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I was wondering if Tesla can increase range by adding ultracapacitors used in parallel with the batteries, using them for boosting, acceleration and leaving the batteries mostly for constant speeds.
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Any questions?
From what I understand, the limitations of batteries is that they can only charge and discharge at the same rate. So while you could design a lower power output battery pack (like the PowerWall uses) by adding super/ultra/hypercapacitors to enable the car's peak acceleration and regen, your battery wouldn't be capable of supercharging.
If you were only ever charging overnight, the argument changes. Tesla doesn't want that approach, so they're inappropriate.
But I'd like to understand other arguments.
• Volume
• Energy Density
• Weight
• Durability
• Longevity
• Fine Control
All super capacitors offer in the plus column is quick discharge... As I understand it. But a quick search did turn up <a href="http://lerablog.org/technology/advantages-and-disadvantages-of-supercapacitors/"><b>this list</b></a>:
<blockquote><pre><h2><b>The advantages:</b>
1. Unlimited cycle life; as compared to the
electrochemical battery, they are not subject to the
wear or aging.
2. On-hand charge methods; no full-charge circuit
required.
3. Quick charging times
4. Low impedance; by paralleling it with a battery, it
enhances the pulse current.
5. Cost effective storage; a very high cycle count
compensates the lower density.
<b>The disadvantages:</b>
1. Low energy density; usually holds 1/5 – 1/10 of a
battery.
2. Cannot use the full energy spectrum for some
applications.
3. Low voltage cells; to get higher voltages, serial
connections are required.
4. Voltage balancing needed; when more than 3
supercapacitors are connected in series, the circuit
needs a voltage balancing element.
5. High self-discharge as compared to electrochemical
batteries</h2></pre></blockquote>
Basically, it seems that super capacitors would be better paired with a hybrid ICE.
Most of the weak hybrids have a small electric motor and small battery so it simply can't do the peak output power, it needs the big ICE for that. So yes a super capacitor and larger motor could allow for a hybrid with a small battery, small ICE generator, and larger electric motor (and I think that would be a useful car temporarily somewhere in the spectrum).
The Tesla P85D outputs up to 515kW from the 85kWh battery, where Tesla has setup the powerwall to output smaller amounts (7kW peak from 7kWh battery), and I would assume that's because it's much cheaper to have those lower limits.
So rather than just useful for a hybrid, could a cheaper big battery with a super capacitor enable the same peak acceleration at a cheaper price? (given that with a super capacitor supercharging would be impossible).
Anyway interesting if it's useful for hybrids.
That said, for dual motor cars such as the 70D, 85D and P85D, it could be possible, when needed, to disconnect the front motor from the main battery and connect it to an ultra capacitor, leaving the main battery exclusively for the rear motor. This would allow both motors to operate at different voltages.
@Plafor, is that right? You don't want to mix batteries and ultracapacitors? One thing to remember is that you would never need the capacitor to charge the battery, since the regenerated power will be used on the next acceleration.
@RedSage, that's what I'm wondering about plugin hybrid variants. If their performance was brilliant then you usher in the generation of tiny ICEs with small batteries, the natural next step is to grow the batteries... then lose the ICE.
if technology suddenly improves as start up companies have claimed for years but never yet delivered, then super capacitors could one day make sense... what is needed is device that can high volts rather than just 2V per cell combined with some cheap, fancy and reliable dc to dc converters.
On Dc To DC converter end, capacitors jump from zero volts empty to full voltage in linear fashion unlike batteries which tend to stay close to full voltage, so probably need fancy dc to dc conversion equipment. (DC to DC conversion is getting steadily cheaper and better, eg mppt solar battery charger)
Theoretically, someone might develop a high-density battery pack with low current capability - perhaps it would quadruple available range, but where discharge currents weren't enough to make the Ricky Racer types happy, and where charge currents weren't high enough to effectively capture regen power. In such a scenario, pairing the battery with supercaps to improve regen and acceleration would be great. But it's really not needed in today's EVs.