标签: capacitors

Supercapacitors (also known as ultracapacitors) are a relatively recent fundamental technology innovation for passive devices, with the first ones coming to market in the 1970s with widespread use by the early 1990's. Prior to their development, the "conventional wisdom" and textbook view that even a one-farad capacitor was impractical for real designs, as it would be the size of a desk. Yet today, the supercap is a standard component in the engineer's bill of materials (BOM) kit.   These capacitors have both advantages and disadvantages compared to rechargeable batteries. They typically can store 10 to 100 times more energy per unit volume or unit mass than standard electrolytic capacitors but have only about 1/10 the energy density of batteries (and thus are physically larger for a given amount of energy); can be charged and discharged more quickly than batteries; and tolerate many more charge/discharge cycles than rechargeable batteries. In many designs they replace or complement batteries for short- or long-term backup and operation. So what about using them in electric vehicles (EVs) and hybrid electric vehicles (HEVs), instead of the battery packs? So far, none of the commercially available EVs and HEVs use them, as far as I can tell. I'm not a battery expert, but I suspect it is a combination of factors: size, cost, perhaps power-management issues, difficulties in using them in series and parallel combinations, failure-mode issues, and other factors. I am sure the technical experts at EV/HEV vendors have considered them and decided they don’t make sense, at least at this time. But that hasn't stopped people from speculating, and this speculation can make it all sound so easy. I recently saw that NASA Tech Briefs gave an honorable mention to an idea – and I emphasize the word "idea" – of using an array of one type of supercap for energy storage in an EV with a 3000-mile (approximately 4800 km) range, see here . Wow, that's impressive…until you realize that this idea is entirely speculative. The detailed contest entry freely uses words like "revolutionary," "easy," and "standard" in the discussion of a large array of multi-layer ceramic capacitors (MLCCs) with dielectric constant (the ratio of the permittivity of a substance to the permittivity of free space) of 300 million.     Using a huge array of MLCCs in an EV: great idea, or one that will be defeated by the reality of implementation? (from Tech Briefs) I'm not saying that such a design isn't possible; we know that when it comes to technology advances, you should "never say never". Nonetheless, the issues associated with such a dense power pack in an EV go beyond the storage component itself. The author proposes an array of 12,000 MLCCs of 5.5 F each, for a total of 66,000 F. That's an amazingly high energy density and capacity, which bring in major issues of safety and actual system design. How do you reliably connect all these MLCCs? What happens when one or more MLCC fails open, or shorts internally? How do you deal with the large current flows and high voltages into and out of such a dense package? Talk to any engineer who has worked with high-energy battery packs ranging from relatively smaller ones used in laptops to larger ones in EVs, and you'll hear that the reality is that the battery/supercap itself is only part of the design and manufacturing challenge. There are many other issues such as internal interconnects; external connections; charge/discharge management; current, voltage, and thermal monitoring; and overall safety monitoring and protection. While it is easy to say that those are all manageable issues that can be easily overcome (a project manager I worked for casually declared these peripheral functions to be "mere details"), these are actually all very difficult problems, especially in a high-volume, manufacturing-oriented product. We often hear reports about the next big thing in batteries (or supercaps) promising five or even ten times the density of today's best units. Yet most batter progress over the past decades has been through modest, incremental improvements adding onto each other, rather than the one big breakthrough. A balanced and perceptive article " Tech World Vexed by Slow Progress on Batteries " in The Wall Street Journal (of all places) pointed out that the time and effort to get a new battery enhancement to the mass market is about ten years, and many promising advances in the lab don’t make it to market adoption due to manufacturing, material, and functional issues, even if the underlying technology is sound. Will an array of MLCCs be the next big thing for EVs? I'll admit it: I don’t know. I do know that when someone says it will be easy, and yet has never actually built and tested an actual unit, it's a good idea to be skeptical. What's your experience with high-energy/high-density batteries and supercaps? Have you even been involved with projects that seemed so easy in concept, until you had to bring them into a moderate/high-volume manufacturing situation?

Supercapacitors (also called ultracapacitors) are a relatively recent fundamental technology innovation for passive devices, with the first ones coming to market in the 1970s with widespread use by the early 1990's. Prior to their development, the "conventional wisdom" and textbook view that even a one-farad capacitor was impractical for real designs, as it would be the size of a desk. Yet today, the supercap is a standard component in the engineer's bill of materials (BOM) kit.   These capacitors have both advantages and disadvantages compared to rechargeable batteries. They typically can store 10 to 100 times more energy per unit volume or unit mass than standard electrolytic capacitors but have only about 1/10 the energy density of batteries (and thus are physically larger for a given amount of energy); can be charged and discharged more quickly than batteries; and tolerate many more charge/discharge cycles than rechargeable batteries. In many designs they replace or complement batteries for short- or long-term backup and operation. So what about using them in electric vehicles (EVs) and hybrid electric vehicles (HEVs), instead of the battery packs? So far, none of the commercially available EVs and HEVs use them, as far as I can tell. I'm not a battery expert, but I suspect it is a combination of factors: size, cost, perhaps power-management issues, difficulties in using them in series and parallel combinations, failure-mode issues, and other factors. I am sure the technical experts at EV/HEV vendors have considered them and decided they don’t make sense, at least at this time. But that hasn't stopped people from speculating, and this speculation can make it all sound so easy. I recently saw that NASA Tech Briefs gave an honorable mention to an idea – and I emphasize the word "idea" – of using an array of one type of supercap for energy storage in an EV with a 3000-mile (approximately 4800 km) range, see here . Wow, that's impressive…until you realize that this idea is entirely speculative. The detailed contest entry freely uses words like "revolutionary," "easy," and "standard" in the discussion of a large array of multi-layer ceramic capacitors (MLCCs) with dielectric constant (the ratio of the permittivity of a substance to the permittivity of free space) of 300 million.     Using a huge array of MLCCs in an EV: great idea, or one that will be defeated by the reality of implementation? (from Tech Briefs) I'm not saying that such a design isn't possible; we know that when it comes to technology advances, you should "never say never". Nonetheless, the issues associated with such a dense power pack in an EV go beyond the storage component itself. The author proposes an array of 12,000 MLCCs of 5.5 F each, for a total of 66,000 F. That's an amazingly high energy density and capacity, which bring in major issues of safety and actual system design. How do you reliably connect all these MLCCs? What happens when one or more MLCC fails open, or shorts internally? How do you deal with the large current flows and high voltages into and out of such a dense package? Talk to any engineer who has worked with high-energy battery packs ranging from relatively smaller ones used in laptops to larger ones in EVs, and you'll hear that the reality is that the battery/supercap itself is only part of the design and manufacturing challenge. There are many other issues such as internal interconnects; external connections; charge/discharge management; current, voltage, and thermal monitoring; and overall safety monitoring and protection. While it is easy to say that those are all manageable issues that can be easily overcome (a project manager I worked for casually declared these peripheral functions to be "mere details"), these are actually all very difficult problems, especially in a high-volume, manufacturing-oriented product. We often hear reports about the next big thing in batteries (or supercaps) promising five or even ten times the density of today's best units. Yet most batter progress over the past decades has been through modest, incremental improvements adding onto each other, rather than the one big breakthrough. A balanced and perceptive article " Tech World Vexed by Slow Progress on Batteries " in The Wall Street Journal (of all places) pointed out that the time and effort to get a new battery enhancement to the mass market is about ten years, and many promising advances in the lab don’t make it to market adoption due to manufacturing, material, and functional issues, even if the underlying technology is sound. Will an array of MLCCs be the next big thing for EVs? I'll admit it: I don’t know. I do know that when someone says it will be easy, and yet has never actually built and tested an actual unit, it's a good idea to be skeptical. What's your experience with high-energy/high-density batteries and supercaps? Have you even been involved with projects that seemed so easy in concept, until you had to bring them into a moderate/high-volume manufacturing situation?

For several years now, my girlfriend and I have been growing restless. We live in Colorado in the US, you see, and yearn for a life in the mountains. Clear air, chilly weather, spectacular views, massive drifts of snow. It's in our very blood and bones. So we decided to do something drastic: We sold most of our household possessions, purchased a travel trailer and some mountain land, and set off for our new lives. If only it were quite that simple.   Garage sale! (All photos: Benjamin Goldstone) You may now be asking yourself how this has anything at all to do with a "product that I tore into to fix or improve it." I ask only for your patience, as this is a story about fixing our lives as much as a product. Or perhaps "hacking" would be a more apt term, as we decided to explore the limits of a travel trailer as well as ourselves. Our plan? To brave the elements at 9,600 feet in one of the most beautiful places in the world to pursue that dream... in a three-season RV. Yep, we must be nuts. As our budget was only $5,000 for our new home, we needed to get creative. A fully winterized, fully furnished RV runs far above the $5,000 mark, so we purchased the best used unit we could find. The previous owners hadn't maintained it to quite the degree they should have, and so a number of repairs were in order. First and foremost was the fridge. It was not properly cooling. In fact, even on the warmest setting, instead of cooling things it would freeze everything in it. Uh oh. The issue could be one of a number of things. Most likely either the thermistor or the control circuit board was bad. I grabbed my multi-meter, set it to detect resistance, and placed the thermistor in ice. It registered 8kΩ, within the 7-10kΩ range it should be in. When placed in warm water, the multi-meter averaged 2kΩ. The thermistor was not the issue. Upon pulling the cover off of the control board, it was immediately apparent that one of the capacitors was having issues as it was bulging. After soldering in a new capacitor, the fridge began to cycle and cool food properly. But wait, now suddenly the light in the fridge was only intermittently working. After ensuring the connections to the power sources (both AC and DC) were solid and that the components on both the control and settings boards were all working as required, I pulled the light itself apart. Two of the contacts within the switch were no longer solidly connecting when the switch closed—one of those cases where a fix to one thing reveals another unrelated issue. I stripped the plastic off of a twist tie for a garbage bag, cut the wire within to size, and wrapped both sides of the switch so when closed, the switch would function reliably. Now the fridge is in perfectly functional order. A number of other minor repairs in the RV were also immediately required. The vent on the roof above the fridge, used to keep the fins on the fridge cool, had been mostly broken off, allowing in the elements. Nothing to do but remove the remnants of the old vent and install a new one. Additionally, the grip tape on the stairs needed to be replaced; the interior was ugly as sin and needed painting; a number of latches were broken; the windows in the door had fallen down into the door; etc, etc. "Oy Vey!" As my grandmother would have said. But this is the life we signed up for. A couple of trips to the RV supply shop and days later everything is back in working order. Now, while we work on clearing our land of dead trees, we have found a gig at a local state park that provides space for our RV and trucks in return for a minor amount of work. As it happens that space is on the top ridge of a mountain, situated at 9,600 feet (convert to m), just below the timberline. Taking an RV designed for three season use and turning it into a living space capable of weathering winters with average snow falls of 80+ inches and temperatures down to -30 degrees F is no small feat. Most RVs are not designed for that kind of living, and ours certainly wasn't. While not really a design fault, we do need something that will keep us and our pets warm through the harsh winter ahead. As it's quite likely that we will be snowed in at least once this winter, redundancy and proper preparation are of paramount importance. We started by making a list. So far, we have resealed the trailer with silicone caulk and expanding foam sealant, insulated underneath, applied heat-tape to the exposed drain pipes, applied heat shrink to the windows, and purchased the supplies to skirt the trailer. We have also purchased bear spray, backup heaters, a generator, a solar panel and charge controller, backup propane, emergency first aid kits, as well as backup food and water supplies—and, of course, a whole mess of snow gear to supplement what we already have. Never one to simply leave things be, however, I have started working on additional projects. A backup UPS for the heat tape and other critical AC systems is a must. A DC-to-AC inverter for running AC systems while boondocking is also necessary. I'm most looking forward to my new Raspberry-Pi/Arduino-based control system idea for controlling and monitoring the entire trailer. While a lot of work, this new lifestyle has certainly delivered our dreams, and I wouldn't trade it for the world. I do, however, now know how the characters in the epic A Song of Ice and Fire felt when they said "Winter is coming." For us, lady winter is truly on her way, and she is going to be brutal. Wish us luck. Ben Goldstone lives in Colorado, US and owsn a small IT consulting business. He has been into everything tech related since he disassembled his parents' lawn mower at the age of eight... and couldn't put it back together properly after the timing gear fell out. His love for tech is matched only by his thirst for knowledge, pursuit for audio nirvana, and love for the outdoors. He submitted this article as part of Frankenstein's Fix, a design contest hosted by EE Times (US).