Power Supply

Power supply in amateur radio

Importance of a good power supply for the radio amateur

The power supply of an amateur radio station is responsible for more than just supplying the basic requirement for the equipment to run. It generally deserves more attention! Suspiciously cheap power supplies often do not live up to the promises in their technical data. A higher-quality power supply has its price. It often does not pay off to save on the power supply unit! On the contrary - it is a solid investment in the station equipment.

At home in the shack

For operating an amateur radio station at home, the 230 AC mains is available. Tube power amplifiers and some, larger transceivers have a built-in power supply, which is usually connected via a mains lead with a suitable plug. In tube power amplifiers, the power supply generates, among other things, the high voltages required for operation; in transceivers and transistor power amplifiers, it generates the low voltages for the semiconductor technology. The majority of transceivers with a standard output power of 100 W without an integrated power supply unit are designed for direct connection to an external low-voltage power supply unit, usually at 13.8V DC.

On the road in a car or on a boat

Mobile operation of a radio station in a car or on board a watercraft places special demands on the power supply. This is especially the case if it is not just a VHF radio, but a KW transceiver with 100 W transmitting power. One is dependent on an on-board battery with sufficient capacity, the continuous recharging of which must be ensured. An older battery quickly reaches its limits with the additional load. After prolonged radio operation when the vehicle is stationary and the engine is switched off, a deeply discharged battery is often no longer ready to start.

The cigarette lighter is absolutely not suitable for connection to the 12 V on-board network. Its supply cable has too small a cross-section for currents around 20 A.

The supply line in a car must therefore be connected directly from the transceiver to the positive pole of the battery and a central earth point by the shortest route.

Of course, the same criteria apply to the connection to the electrical system of a watercraft. It is easier to install a second, separate battery on board a pleasure boat than in a car, to which only the radio is connected as a consumer. However, in the case of a simple parallel connection to the existing on-board battery, the alternator must be capable of delivering the additional charging current. For controlled charging of a separate, second battery, a separate, external charge controller is required.

If the on-board power supply cannot provide the required voltage, a voltage stabiliser offers the possibility of constantly increasing the operating voltage to 13.8 V in the event of a reduction down to 9 V, even with current draws of up to 30 A.

Reference to manufacturer's specifications of the input voltage range

You will find a reference to the permissible tolerance limits of the operating voltage under the manufacturer's specifications in the manual of your transceiver.

Important

What is the power requirement of an amateur radio station?

The current requirement of a typical amateur radio station is 20 to 30 A at a nominal voltage of 13.8 V, +/- 15 %. The operating voltage output must be clean, stable and short-circuit proof. The maximum power output should in any case be above the maximum power consumption of the station with sufficient reserve. After all, external accessories also want to be supplied!

What should be considered when selecting and operating the power supply unit?

In addition to the distinction between conventional transformer power supplies and switched-mode power supplies, there are other important aspects. For example, the size and weight of a power supply unit determine whether it is suitable for portable or stationary use.

No matter which operating principle is used, every powerful power supply unit must be cooled in any case. Whether it is the losses in the transformer core or in the high-performance rectifier, the heat generation at the series transistors of a voltage stabilisation built with discrete components or the heat loss at the transistors of a switching power supply. Primarily, this task is performed by a sufficiently dimensioned heat sink. But most power supply units cannot manage the heat without the additional use of fans. Unfortunately, this is because the fan noise, at the latest in the case of continuous forced ventilation, is perceived as annoying by most radio amateurs. A temperature-controlled, temporary start-up and shut-down of the fan is more suitable and compatible with our home.

An analogue or digital display for current and voltage is common in all larger power supplies, whether transformer or switching power supply.

What are the advantages of linear regulated power supplies?

Conventional power supplies with a transformer that transforms the mains voltage down from 230 V to the low-voltage range are particularly suitable for radio applications where it is important to avoid additional interference signals in the frequency spectrum to be received. Since they operate in analogue mode, they are "clean" and do not generate interfering signals. Unfortunately, transformers of larger design are cost-intensive and heavy components. For portable use, they are already too large and heavy for the power requirements of a 100 W transceiver. If you want to avoid the interference problems of a switching power supply and are not afraid of the higher costs, you are "well served" with a transformer power supply for stationary use.

What are the advantages of switching power supplies?

Digital switched-mode power supplies have a smaller design and a significantly lower weight. Switch-mode power supplies enable output currents of up to 100 A, where conventional transformer power supplies are no longer available for reasons of cost and weight. In relation to size and weight, switched-mode power supplies therefore have greater efficiency than a transformer power supply. This makes them more suitable for portable use, for a fieldday or for taking along on holiday than a transformer power supply.

Do you prefer fixed voltage or an adjustable power supply? ATTENTION!

Power supplies with a wide range of variable output voltage are more suitable for use as a laboratory power supply. In principle, however, such a power supply can be used for operating a radio station, provided it can deliver the maximum required current at 13.8 V.

However, there is a risk in using such power supplies. If, for example, the regulator was accidentally adjusted or you tried something that required a higher voltage, you must not forget to set it back to 13.8 V afterwards. Otherwise, the expensive transceiver and its peripherals will die one day because the operating voltage is set too high. And having to check that the voltage is correct every time you switch on the station can be a nuisance.

For the supply of an amateur radio station, you are therefore only on the safe side with a fixed-voltage power supply unit.

Transformer power supply

large and heavy

Switching power supply

compact and light

What are possible problems with the power supply? And what can be done about them.

In the practical operation of an amateur radio station, problems and malfunctions can occur if

  • The power supply unit is designed too weakly; The current-carrying cabling is inadequately designed and has too many plug connections.
  • The equipment is insufficiently protected by missing fuses.
  • High frequency enters the power supply unit via the cabling of the station or via direct irradiation.
Interference from (simple) switching power supplies.

Unfortunately, digital voltage conversion generates an interference spectrum that can affect the received signal. High-quality switched-mode power supplies can be recognised by the fact that every possible measure has been taken to minimise this problem or, ideally, to avoid it altogether. A regulator with which the switching power supply's clock frequency can be changed and possibly occurring interfering signals, the so-called birdies, can be "shifted" from the current reception frequency provides the "first aid". Switch-mode power supplies that manage without the aforementioned measure and are free of interference in the entire radio spectrum are naturally "ahead of the game" among radio amateurs.

Ripple (residual hum) due to poor filtering

A good, conventional transformer power supply works with a bridge rectification and has an optimally dimensioned filter chain to keep the ripple as small as possible. With the specifications for current consumption, a distinction must be made between the maximum current that is only permissible for a short time and the permanently permissible current consumption. The voltage control must have a sufficient control range to keep the output voltage constant under changing current loads.

Voltage drop due to poor design

If the voltage drops significantly under load and the LED display and instrument illumination become dimmer, the power supply has a serious problem. Either the power supply is fundamentally too weak or high voltage drops occur at contact resistances. For this reason, the low-voltage line to the transceiver, as well as to other external devices, should be kept as short as possible. Furthermore, even for the standard transceiver output power of 100 W, a cable cross-section of 4 mm² or 6 mm² is quite appropriate. The cables must not contain more connectors than absolutely necessary. A small voltage drop occurs at each plug connection, depending on its quality.

Protect against possible overvoltage

As a standard, a fuse holder with a fuse in the positive wire is inserted in the power supply line of transceivers and many other accessories. In the meantime, it has become common practice to insert a fuse in the negative wire as well (see also FAQs). It is recommended to retrofit a so-called "voltage monitor", an electronic overvoltage protection that switches off the supply voltage when 13.8 V is exceeded and protects the equipment from "overvoltage death". Voltage and current monitors switch off at a defined undervoltage of, for example, 9 V, as well as when the nominal operating voltage of 13.8 V is exceeded, and protect the station, in addition to the existing fuse, which reacts more slowly. Even if transceivers have a reverse-polarity protection diode in the reverse direction to the operating voltage, an additional external reverse-polarity protection cannot do any harm. Some distribution panels offer the function of an over-/under-voltage monitor.

Measures for irradiation resistance

The former so-called banana plug is not suitable for connecting a transceiver. Its contact is too weak and unintentional disconnection would be easy. In addition, the required cable cross-section cannot be connected to these plugs at all. The design as a multi-stranded plug is a better alternative. They are suitable for higher currents in temporary use. However, this is not a permanent solution either. In a fixed station, the transceiver should always be connected to the detachable pole terminals of the power supply unit via a connection that cannot be detached spontaneously by means of ring lugs or crimp terminals.

A recommendable alternative, both for stationary and portable use, are the plug connections of the Anderson PowerPole system. These are standardised, sturdy plugs, sockets and connectors with different sizes and current carrying capacities, labelled in other colours in addition to just red and black. The electrically conductive parts, the contacts, are crimped onto the end of the cable with a special crimping tool and the insulating plug sleeve is pushed on, which locks itself in place. For those who do not trust crimping, the contacts are also available for soldering. In the meantime, the first power supply units and radios on the market are already equipped ex works with connections in the PowerPole standard.

What to look for in the voltage distribution in the shack?

As a newcomer, you can manage without a complex power distribution in your first radio station. But as the number of additional devices increases, voltage distribution is necessary to bring order to the growing "rats nest" of cables. WiMo offers a wide range of intelligent solutions for this purpose.

You should not shorten these to the minimum required length, but leave them longer and tie them together with cable ties to form a coil. Experience shows that the arrangement of the devices is never final. After a rearrangement, the connecting cables are usually too short. It is good to have a reserve in the cable length!

Tip
1.
Choosing the right plug

The former so-called banana plug is not suitable for connecting a transceiver. Its contact is too weak and unintentional disconnection would be easy. In addition, the required cable cross-section cannot be connected to these plugs at all. The design as a multi-stranded plug is a better alternative. They are suitable for higher currents in temporary use. However, this is not a permanent solution either. In a fixed station, the transceiver should always be connected to the detachable pole terminals of the power supply unit via a connection that cannot be detached spontaneously by means of ring lugs or crimp terminals.

A recommendable alternative, both for stationary and portable use, are the plug connections of the Anderson PowerPole system. These are standardised, sturdy plugs, sockets and connectors with different sizes and current carrying capacities, labelled in other colours in addition to just red and black. The electrically conductive parts, the contacts, are crimped onto the end of the cable with a special crimping tool and the insulating plug sleeve is pushed on, which locks itself in place. For those who do not trust crimping, the contacts are also available for soldering. In the meantime, the first power supply units and radios on the market are already equipped ex works with connections in the PowerPole standard.

2.
Use distributor strips

The transceiver must always be connected directly to the power supply unit with its own cable. In addition to the type-specific connection cables included in the scope of delivery, WiMo also has universally usable transceiver connection cables in its catalog. Small consumers, such as external accessories, are supplied via their own connection cables. With the increasing number of external equipment, their connection to the power supply unit quickly reaches its limits. Connecting the accessories is no problem with distribution strips placed behind the radio. A second, separate power supply unit with a lower output can also be used for this purpose. The length of the supply lines for accessories, on which usually only a few 100 mA flow, is not so critical.

Power supply for portables on the move

Whether fieldday, IOTA (Islands on the air), SOTA (Summits on the air) - all these activities require a self-sufficient power supply. Simple battery and accumulator packs are only suitable for QRP operation. A full-blown HF transceiver with 100 W transmitting power requires a power source of higher capacity.

Batteries make power mobile

Typical capacity values of lead batteries are between 30 and 50 Ah for cars and up to 180 Ah for truck batteries. However, the latter are out of the question for portable amateur radio because of their size and weight. Smaller car batteries, which today are only offered in closed, almost maintenance-free versions, are more suitable. Compact, light and maintenance-free are the so-called lead-gel batteries. If the power requirement is not too great, they may be the better alternative for portables. A particularly practical idea for portable radio are the portable battery cases called MegaBox and PowerBox. With them, LiPo or LiFePo4 batteries, as well as lead-acid and lead-gel batteries with capacities of up to 40 or 50 Ah hours, respectively, become a portable power source with universal connection options for radio operation on the move.

Tip for radio hams plagued by man-made noise: Operating a stationary amateur radio station from rechargeable batteries or batteries, even if the 230 V mains is available, can at least largely eliminate interference coming directly from the mains.

Tip

Producing electricity with solar panels - also at home

Of course, even at home at the base station, a backup battery that may be available for emergency power supply can be constantly recharged with a solar panel. This is a sensible measure during a power cut at the latest. Normally, stationary units are recharged via a charger from the 230 V mains. In portables, recharging the battery with a solar panel becomes interesting in order to remain self-sufficient in terms of power supply. Only a charging current regulator is required between the solar panel and the battery. The POWERmini2 is designed for 12 V batteries and a maximum charging current of 10 A and is equipped with all monitoring functions necessary for the charging process.

Furthermore, the PowerGate module with extended functions is suitable for this task. It brings together the voltage sources of the power supply unit, solar panel as well as the radio and the battery and regulates its charging or the supply of the consumer.

An emergency power supply by means of a backup battery can be elegantly combined with a solar panel using the PowerGate UPS switch. In normal operation, the radio station receives its power from the mains unit or solar panel. If there is no load or only a low load, the backup battery is charged. If the mains unit fails, for example due to a power failure, the battery takes over as an emergency power source. Switching from normal operation to emergency power operation is automatic and uninterrupted.

Whether you are looking for a power supply unit, rechargeable batteries or solar systems, from plug-in power supply units to high-performance power supply units, whether analogue with a transformer or as a digital switched-mode power supply unit, as well as accumulators of various performance classes and capacities - at WiMo you will find the know-how and advice for a wide range of products.

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FAQs

Why are positive and negative leads fused in some supply cables?

A 2-pole fuse protection of DC connection cables is required for DC low-voltage systems in motor vehicles and on watercraft without a fixed earth or ground reference for safety reasons. For example, there are still some older, English (vintage) car models which, in contrast to the worldwide standard, have the positive pole of the battery connected to earth. In these cases, a short-circuit current could flow completely unprotected, mainly via the negative cable. In this case, positive and negative cables are always fused. The additional fuse in the minus cable prevents the radio from being destroyed, the cable from burning and the battery from blowing up.

How much voltage drop occurs on the connection cable?

The results of a cable calculator, using three common cable cross-sections as examples, give an idea of the voltage drop on the connecting cable of a short-wave transceiver.

300 W DC input power at 13.8 V, corresponding to a current consumption of 21.7 A, was taken as a basis.

Conductor cross-section Output voltage Voltage drop
6.0 mm² 13.67 V 0.13 V = 0.94 %
4.0 mm² 13.61 V 0.19 V = 1.41 %
1,5 mm² 13,28 V 0,52 V = 3,75 %

Many station accessories are small consumers with only a few 10 or 100 mA. Cables with a core cross-section of 0.75 mm² are sufficient for this. In the current range of several amperes, it should be 1.5 mm². For supplying the transceiver with 20 to 30 A, at least 4 mm² are required.

Why does my transformer power supply hum?

This problem occurs with transformer power supplies when the transformer core is badly packed and there is an air gap between the individual transformer laminations. In this case, tightening the core screw connection can provide a remedy. It is also possible that the strong magnetic field of the transformer causes the housing cover to vibrate. Especially if it is a sheet steel housing and the screw connections have loosened. Furthermore, the hum with the 50 Hz mains frequency also occurs when the load limits of the transformer are exceeded. If mains hum is heard during reception, the sieve chain of the power supply unit is no longer working properly; the charging and sieve capacitors could be incorrectly dimensioned or defective.

Can I improve a lack of radiation resistance and remedy interference emanating from the power supply unit?

Yes, something can be done in DIY without interfering with the unit: For this purpose, the mains cable and the 12 V cable on the output side must be choked directly at the input and output into the unit with high-permeability ferrite ring or ferrite folding cores. This measure improves both the radiation resistance and the transmission of reception interference to the transceiver.