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tdscanuck t1_iy8w13p wrote

Reply to comment by EvolutionVII in ELI5:Why aren't ultracapacitors used more often as range extenders in Hybrids? by EvolutionVII

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.

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EvolutionVII OP t1_iy8w989 wrote

>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

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phiwong t1_iy8ywx8 wrote

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).

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Pocok5 t1_iy90a4l wrote

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

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left_lane_camper t1_iy99xw4 wrote

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.

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tdscanuck t1_iy99zhf wrote

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?

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