battery of higher capacity than the calculated value will be necessary. The battery will need to store enough energy to operate the radio until the next charge is available.
3.2.3.6. Low Voltage Disconnect
The information in para. 3.2.3.4. showed that the life expectancy of a battery was increased if it was not fully discharged before recharging. Units are available which automatically disconnect the radio from the battery when its voltage has fallen to a preset value e.g. 11.1 volts. Note that the unit must be capable of switching the maximum current demand of the radio.
3.2.3.7. New Battery for Old
When a battery fails it is frequently only one of its 6 cells that has in fact failed, hence the 12 volt battery becomes a 10 volt battery. From the 12 cells of two old batterys 6 good cells can usually be found. These cells can be connected in series to give 12 volts. One method of finding the good cells is described briefly.
2. After discharging for 30 minutes measure the voltage of each cell. It may be necessary to make small holes in the top of the plastic battery case to enable contact with each cell.
3. Empty the acid from the battery. Connect the 6 good cells in series i.e. negative of one cell to positive of the next. Make these connections in the old cells adjacent to the good cells being used.
4.Refill only the 6 good cells with acid and then recharge the battery.
3.2.4. Solar Battery Chargers
A solar battery charger is simply a flat panel containing photo voltaic material e.g. slices of silicon. When the sunlight reaches the photovoltaic material a voltage is produced which provides a charging current to the battery. In bright sunlight each silicon slice in a panel will generate just under 0.5 volts. The number of slices in a panel can vary from 30 which will produce 15 volts to 40 which produces 20 volts. The amount of current which a panel produces is proportional to the surface area of the silicon slice. To estimate the approximate size of solar panel one can assume that 150 square centimetres of total panel surface area is required to generate 1.0 Amps at 0.5 volts. Therefore the size of a solar panel to produce 18 volts at 2 amps can be calculated, assuming 150 sq.cms. required to produce 1 amp at 0.5 volts.
| Area in sq.cms. | = | ( voltage x 2 ) | x | ( Current in amps ) | x | ( 150 ) |
| = | ( 18 x 2 ) | x | ( 2 ) | x | ( 150 ) | |
| = | 10,800 sq. cms. | |||||
That is a panel area of about 1 sq. metre.
3.2.4.1. Available Solar Energy
The amount of solar energy available can be obtained from ISOHEL maps which show the Average Annual Solar Energy in units of kilowatt hours (kWh). The figure for Western Europe is 1,000 kWh, the Sahara is 2,000 to 2,500 kWh and most of Zaire is 1,700 kWh. Obtain details of the solar radiation for your area of work. An example of how the daily quantity of solar energy varies throughout the year is shown for Kinshasa, which is 4 degrees south of the equator,in Fig.3.1. How the total intensity of solar radiation varies through the day during June is shown for Kinshasa, the capital of Zaire, in Fig.3.2. The total solar intensity comprises both direct sunlight and that diffused by cloud. In Kinshasa the diffused energy reaches its maximum after midday, as the cloud becomes less dense, hence the total intensity peaks at 1300 hours. About 10% of the solar energy which arrives on a silicon solar cell is converted to electrical energy. An example follows showing how to calculate available electrical power. First you must know the following relationships:
Watt hours (Wh) = Watts x hours
Watts = Voltage (V) x Current (A)
Therefore: Wh = Voltage (V) x Current (A) x hours
A solar panel with cells covering 1 square meter will receive 4KWh per day in June in Kinshasa. Of this 10% (0.4 KWh) will become electrical energy.
0.4 KWh = 400 Wh
Charging a 12 volt battery from the solar panel.
Wh = Voltage x Current x hours
400 = 12 x A x h
| That is: | 400 ______ 12 | = | Ah | = | 33 Ah |
In theory the 400 Wh of energy will put a charge of 33 Ah into the battery. In practice the battery will receive a somewhat less charge because the voltage of the solar panel has to exceed the battery voltage before charging commences. The calculations are based on the actual area of solar cells which can be considerably less than that of the solar panel. However the calculations will give an idea of the necessary area of solar panel required. Solar panels are classified according to their voltage and maximum power output.
3.2.4.2. Electrical Connection
Solar panels can be connected together either "in series" or "in parallel". In series" means that the negative of one is connected to the positive of the next see Fig 3.3. The combined voltage of such panels is the sum of the voltage of each panel. So if you connect two 9 volt panels in series you will have an output of 18 volts. The value of the output current will be set by the panel having the lowest current output so this is normally used for connecting panels that produce similar current levels. "In parallel" means that the positive of each panel is connected to the positive of the next and negative to negative of each. It is usually used for panels of the same voltage and the total voltage for all the panels will be only the same as for one of them but the total current output will be the sum of the current of each panel. So if you connect two 9 volt panels in parallel you will get 9 volts out. It is important to get these connections right as shown in the following example. We found in one place two 9 volts panels installed and connected to a 12 volt battery. The disappointed user was certain solar power was no good because the battery was not being charged by the panels. However we discovered that the panels were connected in parallel so giving only 9 volts to the battery. Now you must have a charger that gives at least one volt more than the battery see para 3.2.3.5. so we connected the panels in series and they produced 18 volts which was more than enough to keep the 12 volt battery fully charged.
3.2.5. Diodes in Solar Chargers
Originally only one diode was used with each solar panel as this has always been necessary in a solar charger circuit to prevent the battery from discharging through the panel. Now you may well find several diodes built into a panel. The manufacturers do not always explain either the presence of the diodes or their purpose. For example: there is a label on the back of your panel saying "By-pass Diodes fitted" but you would still require a Main Diode. There will probably be a small plastic box mounted on the back of your solar panel. If you remove the lid of this box you should find the + and - terminals. There may also be diodes in this box and in the absence of any information from the manufacturer you should attempt to identify the purpose of the diodes. A description of a diode and its several uses in solar panels follows.
3.2.5.1. What is a diode?
A diode is a device which permits electric current to flow through it in one direction only. It is, therefore, very important that the diode is correctly connected. One place you should always find a diode is connected between a solar panel and the battery it is charging. A diode is shown in circuit diagrams by the theoretical symbol of an arrow on a line. -->|-- , see Fig.3.3. The arrow shows the direction in which the current flows. The current flows from the one end which is called the anode to the other which is called the cathode. The anode is positive and the cathode is negative. When current is flowing through a diode there will be a loss of 0.5 to 1 volt across the diode. The cathode of a diode may be identified by one of the several markings found on diodes e.g. by a light coloured ring on the dark body of the diode or by an arrow printed on the diode which points to the cathode. If the marking has come off the diode the cathode can be identified using a multimeter.(see para 8.6.2.3.) This method should also be used to test all diodes, including new ones, before they are connected as it is difficult to test them once they are in a circuit.
3.2.5.2. Main diode
When a solar panel is used for charging a battery it is always necessary for a diode to be connected between the solar panel and the battery. The purpose of this main diode is to permit the solar panel to send charging current into the battery whilst preventing the battery discharging current through the panel during the night or when there is no sunshine. The diode may be connected in the + or the - wire provided the diodes direction is correct, see Fig 3 3. Main diodes are sometimes built into solar regulators, see 3.2.6.
3.2.5.3. Blocking diode
When more than one solar panel is connected in parallel it may happen that one panel becomes shaded. The output voltage of the shaded panel will fall and it will absorb current from the other unshaded panel. This waste of current can be prevented by connecting a "blocking diode " between each panel and the battery as shown in Fig 3.4. The fitting of blocking diodes is optional but if fitted to all panels then a "main diode" is not necessary.
3.2.5.4. By-pass diodes
These are used to minimise loss of voltage across sections of a panel or across individual panels, which are connected in series, when a part of the panels becomes shaded. The diodes limit any reverse voltage which may be produced by shading to 0.6 volts see Fig.3.5. If by-pass diodes are fitted to your new solar panel you can discover if they will in fact be of any use. That is , if a section of the panel is shaded so that a by-pass diode is conducting, will the remaining voltage from the panel be sufficient to charge the battery. For example, when two diodes are fitted to a panel which has an open circuit voltage of 18 volts, i.e. 9 volts plus 9 volts, then with one by-pass diode conducting the output voltage would be 9 volts minus 0.6 volts which is clearly not enough to charge a 12 volt battery. If four diodes were fitted i.e. 4.5 + 4.5 + 4.5 + 4.5 volts and one section was shaded causing one diode to conduct then the output is 4.5 + 4.5 + 4.5 - 0.6 = 12.9 volts which is sufficient to put some charge into a battery. By-pass diodes which are serving no purpose could be removed because problems may arise if they failed e.g. due to lightening damage. They can be used as blocking diodes or kept as spares.
3.2.5.5. Diodes for multiple loads
Where there is a solar panel which has been installed to charge a battery e.g. to power your radio, the question may soon arise "Can we charge other batteries from the panel as well?" The answer is "perhaps" and "providing priority is given to the radio battery". First it must be established that the existing panel is capable of providing adequate charge to the battery it was intended to charge. Then if there is surplus current the extra load should be so connected that there is priority to the premier battery. Such an arrangement can be achieved by using a somewhat complex and expensive electronic management system which itself will require power. Alternatively a simpler and cheaper system of diodes can be used see Fig 3.6. However this configuration of diodes does not guarantee that the principal battery will get sufficient charge but it will ensure that the additional load receives at slightly lower voltage and that it will not discharge the principal battery.
3.2.6. Solar Regulator
Current practice is to use solar panels producing up to 18 volts to ensure a high battery charging current throughout the period of charge. With such panels it is necessary to use a regulator to reduce the 18 volts supplied by the panels at peak performance times to the maximum permitted at the battery e.g. 14.5 volts, to prevent the battery from being overcharged. Some solar regulators contain the Main diode. Only use a regulator that can handle the maximum power output of your panel. There are several different types of solar regulators. One has a current controlling device between the panel and the battery which controls the amount of current going into the battery. Another type has resistors which "dumps" some of the current from the panel when the battery voltage exceeds the predetermined limit. Both of these types can provide proportional control that is the charging current is gradually reduced as the battery voltage rises. There are also "on-off" regulators where the full charging current flows for a time then is reduced sometimes to zero fora period of time. Proportional types are preferable.
3.2.7. Pedal Generators
Generators pedalled by people have been used to produce electricity for radio communication purposes since the 1930s. Their use was pioneered by Traeger in Australia for the Flying Doctor Service. Pedal generators were still in use in the British Army in the mid 1980s though by this time production had ceased in Australia. A network of several Traeger pedal powered transceiver, giving a power output of 25 watts PEP each, was established around Dodoma in Tanzania in 1980 and this equipment was still serviceable in 1987. These generators produced power directly but only while they were being pedalled and usually did not incorporate a storage battery. When there is no storage battery it is necessary to pedal all the time whilst you are receiving and waiting for your turn to speak, in practice this can be 10 to 20 minutes. Therefore it is helpful to have a timetable with specific times for contacts which is strictly adhered to. Since production of these ceased many individuals and groups have designed their own generators.
These designs have frequently been based on a bicycle, one incorporated a 3 speed drive, to drive dynamos or alternators from cars. A disadvantage of using a normal car alternator is that it requires a battery to provide current to start it generating and also to stabilise the output voltage. However a battery gives an operational advantage in that it can be used to power the transceiver during what may be long periods of receiving only. Then pedalling commences for transmission and also to charge the battery.
The cost of car batteries in some countries can be very high. Also the life of these batteries can be only 1 or 2 years and they can easily be stolen or borrowed for other purposes. So it is sometimes beyond the financial resources of small groups to provide themselves with a battery. When using a low power transmitter e.g. 25 or 40 watts, these groups could use a new design of pedal power generator which requires no battery although it uses a car alternator. In this design the existing control unit in a LUCAS 17ACR car alternator was replaced by the circuit shown in Fig.3.7. This maintained the output voltage of the alternator between 13.0 and 13.6 volts for a load varying from 0 to 40 watts. The pedal generator has been used to power a 40 watt PEP SSB transceiver.