Supercapacitor Battery Replacement

[freebeard]

Oh! I shoulda checked that. That is impressive!
Still it's strange to me that there are so few posts.

First post was by redpoint5 on 01-08-2014. That's a decade plus...

At this moment there are 2 members (you and I) and 802 bots lurkers.

[redpoint5]

Originally Posted by freebeard

First post was by redpoint5 on 01-08-2014. That's a decade plus...

At this moment there are 2 members (you and I) and 802 bots lurkers.

At some point, I'll have been a member of this forum for over half my life. I think that's about 2040.

[Ecky]

Originally Posted by Logic

In an EV it seems a shame not to buffer the batteries with supercaps.
Capture more regen energy and save the battery from high discharge rates when accelerating.
Perhaps the power added doesn't offset the extra weight and space.
Apparently this is called Hybrid Energy Storage System (HESS) and is a thing still.

All this could use its own topic.

The main issue with supercaps in conjunction with EVs and hybrids is that you can't really put them in series.

If you put two battery cells in parallel, you double their amp hours. If you put two in series, you double their voltage. Both result in doubling the watt output, and double the stored energy.

If you put two capacitors in parallel, you double their capacitance (equivalent to amp hours in battery cells), but if you put them in series, you double their voltage, but also halve their capacitance, so you don't double your energy storage. For a 300 volt hybrid, you would need 100-120 supercapacitors in series, which would divide their capacitance by 100-120, effectively making them useless.

I am not sure why large capacitors have never scaled up in voltage, but there is probably a good physics reason for it.

[redpoint5]

Originally Posted by Ecky

The main issue with supercaps in conjunction with EVs and hybrids is that you can't really put them in series.

If you put two battery cells in parallel, you double their amp hours. If you put two in series, you double their voltage. Both result in doubling the watt output, and double the stored energy.

If you put two capacitors in parallel, you double their capacitance (equivalent to amp hours in battery cells), but if you put them in series, you double their voltage, but also halve their capacitance, so you don't double your energy storage. For a 300 volt hybrid, you would need 100-120 supercapacitors in series, which would divide their capacitance by 100-120, effectively making them useless.

I am not sure why large capacitors have never scaled up in voltage, but there is probably a good physics reason for it.

That's the problem I have wondered why hasn't been solved. Caps have a wide range of voltages, but supercaps don't. If someone optimized a supercap for 15v, that would be perfect (leaving aside the fact that automotive voltage should have been 48v long ago).

[Piotrsko]

With capacitors, the voltage is determined by physical spacing using the dielectric material as the spacer. Better spacer insulation gives you more capacitance because the plates get closer together. However, at some point the plates get so close together that the current flows from one edge to the other. Aka breakdown voltage, aptly named. Caps in series will cascade failure because a larger voltage applied pretty much guarantees sequential failure.

Generally, unless you have some filter scheme that requires frequency taps, Caps shouldn't be used in series

Back in the day, you could "stack" them and be sucessful because the working voltage generally exceeded the signal voltage by a dosen factors and all you had were large value caps in your storage. You used parallel resistance charts and solved for the required values.

You CAN get large value caps at higher voltages but they have to be larger. I have seen a 100 mfd cap for line voltage that was the size of the power transformer on your light pole outside the neighborhood

[freebeard]

www.theregister.com/2025/01/30: A good kind of disorder: Boffins boost capacitor tech by disturbing dipoles

The team made changes to a material group called antiferroelectrics – used in capacitors – in which layers of pairs of positive and negative charges are aligned in one direction alternate with layers in which such dipoles align in the opposite direction. The researchers prepared materials which deliberately disrupt this pattern by including areas of dielectrics – materials with high resistance used in capacitors – which do not exhibit this kind of dipole behavior.

"Overall, capacitors made using this composite material had a greater charge–discharge efficiency and breakdown strength than did devices made using unengineered lead zirconate [a material commonly used in capacitors]," said Piush Behera and Suraj Cheema of MIT in an accompanying article.

The result was an increase in the number of charge–discharge cycles that occur before breakdown. The maximum energy density was also enhanced compared to unengineered lead zirconate
....
"As on-chip capacitor applications continue to advance, frustration-modulated high-performance antiferroelectrics materials can potentially be promising candidates for multilayer, large-scale and three-dimensional capacitors," the study said.

More than you want to know about frustration-modulated high-performance antiferroelectrics materials.

[redpoint5]

I received the 46135 25Ah cells which took about a month in transit and cost $12/cell. Initial discharge of 0.2C (5A) confirmed the 25 Ah capacity, which is about 77Wh.

Fortunately I read a review from another customer prior to testing the other 3 cells and it described receiving 4 cells that all had the polarity mislabeled. I checked the remaining 3 cells and found 1 to be mislabeled. I'd have destroyed equipment if I hadn't read that review.

I'm excited to build a battery with these larger format cells and try them in various vehicles, especially the motorcycle. Having mounting studs and bus bars will make connecting them much more simple than welding thin nickel strips.

Unless I can find a BMS that can output 200A, I'm not going to bother with it. I'll throw on a cheap balance circuit and call it good, being careful not to discharge too deeply. I'm sure a brief ~8C spike in current to start a car will not cause them any harm.

I might try an EC8 connector and 8AWG wire.



This front cell is mislabeled