What is a Lithium-ion capacitor? | Hacker News Reader

What is a Lithium-ion capacitor?

jtekt.co.jp

54 pointsksec32 comments

For anyone that wants to see a real data sheet:

Nominal Voltage: 4.0V High Power and Energy Densities Cycle Life > 50K Cycles Capacitance Range: 10F-1200Farads

https://abracon.com/product-lineup/frequency-control-timing-...

Note that the original data sheets said that these could be wave soldered. ABSOLETLY NOT. Even hand soldering they must be treated with respect, a lot of respect.

One of the major problems with these is there a minimal voltage that they must not go below. Their life gets shortened. I've never seen data on how much.

To my knowledge Li-Ion Capacitors were first introduced to the market by Taiyo-Yuden in 2010. They are no longer in this market. I wrote a blog about it back then:

http://blog.softwaresafety.net/2010/11/introducing-lithium-i...

The direct link to the data sheet:

https://abracon.com/datasheets/AHCR-S04R0S.pdf

So it's some of the performance of a supercap (hundreds of thousands of cycles, up to million-hour lifetimes with a bit of care, less finicky about soldering) with all of the safety of a LiIon battery? I think I'll give it a miss, although it probably has niche applications like use-once military systems where you're not worried about long-term performance before it disassembles itself.

Large, charged capacitors are pretty frightening. Batteries too, but their discharge rate is limited to the speed of the chemical reaction.

Are capacitors not limited by a chemical reaction?

Not AFAIK. A simple capacitor is two metal plates separated by an insulator, allowing an electrical charge to accumulate. Discharge would only be limited by the current-carrying capacity of the wiring.

Not generally, no. Capacitors usually store electrons in a conductor so they are free to move instantly. Movement of free electrons within a conductor is not considered a chemical reaction.

aka a lightning bolt

Not really as large capacity capacitors (this one seems to be 4V) tend to be low voltage as well. You can touch the terminals without harm but attempting to short them is going to be, er, entertaining. I have accidentally touched a 200V capacitor and it was not fun.

That's interesting. What good is 4V in an EV? You'd need cables as thick as your arm to handle the amperage to do anything useful.

You might be able to put more in series if the tolerance of the capacitance value is low enough.

Otherwise, you can use a step-up voltage converter to generate a voltage as high as you want, in order to distribute power at greater distances. You can make bidirectional converters, which work as step-down converters for charging and as step-up converters for discharging.

> attempting to short them is going to be, er, entertaining.

I think of Styropyro's something like 400 car batteries wired together.

Limited by material. They store electric charge by using thin layers of insulating material and pooling negative charge on one side and positive on the other. You can puncture the material and release energy as a typical conductor, it's not stored chemically.

Dumb question but I though capacitors store energy and not power?

They store energy but there's a limit to how quickly you can get that energy out, hence a limit to power. And I suppose you can kinda talk about them "storing power" in the sense that power is what you might be interested in getting out of them.

At least, that's my understanding of it.

Power is just the time derivative of energy, like velocity is the time derivative of position. Both batteries and capacitors store energy, which they can release at some given peak and average power. Batteries tend to focus more on energy density (energy stored per weight), while capacitors tend to focus more on power density (rate of energy stored or released per weight).

I think that just reflects that the typical usage for a capacitor is smoothing out some very spiky load that runs at a high frequency, say a microcontroller running at 100MHz. The average power needs of the MCU are low, but it's drawing almost all of it in a big burst on every clock tick (10ns).

Power supplies handle that badly, and the pulses turn your supply traces in a big antenna and suddenly you're an unlicensed FM radio station.

So for the capacitor that's put in place to buffer that load, the total capacity is important, but what really matters is that the part can manage that 100MHz charge/discharge cycle.

You could have just said yes.

That wouldn't have contributed much to the discussion. Electrical insights often come from analogies. It's easier for most people to understand time derivatives in the context of an accelerating car than it is to understand them in the context of a capacitor or inductor charging.

Another cool insight is around "dual" relationships in circuits. You can often think of some components as roughly analogous to each other, with a switch of current and voltage. For example, if you connect a capacitor in parallel with a power supply and load, the voltage across it will increase as a function of time until it reaches the power supply voltage. Similarly, if you connect an inductor in series with a power supply and load, the current through it will increase as a function of time until it reaches the current that would otherwise pass through the load.

Like most good analogies, it's not 100% airtight, but it provides useful insights.

Let's say you want to make a hybrid car lighter-weight. Where is this useful?

Power density and cycle life are truly impressive. Energy density is super low

Regen braking,

Interestingly it seems to have some applications for high peak power and regen, they had a car in the Dakar rally:

https://www.jtekt.co.jp/e/products/capacitor/capacitor_mobil...

https://www.jtekt.co.jp/e/engineering-journal/assets/1019/10...

You would use these to provide peak power in a system that had short term power needs that were high above the average power needs AND had that power requirement as a bottleneck. Energy is the bottleneck for cars though, not power. unless you're wanting your prius to accelerate like a ferrari

Maybe it would be useful for less losses with regenerative braking? These would presumably be able to charge much faster and then trickle that power out to the normal battery. You'd need actual power numbers for a car to determine if it would be useful or not.

In other words this is for "boy I wish I didn't have to have so much extra battery capacity in order to get the power I need" situation which... cars don't have. Maybe in F1?

> unless you're wanting your prius to accelerate like a ferrari

That's the point of a hybrid.

It’s the best part of any electric drivetrain. Especially when you can remap the throttle to really launch from zero. :)

(I find that electric acceleration makes highway merging much safer.)

My EV has the opposite problem, something like half throw is full throttle and then the rest of the pedal does nothing. They do it for marketing reasons but I still don't like it

My ICE car does the same. The only use for almost half of the pedal travel is shutting down the speed limiter when it's active, with no change at all when the limiter is off.

That’s annoying. The Genesis throttle maps are what you’d expect: Eco counteracts a leadfoot, Comfort has good pickup, Sport is borderline irresponsible in neighborhoods, Boost is unreasonably fun.

I have completely failed to tell any difference between my EV's drive modes. It supposedly has eco, normal and power, but all they seem to do is set a limit on the motor output. Power seems to have no difference from normal.

And no mention of the self discharge rate.

For a similar part in this class:

Low Leakage Current as small as 1µA Low Self-discharge rate, 72 hours @ discharge <5%

https://abracon.com/datasheets/AHCR-S04R0S.pdf

The more the Farads the higher the leakage. The higher the tempature the higher the leakage.

That would work for most UPS applications, but it looks like the price is still too high.

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