A converter’s efficiency tells you how much of the power you put in actually comes out the other side — and what happens to the rest. That single number decides how hot the unit runs, whether it needs a fan, and how much of your battery you never get to use. This guide explains the figures in plain terms and shows how to compare the converters in this shop.

The short version

At 95% efficiency, 5% of the power becomes heat. At 1,000 W that is 50 W of heat — enough to make a small metal case genuinely hot. At 98%, the same 1,000 W produces 20 W. That difference is why a well-designed converter can be sealed and fanless while a mediocre one needs forced air.

What efficiency actually measures

Efficiency is the ratio of output power to input power, expressed as a percentage:

Efficiency = (power out ÷ power in) × 100

Everything that does not come out is lost, and almost all of it leaves as heat. A converter running at 96% does not lose “4% of the voltage” — it loses 4% of the power, which is why the loss grows quickly as you scale up. Double the power and you double the heat you have to get rid of.

The table below shows the heat produced at a few common efficiencies and power levels. It is the most useful way to think about the number, because heat is what limits how small a converter can be and whether it can run without a fan.

Heat produced (watts) at a given output power and efficiency
Output power 90% 95% 96% 98%
100 W 10 W 5 W 4 W 2 W
500 W 50 W 25 W 20 W 10 W
1,000 W 100 W 50 W 40 W 20 W
2,000 W 200 W 100 W 80 W 40 W

Where the losses actually go

Four things consume the missing percentage, and they matter differently depending on how you use the converter:

  • Switching losses. Every time the internal transistors switch on and off they dissipate a little energy. Higher switching frequency means smaller components but more of this loss.
  • Conduction losses. Current flowing through transistors, copper windings and tracks meets resistance. These losses rise with the square of the current, which is why a 100 A converter is a much harder design problem than a 10 A one.
  • Magnetic losses. The inductor or transformer core heats up as the magnetic field changes direction, thousands of times a second.
  • Standby or idle current. Some converters draw a small current even with no load. Where this is documented for a model in this shop, it is listed as a typical and maximum idle current in milliamps — useful if the converter stays connected to a battery for weeks.

Two consequences follow from that list. First, efficiency is not constant: it is usually best somewhere around 30–80% of rated load, and worse at very light loads. Second, a converter quoted at 97% at its rated current may be closer to 90% when it is idling along at 5% load.

Why fanless, high-power converters are possible

Heat has to leave the case somehow. There are two ways: move air over it with a fan, or make less heat in the first place and conduct what remains into a metal body. The second approach is what a high-efficiency design allows.

Across this catalogue, the models with the highest documented efficiency are also the ones documented as naturally cooled — no fan — including units rated above 1,400 W. A fan is a moving part: it wears, it can seize, it ingests dust and it makes noise. Removing it is a genuine reliability and comfort advantage in a van, a boat or a cabinet.

Important caveat

Fanless does not mean cool. A 1,400 W converter at 97% still produces roughly 42 W of heat, which is about as much as a small incandescent bulb. It must be mounted where that heat can escape: on metal if possible, with free air around the case, and never buried under bedding or inside a sealed box with no ventilation.

How to read the efficiency figures in this shop

Every number on this site comes from the supplier’s documentation for the exact model, and is labelled as supplier-stated rather than independently measured. Three habits will keep you out of trouble:

  • Compare like with like. Efficiency is quoted at specific conditions — usually nominal input voltage, rated output current and around 25 °C. Two converters quoted under different conditions are not directly comparable.
  • Expect variation across a range. A product with several models may document different efficiency for each; the higher-current models in a family are often quoted slightly lower because conduction losses rise with current.
  • Treat it as one factor among several. Input range, current capability, thermal design, protection features and whether the output is adjustable usually matter more to whether the unit suits your system.

For reference, the documented figures currently published in this catalogue run from about 89% to 98%, with most models in the 94–98% band. That is typical for modern synchronous switching converters, and it is a long way ahead of the linear regulators and crude “voltage dropper” circuits that still appear in cheap accessories.

Choosing a converter with efficiency in mind

These are the models with the strongest documented efficiency and thermal story in the catalogue right now. Check the input range and current against your own load before ordering — the right answer is the smallest converter that comfortably covers your worst case, not the largest one available.

High-efficiency models in the shop

If you have a wide input voltage — an alternator that swings, or a battery pack that goes from 40 V to 58 V — a wide-input model with a documented range is usually a better choice than one sized tightly around a nominal figure. The guide to stacking and cascading converters covers what to do when one unit cannot cover the whole span.

Practical rules that cut losses

  1. Size for headroom, not for the sticker. Running a converter at 70–80% of its rating usually lands nearer its best efficiency than running it at 100%.
  2. Keep cables short and thick. A 1 V drop in a cable at 50 A is 50 W of heat outside the converter — more than the converter itself loses, and invisible in its efficiency figure.
  3. Feed it near its nominal input. Efficiency is usually specified at nominal input; running far below it increases input current for the same output power.
  4. Give the case somewhere to put its heat. Metal mounting surfaces, vertical orientation and free air all help.
  5. Do not stack hot units. Two converters mounted face to face share each other’s heat and both run hotter than either would alone.

Frequently asked questions

Does higher efficiency mean more output power?+

No. Efficiency tells you how much input power is wasted, not how much power the unit can deliver. Two 1,000 W converters can have very different efficiency and therefore very different heat output, but both are still 1,000 W units.

Is 95% efficiency good?+

For a modern switching converter, yes — it is a normal, solid figure. Above 97% is excellent for a high-current unit, and below about 92% usually indicates an older or more cost-driven design.

Why is efficiency lower at low load?+

Because a fixed amount of energy goes into switching and control regardless of how much power you take out. Spread over a small output, that fixed overhead becomes a larger percentage.

Can I run a fanless converter continuously?+

Yes, if it is mounted with free air around it and within the supplier’s stated conditions. Fanless designs are rated for continuous operation; they simply depend on the installation to carry heat away. Never enclose one in a sealed, insulated space.

Do these figures mean the converter has been independently tested?+

No. The efficiency and thermal figures published here are supplier-stated for the exact model and are not the result of independent testing by PVShop. Where the documentation is missing, we leave the value blank rather than estimate it.

Efficiency, power and cooling values quoted above are supplier-stated for the exact models and are not independently tested by PVShop. Always check the model’s own specification section on its product page before ordering.