Eye on electronics

Motor,  Sep 2003  by Dale, Mike

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The huge storage capability of the Super Caps allows them to be used differently than conventional electronic caps. Instead of blocking DC and passing AC, these caps can be used to store energy to power devices. Super Caps aren't going to replace the car battery, but they're going to complement it by compensating for its weaknesses.

Electrical energy is stored in a battery via a chemical reaction between the lead and the sulfuric acid/water electrolyte, which takes time. This means it takes time to charge the battery and time to take the charge out of the battery. In the case of electrical motors, this really is a disadvantage. A starter motor, for example, may need an initial surge of 600 amps to begin cranking the engine. Once the engine changes from being in static friction to sliding friction, the current requirement drops back into the 100-amps range for the rest of the start cycle. The initial current surge has a big effect on battery life, even though they're designed to meet it.

Capacitors store their energy on the plates and in the dielectric. No chemical reaction has to occur to release energy. Conventional lead-acid batteries are greatly affected by cold weather because time needed for the chemical reaction doubles with every 10[degrees]C drop in temperature. Super Caps are largely unaffected at -40[degrees]G.

The significance of this characteristic was revealed in a study conducted by a university in Germany. Researchers there first measured the starter performance of a BMW. They found they needed a 900-amp initial pulse for breakaway torque, followed by a continuous current of 84 amps. They measured the start cycle as being from 2 to 5 seconds long at a temperature of 1[degrees]C. To supply this amount of power, the conventional battery needed to be of 50 amp/hour capacity.

By using a Super Cap of 1400 farads in parallel to a 7-amp/hour battery, they were able to separate the two current needs. The combination of the motorcycle-size battery and the Super Caps was able to start the engine ten times without the need for recharging at room temperature. A conventional vehicle battery weighs 35 pounds; the combination of Super Caps and small battery weighed less than 10 pounds.

So here's how our diesel-driving friends might benefit from Super Cap technology. The problem with starting diesels in the winter has always concerned fuel gelling, fuel control and the huge amount of current needed to run the starter motor against all of that compression. The first two issues are less of a problem today. Winter-blended fuels currently available are much more gel-resistant, and engine management electronics have greatly improved fuel injection and control.

What was still needed was a better way to power the starter motor. By putting Super Caps in parallel with the battery, it's possible to get up to 50% more starting torque at a higher cranking rpm. That's what's needed to get a cold diesel going.

Super Caps do not degrade with time like lead-acid batteries. Their useful life should be the same as that of the vehicle. By taking the peak starter current load off the battery, the Super Caps actually improve battery life. Again, unlike conventional batteries, the Super Caps contain no toxic metals.