Norman Albers Posted February 26, 2006 Posted February 26, 2006 I read something (zpenergy) that supercapacitors are being strongly developed to usable battery capability. Who's got the scoops here? We need such things in many application scales. I remember the Princeton tokomak with its own two-story flywheel and walls of capacitors, to average the grid drawdown with pulsed operation.
wpenrose Posted February 26, 2006 Posted February 26, 2006 My understanding is that supercaps are already in regular use, largely for high efficiency, long time-constant power storage, as in hybrid cars. Example: http://www.maxwell.com/ultracapacitors/applications/case_study.html Dangerous Bill
Norman Albers Posted February 26, 2006 Author Posted February 26, 2006 I'd like to hear how they 'pack it in' and have leakage down.
wpenrose Posted February 26, 2006 Posted February 26, 2006 I'd like to hear how they 'pack it in' and have leakage down. http://en.wikipedia.org/wiki/Supercapacitors Dangerous Bill
Norman Albers Posted February 26, 2006 Author Posted February 26, 2006 Sounds like they are just getting light-weight, approaching batteries, but have high draw-down rate innately, and wear well.
gcol Posted February 26, 2006 Posted February 26, 2006 I have been tinkering with some as storage for a gravity (weight) powered generator. Pro's.......can be charged and discharged at extremely high current, unlike ni-cads and lead-acid. Con's.......Do not maintain a constant voltage. When connected in series to achieve higher voltage, require dynamic balancing between cells. I either charge a bank according to the requirements of the "weakest link", or use cells of similar characteristics selected by test. No long term leakage observations to make, but short term no problems.
Norman Albers Posted February 26, 2006 Author Posted February 26, 2006 Once I had a flash and called an electronics friend. To my pleasure he agreed that one could make a voltage doubler by alternately charging two caps and by appropriate switching, stacking them into the output cap on a duty cycle. Is this sort of what you have to do to dynamically balance your stack? Is there no way to Zener off excess cell voltage?
gcol Posted February 26, 2006 Posted February 26, 2006 You had a flash and called an electronics guy? Had you a flush, would you have called a plumber? Seriously though, when declared surplus to requirements in the computer industry twenty years ago, I literally switched off. Some googling of "super capacitors" will start you off, where dynamic balancing is often mentioned, but I think the best way of doing this is commercially sensitive. We need to shake the forum tree more vigourously and see if an expert falls out.
Norman Albers Posted February 26, 2006 Author Posted February 26, 2006 Here's To Shaking The Tree With You. Norm Albers
YT2095 Posted February 26, 2006 Posted February 26, 2006 I`m currently building another Cockroft Walton voltage multiplier at the moment if that`s any use? and I have a few Quals in Electronics too, although the OP seemed more like a Physics Question rather than an Electronic one (so I said nothing).
Norman Albers Posted February 26, 2006 Author Posted February 26, 2006 I don't care, go for it! I love PETER GABRIEL. . . . . . . . . . . . I just looked at one Cockroft Walton generator and I see many diodes and caps! Are zeners used? This drew an interestingly muted response from our friend!
Molotov Posted February 26, 2006 Posted February 26, 2006 I posted this link in another thread. Now if the price of nanotubes would drop... http://lees.mit.edu/lees/posters/RU13_signorelli.pdf "Our analysis shows that the utilization of a matrix of vertically aligned CNTs as electrode structure, can lead to an ultra capacitor characterized by a power density greater than 100kW/kg, a lifetime longer than 300,000 cycles, and an energy density higher than 60Wh/kg."
YT2095 Posted February 26, 2006 Posted February 26, 2006 zeners arent typicaly used, it would actualy defeat the the whole purpose of the idea to employ them in the main body of the cct.
wpenrose Posted February 27, 2006 Posted February 27, 2006 Once I had a flash and called an electronics friend. To my pleasure he agreed that one could make a voltage doubler by alternately charging two caps and by appropriate switching, stacking them into the output cap on a duty cycle. Is this sort of what you have to do to dynamically balance your stack? Is there no way to Zener off excess cell voltage? Look at http://www.maxim.com and search on 'flying capacitors'. This is prettily packaged switching to do exactly this. Dangerous Bill
gcol Posted February 27, 2006 Posted February 27, 2006 I looked. It is a drug company doing research into pain relief. What did I miss?
gcol Posted February 27, 2006 Posted February 27, 2006 Once I had a flash and called an electronics friend. To my pleasure he agreed that one could make a voltage doubler by alternately charging two caps and by appropriate switching, stacking them into the output cap on a duty cycle. Is this sort of what you have to do to[/i'] dynamically balance your stack? Is there no way to Zener off excess cell voltage? This is my simplistic and "kitchen table" view, and works so-far: No. Not voltage doubling, entirely different. Each cap of the same spec in a stack will hold a similar charge, but will attain a slightly different voltage. They are sensitive to over-voltage charging, reducing lifetime. Either under-charge the stack so that no individual cap exceeds its rating, or put a bleed resistor across each cap to allow equalisation. This will cause leakage, but you can choose higher or lower resistance according to charging power, and duty cycle between charge/discharge. Dynamic balancing requires an op-amp across each cell, but it adds to power drain, cost, and reliability. Hyper, super, ultra, whatever are just trade names, and technological variations are appearing all the time. All require the same care.
YT2095 Posted February 27, 2006 Posted February 27, 2006 I agree, although an op-amp at the sort of voltages some deal with would be a triffle impractical. in a typical CW (no matter how many stages) the diodes should be rated at or a little higher than the ACin peak voltage and the caps at least double that (as a general rule of thumb). any variance in the caps voltage if this or better than is adhered to, shouldn`t present a problem (all other Precautions excluded).
gcol Posted February 27, 2006 Posted February 27, 2006 1. CW? wot that? 2. Not sure why ac mentioned. When charging cap banks as an alternative to batteries, There should be no ac component. Like electrolytics, they dont like it. 3. Super cap banks used in hybrid vehicles use dynamic balancing, which from the literature, appears to be op-amp based, (one op-amp per cell, I think) but perhaps made from discrete components. Exact details are hard to come by, being commercially sensitive.
YT2095 Posted February 27, 2006 Posted February 27, 2006 1. Cockroft Walton = CW 2. again that entirely depends on the charging method/application, a CW charges at DC per cap, only the Input is AC. the caps never see AC ever. 3. agreed, it would have to be a discrete for the pole shunt, perhaps op-amp controled?
gcol Posted February 27, 2006 Posted February 27, 2006 You have trumped me and stumped me there. Time for me to leave the field. Any further observations would betray my ignorance. Didn't take long, did it?
Norman Albers Posted February 27, 2006 Author Posted February 27, 2006 We asked for it and I appreciate it, YT.
Norman Albers Posted March 1, 2006 Author Posted March 1, 2006 OHMYGOD. I just read about z-pinch. DOY DOY my masters was in plasma
gcol Posted March 1, 2006 Posted March 1, 2006 Would that be DOY! as a variation of DOH! or day of the year, a male version of the feamale day if the month?
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