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I was thinking today that it wuld be possible to scrap the whole charging system, and the NiHM pack... and replace it with an array of lightweight capacitors. Any thoughts? Good idea? Bad Idea?
(perhaps no scrap the charge control all together, but fool it so that it allows 100% charge and drain of the caps since they can handle it)

Thanks in advance
 

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The IMA stops working when the pack drops to 120v, the pack is full and accepts no further charge at ~180V(BCM controlls this)
The discharge curve of the batteries is pretty flat, so the batteries stay within that voltage window. Caps drop voltage quickly as they discharge, since they store charge electrostatically, so the caps would drop to 120V in seconds.
A complete new system would be needed to run off only caps. I believe Cap based systems have a voltage converter that allows the cap voltage to drop while keeping the output voltage constant.
So bad Idea with our present electronics.
 

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Honda initially wanted to use ultracaps in the Insight, but switched to NiMH batteries at the last minute. Ultracaps are still used to buffer the Honda Fuel Cell Vehicle and the Nissan diesel hybrid truck is ultracap powered too (Japan market only).

BMW also favour them, as their philosophy is that with batteries you can't use 100% of the available storage - only about 40%, so the rest is just being carried around as dead weight. Also, caps can be charged 0-100% and back to 0% again with huge power outputs and minimal losses, while also being good for millions of cycles, so in these respects are better than batteries.

You can buy ultracaps from Maxwell, but the main issue is the low energy density - currently about 3 - 5 watt-hours per kilogram. Compare that with the 46 Wh/kg of the Insight battery and you can see how heavy the ultracap pack would have to be to provide the same charge buffer (about 100kg before adding the DC:DC converter etc?).
 

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Interesting that the Insight was originally going to have ultracaps.
clett said:
You can buy ultracaps from Maxwell, but the main issue is the low energy density - currently about 3 - 5 watt-hours per kilogram. Compare that with the 46 Wh/kg of the Insight battery and you can see how heavy the ultracap pack would have to be to provide the same charge buffer (about 100kg before adding the DC:DC converter etc?).
Yeah, but the IMA works most effectively just to store regen energy and use to it accelerate again--25 kg of ultracaps could store the full energy to accelerate from 0 to 60, and you need less than that since you can't accelerate on IMA alone. So I think it would work very well if interfaced properly.

Charlie
 

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Even Maxwell does not recomend their caps for 100 percent of energy storage but suggests that they be run in parrallel with a tradditional battery. Ultra caps have the down side that they can produce almost infinite current if shorted. This makes them dangerous and serves no practical function as the motor and associated electronics can only draw a limited amount of current. Ultra caps would probably fail as often as Nmh batteries as the primary causes for failure are manufacturing defects and evaporating electrolyte (ambient heat related). Capacitors can not be used fully as the conversion electronics becomes increasingly inneficient as the source voltage decreases.

Ultra caps are an excellent idea for the future, but the control electronics and long term reliability remain to be proven.
 

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The current from the Ultracaps is easily limited by a resistor, removing most of the danger. Ultracaps are also not very prone to failure as they contain no electrolyte, nor are they "rolled" from discrete materials like electrolytics, so there are no pieces that can come apart if it is improperly manufactured. They are virtually failure-proof.
 

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Ok I was wrong. A quick check of Maxwell?s site shows that they are making a paper available describing a practical method of using only Ultracapacitors in a hybrid vehicle. The paper did note however that due to the low power density of existing Ultracapacitors, the system was only suitable at present for mild hybrid use for acceleration and braking.

The Maxell Ultracapacitor is constructed using a metal foil bonded to an activated carbon mat. The activated carbon is separated by a glass paper and layered or rolled into a container. They use Quaternary salt (tetraethylammonium tetrafluoroborate) and Organic solvent (acetonitrile) as the electrolyte. The electrolyte is flammable and toxic. The activated carbon consists of a sponge like matrix structure of microscopic scale. An aluminum backing is used to lower resistance and provide an electrical path. Ultra capacitors have an expected life of 10 years according to Maxwell. Life expectancy is generally limited by the integrity of the insulated seal on the capacitor. A better seal gives you a lower power density. It is a tradeoff.

If you put a resistor in series with an Ultracapacitor efficiency suffers.
 

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Re the whole safety and reliability issue - it's worth pointing out that ultracaps are out there on the roads already. The Nissan diesel hybrid truck as I mentioned but also Toyota's Prius. It uses them as an emergency energy store for the brakes. I think if Toyota are happy with the reliability and durability of ultracaps over the life of a car to look after something as major as the braking system, then we can be relatively confident they are quite reliable!

b1shmu63 said:
due to the low power density of existing Ultracapacitors, the system was only suitable at present for mild hybrid use for acceleration and braking.
Surely you mean energy density? Maxwell caps are at about 3-5 Wh/kg, which compares with about 46 Wh/kg for the Insight battery and >220 Wh/kg for lithium-ion.

The power density of ultracapacitors is spectacular - several kilowatts per kilogram is no problem.

This group are working on the next generation of ultracap - 10-20 fold improvement in energy density and 100 kilowatts per kg power density! :shock:

A capacitor like this weighing only 540 grammes could produce the same amount of power (73 bhp) as the entire Insight engine! (Although only for 2 seconds before running out of juice.... :wink: )
 

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Ultra Cap

the site you listed shows...

"Our analysis shows that the utilization of a matrix of vertically aligned CNTs ( Carbon Nano Tubes ) as electrode structure, can lead to an ultracapacitor characterized by a power density greater than 100kW/kg (three orders of magnitude higher than batteries), a lifetime longer than 300,000 cycles, and an energy density higher than 60Wh/kg."

Energy Density is what will determine how long it will run for ... so the 46Wh/kg of the current Insight NiMH Battery pack that is more than 7 year old technology has just about the same ( ~77% ) as the possible future "can lead to" theory number of 60 Wh/kg... the benifit would be in rapid use Acceleration and Rapid Charging Regenerative Braking.

Of course power density is higher in a cap... it had better be that and cycle life are 'almost' the only reason to use caps for anything... these theory numbers they are showing which are still all theory with no even protypes having been built...

Curent Li Batteries in production can beat the crap out of these theory Capacitors for Energy Density.... Heck Current 12 Ah D Cell NiMH batteries which are far from the best NiMH Batteries Have greater Energy Density than these Theory Caps.

Sorry Dude.... My Money is on NiMH and Li Batteries... Caps are good to make electronics.... Ultra Caps can be useful for 2 or 3 seconds worth of hard acceleration or braking.... and that is about it for Caps.

My 2 Bits
 

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I hate to rain on MIT's parade, but JEOL has already completed ultracapacitors packing up to 75 Wh/kg. In fact, they have already partnered with Nissan Diesel to bring the technology to market on hybrids. Won't they be disappointed when they finish their research and find that the technology is already obsolete. :?
 

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"The power density of ultracapacitors is spectacular..."

That's only a trifle compared to what capacitors can do. Used to work in a lab next door to the Nevada Terawatt Facility, which uses capacitors to power a Z-pinch plasma device. They put out a power level about the same as the whole US electric grid - but they could only sustain that level for a few microseconds - or maybe it was nanoseconds.

Anyway, that's the trouble with capacitors for energy storage: that logarithmic relation between power & voltage.
 

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High voltage capacitors can store more energy than ultracapacitors - but they do it with capacitors that have very high voltage at very low capacitance. If regulated to a low voltage, this also has the advantage of virtually eliminating the discharge curve. The problem with that is that you then need very high voltages to charge them, which would involve some inefficiencies in regen, not to mention the hazards and the bad press. The firefighters were complaining about the "500 volts" in the Prius on the radio today. (ignorantly suggesting that the car's entire electrical system was 500 volts by directly contrasting it with "the 12 volts found in other automobiles") I imagine they'd throw a fit at a bank of 2,000,000 volt caps in the back of the Insight.
 

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Clett, my bad! :oops: I did mean energy density.

Here is a press release from Joel dated March 19 2004.

Nanogate Capacitor

JEOL Ltd. has been focusing on the improvement of energy density of a capacitor element (another name for condenser. Since it does not require chemical reaction in accumulating electricity as is the case with the conventional battery, its volume of accumulated electricity is remarkably great), which used to be the biggest theme in a capacitor accumulating electricity system. And in October 2003, they succeeded in developing an epoch-making capacitor (Nanogate Capacitor) with 50 to 75Wh/kg energy density. Although it is still at laboratory level, the energy density of this capacitor can greatly improve the performance of products currently in the market.
Nanogate Capacitor has high energy density close to the one of nickel-hydrogen battery, large size lithium-ion battery for large capacity of electricity, while keeping the unique advantage of a capacitor such as "extremely short charging-discharging time" and "extremely long lifetime".
Electricity accumulation system using Nanogate Capacitor makes it possible to put various products to practical use, such as hybrid automobile, electric automobile, buffer for solar and wind power generation, storage to accumulate electricity for night time and it can be considered to make a great contribution to the resolution of global energy issues and environmental issues.

Ultimately I believe we will have to use lithium batteries or ultracapacitors as there is a shortage of cobalt for NimH batteries. Where there is a need and money, technology will find a way. :D
 

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A little off topic here, but you guys may enjoy the story.

My only direct experience with SuperCaps was when my nephew asked me to help him design a robotic hacky sack throwing robot for a contest at Boston University.
The contest was simple, the power source had to be 2 AA alkaline batteries. The race was an 8 foot run from the starting line to the drop point. Two robots raced from opposite sides of a 16 foot track to throw a hackysack into a central hole. The rules allowed capacitors. We put a 22F super cap across each AA battery, and one more that was charged when the power switch was off(a little cheating). When the power was turned on, the three supercaps were put in series which gave us ~5.5V total. We used a dual motor electric airplane motor, and had enough power to scrub out most of the way down the track(2.2V motor), so we had to ramp the PWM H bridge up to maintain traction. The race time to the drop point was the same with or without the AA batteries, so the super caps were providing all the power. Three runs, and we had to change the batteries, because charging the caps drained them. Was lots of fun, they did not win because the contest timing was visually determined, and they were disqualified for what the judges said was a 0.2 second delay in returning to the starting line.
http://pages.cthome.net/genesisone/finalburobot.jpg
:wink:
 

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Re: Ultra Cap

IamIan said:
Sorry Dude.... My Money is on NiMH and Li Batteries...
Mine too actually!

Well, lithium-sulphur to be precise. 420 Wh/kg from Polyplus, and 350 Wh/kg from Sion already, with both projecting 500-600 Wh/kg in the near future. Power density is > 1kW per kg, safe(-ish!) chemistry means they can be overcharged or shorted out with no risk of fire, and work at -40oC. Main problem as yet is cycle-life. An EV version of the Insight with these installed should be capable of 1,000 miles range between charges.

However Polyplus are not content with 500 Wh/kg, and have developed a "Lithium-Aircell" with a theoretical energy density of 11,600 Wh/kg! :shock: Goodbye gasoline! 8)
 

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site

clett...

A bit off topic... but I just visited and went through your site....

Rocks.... :shock:

I especially like the 1,000 Mile Electric Insight Idea.. and the Solar Electric car idea.. :shock: :D

I can only hope that these lab technologies make it to the production lines in the next few years for when I plan to do my conversion from Insight Hybrid to Insight Electric... Of course I will eventually ... cost effective or not.. put solar cells on it or replace the body panels with solar electric ones after it is converted to and EV.... Great stuff though... :D
 
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