Ultracapacitors: The Key to Effective Electric Vehicles?

One problem with Ultracapacitors (or any storage medium) that I seldom see addressed is since they can release energy so quickly what happens when they do accidentally like in a motor vehicle accident or after during the rescue? Ultracapacitors may have their place in conjunction with batteries but to store all of a vehicle's power in a capacitor would be super dangerous if it was discharged all at once via a direct short.

The direct short issue isn't the major problem. All systems (battery or capacitor) capable of storing and providing energy for vehicle use would have the same issue. The power density required for vehicles mandates this. The problem is typically overcome with small localized fuse systems and other safety mechanisms. As a bonus most capacitors aren't made of materials that burn or explode like the organic electrolytes found in Li Ion cells. Thermal runaway can be a bitch.

The major problem with capacitors right now is that of specific energy density. How many Watt Hours can you store per pound(kilogram) of capacitor. Regrettably capacitors are still lagging WAY behind lithium based rechargeable batteries. The best Ultra Caps I have seen are running at about 1/10 the specific energy density of the new generation of Lithium rechargeables.

There are rumors of this changing. EEstor is one company that is claiming to have a capacitor with enormous capacity. So far they seem to be just vaporware, but who knows. At this point most experts are sceptical of their claims.

Capacitors with a high enough specific energy density would be the holy grail of electric vehicles. Super quick charging, almost unlimited power density and extremely long life-cycle. The person who creates it will be a gazillionaire.

Good luck someone.

-Doug

Well that just seems like something we will have to get past. I have always believed that capacitors would be the real key for reliable electric cars. Their many variances and turnover rate for energy could really be used as an advantage with vehicles. Yes, there are plenty of problems to begin with, but the same is true for the invention of motor cars to begin with.

What about using the entire skin of the vehicle as a laticework of capacitors topped with solar cells? Just think of the great anti-theft features that could be integrated.

I used a lift truck condenser to great effect.

Brad

I'm curious, what is the best way to discharge an ultracapacitor to do work?

Are they large amperage and nominal voltage, and the load directly attached in series with a control or does the voltage have to be limited?

Brad

Good question,

I confess I don't know enough about the subject and I don't have any need presently to find out. My garden needs tending, car needs an oil change, dog needs to be walked - yes dear, I heard you - bye now

The answer really depends on the capacitors and the application. The Ultra Caps can be run either in series for more voltage or in parallel for more capacitance(storage). The internal impedance of the Ultra Cap determines much of its functional characteristics. Also the way an Ultra Cap is constructed also determines what voltages it can handle, etc. There are a wide variety of Ultra Caps out there now and each one has different specs.

A strong word of caution. If you ever use Ultra Caps in a higher voltage array (anything 50 volts or up as a safe limit) use extreme caution. They can dump HUGE current over an extreme short burst. Easily enough to kill you. Just a friendly thought to keep in your head.

In a motor control environment you would typically take one of two approaches. On PM motors you would run the output from the Ultra Caps through a DC-DC converter to get it up to the correct working voltage. Then you would control the motor speed through Pulse Width Modulation and a series of IGBTs controlling the power going to the motor.

If you are using some form of AC motor you would take the power from the Ultra Caps and run it through a DC-AC inverter and motor controller. The motor controller would be responsible for modulating the AC at the correct frequency to run the motor.

All of this is a gross simplification, but it should give you the broad picture of how they are used. Actually in these examples the caps can be replaced by rechargeable batteries and the concept is the same.

Currently there are no Ultra Caps that can store enough energy for their size and weight to be practical in any useful vehicle. Hopefully this will change at some point because they are a much better technology than rechargeable batteries.

Thank you drobertson,

About, roughly, 8 years ago one of the "feel good" science mags published an article about a Semi tractor trailer using 2 4X4X2 foot Ultracapacitors filled with carbon foam plates and a liquid electrolyte that had very impressive some what vague specs. This tells me that the Ultracapacitors they used were not a single cell but more likely many small cells in a single case.

What I don't understand is why is range such an issue when recharge could be done at a stop light. Theoretically it could even be done while moving at what ever speed. Most driving is done within 100 miles of home so even this would be moot over 90% of the time.

As for the high voltage or amps, that is an issue that precautions and common sense will sort out.

I have no clue what losses are for Ultracapacitors, Converters, and Controllers but with electric motors at 92-98% it has to be way better than gasoline ICE.

Thanks again

Brad

Hello U V

<"....What I don't understand is why is range such an issue when recharge could be done at a stop light....">

OK, so you have this electric car, with a supercapacitor on it rated at 300 Volts, and you stop at a Stop light, plug in for a charge, to drive another hundred miles.

Think about the energy requirements for driving that hundred miles in your fancy electric car, powered by that supercapacitor.

So....at the stop light, you have 1 minute to stop, get out, plug in a cable from the roadside charger unit to your supercapacitor, swipe your charge card, switch on the charger unit, wait the 30 seconds or so for the charge, switch off the charging connection, remove that charging cable, place it back at the charger unit, ready for the next customer, remove your payment swipe card, and get back into your car, ready to drive off.

So...in some 30 seconds - and others are trying to do the same operation at the same time....you have to obtain enough energy into your 300 Volt supercapacitor to drive 100 miles in your car.

How large a power distribution network plus the charging network are you going to need, and don't forget that cable which is going to have to carry several million amperes, and you will need a crane to move it to get it to your car, then the socket on your car is going to be half the size of the car, which means by the time you get the supercapacitor in the car as well, to take and store all that energy, you have no room for a driver.

Several million Amps, you say? what do you mean?

At the instant of charge commencement of a capacitor, it draws maximum current, which tapers off exponentially as the Voltage between the plates rises - a well-known phenomenon used in timing circuits, radio, TV and electronics.

So let's face it, folks, the supercapacitor on it's own, at present and possibly future stage of development, is only ever going to be a short-term energy output device, and charging it will take time, far longer than most people realise.

The supercapacitor, like all electrical devices, does have extreme mechanical strain placed on it, as it charges and discharges, which means it needs to be made very strongly, to avoid rupture, which would be sudden and catastrophic.

Kind Regards....

Read about an extremely successful electric vehicle here, and it did incorporate supercapacitors, for massive short-term discharge power, as needed.

PML Builds 640hp Electric MINI

Eat your heart out, take up a collection, to buy me one for Christmas 2008, please.

Note that no prices for this supercar have been given in that article.

Kind Regards....