Subject: Very High Energy Density Lithium Sulphur Batteries - msg#00014

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Re: Ultracaps, Vol 46, Issue 3

Quoting Nick Hein <nick.hein@xxxxxxxxxxx>: > Andy, > Thanks for sharing your information. Sounds like they would be good for > starting/stopping power but not hill-climbing. Any idea what a mechanical > spring with the same storage would weigh? Air tank? > One of the handiest documents in my library is in Bicycling Science. It rates Lead-acid batteries at 85 watt-hr/lb. Compressed gas and container - 10 wh/lb, with risk of gross inefficiency if the gas cools in the tank. Rubber springs - 1 wh/lb. Steel springs - .06 wh/lb. This is handy information for the design of suspension parts, too. Steel springs are surprisingly heavy, as Julian noticed. Best, Bob Stuart

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Re: Ultracaps, Vol 46, Issue 3

Mark wrote; >Imagine a Velomobile that is aerodynamically clean (relatively) so that 20-30 mph is not only possible but practical and having an electric booster that allows it to MAINTAIN that speed, or something better than the usual 3-4 mph, up hills. .....Mark what your talking about here is not a Human Powered Vehicle but a motorized vehicle. The power required at the speeds and grades your talking about are well beyond what a human can contribute. That means the electric power essentially had to be on almost all the time. Your dream is to go from 3 to 4 mph up a hill to 20 to 30 mph. If you doing 3 to 4 mph then the grade may be up around 5% to 6% and around 130 watts (for a 75 pound vehicle and 157 pound rider). To climb around 20 mph would require 700 watts. The human could contribute say only 120 of those 700 watts. Another issue is cruising at say 30 mph on a more continuous bases is for a HPV a fairly fast speed. Yes we can get to these speeds down grades but that lasts for some number of seconds. To maintain high speeds over a long period of time means that the vehicle has to have much better suspension, stronger wheels, bigger tires, better brakes, better lights at night, and better crash protection - all of which means much more weight. This means the human has even less percentage of assistance capability. And at 30 your still not likely able to take the lane. Your too slow. Yes a motorized vehicle can be much more efficient than the monsters we drive now so its definitely worth investigating. A couple of my vehicles can cruise in the 30 mph range and haul down the slightest grade. 30 isn't too bad but by the time you get to 35 things are happening fast. At 40 to 45 its all out concentration to stay out of trouble. I only want to do this for the time it takes to go down a grade - not on a continuous basis. And your pushing the bike size components on a HPV. I find 20 to 25 to be comfortable speeds for the HPV and the rider. I hearken back to a fundamental philosophy. The beauty of combining the super high efficiency of the bicycle with the rather low power capability of the human is indeed a elegant combination. I for one want to strive to maintain this elegant combination. I agree that struggling up a hill at 3 to 4 mph is a daunting task. How about say 7 mph with the same power required from the rider as on flat ground. The rider isn't being pushed and the speed is more reasonable. To do 7 mph up a 6% grade would require 220 watts (on a 75 lb vehicle). How about say 100 from the rider and 120 from the assist. Instead of loading down the vehicle with 20 or more pounds of high power, a 120 watt system could weigh less then 10 pounds. Combine that with a light weight vehicle and we are gaining even more. Then the human remains a decent contributor here. Just some thoughts. John Tetz

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Re: Ultracaps, Vol 46, Issue 3

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi all, I actually looked into the Maxwell Ultracaps several times over the past few years. Every time i look back they have been making pretty steady progress on new model specs. They can deliver and accept large currents, in other words their power density is great. However, their energy density is not so great, especially when you are just using the top few volts of their discharge curve to mimic the power source a battery would provide. I was primarily interested in seeing if they would be sufficient to replace or reduce battery weight and improve storage performance in cold temperatures. The effort was to not have to bring a battery pack indoors when it gets down between 38 F and -20 F. To give you an idea about how they compare, I sized a pack to replace a 24v bionx battery. There are some good whitepapers and PDF's at maxwell technologies website, including a bunch of excel tools. (links at end) I made my own tool to do the calculations, (before they had posted any tools) but checked it with their spreadsheets. With the 3000 Farad cells, http://www.maxwell.com/ultracapacitors/products/large-cell/bcap3000.asp you need one string of 9 cells in series (with the special balancers) to get the voltage discharge range you want. This Ultracap bank will output 200 Watts for 82 seconds. This assumes a 24V working voltage and a 22 V min voltage for the system, meaning the discharge happens over 2V. The cells add up to about 3.6 kg or about 7.9 lb. Last time I looked, a pack like that (sans enclosure) cost around $800.00 - $1,000.00 With the 2600 Farad cells instead, http://www.maxwell.com/ultracapacitors/products/large-cell/bcap2600.asp the same configuration gives you 200 Watts for 69 seconds, or 350 Watts for 40 seconds. If you up the power, obviously, it discharges faster. In a parallel hybrid system like bionx, where there could be another electrical input (60 Watt peak power photovoltaic panel) I think they have some pretty nice, but not great characteristics as a high power (read current) buffer for acceleration and regenerative breaking where you don't have to pay the 10-25% efficiency penalty of cycling a battery's chemical reactions to store the energy. I have a feeling they would really shine in a series hybrid vehicle. They would probably be able to replace battery storage completely, especially if there was an additional constant charging input; pedalling (of course), photovoltaics, etc. I do have some reservations about accidental shorting, discharging as this could be a huge danger (the ultracaps can deliver more current than a shorted battery!) The other thing, is the tremendous number of cycles these can take. Even if you cycled the cell string 250 times in a day, ( over 4 hours of continuous discharge and recharge every day, accelerating or regen breaking) the string should last over 10 years. links: http://www.maxwell.com/ultracapacitors/technical-support/application-notes.asp http://www.maxwell.com/ultracapacitors/technical-support/tools-models.asp http://www.maxwell.com/ultracapacitors/technical-support/manuals.asp HTH andy Nick Wrote: > I just came across this information about the latest commercially-available > ultracapacitors. Performance specs show as much as 500F capacitance in a > bike-packable package with a weight of about 12 lb and power density of 2100 > W/kg. This is pretty good isn't it? Like good enough to replace a battery? > http://www.tecategroup.com/capacitors/datasheets/maxwell/mc_energy_series_16v_1009362.pdf > > Cost of the biggest unit is $700. Chris Wrote: > Power density just tells you how quickly you can pull the power out -what > you need to know is the energy density - In other words - how LONG can you > pull that power out. Power times time = energy. > > So that's about 10000 watts for the pack - is that for 1 second or 30 or a > minute? > > Chris P > Bob Wrote: > > So far, the energy density is ten times worse than a lead-acid battery, but > it > might find application to supply the first bit of charge or discharge on each > cycle. For stop and go traffic or rolling hills, it is all you would need, > and > it would be more efficient than batteries. > > Good Find. > Bob Stuart -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org iD8DBQFFdhCoTHCOtwancvwRAlgWAJsGLBdmF1FLPju0OE9yfPrknBs1mACdHkqa htpFYXT7Auj2M6BcseEKYlc= =xJgu -----END PGP SIGNATURE-----

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Power Assist Philosophy

Hi all, I agree with John too. VMUSA has developed a PA system using the Cyclone-tw 500 w motor/gearbox and four 24v 66 Ah NiMH battery packs for our FAW+. These battery packs sit under the floor so take up no baggage space. We started with the Cyclone freewheel crank system but on the experience of our customer Fred Ungewitter we also tried the system without the freewheel cranks. This was pioneered by the Stokemonkey company. Now that I am used to it I don't need freewheel cranks anymore. A pedal/electric assist hybrid is very nice for such an old guy (I am 71). We mount the 7 lb motor/transmission on the front bulkhead and drive a 53 T chainring on a double crankset. The freewheel on the motor shaft decouples the motor during pedal-only operation. That gives a maximum motor-driven crank rpm of around 90, which is ideal for me. This system allows using the motor torque in any of the 24 gears provided by the SRAM Dual Drive hub. The batteries weigh 10.75 lb, for a total PA system weight of about 18 lb. Total bike weight is about 90 lb. This is a very versatile and reliable system. I've ridden this system for about 200 mi (322 km) now and am very happy with it. I ride mostly on lower traffic city streets, but have to use 40 mph (64 km/hr) arterials fairly often. By fitting in between traffic light cycles and with the motor on full and pedaling hard I can reach and hold about 30 mph (48 km/hr) for long enough to get off the arterial. I don't slow the cars down much at all. Of course the Dutch with their flat polders with beautiful fietspads (bike paths) hardly need a PA system. They also don't need brake lights, but riding in car traffic we do need them. I tried not to use a PA on principle, but customers pushed me to do it. I ride 95% for transportation and hardly have time for recreational riding. Now that I have a reliable PA system I can have the best of both worlds and go almost twice as fast in traffic. On the low traffic streets I don't use the motor much, except for acceleration. If I am not in a hurry and need full exercise I don't use the motor at all. Since I can do 30 mph (48 km/hr) pedaling hard and that is the speed limit on minor arterials, I can go about as fast as the cars in heavy traffic, although quite a bit slower to accelerate. And after a big meal or when a bit sick I use the motor for acceleration up to speed. The PA system removes all worry about headwinds or speeding up to catch a traffic light. John et. al. are exactly right about speeds and safety. 20-25 mph (32-40 km/hr) is a good speed for a recumbent/ VM for safe riding. Going faster requires a higher level of concentration as from a low vehicle sudden changes ahead of you are harder to see. Cars at cross streets may miss a smaller vehicle when scanning to decide when to cross. I had to do a panic stop for one yesterday. At night or in the rain high speeds in traffic on a low recumbent are very exciting and border on being dangerous. I am using an HID headlight of 13 w that really lights up the night, so going fast at night is safer with it than with weaker headlights. The HID headlight is mounted on the left cowl ahead of the side-view mirror to shine downward so as not to blind oncoming drivers. A relative calls my VM the Lexis of bikes, with its HID headlight, bright DOT approved turn signals and bright car-style LED tail light and brake light. I tried the Bionx system at Interbike and find it rather nice too. It would be great for long, steep downhills, as the -3 and -4 settings on the control give regeneration that has a very powerful braking effect. David VMUSA Midland, TX USA