The case for using Supercapacitors with Lithium-Ion batteries in EV's

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DaveP68   100 µW

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The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by DaveP68 » May 28 2021 9:46pm

Would like to propose a discussion on the merits of integrating a Supercapacitor bank with Lithium-Ion batteries in EV's

Supercapacitors are suited for the one dedicated function as a very efficient “Kinetic Energy Recovery System (KERS)”. Supercapacitors are a complimentary device to the Lithium-Ion Batteries to improve the overall system efficiency in an Electric Vehicle powertrain. Most of the gains are obtained from the very low ESR of Supercapacitors for their weight and volume, along with their much higher power density per kg and only used over short time periods.

Below is an actual graphed Tesla Model S P100D during an acceleration run from 0-60 in 2.7 seconds including roll out.
Tesla Model S P100D with acceleration 3.9 seconds.jpg
Tesla Model S P100D with acceleration 3.9 seconds.jpg (114.05 KiB) Viewed 403 times
The important detail to pick up in the above graph is the rather large 77 Volt drop in the green line. The combined power extracted from the Battery is 716,000 Joules of peak power per second including its internal loss (lost as heat) of 141,000 Joules which combines with 575 kW delivered as electrical energy at the terminal. The nominal P100D Battery ESR is around 42 mΩ’s in launch mode which is estimated from that observed 77 Volt voltage drop. The energy transfer efficiency of the battery in this situation is 80% of the total energy released at peak power. So that 20% of energy lost released as heat internally in the battery and is in addition to all other losses in the powertrain, gear box, rolling resistance etc. When we take the total energy in to what ends up stored kinetically in the mass of the vehicle it comes out to 61%.

The following is a simulation graph of how much more efficient a Model S P100D becomes when an only 284 W/h Supercapacitor weighing about 55 kg is integrated into the powertrain.
Tesla Model S P100D with a 284 Wh Ultracapacitor Simulation fully integrated graph.jpg
Tesla Model S P100D with a 284 Wh Ultracapacitor Simulation fully integrated graph.jpg (119.18 KiB) Viewed 403 times
My simulation dataset only goes out to 2.8 seconds. Would like to gain a larger dataset as my simulation software will be able to provide some interesting numbers from say an hour’s worth of real world driving.

There is a calculated 60% reduction to the 141,000 Joules energy lost as heat in the battery when the Supercapacitor is in a 50/50 power sharing mode for those 2.8 seconds during acceleration.

The Supercapacitor bank has a very low ESR for its volume and weight at only ~27-28 mΩ’s. When integrated into the powertrain, it reduces the battery Volt drop to around 40 volts peak instead of Battery only 77 Volts. That is a reduction of just over half and the battery peak current only reaches a peak of 950 Amps, along with the Supercapacitor delivering the balance. Considering the battery doesn’t need to be pre heated to 50 Deg C for launch mode the system losses are more than halved and the battery ESR can remain at its nominal 50-52 mΩ’s. When a Supercapacitor is added in, the combined peak power losses converted into heat during acceleration is reduced to around an average of 54,000 Joules over a second at peak power hence the 60% reduction in lost energy. Looking at it another way only 80% of the total energy extracted is available at peak power from the battery only system. This improves to 91% of the total energy delivered to the drivetrain when the Supercapacitor is integrated in with the battery, that 11% is a massive improvement and cannot be ignored.

The main point here is the Supercapacitor is only a kinetic energy device with its sole function being to provide a large amount of peak power to get you up to speed over a short period (a few seconds in this case). Once the vehicle is traveling at a constant speed the Supercapacitor goes offline, but is then on standby for any breaking application to recover the maximum amount of kinetic energy having been stored in the mass of the vehicle. The amount of peak regen power from a Dual motor system could be up to 200 kW’s 3-4 times what it currently is currently available in Tesla vehicles. The cycle life of a Supercapacitor can be measure at greater than 1,000,000 cycles! Please also note the Supercapacitor is not sized to extract any “Gravitational Potential Energy” when going down a hill. This just so happens to be a much smaller amount of power when measured at per-second rate and can be still be sent back to the Battery.

The depth of discharge of the Supercapacitor at the 2.8 second mark is around 53 % which just so happens to be about the right point for capturing most the Regenerative braking energy in this simulation.

Below is a graph of the peak power of regen increased to 200 kW’s (from Dual Motors) which is less than half of the Supercapacitors peak power rating.
Tesla Model S P100D with a 284 Wh Ultracapacitor during Regen braking graph.jpg
Tesla Model S P100D with a 284 Wh Ultracapacitor during Regen braking graph.jpg (129.04 KiB) Viewed 403 times
Note this is based on a form of ideal conditions simulation with the kW’s and Amps as negative numbers (-) being from the combined Dual motor inverters feed into the Supercapacitor.

The graph timeline shows the vehicle coming to a stop in around 6 seconds without the needing to use friction braking.

Many others have tried just placing a Supercapacitor bank in parallel the battery terminals without yielding much in the way system performance. This is mostly due the Supercapacitor needing to be at least 500 W/h or more to make much of a difference. That becomes a very expensive exercise when increasing the energy density of the Supercapacitor to gain any more system performance.
Tesla Model S P100D with a 505 Wh Ultracapacitor in paralell with Battery graph.jpg
Tesla Model S P100D with a 505 Wh Ultracapacitor in paralell with Battery graph.jpg (121.47 KiB) Viewed 403 times
As can be seen above the 65 Volt drop across the Battery is an improvement over 77 Volts, but that is no match for my system in the second graph at 40 Volts with a 37 Volt reduction. If this parallel simulation is run for about another 1.5 seconds the Supercapacitor will begin to equalise with the battery voltage and we are back to our 77 Volt drop again with lots of heat build up to manage if the high current drain is maintained. The depth of discharge of the Supercapacitor in this example is only 26%, hence why it needs to be at least twice the capacity of my system to add any minimal benefit.

The flip side of this is when the vehicle is at a constant speed consuming say around 17-18 kW’s (~290W per mile) at 60 MPH, the battery will begin back feed a lot of current back into the Supercapacitor. This high current will start off at around 650A and then progressively roll back from there, as the Supercapacitor SOC increases to equalisation with the Battery at some point over the next few seconds. Once the Supercapacitor is at this equalisation SOC and the Regen braking is applied, it is of little assistance with the change in SOC difference being so small the battery will end up soaking most of the regen energy within just over a second. Back to our limit of 50-60 kW’s of regen.

This is not the case with my proposed system, as the vast majority of the recovered Regen braking energy can be prioritised to the Supercapacitor which can also be about half size of the above parallel example, a significant cost saving.

Below is another system architecture example of how many others have tried to integrate a Supercapacitors via DC-DC converter to power inverter with the battery in parallel again.
Ultracapacitor System with Buck Boost converter.png
Ultracapacitor System with Buck Boost converter.png (158.38 KiB) Viewed 403 times
This still has fundamental problems using an expensive Buck/Boost (DC-DC) converter adding additional complexity along with being somewhat current limited. Buck/Boost (DC-DC) converters due to size and weight constraints are peak power limited to 60-100 kW’s.

Instead my approach is to use separate inputs into the Drivetrain power inverter without the need to use a “current limiting DC-DC converter”. The Supercapacitor can transfer >400 kW of peak power for just over second when it’s needed, so isn’t the “limiting factor”.
Supercapacitor with Battery in an Electric Vehicle.jpg
Supercapacitor with Battery in an Electric Vehicle.jpg (59.04 KiB) Viewed 403 times
The complexity of my system is in Drivetrain inverter(s). It’s cheaper to just added more silicon switching devices rather than having a very large expensive inductor in DC-DC converter which just so happens to pre-exist in the traction motor winding's. After all that’s what the Regenerative braking mode makes use of, those 3 coils in the motor.

The following is list of benefits a small Supercapacitor bank has the potential to provide;
1. Greater peak power at acceleration with the potential to supply enough to a Tri motor Drive train setup (800+ kW’s) not currently possible with the most Tesla battery packs power density. Example the current Tesla Model S P100D battery pack is output limited to 580 kW’s of power in launch mode and with the battery pre heated to 50 Deg C. When not in Launch mode the power density reduces to around 460 kW peak. The Supercapacitor (550 W/h’s) can deliver an additional 400 kW’s for a few seconds, with no requirement to pre heat the battery to its 20% lower ESR another to increase the battery only peak current yield without the battery voltage sagging too low. Yes the new Plaid Model S is rated at 800+ kW’s, but can it do 200 kW’s of regen braking when the Battery is at a SOC of >80%? No it will never be able too.
2. System efficiency can be improved by around 10-15%, translating to a range boost and/or improved top end performance. This 10-15% is a return loss number that depending on the configuration could end up being higher and go up to 20% depending on how well it integrates into the system. This range improvement is mostly yielded in City/Urban driving with that dropping to less than half for highway driving. Please note the range boost is not directly correlated with efficiency gain but will still be a meaningful number.
3. An increase in battery life. This being achieved by removing the high peak current demands both during acceleration and regen braking, thus reducing the battery internal temperature rise. Also prioritising the regenerative braking energy to the Supercapacitor reduces the number of part charge cycles a Battery only system would receive (Gravitational Potential energy is still sent to the Battery).
4. Energy used for thermal management of the Battery temperature can be reduced, translating into an additional reduction in total energy consumption. That energy to drive the cooling process has to come from somewhere. This may not be much over short period, but will add up during longer trips involving continuous driving.
5. The Battery can become slightly smaller, with the space and weight freed up, available for the Supercapacitor bank along with a Capacitor Management System.
6. A cheaper type of battery could be used by making the anode and cathode materials thinner which should translate into a bill of materials saving. This proposal is only for cost sensitive applications. The main aim would to be go for higher energy density and not be so concerned by an increase the resulting internal resistance (ESR) and would need to be very carefully weighed up if the benefit is there. This higher Battery ESP would be offset by the Supercapacitor at times of high peak power demand. The battery is the single most expensive component in the electric vehicle, currently representing around 40-50% of the total materials cost (this cost is dropping though).
7. A much higher level of Regenerative Energy can be recovered from a Dual motor configuration as the Supercapacitor has very high specific power density that is not possible with a battery only system. Currently Regenerative Braking Energy is limited to around a maximum of only 50-60 kW, which could be increased upwards to 150-200 kW’s with a Dual Motor configuration.
Currently battery only systems @ 80-100 % State of Charge, it’s not as much Regenerative Braking energy can be recovered due to exceeding the Batteries highest terminal voltage with high bursts of power over short periods of time. The Supercapacitor solves this problem by being at a much lower State of Charge due to it providing most of the energy to accelerate the vehicle initially.

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by flippy » May 29 2021 3:07am

you can grapth it all day, but in the end the end result is the same: supercaps are stupid in vehicles. in the end its better to just increase the battery size then removing battery size to make room for supercaps and absorb the hit on added wear from hard accelerations.
Last edited by flippy on May 29 2021 3:13am, edited 2 times in total.
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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by sleepy_tired » May 29 2021 3:08am

The problem with naive approach to using capacitors, that is putting the capacitors in parallel with the battery. is that the capacitors are going to be in constant competition with motor for drawing current from the battery.

Any time you accelerate and get a voltage drop from the battery you will get a voltage drop in the capacitors as well. Which needs to be filled back up from the battery.

If the battery doesn't fill up the capacitors by the next time the motor requires significant current then the end result is just a lower overall average voltage of the system. The battery simply isn't able to keep up with the current demand and the capacitors do nothing to resolve that issue.

if the battery has plenty of time to fill up the capacitor then between hard acceleration. Then yeah I can see it will help acceleration slightly by "smoothing out the peak" if the battery is not able to keep up with current requirements on it's own. It doesn't seem like a big win to me, though.


Now in your case, you want to recharge the capacitors from regenerative braking and keep them separate from the battery. Claiming that this will increase capacity for regen braking and improve acceleration by taking much of the load off the main batteries during acceleration.

The problem that comes to mind in this scenario is that you are introducing a lot of inconsistencies into the system. Your car performance is dependent on the state of the capacitors, which is dependent on how much braking or hard acceleration you have done in the past.

Example:
If you accelerated hard and coasted to a stop then you won't be able to accelerate nearly as hard next time. If you want to ensure that you have consistent acceleration you need to remember to stay at a high speed and brake hard to come into a stop.

If you are going down a hill and is using regen to slow the car down then as soon as the capacitors fill up you lose a lot of regen capabilities.

Of course those are not the only two situations were inconsistencies are going to happen. It's just a couple extreme examples to illustrate the problem.

It's interesting subject though. Hurts my head thinking about it.

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by Pajda » May 29 2021 4:55am

Anyone who is a little interested in ESS has thought about the supercapacitor. One thing is the potential of technology and the other is the current state of knowledge. The last time I compared the parameters of supercapacitors and lithium batteries currently available on the market it was when the 100kWh Tesla battery pack was released. At this time the comparison came out so that 1kWh in the supercapacitor (Maxwell) will be bigger, heavier and above all more expensive than 100 kWh in the current LIB technology.

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by DaveP68 » May 29 2021 4:33pm

sleepy_tired wrote:
May 29 2021 3:08am
The problem with naive approach to using capacitors, that is putting the capacitors in parallel with the battery. is that the capacitors are going to be in constant competition with motor for drawing current from the battery.

Any time you accelerate and get a voltage drop from the battery you will get a voltage drop in the capacitors as well. Which needs to be filled back up from the battery.

If the battery doesn't fill up the capacitors by the next time the motor requires significant current then the end result is just a lower overall average voltage of the system. The battery simply isn't able to keep up with the current demand and the capacitors do nothing to resolve that issue.

if the battery has plenty of time to fill up the capacitor then between hard acceleration. Then yeah I can see it will help acceleration slightly by "smoothing out the peak" if the battery is not able to keep up with current requirements on it's own. It doesn't seem like a big win to me, though.


Now in your case, you want to recharge the capacitors from regenerative braking and keep them separate from the battery. Claiming that this will increase capacity for regen braking and improve acceleration by taking much of the load off the main batteries during acceleration.

The problem that comes to mind in this scenario is that you are introducing a lot of inconsistencies into the system. Your car performance is dependent on the state of the capacitors, which is dependent on how much braking or hard acceleration you have done in the past.

Example:
If you accelerated hard and coasted to a stop then you won't be able to accelerate nearly as hard next time. If you want to ensure that you have consistent acceleration you need to remember to stay at a high speed and brake hard to come into a stop.

If you are going down a hill and is using regen to slow the car down then as soon as the capacitors fill up you lose a lot of regen capabilities.

Of course those are not the only two situations were inconsistencies are going to happen. It's just a couple extreme examples to illustrate the problem.
Please completely re read my topic more closely as I have covered off most of what you have stated.

1st I' never stated that it was a good idea to place the Supercapacitor in parallel with the battery.
DaveP68 wrote:
May 28 2021 9:46pm
Many others have tried just placing a Supercapacitor bank in parallel the battery terminals without yielding much in the way system performance. This is mostly due the Supercapacitor needing to be at least 500 W/h or more to make much of a difference. That becomes a very expensive exercise when increasing the energy density of the Supercapacitor to gain any more system performance.
Tesla Model S P100D with a 505 Wh Ultracapacitor in paralell with Battery graph.jpg
As can be seen above the 65 Volt drop across the Battery is an improvement over 77 Volts, but that is no match for my system in the second graph at 40 Volts with a 37 Volt reduction. If this parallel simulation is run for about another 1.5 seconds the Supercapacitor will begin to equalise with the battery voltage and we are back to our 77 Volt drop again with lots of heat build up to manage if the high current drain is maintained. The depth of discharge of the Supercapacitor in this example is only 26%, hence why it needs to be at least twice the capacity of my system to add any minimal benefit.

The flip side of this is when the vehicle is at a constant speed consuming say around 17-18 kW’s (~290W per mile) at 60 MPH, the battery will begin back feed a lot of current back into the Supercapacitor. This high current will start off at around 650A and then progressively roll back from there, as the Supercapacitor SOC increases to equalisation with the Battery at some point over the next few seconds. Once the Supercapacitor is at this equalisation SOC and the Regen braking is applied, it is of little assistance with the change in SOC difference being so small the battery will end up soaking most of the regen energy within just over a second. Back to our limit of 50-60 kW’s of regen.
2nd As for "introducing a lot of inconsistencies into the system" again I have covered these off already.

The vast majority of brake applications are for seconds, especially driving in an Urban/City areas. Yes there will be edge cases that could crop up where there could be a fast acceleration and coast to a stop, but this will be rear and not have much of a impact on the overall system operation along with efficiency. Try not to look at the "exception only" as it has no real influence on the rule.
DaveP68 wrote:
May 28 2021 9:46pm
Please also note the Supercapacitor is not sized to extract any “Gravitational Potential Energy” when going down a hill. This just so happens to be a much smaller amount of power when measured at per-second rate and can be still be sent back to the Battery.
Thanks for your contribution even though you state it made your head hurt...

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by DaveP68 » May 29 2021 4:52pm

Pajda wrote:
May 29 2021 4:55am
Anyone who is a little interested in ESS has thought about the supercapacitor. One thing is the potential of technology and the other is the current state of knowledge. The last time I compared the parameters of supercapacitors and lithium batteries currently available on the market it was when the 100kWh Tesla battery pack was released. At this time the comparison came out so that 1kWh in the supercapacitor (Maxwell) will be bigger, heavier and above all more expensive than 100 kWh in the current LIB technology.
I have heard the reference of placing a 1 kW/h Maxwell Supercapacitor, but I'm not sure if those numbers relating to being bigger, heavier and above all more expensive than 100 kWh in the current LIB technology match up even for 5 years ago.

A 1kW/h Maxwell Supercapacitor would weigh about 120 kg's compared to the 625 kg's for the 100 kW/h LIB battery. It would measure just 1.5 m L by .56 m W and .14 m H which again is much smaller foot print than the LIB battery. As for cost I can't answer that, but may end up being a 1/4 of the LIB battery.

Those numbers still don't stack up economically and by no way a comparison with what I came out with in my topic being that the Supercapacitor only needs to be just over a quarter of that at 284 W/h's.
Last edited by DaveP68 on May 29 2021 6:50pm, edited 2 times in total.

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by DaveP68 » May 29 2021 4:58pm

flippy wrote:
May 29 2021 3:07am
you can grapth it all day, but in the end the end result is the same: supercaps are stupid in vehicles. in the end its better to just increase the battery size then removing battery size to make room for supercaps and absorb the hit on added wear from hard accelerations.
Just in case you didn't read the reference to "Simulations", it's still worth while to looking into the concept.

A battery is not a one size fits all!
Battery and Supercapacitor Power Density.png
Battery and Supercapacitor Power Density.png (25.3 KiB) Viewed 334 times
The Supercapacitor wins in the short sprint race every time, it's not trying to be a marathon runner like the battery 8)

They are complimentary devices, to put it another way.

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by flippy » May 29 2021 5:14pm

DaveP68 wrote:
May 29 2021 4:58pm
Just in case you didn't read the reference to "Simulations", it's still worth while to looking into the concept.
A battery is not a one size fits all!
Battery and Supercapacitor Power Density.png
The Supercapacitor wins in the short sprint race every time, it's not trying to be a marathon runner like the battery 8)
They are complimentary devices, to put it another way.

i have done the math plenty of times, and so did companies like tesla and even rocket labs. its simply more effective, cheaper and useful to increase the size of the battery then its to dick around with capacitors.

just look at a tesla, it can push basically a megawatt of power out of a 400V 100Ah battery.
especially hardcore cars like the rimac are simply traction limited by physics. its simply no possible to accelerate faster for those cars with the current laws of physics. adding supercaps to that equasion simply does not do anything useful exept adding cost and a ton of complexity.

pleae take of your blinders and look at the whole picture, you are blinding yourself with a single statistic to such a degree that you are ignoring everything else. just look at what mosfets would cost to control that power, how big those are, added crap you need to cool them, bigger motors, gears and so on. its LOADS cheaper just to put that volume and money into a bigger battery.

the only place where supercaps might be useful is on a dragstrip when you only have to drive for half a mile.

ps: that graph means exactly jack shit.

ps2: most of these "pro-supercap" articles are written by the people that make and sell them. its advertisement to get investors. the math does not add up in the real world.
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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by Hillhater » May 29 2021 6:34pm

The gains are minor in a vehicle that already has more performance than most of its owners can use safely.
This type of performance enhancement is probably only of interest to anyone considering a competition program..race, rally, drag strip, etc.
Maybe you can propose an application that improves range, or performance on a EV with a lower performance level, or battery capacity, such as the Leaf, Nexo, etc .... where the improvements can be beneficial.
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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by DaveP68 » May 29 2021 7:18pm

Hillhater wrote:
May 29 2021 6:34pm
The gains are minor in a vehicle that already has more performance than most of its owners can use safely.
This type of performance enhancement is probably only of interest to anyone considering a competition program..race, rally, drag strip, etc.
Maybe you can propose an application that improves range, or performance on a EV with a lower performance level, or battery capacity, such as the Leaf, Nexo, etc .... where the improvements can be beneficial.
Yes you make a valid point. I haven't restricted the use case to performance vehicles. It just so happen in this illustration just so happens to be based on one.

Take commercial vehicles that like Rubbish trucks, delivery vehicles and light passenger vehicles like taxis. They all have one thing in common, lots of high go/stop activity predominately around urban/city driving routes.

Personally I drive a Nissan Leaf very carefully around town averaging about 80km per day. Able to average 9.5 km per kW/h (10.5 kW/h per 100 km's) in a moderately hilly city of Auckland NZ, including some motorway driving. Haven't come across anyone who even comes close to that level of efficiency. The trick I use is to accelerate/brake slowly making the transfer of electrical energy from the battery to the mass of the vehicle and back as efficient as possible.
IMG_20200510_163412.jpg
IMG_20200510_163412.jpg (4.22 MiB) Viewed 315 times
Add a Supercapacitor into that vehicle and drive it a more lead footed and the numbers will stay the same.

Any use of friction brakes is a loss of energy as heat and I still have minor wear on my pads, but nothing compared to an ICE vehicle.

It's all about the return losses in the system.

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by flippy » May 29 2021 8:52pm

the biggest airport in europe only uses teslas a taxis for many year now. they actually NEED that range to be able to fill their drivable hours.

i understand you think you can find an application for supercaps but they simply dont exist. not in any commercial or financial sensible place at least.

outside a drag strip you wont find any real use case.

ps: you can already regen-brake so hard that the wheels would lock up if you wanted to. its simply not enabled in cars. something something safety.... it has nothing to do with the battery not being able to absorb that power.
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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by Pajda » May 30 2021 4:05am

DaveP68 wrote:
May 29 2021 4:52pm
A 1kW/h Maxwell Supercapacitor would weigh about 120 kg's compared to the 625 kg's for the 100 kW/h LIB battery. It would measure just 1.5 m L by .56 m W and .14 m H which again is much smaller foot print than the LIB battery. As for cost I can't answer that, but may end up being a 1/4 of the LIB battery.
Please show us already existing supercap vehicle pack with that parameters? If I take Maxwell BMOD0165 P048 C01 module which seems to be a new one, suitable for automotive application it have energy density of about 3.65 Wh/l and 3.5 Wh/kg. And it is only module, not the whole pack which must give structural strength to the vehicle if instaled under the floor. Also this supercap module does not include thermal management system so another weight to count. So I still did not see any significant change and practical ratio is still about 100:1 in favour to the LIB. And you still need that big battery!

With this ratio is connected another issue. If you need 600 kW peak power for your application (Tesla Model S) you need a LIB cell with 6C peak current from 100 kWh pack but 600C peak current from 1 kWh SC pack.

As was already said: "Supercapacitor is excellent piece of modern technology with almost no use or it."

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by Darren2018 » May 30 2021 4:54am

If it is still to be manufactured wouldn't it be easier to spend the money on a lower IR battery. Less system complexity plus probably more capacity. The only negative is weight but does that really matter when most EVs are already quite heavy. Already existing EVs with tired batteries or racing EVs I can understand but new ones I don't think would be worth it.

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by flippy » May 30 2021 8:08am

Darren2018 wrote:
May 30 2021 4:54am
If it is still to be manufactured wouldn't it be easier to spend the money on a lower IR battery. Less system complexity plus probably more capacity. The only negative is weight but does that really matter when most EVs are already quite heavy. Already existing EVs with tired batteries or racing EVs I can understand but new ones I don't think would be worth it.
you actually need the weight to get sufficient traction.
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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by fatty » May 30 2021 6:48pm

sleepy_tired wrote:
May 29 2021 3:08am
The problem that comes to mind in this scenario is that you are introducing a lot of inconsistencies into the system. Your car performance is dependent on the state of the capacitors, which is dependent on how much braking or hard acceleration you have done in the past.
Of course [these] are not the only two situations were inconsistencies are going to happen.
While good to consider, these are comparatively easy to address (or already addressed):
sleepy_tired wrote:
May 29 2021 3:08am
Example:
If you accelerated hard and coasted to a stop then you won't be able to accelerate nearly as hard next time. If you want to ensure that you have consistent acceleration you need to remember to stay at a high speed and brake hard to come into a stop.
True, but vehicles in this category/usage profile already include similar requirements: user-selectable launch control requires parameters in range, with limited frequency of launches. In this case, a depleted supercap bank could be selectably charged from the traction battery for a launch.
sleepy_tired wrote:
May 29 2021 3:08am
If you are going down a hill and is using regen to slow the car down then as soon as the capacitors fill up you lose a lot of regen capabilities.
Also true, but EVs already include friction brakes sufficient without any regen, so this would be transparent to the user.

sleepy_tired   100 W

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by sleepy_tired » May 30 2021 10:40pm

True, but vehicles in this category/usage profile already include similar requirements: user-selectable launch control requires parameters in range, with limited frequency of launches. In this case, a depleted supercap bank could be selectably charged from the traction battery for a launch.
It would have to be transparently controlled by computer. If it was human selectable it would never get used. People already have too much going on dealing with traffic.

Ignoring all that... while the caps are depleted you will be diverting power from car to the caps in order to recharge them, but not charge them so much they can't store the power from any potential braking you might want to do.

The Peter robbing Paul stuff goes back to the original reason super caps don't really augment battery system. I understand that OP is claiming to use regenerative braking to avoid this trap, but I don't think it's going to be possible to really pull it off in the general case.

That is the cases were this extra complexity is beneficial is more niche then were it's not.

To make all of this make sense you would need to throw benefit-cost analysis at it. If you had $10,000 on energy system for a EV. Which would be better?

A) $10,000 worth of battery + super caps + all the wiring + ECU (or ecu components) etc

OR

B) $10,000 worth of (bigger) battery ?

Which car do you think would get better range? A car using A or a car using B?

I think very much that B would give better range and it wouldn't lose out anything on acceleration or braking performance.

I would love to see this system implemented in a scooter or bicycle or go-kart and prove me wrong, of course.

DaveP68   100 µW

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by DaveP68 » Jun 04 2021 11:18pm

Pajda wrote:
May 30 2021 4:05am
With this ratio is connected another issue. If you need 600 kW peak power for your application (Tesla Model S) you need a LIB cell with 6C peak current from 100 kWh pack but 600C peak current from 1 kWh SC pack.

As was already said: "Supercapacitor is excellent piece of modern technology with almost no use or it."
Yes it is hard to believe that a Supercapacitor can have a 600C peak rate and in some cases that can be exceeded for periods of no more than one second.

Batteries are energy dense devices and should never be compared to a Power dense device like a Supercapacitor, they are just not the same thing...

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by JackFlorey » Jun 05 2021 12:17am

DaveP68 wrote:
Jun 04 2021 11:18pm
Batteries are energy dense devices and should never be compared to a Power dense device like a Supercapacitor, they are just not the same thing...
Agreed. But people want energy dense systems, not power dense systems. You cannot physically accelerate faster than about 2G's with tires, so more power than that is sort of wasted (and vehicles are hitting that now.)

There are, to be sure, applications for supercaps. Laser pulsed power sources, regen systems on vehicles without traction batteries (like locomotives) things like that. But for mainstream EV's - the math just doesn't work out.

Pajda   1 kW

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Re: The case for using Supercapacitors with Lithium-Ion batteries in EV's

Post by Pajda » Jun 05 2021 12:55pm

DaveP68 wrote:
Jun 04 2021 11:18pm
Batteries are energy dense devices and should never be compared to a Power dense device like a Supercapacitor, they are just not the same thing...
No, the only right approach is to compare all available technologies for a particular application and use the best one.

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