TURN8 - 07 September 2008 07:05 AM

hobbymanbill - 12 August 2008 09:40 AM

Two potential problems, the one you see here, and the fact that lithium-ion or lithium-polimer batterys can burst and ignite. They burn at 2300DEGF. I haven't heard problems with the ones in the Prias, so I don't know if there is one or they are doing something to isolate them from the chassis/bodywork. That shock was just like you would get from touching the anode and chassis of an old TV type picture tube. Thousands of volts, but with only milliamps driving it. It does however actually throw you back. I don't think it was the mechanic being surprised, it was the high voltage physically pushing him. With any amperage, that would have been fatal. Somehow they need to better isolate the system from the chassis/bodywork. AA JMHO

Bill

The voltage didn't "physically push him back". It caused an involuntary muscle contraction.
I think the fears here are over stated. The systems are going to bats or super capaciters, which tend to be low voltage systems. (Running the current back and forth through inverters would seem to be a waste.) Low voltage systems, 12 to 36 volts I would think. No more of a fire or electricution risk than any road car electrical system really.

Care to grab a car battery with both hands? Not only will you get severe burns, you'll probably stop your heart as well. When you add a capacitor to you increase the amperage that can be delivered. Noting that the performance gains that are percieved to be achieved, as much a 20 seconds benefit per lap of use, this must be a large amount of storage for a 25-35 hp increase.
It's not the voltage that kills, it's the amps and how many are delivered at one time that does the damage to the human body.
It is still an unknown what happens to this "energy" if it is allowed to escape all at once due to an accident. The potential is there to burn or render the driver a stun gun effect as the car is still carrying on after an impact.

As an early adopter/owner of a hybrid (2000 Honda Insight) and an electric vehicle builder (assisted a friend of mine in coverting a 1999 Ford Ranger [AC conversion] and a 1987 Toyota MR2 [DC conversion]) I find it interesting the amount on confusion and misinformation swirling around the F1 community regarding these systems. Hopefully I can answer some of the questions. Greywolf74 did a good job describing the difference between series and parallel hybrid (KERS) drive systems, so I'll focus on the battery, motor, and inverter side of things.

Motors

Just as with everything else electric there are two main forms of energy delivery; alternating and direct current.

DC motors use a combination of permanent magnets (lumps of rare earth materials) and electric magnets to spin the drive shaft. They have fixed commutators of permanent magnets in a fixed orientation (though some EV racers are working on servo adjustable commutators). EV racers generally adjust the timing (advance the placement of these commutators) in order to assist with torque at higher RPMs. A typical DC motor can produce all of its torque at 0 RPM, but they are limited to a fairly low redline (6500-7000 RPM) even with Kevlar reinforcement. Much above that speed and the motor starts to fly apart, commutators arc internally and things go bad quickly. Another issue with DC motors is that they tend to be lower voltage than their AC counterparts and have trouble dealing with "back EMF"; where the spinning motor starts acting like a generator and tries to push power back into the batteries which effectively becomes a force you have to overcome at higher RPMs in order to continue accelerating.

EV enthusiasts like DC motors because they are relatively cheap, readily available, and provide monstrous torque from 0 RPM on up.

AC motors use multi-phase coiled electric magnets. They can fit into much smaller packages and are readily liquid cooled if needed. AC motors do not have the same issues as DC motors with high RPMs and can easily exceed 12,000+ RPM with off the shelf components. AC motors still have a lot of torque at low RPMs, but it takes them a little bit to hit peak torque (500-1000 RPM is pretty common). Once they hit that level, though they maintain that oomph through the rest of their "curve." When my friend and I took the '99 Ranger to a performance shop to dyno it as an electric the guys in the booth just about died when then saw the rapid spike and then solid maxed plateau of a torque curve it produced.

AC system require more complicated inverters (as they are multi-phase where as DC is single phase) and readily available units can't take as much current as DC systems (though there is no technical reason that they couldn't, just not many high current motors already on the market) so they tend to be higher voltage to get the same amount of HP/torque.

Voltage and Current

All EV/hybrid systems are pretty high voltage and high current in comparison to what you are used to with your typical car's electrical system. The Honda Insight, for example, uses a 144V system to power a tiny 10KW pancake motor. The 120 D-cell(ish) sized NiMH pack stores 6.5 amp hours of energy. Enough for a few minutes of full power use. DC electric vehicle dragsters typically run 240V or higher and draw as much as 2000 amps (using upwards of a megawatt of power at peak acceleration).

The F1 KERS systems are likely to be fairly high voltage (144-220V) and relatively high current (500A or more).

Battery Chemistry

Lithium-Ion - Here's one of the things that has surprised me about the F1 systems tested so far. Lithium-ion batteries have some of the best energy density (amount of power stored for a given volume, gasoline has a huge energy density, but combustion wastes the vast majority of it as heat; batteries have awesome efficiency, but energy density is not nearly as good) ratings of any battery chemistry; that's a given. But there are many formulations of lithium-ion and the older ones can be super dangerous. In fact, one of the big manufacturers (I can't remember if it was McLaren or Ferrari) had an incident a little while back where a lithium ion pack went into thermal runaway (thermal runaway is where sufficient heat causes a chemical reaction in the battery that generates more heat so it gets caught in a loop and burns super hot until it is all gone) and burned up. This is the same sort of issue that Dell has had with their Li-Ion batteries recently. The thing is, there are multiple companies out there producing new Li-Ion variants with unique chemistries (like A123's lithium nano-phosphate)that have zero thermal runaway problems. F1 teams have huge budgets and awesome technical resources, so why are they use older Li-Ion formulas like lithium-polymer?

While some form of Li-Ion battery is likely to power most F1 KERS systems (due to the high energy density) it is worth briefly talking about the alternatives.

Lead Acid - This is one of the oldest forms of battery chemistry and what you find under the hood of your car or powering a golf cart. PbA (lead acid) batteries are very heavy (thanks to the lead) and have mediocre energy density (though some sealed PbA batteries are pretty good). They also produce hydrogen gas as a by-product as part of the chemical reaction that produce the electricity.

....continued from last post.

Valve regulated, sealed, lead acid batteries don't out-gas as they have a chemical make-up that converts the hydrogen back into the electrolyte, but old style flooded cells (like most cheap car batteries) do. PbA batteries are big and rugged, though and can be built to take massive current draws. F1 won't be using lead-acid (even though it is actually super safe) because of the poor energy density and high weight.

Nickel Metal Hydride - This is the formulation that powers most current commercial hybrid cars. Good energy denisty, no thermal runaway, and mediocre current capacity. These batteries are light and work well in hybrid systems, but they just can't produce a lot of current and are made of exotic and expensive materials. This is why the auto manufacturers are moving towards li-ion in newer models.

Nickel Cadmium - Excellent energy denisty, some thermal issues, good current draw. NiCad's main drawback is the extreme toxicity of the chemicals in these batteries. In most other respects they are a good battery choice for a hybrid (or KERS) system.

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I hope the above and my previous post help make some sense out of the electrical side of things in the new KERS world of F1. It will certainly be an interesting additional to the technical side of F1 racing. Now, about those new low-aero rear wings...