Peter Knudsen
5 min readMar 7, 2016


The Fix for High Electrical Loads at Low Engine RPM

Put simply, what does an alternator actually do? Obviously, it’s an integral piece of any vehicle, but what is the textbook definition of the function of an alternator? Quite fundamentally, an alternator generates electric power while a vehicle is running. Another way to put this is that alternators generates electricity to satisfy the electrical load of vehicles. Batteries are electrical power storage devices that have a limited storage capacity and they require that it is replenished as vehicles travel.

For most vehicles, such as commuter automobiles, SUVs, and small pickup trucks, the electrical load that an alternator satisfies is small. Everyday ordinary vehicles do not have a need for a heavy-duty, high output alternator. They simply don’t need one. A stock alternator works well and most likely will not need replacing until after 100,000 miles.

Let’s think for a moment about larger, heavy duty vehicles. These heavy duty vehicles include fire trucks, utility company bucket trucks, refuse collection trucks, and construction vehicles. Most of the time, these vehicles are equipped with stock alternators that are assumed to never spend significant amounts of time at a work scene where their batteries storage capacity will not be depleted. There are several reasons why this can cause problems.

Why does a heavy duty vehicle require a special alternator?

Looking back at commuter cars or SUVs for a second, let’s think again about the electrical load required to be satisfied by their alternators. There are not electrically powered devices beyond the radios, dash and head lights, and heating/air conditioning fans that alternators need to power. In a vehicle such as a fire truck, however, there is an enormous electrical load , especially when the vehicle is operating at idle working at the scene of a fire. The same goes for refuse collection vehicles and utility company bucket trucks — all of these vehicles have one thing in common: a large electrical load that must be satisfied at idle. A simple, run of the mill stock alternator does not handle this well. The most important specification for these types of vehicles is a heavy duty alternator that performs well at low engine RPM and at engine idle.

Why is the output of heavy duty alternators at low RPM so important?

A typical alternator is designed either for optimization at low RPM (idle) or high RPM (driving), but not both operating scenarios. Because of this, most alternators are optimized at high RPM, and are marketed with these high output numbers in mind. When optimization at low RPM is needed, however, these have an exceedingly low output. The first thing a prospective buyer of a heavy duty alternator should do is find out the Ampere output at idle, not at high speed. Our alternator gets 50–250% better output at idle than similar sized heavy duty alternators.

High output at high RPM is not the golden goose. The golden goose is high output at low RPM, while also reducing fuel usage and increasing engine life. It’s simply common sense to ask yourself, “Shouldn’t your alternator give you the output necessary just when it is most critical while working at the scene?”

Eco-Tech’s use of permanent magnets in their heavy duty alternators allows for a generation of approximately 260 Amperes at idle at 1,800 RPM compared to its competitors, which would need to much higher engine RPM to produce the same output. First of all, this is tough on the engine. While a stock alternator in a heavy duty truck may last for a few years, the extra pull required on the engine leads directly to more maintenance, more service, and in some cases, replacement. Eco-Tech’s heavy duty alternators are designed for optimization at low RPM in part to increase the life of the engine. In a heavy duty vehicle with a stock alternator, the engine has to work harder to carry the same electrical load.

Other Benefits of Choosing Eco-Tech

Beyond extending the life of the engine, which is an important issue for a heavy duty vehicle, a low RPM alternator will also extend the life of the battery. What happens when a high electrical load is needed at idle and the alternator does not supply the full need? Battery deep discharge cycling occurs when a stock alternator simply can’t handle the load. Using a heavy duty Eco-Tech alternator may eliminate this problem and extend the life of the battery. This also puts less strain on the alternator as well, extending its life. An Eco-Tech alternator can handle the electrical loads of emergency vehicles, including vehicles that are equipped with static inverters and magnetic brake retarders.

Eco-Tech can also save money for vehicles that require extra components to be installed to bear the brunt of a large electrical load. In heavy duty vehicles that still carry a stock alternator, devices such as high idle devices, load shedding devices, and multiple battery packs and switches are common. The choice of an Eco-Tech alternator usually eliminates the need for any of these extras.

Reduction of the Carbon Footprint

My road to the creation of the perfect heavy-duty alternator came because of my interest in reducing emissions, and creating something that was on the whole, environmentally friendly, and ideal for both consumers and the environment. I actually graduated from Yale with a B.A. in economics, and then after two years on active duty in the U.S. Navy Pacific Fleet, I attended the Graduate Business School at Northwestern University and received an MBA. During these years, I developed an interest in improving fuel economy. My early partner at Ecoair was a physicist, who basically taught me the ropes of environmental engineering. After years of hard work, we developed the line of Eco-Tech alternators.

One of the most important facts to me about our products is the improvement of fuel economy. Trucks such as utility bucket trucks, garbage trucks, tow trucks and ambulances drive routes, and/or long distances — it just makes sense to improve fuel economy for heavy duty vehicles. In the improvement of fuel economy, the carbon footprint is also reduced. An Eco-Tech alternator eliminates the extra fuel needed during high output operation. For the 7.3L Ford engine specifically, this was a 52 percent reduction. For all engines tested, there was a 50 percent reduction in engine drag due to the high efficiency of Eco-Tech heavy duty alternators and the elimination of high idle systems, i.e. devices whose function is to increase engines’ RPM’s only to increase the electrical power generated. Does it really make sense to rev up a 200 to 500 horsepower engine to supply the 5 to 10 horsepower needed for the alternator?

The Bottom Line?

At the end of the day, one of the most important things to clients is saving money, and switching to Eco-Tech accomplishes this. In the first year of operation the fuel cost can pay for the total cost of an Eco-Tech alternator. When you take into account the costs for wear and tear, maintenance, and battery replacement, an Eco-Tech high efficiency, heavy duty, low RPM alternator just makes sense.



Peter Knudsen

Engineering Solutions to make a better world.