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Ultracapacitors and Bridge Power PDF Print E-mail
Written by Greg Allen   
Thursday, 06 November 2008

Bridge Power is often described as short term power to “bridge” from a long term power source to another power source.  Green EnergyAlthough there are many applications where it is used, typically bridge power is used in mission critical applications like a data center or communication center where you cannot have any interruptions in power and downtime. 

So when you have a power failure in one long term power source.. you need a short power source to bridge you to the other standby power source.  Most large buildings and hospitals have a generator that will kick in if the power fails. Since there is a lag between the main power source and generator, batteries are typically used as a temporary power source to bridge the power.

A couple of problems have been the reliability and the high cost associated with extending bridge power beyond a few minutes.  In August 2003 there were major power outages in Canada, New York, Pennsylvania, and Ohio.  Once a massive failure occurred in one station, it continued like a domino effect to other power stations across the north east.  I remember lots of conversation about the reliability of the batteries that were to keep the stations up and running.  The batteries were not maintained and replaced as needed and became a failure point for the power stations.

Are you looking for a green way to bridge power? Ultracapacitors are a perfect for use as a because they are very reliable with hundreds of charge/discharge cycles. Batteries are sized to give power of a period of time where ultracaps will supply a high amount of power for a short period of time and have the operating life of 10 or more years. There is no way you could get that out of a battery.   You can keep an ultracapacitor on charge for extended periods of time without loosing capacity (batteries lose capacity when held on charge).


Readers have left 5 comments.
 No.1  Untitled
Please address two issues, upfront cost for ultracaps relative to batteries and ultracap power leakage.
Jeff (Unregistered) • 2008-11-06 17:36:05
 No.2  Untitled
I'd like those issues addressed too!

I'm told leakage is very low, can someone post some detailed ultra cap specs?
Guest (Unregistered) • 2008-11-15 09:49:01
 No.3  Untitled
The up front cost of Ultra capacitors is comparable to the difference between NI-MH batteries versus Alkaline. They cost more in the beginning but last far longer then any chemical battery. Ultracaps don't hold as much power but are very fast charging.

For instance - an electric cordless shaver normally has 2 NI-CD batteries (1.2 volt each) which when charged could run the shaver for over 2 hours. The Cadmium batteries then take 18 hours to charge. Two Ultracaps ( 200F 2.7 volt) will fit in the same space and the shaver would last about 20 minutes. The caps will only take 5 minutes to charge. The caps will never fail to hold a charge and could sit on a shelf for months at minus 20 degrees C. Of course because Ultra caps only take 5 minutes to charge - there is not much waiting for a shaver. Ultracaps do not have any memory and could be used down to zero volts. There is no toxic waste (such as Cadmium, acid or alkaline paste) or valuable materials (such as Cadmium or Nickel) in their construction.

As far as detailed specs - because of the different types of capacitors (carbon, aero gel, plastic etc.) and the different manufacturers we can only begin to advance your search for the ideal Ultracap. You should narrow your search to a cap size for a particular use then, prospect the manufacturer's for data on the best caps fitting your spec.
Michael C (Author) • 2008-11-17 12:42:47
 No.4  Sorry for the delay in answering...
Without specific application requirements, it is difficult to make general analyses on upfront cost. In general, if batteries are being used for power-rich applications, replacing batteries (which are most likely oversized) with ultracapacitors may not incur too large a upfront cost. In addition, the replacement may be more easily justifiable based on ROI. However, if one is contemplating replacing batteries with ultracapacitors in energy-rich applications (which I can't think of why one would pursue that route), the upfront cost + ROI will most likely not justify the replacement.

As for the "power leakage," the phrase itself needs to be defined further because what appears to be "leakage" can be due to self discharge, as well as capacity/internal resistance degradation. In general, ultracapacitors exhibit more self discharge than batteries. However, they are less affected by temperature (e.g., superior performance at low temperature compared to lithium ion). In addition, capacity/internal resistance degradation over time can be less for ultracapacitors. However, these are all related to application environments, and as such, without specifics, it is hard to make a general statement.
Greg (Super Administrator) • 2008-11-21 10:43:18
 No.5  Super Cap developer/researcher
Most electrochemical super caps have relatively low self-discharge rate if they are only half charged. But the self-discharge rate can be substantial if they are maintained in a charged condition. But the fact is, they can be charged to 80% of capacity in about 1 1/2 minutes. For many applications that is enough to not have to bother to keep them charged. EEstor capacitors seem more akin to electrolytic capacitors as they use barium titanate, the substance with the highest known dielectric constant. Electro-chemical super capacitors/ultra capacitors actually use the solvent molecule as the dielectric. Therefore the capacitor's voltage is limited by electrolytic breakdown voltage of the solvent. This creates a capacitive storage with the opposing charges in the high surface area solid electrode with the solvent molecules lined up at the interface and the second electrode being a layer of ions attracted to the opposite charge.
Guest (Unregistered) • 2008-12-24 23:33:41
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