Understanding Ham Radio Power Supply Basics
Voltage and Current Requirements for Amateur Radio Equipment
Today's Ham radios operate on 13.8-volt power. It's the average voltage that an automobile electrical system produces, allowing your radio to be powered in your vehicle or at home. Most amateur radio equipment is designed with this standard in mind, though most Amateur equipment is marked with a tolerance figure in addition to the nominal voltage and this is usually given as 13.8 +/- 15% which would mean it is safe to run it at any voltage between 13.8 less 15% (12V) and 13.8 plus 15% (15.87V).
When it comes to current requirements, a transceiver with a maximum output power of 100W requires about 25A of current at 13.8V when you are operating the radio at full throttle. This high current draw is due to amplifier efficiency factors, as RF amplifiers are not 100% efficient. In fact, some are only around 70-75%, others as low as 50%. That gives a current consumption in the 12A to 15A range alone, let alone powering other circuits in the radio.
DC vs AC Power Considerations
With a few exceptions—like amplifiers—you won't plug your gear directly into a 125V wall socket. Instead, you'll need a good power supply to operate your station. The reason for using DC power stems from practical considerations: without an inverter or internal transformer, DC power is essential. It does not directly plug into an AC outlet. DC power performs better than batteries and will feed the voltage that a system needs.
Power safety in DC systems differs from AC systems. In DC systems, because of the generally low voltages involved (less than 30 volts), power safety is less concerned with preventing shock than with minimizing excessive current and poor connections, which create a lot of heat and are significant fire hazards. You must pay careful attention to conductor size and keep connections tight and clean.
Power Consumption of Different Radio Types
Different types of amateur radio equipment have varying power requirements. A typical transceiver might draw around 20A during transmit, while other accessories may only require a few amps. Additionally, amplifiers can significantly increase power consumption, sometimes exceeding 100A at peak loads.
When calculating power needs, it's important to consider all equipment in your station. Calculating your total power needs involves summing the current draw of each device under maximum load. Selecting a power supply that can comfortably deliver current above your maximum combined load ensures stable operation and prevents overload issues.
Types of Ham Radio Power Supplies
Linear Power Supplies: Pros and Cons
Linear power supplies are one of the grand elders of ham radio. They've been around as long as radio itself. The principle of operation is fairly simple. The linear design uses a beefy transformer to take the AC input (typically 120VAC or 240VAC) and step down the voltage, then rectify and filter the input into a DC output of 13.8 VDC.
Linear power supplies offer significant advantages for amateur radio applications. They produce clean, quiet DC voltage with little to no electromagnetic noise. This makes the linear power supply a great choice for use in radio communications. Although it's possible with a linear supply they almost never make any RF noise, making them particularly suited for sensitive receiving applications.
However, linear supplies have notable drawbacks. These power supplies are often large, heavy, and more expensive than switching power supplies. The large transformers and filter circuits generate a lot more heat, which in turn requires large heat sinks to compensate. Due to all these components, they are also quite heavy. The more power they provide, the heavier and larger they become. In addition, their energy efficiency is fairly low compared to a switching power supply.
Switching Power Supplies: Efficiency and Noise
Switching power supplies are a relative newcomer to ham radio. Their operation is more complex: In a switching power supply, AC input is immediately converted to DC, but it is not stepped down to a lower voltage right away. The high voltage DC is fed into a switching transistor. The switch pulses or "switches" the DC on and off at a very high frequency, effectively making it AC again.
The main advantages of switching supplies are their efficiency and compact size. Switched Mode or Switching power supplies are smaller, lighter and more advanced. They also operate at considerably higher efficiency than a linear model. Switch power supplies also generate less heat, which can be an important advantage when operating in a small ham shack or in an area with limited air circulation.
The primary concern with switching supplies is potential RF interference. The drawback to switching power supplies is that they can introduce RFI noise. This can be a problem with inexpensive, lower quality models and small, "brick" style power supplies intended for general consumer electronics, but is not generally an issue with power supplies intended for radios and built by high quality, name brand manufacturers.
Battery-Based Power Systems
Battery systems offer unique advantages for amateur radio operations. They provide clean, RF-quiet power and can serve as backup during power outages. Typical capacity values of lead batteries are between 30 and 50 Ah for cars and up to 180 Ah for truck batteries. 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.
Modern portable battery solutions have evolved significantly. 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.
Key Specifications and Features
Current Rating and Amperage Requirements
Proper sizing of power supply current capacity is crucial for reliable operation. Choose a power supply that can handle at least 25–30% more current than your radio's maximum draw for reliable performance. Running too close to the limit can lead to voltage drops or overheating during transmission.
You'll want a well-filtered supply with the proper DC output voltage and a continuous current rating at least 20 percent higher than your maximum requirements. This safety margin ensures reliable operation during peak demand periods and allows for future station expansion.
Voltage Regulation and Ripple Specifications
Voltage stability is critical for proper radio operation. The operating voltage output must be clean, stable and short-circuit proof. Poor voltage regulation can cause significant problems: Low voltage, especially when transmitting, can cause radios to exhibit all sorts of strange behavior. The microprocessor may not function correctly, leading to bizarre displays, loss of external control, and incorrect response to controls. Low voltage can also result in low power output or poor RF stability.
Ripple voltage specifications are equally important. Choose a power supply with low ripple voltage to minimize interference. Look for specifications recommending ripple under 100mV for optimal radio performance. Power supply outputs need to show less than 100 mV of AC to ensure clean operation.
Thermal Management and Cooling
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.
Fan noise can be a significant concern in ham shacks. 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.
Protection Circuits and Safety Features
Modern power supplies should include comprehensive protection features. Over-voltage and over-current protection are essential safety features to mitigate risks to your equipment and prevent any potential hazards. 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.
Proper fusing is essential for safety. 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.
Popular Ham Radio Power Supply Models
Astron Linear Power Supplies Review
Astron power supplies have earned an excellent reputation among amateur radio operators. I recommend the Astron power supplies without any reservations. I have lots of Astron SS series power supplies and they are very reliable. I've had some running continuous for so long I can't even remember how longs its been, maybe 25yrs?
The reliability extends beyond just operation to service support. Astron also has the best warranty in the business, if anything goes wrong they just fix it for free or send you another. You can even buy a broken Astron power supply cheap at a swap meet, take it to Astron and they will fix it for about $20 flat rate.
For switching supply options from Astron, Some switchers yes, Astron not really, no HF noise detected that I or any of the dozens of friends who have them have found. There are a whole bunch of Astron switchers in HF operation and if they had problems we would be hearing about it.
MFJ Switching Power Supplies Comparison
MFJ power supplies are manufactured by third parties and rebranded. While people laugh about the lack of quality in MFJ products, the 4230 is made by somebody else, & also sold under the Jetstream, & QJE name. These supplies are made by a company called Nissei Electric, & sold under the MFJ, Jetstream, & QJE names. Mine has always been perfect, & I have been very pleased.
User experiences with MFJ units have been generally positive for VHF/UHF applications. The fan does not make noise on the MFJ, & it runs slowly all the time, though some users report minor HF interference issues with certain models.
Samlex and TekPower Options
Samlex power supplies are well-regarded in the amateur radio community. Samlex 1223 - 23/25 Amp switching - SEC-1223 - $115 This switching power supply was a workhorse for five years. I probably turned it off five times during the five years. It was used almost daily so I just left it on. It powered an HF and mobile radio simultaneously.
For budget-conscious operators, TekPower offers viable options. It's the TekPower TP50SW 50 Amp 13.8V Analog DC Power Supply with Cigarette Plug which has both post terminals on the back, and a 12V plug on the front. It has a meter that displays volts or amps. I haven't had to use that last one, and haven't detected any RFI from the unit.
Installation and Setup Guidelines
Proper Grounding and Electrical Safety
Grounding serves multiple critical functions in amateur radio installations. The first thing to know is that there are three functions served by grounding in ham shacks: 1. Electrical Safety 2. Stray RF Suppression (or simply RF Grounding) 3. Lightning Protection. Each has it's own set of requirements, but not all station setups need every kind of ground.
For safety grounding, proper wire sizing is essential.
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