When you’re building a 12, 24 or 48V power system for touring Australia, whether that’s in a 4WD, caravan, camper trailer, truck, or boat, you’ll eventually come across the term DC-DC converter. And while converters are simple in concept, understanding the difference between isolated and non-isolated models is key to making sure your setup is safe, reliable, and compatible with your gear.
In this guide, we’ll break down what DC-DC converters do, how each type works, and when you should choose one over the other.
TL;DR
❓ What is a DC-DC converter?
- A DC-DC converter takes the voltage from a power source, like a battery, and changes it to a different voltage to power an appliance, like a kettle.
- You need a DC-DC converter when your appliances need to run at a different voltage to the voltage of the battery in your system
❓ What is the difference between isolated and non-isolated converters?
- Isolated converters have completely separate negative terminals, meaning there's a negative terminal for the input and a separate negative terminal for the output
- Non-isolated converters have a shared negative terminal. This means that the input and output negative is 'commonly grounded' and there is only one negative terminal.
❓ Where would you use each one?
- An isolated converter is needed in a system that has electrically-sensitive loads, or when components can't be commonly grounded
- A non-isolated converter can be used in simple or straightforward systems, when cost matters and when the loads aren't electrically-sensitive.
What is a DC-DC converter?
Let’s jump in right at the start - what is a DC-DC converter and what does it actually do? A DC-DC converter is a device that takes a direct current (DC) from a source at one voltage level and converts it to another DC voltage level to supply to an appliance. For example, you might have a vehicle battery system at 12 V, but an accessory that needs 24 V. A DC-DC converter steps up (or sometimes down) the voltage so that your gear can run.
A DC-DC converter is often used to step up the voltage, but they can also step down the voltage, and some even do both - but this all depends on the specific model you buy and the application you need it for.
DC-DC converters are most commonly used in mobile power systems, so your 4WDs, caravans, RVs, boats or any off-grid rig. These converters show up when the accessories or appliances don’t match the battery voltage, so they are an integral part of the energy system.
One key thing to remember here is that DC-DC converters are not the same as DC-DC chargers, and each of them has a different role to play in your system.
Read More: Converters vs Chargers
When it comes to DC-DC converters, their efficiency, size, noise, heat dissipation and wiring requirements all matter, especially when you consider the space and usage of the vehicle or boat you're putting it into. So, let’s have a look at the two main types of converters: isolated and non-isolated.
Isolated converters
What does “isolated” mean?
When we say a DC-DC converter is “isolated”, we mean the input side and output side are galvanically (electrically) separated, meaning there is no direct electrical conduction between them. In an isolated converter, the energy is transferred via the converter itself.
This means that the converter will have four terminals: a positive terminal and a negative terminal on the input side, and a positive terminal and a negative terminal on the output side. The negative terminal on the output is not tied to the negative terminal on the input in any way (except if you choose to tie it externally). That disconnection is referred to as an isolation barrier, which provides a number of benefits and a few trade-offs in the system.
Isolated converter benefits
1. Safety and protection
Due to the output being electrically isolated, the risk of ground loops, unexpected current pathways, or stray voltages is reduced. This can be important on a boat (particularly a fibreglass hull) or caravan where the chassis ground may not be equivalent everywhere.
2. Noise/interference control
The isolation of the input and output terminals helps to minimise electrical noise and interference from polluting the output energy. This is important for applications that require a clear and consistent energy input, such as radio and communication devices and medical equipment.
3. Flexible grounding / floating outputs
Because the output is separated from the input, you can choose to ground the negative output to your chassis or isolate it further. In marine systems, this flexibility can simplify the wiring, allowing for the possibility of a separate negative bus or a separate isolation between the engine bank and the domestic bank.
4. Multiple voltage rails or high difference scenarios
Some isolated converters allow a wider input-to-output voltage difference as the internal transformer handles the change in voltage. This makes isolated converters especially useful when the source voltage and load voltage are significantly different.
Isolated converter disadvantages
1. Cost
The internal transformer, extra componentry and insulation materials increase the cost of this unit compared to non-isolated units.
2. Size and weight
Transformers like these take up additional space and add bulk, which in a tighter 4WD canopy or small boat could have an impact on the usability of the space.
3. Efficiency losses
Due to the addition of the extra internal componentry, the energy flow has extra steps it needs to go through, which can increase the risk of efficacy loss and make the system less efficient than a non-isolated system.
4. Complexity of the installation
The wiring for isolated converter systems is more complex than that of non-isolated systems. When wiring an isolated converter, it is important to ensure that everything that needs to be separated is so, and the system is wired correctly.
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Non-Isolated converters
What does “non-isolated” mean?
If a DC-DC converter is a “non-isolated” model, the input and output share a common ground (negative terminal), and there is no galvanic isolation barrier between the input and output energy. Simply put, the negative of your battery bank would be the same negative as the output negative.
These converters typically have three terminals: a positive terminal on the input side, a positive terminal on the output side and a negative/ground terminal in the middle. Because these converters are simpler than isolated versions, they’re widely used when isolation is imperative.
Non-isolated converter benefits
1. Lower cost
As these converters don’t include the internal transformer and additional componentry, they are often significantly more affordable than an isolated converter.
2. Higher efficiency
These guys have fewer steps for the energy flow to follow, meaning they’re often more efficient. Simply put, fewer components = fewer conversion stages = less wasted energy.
3. Smaller size & lighter weight
The non-isolated converters have less internal componentry, making them lighter and more compact. Because of this, they are ideal for fitting in a compact canopy, in a tight cabinet or within a small boat power centre.
4. Simpler wiring
The common negative offered by non-isolated converters makes them simpler to wire into your system. This means you won’t have complex wiring or have to worry about ‘floating’ negatives in your system.
Non-isolated converter disadvantages
1. Shared negative issues
Due to the input and output sharing a negative, stray current, electrical noise, or different ground potentials can cause some issues in specific systems.
2. Limited in certain isolation-critical applications
If you have sensitive loads in your system, then a non-isolated converter probably won’t be right for you - this should be a major deciding factor for which converter type you need.
3. Wiring must work with the chassis/common ground design
You need to be confident that your chassis-grounding scheme is sound, external negative paths are properly designed, and you’re not introducing unintended return paths via boat hulls, trailer frames, etc.
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Which converter should you use?
What you need to consider
1. Your grounding, chassis or hull situation
- If you are in a vehicle (4WD, caravan) where the chassis is used as the common negative, and your accessories share that ground, a non-isolated converter is typically fine.
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If you’re on a boat or hull where ground reference is more complex, or you cannot rely on a single common negative or chassis ground, then an isolated converter might be more beneficial.
2. The sensitivity, noise and load of your electronics
- If you’re powering very sensitive equipment such as radios, monitoring gear, and medical devices that might pick up electrical noise, then isolation would be the better option.
3. The difference in voltages
- If the difference between your source and load voltages is large, or you want flexibility in how the output is referenced, an isolated converter may give more design freedom.
4. Space, cost and efficiency
- For standard automotive tasks where isolation is not required, you might prefer the non-isolated option because it’s more compact, efficient and cheaper, which often makes sense in a touring rig.
5. Environment, safety and installation context
- For fibreglass hull boats and other marine applications, there may be additional safety features required and the risk of corrosion increases. An isolated converter may help mitigate stray current corrosion and galvanic problems.
- In a 4WD with an integrated system with wiring close to the chassis and other loads, the wiring simplicity of a non-isolated converter may win.
Final thoughts
When planning your mobile power setup (whether you’re 4WDing across the Simpson, caravanning the Big Lap or boating the Aussie waterways), your choice of DC-DC converter should reflect how your system is wired, what loads you have, and where you are installing within the vehicle/boat.
Our rule of thumb:
use a non-isolated converter when your system is straightforward, cost matters, and the ground is shared, and use an isolated converter when design complexity, grounding issues or sensitive loads demand it.
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Isolated vs Non-Isolated DC-DC Converters