Ultracapacitors are terrible at storing large amounts of energy, compared to batteries.

They're very good at charging/discharging quickly, and going through lots of cycles, but at best they can only hold something like 1/300 to 1/1000 of the energy that an equal weight lithium battery can.

Range extension requires storing a lot of energy...batteries are reasonable for that. Hydrocarbons are extremely good. Capacitors are awful.

Yes I understand that aspect, but the concept I have in mind would constantly discharge the Ultracapacitors while being charged by an ICE.

A 400F supercap holds about 1/20th the energy of a single AA battery. Whilst being both heavier and larger. That probably answers your question.

But they charge much quicker. That's why there are concept for stop&go applications like public transportation. But I have not found any information regarding constant charging via ICE.

And what's supposed to be the advantage of feeding the electrical power from an ICE through a supercap into an e motor, instead of just feeding it directly into an e motor ?

In that case, why wouldn't you just connect the ICE straight to the drive motor? What is the ultracapacitor helping you with?

If the ICE is putting out more power than the motors need the ultracapacitor will fill up very quickly. And if the ICE isn't putting out enough power then it'll discharge very quickly. You'll get a *slight* evening out of load on the ICE but it won't be very big, definitely not enough to provide meaningful range extension.

Well I imagine the engine could constantly run at a sweetspot like 2000 rpm for increased fuel efficiency.

>In that case, why wouldn't you just connect the ICE straight to the drive motor? What is the ultracapacitor helping you with?

constant rpms of the engine

That doesn't require a super cap. You can just strap the e motor to the engine directly. Or use a battery as buffer.

So long as you don't NEED super fast charge/discharge, which this application doesn't, batteries are pretty much always better than caps.

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This is essentially the Chevy Volt from 12 years ago. An ICE to charge up batteries with no direct engine to wheel connection.

Constant RPM on an engine isn't going to increase the running efficiency so much that it offsets carrying 200kg of additional batteries ( or supercapacitors).

Plus the extra efficiency loss of mechanical-electric-mechanical conversion.

Usually batteries are used for this, as they can store far more energy and if they're big enough, their maximum power is also large enough for quick charge/discharge. This means that an ultracapacitor isn't necessary for power density reasons and the battery is better for energy density reasons.

For example, a number of electric cars are already traction-limited for acceleration and capable of driving two to three times any finite speed limit they encounter, while still having a 300-400 mile range at full charge.

Conversely, late-generation Honda Insights use a small, but high efficiency motor that is used mostly to charge a battery. It turns on, runs at max efficiency charging the battery, then turns off when the battery has enough charge. The battery provides electric traction and is capable of both load-leveling (since the motor is providing more power than is usually necessary for driving at any given moment) and is capable of providing more power than the motor is in short bursts! This drivetrain is not entirely dissimilar from a diesel-electric train.

Due to ultracapacitor's low energy density, they are only good where you need extremely high power densities (higher than are generally needed by modern electric vehicles) or extremely high charge/discharge cycles. So they've been examined for public transit purposes (where they might not even be carried by the vehicle itself, but rather be installed in a fixed location and connected to the vehicle by rail or overhead lines), but they don't really make sense for cars and trucks.

You don't need an ultracapacitor for that. You're describing a genset...ICE engine running at constant RPM powers a generator, generator powers the wheels. You adjust power by adjusting throttle, you don't need to change engine RPM. So, again, what is the ultracapacitor providing?