Anyone who uses batteries in model aircraft, RC cars, or model boats has probably come across chargers that are not plugged directly into a wall outlet. They need a DC power supply, often 12 V, provided by an external source.
Depending on the battery and the selected charging current, this power supply needs to be capable of delivering a considerable amount of current.
One solution I use on my workbench is a high-current switching power supply. It is relatively compact and lightweight and can power both a battery charger and other electronic projects. In my case, I use one of these power supplies specifically to power my LiPo battery charger.
But why use a switching power supply? What is the difference compared with a linear power supply? And how do you choose a suitable power supply for the charger?
What Is a Power Supply?
A power supply has the function of providing equipment with the voltage and current required for its operation.
If we have a device designed to receive 12 V DC, for example, we need to convert the energy available from the electrical mains into an appropriate power supply.
There are different ways to do this.
Two well-known architectures are:
linear power supplies and switching power supplies.
Although both can provide, for example, a 12 V output, internally they operate in quite different ways.
How Does a Linear Power Supply Work?
In a traditional linear power supply, we find a transformer operating directly from the mains frequency, along with rectification, filtering, and, depending on the design, regulation stages.
The transformer can reduce the mains voltage to a value suitable for the circuit.
For example, we can start with a high voltage at the input and obtain a much lower voltage at the transformer’s secondary winding.
This AC voltage can then be rectified and filtered to produce DC.
One interesting characteristic of good linear power supplies is that they can have low electrical noise, which is why they remain useful in sensitive applications. The original article specifically highlighted this characteristic.
The Problem Appears When We Need a Lot of Current
A conventional transformer capable of supplying a relatively small current can have quite reasonable dimensions.
But imagine that we need:
10 A, 20 A, or 30 A.
The transformer required to provide higher power can become considerably larger, heavier, and more expensive.
That was exactly the comparison I made in the original article: a linear power supply capable of supplying something like 30 A would require a fairly large and heavy transformer.
For a workbench where we want to power a battery charger, this can be inconvenient.
How Is a Switching Power Supply Different?
A switching power supply, also known as an SMPS (Switched-Mode Power Supply), uses semiconductors operating in switching mode and conversion at frequencies much higher than the mains frequency.
This approach makes it possible to use smaller magnetic components for the same power range.
In practice, we can build power supplies capable of delivering relatively high power with much less weight and smaller dimensions than would be required by many equivalent linear solutions.
That is why switching power supplies are now found almost everywhere.
Chargers, computers, televisions, and countless other devices use some form of switching power supply.
Why Were Switching Power Supplies Important for Computers?
This is an interesting example for understanding their advantage.
A computer requires a significant amount of power and several different supply voltages.
Imagine placing inside a computer case a power supply based on a large conventional transformer sized to provide all that power.
We would have a much larger and heavier device.
The use of switching power supplies made it possible to provide high power without introducing a huge low-frequency transformer inside the case.
This relationship between power, size, and weight is one of the major advantages of this technology.
Why Use a Switching Power Supply for a LiPo Charger?
Now we return to modeling.
When we charge a battery, energy is transferred from the power supply to the charger and from the charger to the battery.
The greater the charging power, the greater the power that may be required from the power supply.
For this reason, a small power supply designed to power circuits of only a few watts may not be sufficient under certain charging conditions.
Bench or industrial-type switching power supplies are interesting because we can easily find models capable of supplying high currents, such as 10 A, 20 A, and 30 A, while maintaining relatively small dimensions.
That is exactly why I started using one with my charger.
Is a 10 A Power Supply Enough?
It depends.
In the original article, I mentioned that a 12 V power supply rated at approximately 10 A can work very well for many charging situations encountered in modeling.
But it is important to understand what this number means.
A power supply rated at:
12 V / 10 A
can ideally provide an output power of up to approximately:
P = V × I
P = 12 × 10 = 120 W
So we are talking about a power supply in the 120 W range.
But this does not automatically mean that any charger rated up to 120 W can be operated at its limit under all conditions. There are conversion losses, limitations of the power supply itself, and specific characteristics of the charger.
The correct approach is to check the charger’s maximum input power requirement and size the power supply with an appropriate margin.
The Charger Does Not “Receive 10 A” All the Time
This is an important concept.
A 10 A power supply does not necessarily push 10 A into the equipment.
This value indicates the current it is capable of supplying under its specified conditions.
The connected load determines how much current will be drawn.
If a particular device requires only 2 A at that moment, it will not suddenly consume 10 A simply because the power supply has that capacity.
Therefore, using a power supply with a current capacity greater than the equipment requires is perfectly normal, provided that the voltage is correct and all other specifications are respected.
Charging Current and Charging Power Are Not the Same Thing
This is another area where confusion can arise.
Imagine that we configure a charger to charge a particular battery at 5 A.
This does not necessarily mean that the 12 V power supply will provide exactly 5 A.
The charger is an electronic converter. It receives a certain voltage and current at its input and delivers a different combination of voltage and current to the battery.
What we primarily need to consider is power, along with the losses in the process.
Therefore, to choose the correct power supply, it is better to check the charger’s input specifications rather than simply looking at the charging current configured for the battery.
Can I Charge More Than One Battery?
Some chargers have multiple channels or allow configurations intended for charging more than one battery.
In this case, the total power demand can increase significantly.
In the original article, I mentioned that a power supply with good capacity can even allow you to work with more than one battery.
But once again, we need to do the calculation.
If each channel requires a certain amount of power, the power supply must be capable of meeting the sum of the demands, while also taking losses and an appropriate operating margin into account.
It is not enough to simply observe that the power supply has several connections available.
Switching Power Supplies Can Produce More Electrical Noise
So far, it may seem that switching power supplies have only advantages.
That is not quite the case.
The switching process used internally produces high-frequency components that can appear as electrical noise at the output or propagate through other paths.
This was precisely one of the limitations I highlighted in the original article.
For powering a battery charger, this usually does not represent the same problem that it might in certain sensitive circuits.
But imagine using this same power supply to power a small audio amplifier.
Depending on the power supply and the circuit, the noise may appear in the audio system as interference.
Is It Possible to Reduce This Noise?
Depending on the problem, we can use filtering techniques.
Capacitors and inductors, for example, can be part of filters designed to reduce certain unwanted components. This possibility was already mentioned in the original article.
But there is no universal filter that we can simply place on any power supply and eliminate all noise.
We need to know what noise we want to reduce, its frequency, its amplitude, and how it is reaching the circuit.
This also shows why a power supply that works perfectly in one application may not be the best choice for another.
Can I Use the Power Supply for Other Things on the Workbench?
This is one of the reasons why I consider it useful to have this type of power supply available.
It does not need to be dedicated exclusively to the charger.
If we have a 12 V power supply with good current capacity, we can use it in various projects compatible with this supply voltage.
Motors, circuits, lighting, and various workbench tests can potentially be powered by it, provided that the electrical characteristics of each setup are respected.
That is why, in the original article, I specifically recommended reserving a small space on the workbench for a switching power supply.
It ends up becoming a tool.
A Switching Power Supply Is Not the Same as an Adjustable Bench Power Supply
It is also useful to make this distinction.
Those metal 12 V switching power supplies that are widely available are normally designed to provide an approximately fixed voltage, although some models allow a small adjustment.
An adjustable bench power supply has a different purpose.
It may allow you to vary the voltage and limit the current, as well as provide displays and other features intended for experimentation.
One does not necessarily replace the other.
To permanently power a charger that requires 12 V, a fixed switching power supply can be an economical and efficient solution.
For developing circuits and experimenting with different voltages, a good adjustable bench power supply offers additional advantages.
Pay Attention to the Power Supply Connections
Some of these metal switching power supplies have exposed terminals.
We normally find connections for the mains input, grounding, and DC output terminals.
This requires attention.
The input operates directly with mains voltage, which can cause serious or fatal electric shock. Do not make connections or adjustments while the power supply is energized, and the mains-voltage parts must remain properly protected against accidental contact.
If the power supply has a selector switch for different input voltages, its position must also be correct before energizing the equipment.
If you do not have experience working with mains electrical installations, use a power supply already protected in a suitable enclosure or seek assistance from someone qualified.
Ventilation Is Also Important
A power supply capable of delivering tens or hundreds of watts produces heat.
Models with perforated metal enclosures use this construction specifically to help with ventilation.
Therefore, do not place the power supply inside a completely closed enclosure without considering its cooling requirements.
Also avoid covering its ventilation openings.
If the idea is to build a small permanent battery-charging station, leave enough space around the power supply for air circulation.
What About LiPo Battery Safety?
The power supply is only one part of the system.
The charger must be appropriate for the battery chemistry and configuration and must be used according to the manufacturer’s instructions.
This is particularly important with LiPo batteries.
A powerful power supply does not make charging better by itself. It simply provides energy to the charger.
It is the charger that must correctly control the charging process.
Therefore, never connect a LiPo battery directly to a 12 V power supply in an attempt to charge it.
The correct system is:
electrical mains → power supply → appropriate charger → battery
A High-Current Power Supply Is a Useful Workbench Tool
Once we start working with modeling and electronics, we realize that many setups require 12 V.
Having a power supply capable of providing a good amount of current available on the workbench avoids improvisation and allows the same equipment to be used for different experiments.
That is exactly how this power supply became part of my workbench.
First, because I needed to power my LiPo battery charger. Later, because of the possibility of using it in other applications.
See the Power Supply I Use in the Video
In the video below, I show my switching power supply in detail and how I use it when charging LiPo batteries.
Want to understand the system instead of just connecting the wires?
Choosing a power supply seems simple until the questions begin:
How many volts? How many amps? How many watts? Why doesn’t a 10 A power supply force 10 A into the equipment? Why does a power supply get hot? Why can a switching power supply generate noise?
When we understand these concepts, we stop choosing components simply because “someone said it works.”
Understanding these concepts helps us choose the right power supply for different applications, considering voltage, current, power, efficiency, and the characteristics of the equipment being powered.
This knowledge also allows us to analyze switching power supplies, regulators, and converters more safely, with a better understanding of how they work and their practical limitations.
To continue exploring content about switching power supplies, rectification, filtering, regulators, converters, and other power supply projects, visit the Power Supplies section.