Ultracapacitors... personal experience?

[Scibbema]

I've read through a lot of the threads concerning Ultracapacitors and looked at some of the data sheets from Maxwell and Eestor. It all looks very promising from my untrained point of view. Has anyone here applied the technology to EV that has some real world feedback?

[Doug Lord]

My doctor(and friend) has bought one of the first cars with the system-delivery next year(?).

[CDK]

You cannot expect anybody on this planet to have personal experience with something that does not exist (yet).

[Scibbema]

Then why is Maxwell offering them for sale to consumers?

http://www.maxwell.com/ultracapacito...ucts/index.asp

[marshmat]

Maxwell's "ultracapacitor" lineup is not the same kind of product as the rumoured EEStor device.

Maxwell's big capacitors are designed to handle the short-term / transient loads on a DC system- things like regenerative braking in a car, or pitch controls on a wind turbine. These are examples of conditions that produce large deviations from the baseline load, on time frames of a few seconds. This sort of thing is easy for a capacitor, but very hard on a battery- these capacitors are meant to be used in conjunction with a battery or other DC supply, not as stand-alone power sources. (Maxwell's biggest ultracapacitors hold something like 55 watt-hours for a 25 kg device, compared to ~600 watt-hours for a 100 Ah 12 V deep cycle battery, of similar physical size to the capacitor, cycling between 40% and 90%.)

Most controllers for high-efficiency BLDC motors include some form of high-capacitance buffer; the capacitors help to damp out the rapid fluctuations that a BLDC controller can create on the DC bus. Without its buffering capacitors, such a controller can create something that looks a bit like a high-frequency AC ripple on the DC bus- not at all good for the batteries. A honkin' big capacitor takes care of these fluctuations.

The rumoured EEStor ultracapacitor, if it makes it to full production, is expected to come in at around 400 to 700 watt-hours per kilogram (Wh/kg) (although it would have to operate at over 3000 volts to reach these figures). Thus, with suitable control electronics to turn its 3+ kV into something useful, it could serve as a primary energy storage system. The Maxwell ultracapacitors currently available are at 2 to 3 Wh/kg- clearly not the same animal. Conventional lead-acid batteries are anywhere from 20 to 50 Wh/kg and the various forms of lithium batteries tend to be in the 100 to 200 Wh/kg range.

[Scibbema]

Thanks Marshmat... I am not an engineer and am just beginning to learn this. I appreciate the straight answers, such as you gave, rather than being put down for asking what I thought to be a legitimate question.

[CDK]

Originally Posted by Scibbema

Thanks Marshmat... I am not an engineer and am just beginning to learn this. I appreciate the straight answers, such as you gave, rather than being put down for asking what I thought to be a legitimate question.

Matt gave you a clear explanation.
What Maxwell is offering is basically what is used in TV sets and video equipment to power the memory and timekeeping in case the mains plug is pulled. These "gold caps" are tiny cylinders with 1 F. or larger capacity.
Maxwell only increased the scale and tries to encourage new applications.

In my opinion, the EEstor product belongs to the Star Trek category until they prove otherwise.

[marshmat]

Originally Posted by CDK

In my opinion, the EEstor product belongs to the Star Trek category until they prove otherwise.

Ahh, Star Trek.... oh, to have an engine the size of a briefcase that can power a five-tonne shuttle at warp speed with no fuel.....

My main concern about the EEStor system isn't that it won't work- so far, I haven't seen any claims about the device itself that don't match up with basic electromagnetic theory. I'm a little more worried about how difficult it will be to make something useful out of it: the thing cycles between nearly zero volts when drained and 3.5 kilovolts at full charge. Imagine the complexity of the power electronics. (Also, imagine having a 3.5 kV electrical component six inches from your butt as you cruise down the highway.)

[CDK]

I do share your concern about safety, but the risk may be not as severe as it sounds. The 40 kV acceleration voltage for a color TV picture tube didn't keep any housewife from wiping the dust away while the set was on.

To obtain the required capacity, a large number of capacitors will be parallel wired. A short between the two output rails would cause a catastrophe but it is not likely to happen because they will be quite well insulated and/or far apart.
A dielectric breakdown in a single cell is much more obvious, the layer will be extremely thin. But so are the conductors there: the cell will probably evaporate instantly and if the adjacent cells survive, nobody will notice what happened. The achieve that, there must be some empty space or a flexible wall that can handle the impact.
Finding the compromise between overall size and safety seems a difficult task to me. From time to time there surely must be large bangs in the EEstor lab.

[Fanie]

Very funny Skotty, now beam up my clothes... and some more capacitors.

Capacitor technology is not ready for commercial use yet.

[wardd]

Ahh, Star Trek.... oh, to have an engine the size of a briefcase that can power a five-tonne shuttle at warp speed with no fuel.....

of course theres fuel, parallel universes are burned, of course the down side is if someone in a parallel universe burns ours up