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September 11, 2007



Wow another automobile company working on electric drives. I can see where a capacitor in addition to the battery can enhance efficiency. Short term dynamic braking and quick acceleration demand can be handled with the capacitor. The energy delivery/energy storage efficiency is nearly 100% for a capacitor. A chemical battery energy storage vs. power delivery efficiency is not nearly as efficient, but the amount of energy stored is typically much greater.

If this is indeed the concept of the Mercedes team, it seems like a good direction. Very interesting. JohnBo


There has been a lot of work done with ultracapacitors and hybrid electric vehicles over the past 10 years. In Australia there have been 2 capacitor boosted hybrid cars built and demonstrated. One was a series and the other a parallel hybrid. The parallel hybrid was used in the 2000 Olympic's opening ceremony. I understand similar projects have been undertaken in Europe, Japan and USA.
Capacitors are great for high power boost and capturing power from regenerative braking, but as with all storage devices, the losses are real and increase with power. To deliver maximum power (not energy), the capacitor will dissipate 50% of the energy internally as heat. Typically under lower power conditions 75-90% of the energy can be stored or delivered. I think ultracaps will eventually be used in most hybrid and electric vehicles but their cost needs to come down a lot.


Hi TonyV,

You would never deliver maximum power from a capacitor (or a transformer) unless it is in a signal circuit. In well designed power applications the efficiency of capacitors and transformers is quite high. JohnBo


I seem to recall short-circuit discharge times on the order of a second. If you are planning to significantly drain the Cap in a few second burst the internal resistive loses would be pretty high. If you charge/discharge in a minute or more, not so bad.


One would not do short circuit discharges in a power application on purpose. The circuit design must limit the current. Therefore, the energy transfer rate must be kept within limits to prevent the significant heat you mentioned. Even a few percent of large kW is a lot of heat. As you can imagine, a capacitor in a high power application must be used efficiently to prevent it from over heating. The internal resistance of power capacitors is very low.

Jimmy Mythbuster

I could really use some help tweaking my mercedes engines which have been lying in the garage for months.

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Firs of all congrats Maxwell. In 1966, Maxwell Laboratories, Inc. was formed by former General Dynamics engineers who had developed capacitors for pulsed plasma thrusters.

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