EEStor and Zenn cannae break the laws of physics

18 March 2007

We keep hearing odd things about US startup the Zenn car company and its exclusive deal with ultrasecretive ultracapacitor startup EEStor [PDF]. An ultracapicitor, for the uninitiated, is like a big battery but it stores energy as a static electric field, rather than through a chemical process. You can think of it as a bag into which you can shove electrons, keep them there for as long as you want (given a little leakage), and get them out again as rapidly as you like (with much less waste-heat-generating internal resistance than a battery).

According to more than one enthusiastic report, the combination of these two inventive companies will result in a car that can travel 200-300 miles on just a five-minute charge. Real soon now.

Well, we are here to tell you that, whatever technology lurks inside the eventual EEStor-powered Zenn, it will not be charging itself up in five minutes.

The problem lies with the nature of electricity.

Let’s be ultra-generous and assume that the EEStor and Zenn combination will be lots more efficient than the G-Wiz and will squeeze 200 miles out of the same amount of stored energy that takes the G-Wiz just 40 odd miles: 10kwh. This is not really feasible, but it is being very kind to the two plucky startups. It might just be possible if you drive veeeeerrrrrrry sloooooooooowly.

Anyway, to get 10,000 watt-hours into the battery in five minutes you need to feed in at a rate of 120,000 watts. This is just basic maths. You can imagine this quite simply: it’s like plugging in 120 single-bar electric fires and switching them on at once. As you might imagine, this will likely blow the odd fuse in your house.

Put another way, to supply this from a domestic UK 240 volt supply, you will need to charge at 500 amps. The maximum you can get out of one three pin socket is 13 amps, so you will need to plug your Zenn into about 40 sockets at the same time to avoid blowing any plug fuses.

Assuming you have 40 spare sockets, and the patience to plug them in, you’ll immediately blow the main fuse. Domestic electricity supplies just aren’t built to supply 500 amps.

So will you instead charge your Zenn at a sort of electric petrol station? No. First, there are none. Second, a 500-amp cable would need to be roughly 40 times as heavy and stiff as a domestic kettle’s cord. Unless you pump iron every day, you’ll find it difficult to plug in.

No, it’s much better to charge an electric car over a period of hours, during the part of the day when it’s not moving (given that nobody – barring a few madmen at Le Mans – drives for 24 hours a day).

Instead of charging over five minutes, charge for 40 times as long – at least 3 hours and 20 minutes – and you can use a normal three pin plug.

That’s the future of electric cars, no matter what. Unless you use a fuel plus generator or fuel cell to make electricity on the spot, electric cars are going to take hours to charge. No breakthrough in battery-style storage is ever going to change that. It’s just maths.


Raymond said...

If you have a second EEStor capacitor at home that charges all day, you could charge your car battery in 5 minutes. Only problem would be the thick cable. But that doesn't sound too much of a problem.

thudhead said...

I was looking for you to tell me something new. Some actual laws of physics that might cause a problem for EEstor, as I reserve a "show me" mentality with regard to the promise of this technology.

Nowhere has Zenn nor EEstor imagined a 5 minute refilling at anything but a specialized service station, which presumably, would have more than a 20 amp fuse.

To the extent that EEstor would present a disruptive technology, it's not unsmart for these folks to be extra cautious and secretive. If they are successful, it will have a large impact on other parts of the transportation sector.

Anonymous said...

Very good points.
In terms of today's familiar systems.

What if there was a home EEstor unit that had already been fully (slowly) charged at the ordinarily familiar residential rates and voltages?

Rapidly recharge the vehicle's EEstor unit from the home EEstor unit?

If EEstor's native voltage is around 3,500V and safely accessible, it would permit substantially smaller / thinner / lighter cabling.
(Gonna' need really good insulation!)

Auto IT said...

If you have a second, fully-charged EEStor battery at home, the safest course of action to recharge your car would probably be to physically swap the EEStor power packs. This could conceivably be done in five minutes, given a clever enough battery-on-wheels design. It would be better than messing around with high-current, high-voltage power transfers and the associated danger (plus the inevitable thermal power losses).

Alfred said...

Of course it is really interesting for EEStor to sell more than one storage system for each car. What about costs?

Anonymous said...

Cost for a 336 pound, 52 Kwh unit is estimated at $2100 when mass produced. However, Zenn will be receiving 100 pound, 15 Kwh units. They can be created in any size.

Anonymous said...

Technopete says:-

Since Auto IT is so keen on invoking maths when being negative about Eestor ESU recharging on a Zenn electric car, than maybe you would like to consider the maths below.

A quick measurement and calculation shows that a second Eestor unit charged slowly in the home would work fine for recharging an Eestor unit in a Zenn. I've just measured a mains extension cable wire at 0.2 ohms for 5 metres, or 0.04 ohms per metre. Lets say that the charging cable wire for a Zenn would be 10 times the thickness or 0.004 ohms per metre. There are two wires in the charging cable.

To transfer this charge to a 10kwH Eestor unit in 5 minutes at 3,000 volts would take 120,000 watts as Auto IT correctly says. At 3,000 volts this is 40 amps. The voltage drop on the cable would be 40 amps x 0.004 ohms = 0.16 volts per metre, and the power lost in each cable wire would be 0.16v x 40 amps = 6.4 watts per metre, but we have to multiply this by two because we have two wires in the cable (same as a mains cord). So the total cable power loss is around 13 watts per metre or around 0.01% per metre (or one ten thousandth) of the energy being transferred. What power losses Auto IT???

For a 50 KWHour unit needed by the Tesla Roadster to charge in 10 minutes then the maths are similar. Assuming a cable twice as thick (twenty times the thickness of a mains cord).

Charging rate - 300,000 watts;
current - 100 amps;
cable ohms / metre = 0.002;
cable voltage drop = 0.2 volts / metre (one wire);
cable power lost = 40 watts per metre (both wires)

OK so you can feel it gets warm, but this is less power than your brain!

The 10 KWH charging cable will probably weigh rather less than those used on gas pumps right now, though come to think of it the petrol pump cables are a bit on the heavy side!! The 50 KWH cable might be a similar weight to the gas pump cable.

What about the risk of electrocution from having such a high voltage around? Well some of us still have higher voltages than this powering our CRT TV's and screens. I haven't heard of any accidental deaths from TV's and CRT's. Obviously the insulation around a high-voltage charging cable must be very good and you will need some sort of super fast RCD (residual current detection) device to ensure that any current leakage (e.g. to a person) shuts off the charging before the leakage current gets high enough to kill anyone.

So please stop all this nonsense about swapping 50 lb or 150 lb Eestor units.

For those who understand that the voltage on an Eestor capacitor would be proportional to the charge stored, then I would point out that equipment at each end of the cable is required anyway to keep the cable voltage and current constant, as, during charging, the house ultracapacitor voltage decreases over time and the car ultracapacitor voltage increases.

It would be nice to hear an acceptance from Auto IT that the maths actually show that such a high voltage medium current transfer to the Eestor unit would be possible without significant power loss or cables that no-one can lift! Or should facts not be allowed to get in the way of opinions?

Gypsy said...

The G-Wiz must by only so-so when it comes to EV's. At only 40 miles on a 10KWH charge it is only getting 250 watt hr. per mile or 4 Miles per KWH. The Rav 4 EV is said to use 330 watt hr. per mile but the more efficient cars are doing 120-180 watts per mile while the competition EV have gone 50 miles on one KWHr (20 watt hr. per mile) at 50 mph. Given the size and efficiency of the Zenn to go 200 miles on a charge of 15 KWH it would need to run at 75 watt hr. per mile.

Anonymous said...

Because you can charge in five minutes isn't the same as you have to charge in five minutes.

The U.S. military already has a standard that would cover a ten minute charge.

If EESTOR comes out with this product and it's half as good in every stat than they claim it will be the least of our new problems will be figuring out how to charge it up.

Auto IT said...

To answer Technopete:

The voltages inside CRTs and TVs can very easily be fatal. Experienced TV technicians tend not to delve inside the case with both hands to avoid across-the-body shocks (it's common to stick one hand in a pocket to avoid doing so by accident). Residual charge can make this dangerous even when the TV is unplugged. The designs also tend to incorporate 1:1 isolating transformers for added safety. Interestingly, you can easily stop your heart with a 9v flashlight battery. All you need is an across-the-body circuit made by grazed knuckles on both hands. The skin is an insulator but blood is not, and a little bit of DC current will stop your heart real quick.

Anyway, Auto IT's calculations were based on the assumption that no manufacturer would get federal/EU approval for a home charging system operating at kilovolt potentials. Hence working from the 240V UK domestic situation. In the US, any AC supply over 600V is considered high voltage from a safety regulation perspective.

Note that the Tesla electric sports car, by comparison, takes six hours to charge from a standard US domestic supply - and it's being built by some pretty smart cookies.

If Technopete would like to mess around with 3,000 volts, Auto IT would advise:
(a) don't do it in the rain, or within a few days of driving in the rain
(b) wear rubber soled shoes and thick rubber gloves
(c) wear eye protection, head protection and, if possible, a blast suit
(d) remember to switch off and bleed down the system before unplugging unless you want to do a little impromptu arc-welding
(d) don't do it anywhere near Auto IT.

Technopete might want to read this:

Anonymous said...

[quote]Unless you use a fuel plus generator or fuel cell to make electricity on the spot, electric cars are going to take hours to charge. No breakthrough in battery-style storage is ever going to change that.[/quote]

I guess you haven't heard of Altair Nanotechnologies. They have a battery that can be fully recharged in less than ten minutes. That's the PRESENT of electric cars. What will the future bring? Hopefully, less bullshit from people like you who don't do your homework.


Jeff said...

Technopete is right. Looking over his commenting his calculations are correct, practical and CAN safely be implemented. Lets not even get into the coming "wireless power" age.

P.S. electrical engineering student. Just my two cents guys. :)

Anonymous said...

first of all where are you going to get 3000V to charge the capacitor, you would need a converter to convert up the 120V or 240V from your house to 3000V, now assuming you have a conveter to do that, there is no way the electrical circuits supplied to a residental house can support a power transfer rate of 120kW. A typical single family home maximum power consumption is probably less than 5kW.

Anonymous said...

But wait a minute.....This will be a "CAPACITIVE" load, not an inductive load. Charging a capacitor should not even register on your electric meter. How about this. Charge the super-caps off the grid, use an inverter to change the DC from the Cap. to AC, and power your home for free!!!

Anonymous said...

Techopete says:

I think you have lost this argument. If you had already considered that high voltage charging could be used, and knew that USA regulations already allowed feeds up to 600 vols for domestic equipment, then why did you do your calculations with 240 volts? At least that was deliverately trying to mislead.

Although I try to avoid it as much as possible, I have been fixing CRT colour TV's (not "color" as all of them were UK models) for the last 35 years - though not very regularly. Last time was a year ago when a capacitor in the black-level clamping circuit in my 25(??) year old TV failed and I worked it out and fixed it (first component I replaced) but only AFTER getting my wife to agree that we should buy a decent HD TV. I wear rubber gloves, but never go anywhere near the EHT (12KV circuit) - but 240 volts is quite enough to kill you anyway. CRT's also emits a minute dose of X-rays, by the way, but you would not notice unless you sat with your nose in front of them. Refused to even attempt to fix a friend's microwave a few years ago - far too dangerous - much higher voltages in the Klystron than in a colour TV, I believe.

The point that you seem to be determined to miss is that a high voltage (e.g. 3000 volts) medium current feed can be designed to be safe with decent multi-layer insulation (same as colour TV's and microwaves can be designed to be safe). Further, unlike the Eestor unit itself, producing such a charging system involves no new technologies - just a methodical application of existing ones. If you wanted to be ultra safe you could insist that the charging cut off if the outside of the cable was even touched by a human being. Certainly high-voltage charging would never start unless the connectors were properly and fully inserted.

If you are determined to commit suicide with such a charging system then you can probably succeed, but that applies to quite a few human items and should not be a bar to government acceptance.

Of course the oil industry might try to persuade governments that such a charging system should be banned, but that is politics, not technology.

I know of no USA or UK regulation which ban CRT's or microwaves, so why should they ban a properly designed 3000 volt charging system? Yes, I hope that the government will produce regulations to ensure that such domestic charging systems are safe. But there is no case for banning them.

Anonymous said...

The usual (publicity) implication is that an EEstor/Zenn could be recharged at home in five minutes (but even being able to do that at a charging station would be a good thing if everything else worked).

In the US a typical modern home electrical entrance panel is rated for 200 amps at 220/240 volts (your voltage may vary). The largest outlet is most likely 50 amps for an electric stove, but that's pretty expensive to install. Of course, you can make a deal for higher voltage (pay for different power company transformer), install suitable entrance and breakers, etc., but that gets you further from the implied simplicity and cost.

As for higher voltage, I "generate" that quite often (100,000 volts plus or minus), just walking across a carpet!

I think that for home based charging the assumption should be at most 240 volts at 30 amps. That's still a special circuit--120v at 15 amps would be the conservative assumption. In the mean time, turning on just a 50 amp load would dim your lights (and your neighbor's, too, if on the same transformer). Long term, grid power arrangements could be changed.

Superconducting cable would also help!

Anonymous said...

Technopete wins. It's obvious that Auto IT is a hater. Good thing mankind does not require people like him in order to progress.

Those who can, do.

Those who can't author sarcastic blogs.

j.s.mawejje said...

The whole drive to electric cars will sooner than later demand extensive changes in not only domestic power but national grid supply, same as growth in contemporary (20th century) vehicle populations drove innovation in road building (multi-lane motorways, fuel service stations, etc), the increase in EVs will drive public authorities to accomodate likewise. At the same time, the solution (i.e. best EV configuration/system- either hybrid/hydrogen or pure electric) may be even simpler than the kind here discussed (EEStor), once a public/universally applicable infrastructure is in place to support the system. Ultimately, the very complexity of some of the new systems as EEStor/Nanotechnology compared to normal BEV will work against their widespread adoption, however brilliant, as most ordinary people would find it too expensive to run/maintain. I would guess this is partly what Auto IT wanted to put across!

Anonymous said...

Has any considered superconducting cables to charge the car? so the electrical resistance is zero

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