Ultracaps vs. Lead-Acid: Weight Optimization.

Hi!

Weight reduction is beneficial in two ways: It's just as interesting for those who love acceleration as it is for those who want to save fuel, as it improves the vehicle's power-to-weight ratio and reduces braking energy.

Ultracapacitors are based on a new technology and have recently become available in the component trade. They are capacitors with extremely high capacitance and power density. However, their energy density is lower than that of lead-acid batteries.

Here are the basic characteristics of ultracaps: http://www.udomi.de/fuelcell/ultracap-basics.html

Ultracapacitors are ideal for those who only need their starter battery for starting the engine and don't want to drain it by powering other electrical components when the engine is off. Of course, a small buffer battery is still necessary, as the vehicle's electrical system needs to be maintained at a constant voltage even when the engine is not running.

To my knowledge, only individual 'cells' of 2.3V and various capacities have been offered so far, for example, here: (click on the ultracap) http://www.billig-digitalkamera.de/B_22xxx501973_ULTRACAP600F23V.htm

Based on a rough calculation, 7 'cells' with a voltage of 2.3V and a capacity of 100F would be sufficient to start my car. Ideally, 10 high-current NiMH cells with charging electronics would be used as a buffer battery. However, the cost would be higher than a new battery: 7 cells at €30 each would cost €210 just for the ultracapacitors. However, considering what some enthusiasts spend for a tiny bit more acceleration, this is a negligible amount.

Well, the weight-saving effect isn't outstanding: perhaps 15-20 kg. However, the center of gravity lowers, and the car becomes more stable, because batteries are usually mounted high in VW compact cars.

Regards,
Holger.

Just remove the rear bench seat and all the insulation materials, etc.

It costs nothing and delivers more.


CU Gremlin.

I already did that a long time ago, even including the spare tire and accessories. That's why my car looks so high in the back now, especially with an empty tank. But it only adds about 20-30 kg.

Hello,

"Automakers have been testing this for quite some time, and it works quite well. However, newer cars have a significant idle current problem due to the large amount of modules that need to remain active even when the ignition is off, constantly listening for signals on the CAN bus (wake on CAN or Wake on MOST) and therefore cannot be completely turned off. You might consider how your remote key fob works to unlock the doors. Nowadays, battery capacity is more often limited by the idle current consumption than by the starter motor draw."

Ask EPCOS; they have exactly what you're looking for.

Best regards,
Christian.

Well, the current trend towards more and more gimmicks goes against weight reduction. Those who uncompromisingly prioritize good acceleration and lower fuel consumption should consciously avoid all the pampering and luxury gadgets.

I would still buy a car without air conditioning, power windows, or central locking if it otherwise meets my requirements. Okay, having a power window on the driver's side is actually quite useful without air conditioning, because I always drive with the window open in towns during the summer, and then crank it back up when I'm driving outside of town.

Does EPCOS already offer ready-made 'battery' solutions for retrofitting vehicles?

Best regards,

Well, the current trend towards more and more gimmicks goes against weight reduction. Those who uncompromisingly prioritize good acceleration and lower fuel consumption should consciously avoid all the pampering and luxury gadgets.


Okay, just a note: The vehicle's weight only matters when accelerating and decelerating. If you're driving at a constant speed of 130 km/h on the highway, it's practically irrelevant whether your car weighs 1 ton or 2 tons.

Low rolling resistance tires, an aerodynamic body shape, sufficient tire pressure, and above all a proactive driving style save fuel.
I certainly won't forgo such useful features as climate control, power windows, and central locking, because my car needs less than my previous one, which was about ~160kg lighter.

Julian wrote:

I certainly won't forgo such useful features as climate control, power windows, and central locking, because my car needs less than my previous one, which was about ~160kg lighter.

And I refrain from using it, among other reasons, because I know that every car, without that stuff, consumes (still) less fuel and performs better than with the stuff 8)under the same driving conditions.

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Then you would have had to be consistent and also save on the brightness control in the AI.

If you drive at a constant speed of 130 km/h on the highway, it is negligible whether your car weighs 1 ton or 2 tons.

However, this only applies on perfectly flat terrain. When going uphill, fuel consumption increases with the weight, because you don't fully recover the energy you used when going downhill. A portion of it is lost through the brakes.

Speaking of gimmicks: My first Trabant was a 'standard' model and had a hand-operated windshield washer pump. You pulled a mushroom-shaped button 5cm out of the dashboard, which was the stroke of the piston. Due to the spring force, it slowly slid back in and sprayed, but you could also press it further to spray more forcefully. It always worked great. And it saved on an electric motor and wiring.

Regards,
Holger.

The same old crap, but a different day.

'Currently, I'm getting similar fuel consumption figures with our Passat as we used to get with our old one (according to the MFA, which is still showing the old data). This is despite the new car being 300 kg heavier, having more features, and using PD technology. The extra weight can be effectively converted into longer gliding phases with the coasting function enabled. Also, you tend to use more full throttle during acceleration, which increases the overall efficiency.'

Best regards, WarLord.

WarLord wrote:

Also, more full-load phases are needed during acceleration, which increases the overall efficiency.

A copywriter has gone missing, and it's your fault .
Uninformed people might misinterpret that to mean "excess weight reduces fuel consumption," even though that's not what you wrote.

@Arosa SDI:

I believe that capacitors are not particularly suitable for buffering an undersized starter battery due to their discharge curve, as their voltage decreases linearly with each joule drawn from them.

Very quickly, the remaining voltage of the Cs drops to the level of the battery, and then it can essentially power the starter motor on its own.

Unless a high-performance DC-DC converter is placed between the battery (Cs) and the starter motor, which converts a decreasing input voltage into a constant output voltage, all while handling load currents of several hundred amperes.
I believe that the cost and weight would make the capacitor idea completely impractical.

And I choose not to use it, among other reasons, because I know that every car, with the same driving profile, still consumes less fuel and performs better without that stuff than with it.


Well...

I'll only get rid of it over my dead body. It would probably decompose quickly anyway, especially without air conditioning in a temperature of 38°C.

'After all, the Octavia, with its 90 horsepower, runs just as fast as the old-timer car.'
and that despite being 300 kg heavier.
The fuel consumption should be adjusted based on energy content (10.5 liters of gasoline equivalent to 6.2 liters of diesel).


Whether using all caps is a good idea is a valid question.
It would be extremely useful to charge the batteries from a Li-ion battery just before starting, as a Li-ion battery is actually lighter than a comparable lead-acid battery .

Somehow, I need to think about the good old crank again .

By the way, a DC/DC converter doesn't weigh much... you just shouldn't build it with a laminated iron core transformer.
Starting around 150 kHz, the switching clock frequency becomes acceptable even under high load conditions.


CU Gremlin.

Hi.

Okay, one more thing about the captions - everything reads really well, but:

You need a charging control circuit/maximum voltage control for the capacitors. They must not exceed 2.3 volts! However, the 12V voltage in the car fluctuates significantly. Simply adding a diode won't work; the first voltage spike will cause arcing when all the diodes switch on.

You can forget about it with a diesel engine, because the preheating system would already take care of discharging it.


In a gasoline-powered car: If the first start-up attempt fails, you'll definitely need jumper cables. If you arrange the cables in a way that allows for multiple attempts or pre-heating, a lead-acid battery is cheaper. You can use a smaller lead-acid battery, and I think you can achieve more with less.
For example, a 20Ah battery is usually sufficient for starting most gasoline engines. However, the battery doesn't last as long, and you won't have any reserve power for winter or periods of inactivity.

And the issue of quiescent current is actually the main deciding factor.

What advantage does a 20kg weight difference provide?

I don't even notice the difference between a full and an empty tank.

Gremlin wrote:

By the way: a DC/DC converter doesn't weigh much... you just shouldn't build it with an iron ring core transformer... Starting around 150 kHz, the switching clock frequency becomes tolerable even under high load conditions

.
If "high current" now covers current levels of around 400 A without costing as much as 5 starter batteries, then it might actually be feasible... what are the efficiencies of such components?

The extra weight can be very effectively converted into longer gliding phases during the thrust reduction. Also, more full-power phases are needed during acceleration, which increases the overall efficiency.

Yes, no, it's obvious. The extra weight will be offset because the engine efficiency increases. I'm going to put an old cast iron radiator as ballast in my trunk, just like in 'Manta, Manta'. It improves the handling .

Regarding the capacitors - everything reads very well, but: you need a charging control circuit/maximum voltage control for the capacitors; they must not exceed their 2.3 volts!

'Wrong, there are already ready-made modules available for automotive applications. The capacitors are simply connected in series, just like the cells in a lead-acid battery. Specifically to protect the capacitors when they have different capacitances/residual currents, EPCOS offers a balancing module. This module essentially uses power Z-diodes in parallel with each capacitor, but these diodes only become conductive when there are relatively large voltage differences, meaning when a capacitor is defective or damaged.'

In a diesel engine, you can forget about it, because the preheating system already takes care of discharging the electricity.

'If you use NiMH high-current cells as a backup battery, it works perfectly. The pre-glow phase only requires 10-20% of the power needed for starting.'

If the first attempt to start fails, you will definitely need a jump cable.

You're wrong again. The energy in the buffer battery is enough for several attempts. It works on the same principle as the flash in cameras: an electrolytic capacitor is charged to provide a very high pulse of power. After that, it takes a while for the capacitor to recharge, because the power is drawn from the batteries very slowly.

Let's calculate: One start attempt, lasting 2 seconds and requiring 1 kW of starter power, consumes 2000 Ws = 2000 Joules of electrical energy. In 10 high-current NiMH cells with a capacity of 5Ah each, there is a stored electrical energy of 60Wh = 216000 Ws = 216000 Joules. Assuming a 50% loss during recharging, that still leaves 100000 Joules. Therefore, when fully charged, it should be enough for 50 start attempts.

The charging efficiency is increased when, instead of a charging resistor, a low-power DC-DC converter (100W is perfectly sufficient) is used to charge the capacitors by adjusting the voltage to maintain a constant power, so that the buffer batteries are also discharged at a constant power.

I believe that capacitors are not particularly suitable for buffering an undersized starter battery due to their discharge curve, as their voltage decreases linearly with each joule drawn.

I believe capacitors are actually very suitable for the starting process, even considering their discharge curve. This is because the power demand of the starting process decreases as the capacitor voltage decreases, resulting in a smoother and faster start.

Trigger event:
At second 0: The pinion engages: The starter motor must accelerate the heavy engine, including the flywheel, from a standstill. The starter motor acts like a resistor with a resistance of 0.05 ohms.
At 0.2 seconds: The starter motor is working against the initial compression. At that moment, there is no counter-expansion in the other cylinder, as the excess pressure has escaped during the idle time.
At 0.4 seconds: The initial compression phase is overcome, and the first expansion (without ignition, just the effect of the gas spring) greatly accelerates the further rotational movement.
At 0.5 seconds: The next compression cycle is significantly more agile because the flywheel has now been properly accelerated by the first expansion. The current draw of the starter motor decreases noticeably.
At 0.6 seconds: 1. Ignition, increase in starting speed by 50% during the first 1/4 of a revolution after the initial ignition. The starter motor only draws a fraction of its starting current. This is a hypothetical slow-motion observation (regarding the time indications). It would be really interesting to use a storage oscilloscope to measure the starting current.

'Capacitors have a significantly lower internal resistance compared to a standard starter battery. This results in less power loss within the capacitors themselves during the starting process, meaning the voltage doesn't immediately drop to 8V or less. The voltage gradually decreases, but this happens counter to the increasing starter motor speed, which mitigates this effect. With properly sized capacitors, the starter motor speed never drops to the point of stalling (except in cases of starting problems due to engine issues).'

'But, as has already been correctly pointed out, the key argument is the desire for a high energy reserve when the engine is not running, whether it's for nighttime parking lights or a car hi-fi system. I personally could do without it, as I practically never use the battery for extended periods while the car is stationary. This may be different for others. In the event of an accident with prolonged flashing hazard lights, the capacitors and small buffer battery also have a disadvantage. The energy density is higher with a conventional lead-acid battery, while the power density is higher with capacitors.'

Regards,
Holger.