Super Capacitors for "Burst Mode"?

Batteries, Chargers, and Battery Management Systems.
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Super Capacitors for "Burst Mode"?

Post by rg12 » Nov 07 2019 3:36pm

I was thinking why not use a super capacitor bank along with a li ion battery pack and build some kind of a management system to handle the charge/discharge of the super capacitors.
I was thinking why not have lets say a 20S 8P 25R pack with a 120A controller and have the capacitor bank be used first for every hard pull until the hard pull goes to average power or until the capacitor bank is empty and then it goes back to the li ion battery.
It should be a mix so they work together in different percentages to maintain voltage as super capacitors will be depleted to 0 from what I learned...
What do you guys think?

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Re: Super Capacitors for "Burst Mode"?

Post by Addy » Nov 07 2019 3:51pm

Take a look at this chart:

Image

Yes, supercapacitors have good power density, but their energy density is typically much worse than lithium-ion cells. You could add supercapacitors in a hybrid setup, but they will only be useful for very short bursts and they require a special system to allow the full capacity of the supercapacitors to be used.

I'd say you're better off adding some high-rate lithium cells in a hybrid setup, or just making your battery pack large enough to provide the discharge/charge rates that you want.

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Re: Super Capacitors for "Burst Mode"?

Post by rg12 » Nov 07 2019 4:56pm

I was aiming more for the engineers out there to maybe build a system that can be adopted into different packs with different needs.
I sure don't have the knowledge to pull of something as complicated as that.

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Re: Super Capacitors for "Burst Mode"?

Post by Hillhater » Nov 07 2019 5:53pm

The idea is not new.
But the fact that no one has bothered developing it...including Tesla or any big tech company, ..should tell you something about it !
Few need the rapid power delivery of capacitors, but most do need the energy capacity of Lithium, which then provides all the power you might need.
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Re: Super Capacitors for "Burst Mode"?

Post by methods » Nov 07 2019 8:50pm

Super Capacitors have a super high internal resistance.
You would need a super-wheelbarrow load to get anywhere I suspect?

Here is a similar concept:
When...
You want to have high pressure air on tap (for say charging a Paintball gun) you do it with several tanks.

The first 4000PSI tank does bulk fill
The second 4000PSI tank does top-off

As the first tank depletes to 3500... 3000... 2500....
The second tank depletes to 3900... 3800... 3700....

So if I am reading you correctly the goal is to relieve the battery of the big fluctuations of current and have it work in a more nominal zone for longer life?

Sounds like a good idea to me.
That is what the Capacitor Bank in the Controller is tasked with yes?

.. In Car Audio we regularly hook up large 1F or 6F cap banks the size of a car battery to absorb transients.

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Increasing battery voltage and controller current limit will result in a non linear experience

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Re: Super Capacitors for "Burst Mode"?

Post by amberwolf » Nov 07 2019 10:47pm

rg12 wrote:
Nov 07 2019 3:36pm

What do you guys think?
Some reading:
search.php?keywords=supercap*&terms=all ... mit=Search

There's more, you'd have to search for it.

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Re: Super Capacitors for "Burst Mode"?

Post by neptronix » Nov 08 2019 12:31am

Spec a battery far beyond what you'd need for discharge output and this thought will never come to you again :thumb:

Bonus: as it ages, and gains internal resistance, it will still kick out tons of power.

The energy density of supercapacitors is like lead acid batteries, if that. Add more lithium until you have the power output you need - preferably more so that you can crank up the amps for more torque later.
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Re: Super Capacitors for "Burst Mode"?

Post by methods » Nov 08 2019 3:13am

Agreed
That is good advice

It will also eliminate Range Anxiety

...

-methods
Increasing battery voltage and controller current limit will result in a non linear experience

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Re: Super Capacitors for "Burst Mode"?

Post by flippy » Nov 08 2019 4:06am

if you suffer from power delivery issues it simply means the battery is too small.

adding caps will never work.
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Re: Super Capacitors for "Burst Mode"?

Post by CryB4Die » Nov 08 2019 4:20am

There can be a way to have an advantage of the power density of supercapacitors:

Have your normal Li-ion battery pack to keep it simple 100V nominal.

Get a motor controller that can handle a higher voltage let's say 400V

Get a super capacitor bank that that is 400V Max charged.

Get some kind of charging circuit to the capacitors from the battery or/and from regenerative braking.

Get a ideal diode circuit between the 100V li-ion pack and 400V capacitor pack.
Super Cap Hybrid.PNG
Super Cap Hybrid.PNG (12.69 KiB) Viewed 1092 times
and lets say 100V and the power density of the li-ion pack is required for nominal use.

What do you think? And ofcourse this is only for cars or larger vehicles because the super caps take alot of space.

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Re: Super Capacitors for "Burst Mode"?

Post by flippy » Nov 08 2019 4:30am

CryB4Die wrote:
Nov 08 2019 4:20am
What do you think? And ofcourse this is only for cars or larger vehicles because the super caps take alot of space.
space is not the issue, its a massive conversion losses and weight issue.

also you dont gain anything with it.

if you just make a 400V battery you dont need the conversion in the first place and that diode will do nothing but generate heat.

there is nothing to gain, or do people forget your controller is crammed with (usually) high quality low ESR caps on every stage that do exactly what you are trying to do with external caps?

if you experience sag you need to solve the sag. i am 100% sure that adding the money those supercaps cost into increasing the battery you will get far better results. i know this because of simple mathz.

try buying 50 caps and see what they cost and comare that the performace gains you would get if you were to put that money in simply building a bigger battery.
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Re: Super Capacitors for "Burst Mode"?

Post by CryB4Die » Nov 08 2019 7:02am

flippy wrote:
Nov 08 2019 4:30am
CryB4Die wrote:
Nov 08 2019 4:20am
What do you think? And ofcourse this is only for cars or larger vehicles because the super caps take alot of space.
space is not the issue, its a massive conversion losses and weight issue.

also you dont gain anything with it.

if you just make a 400V battery you dont need the conversion in the first place and that diode will do nothing but generate heat.

there is nothing to gain, or do people forget your controller is crammed with (usually) high quality low ESR caps on every stage that do exactly what you are trying to do with external caps?

if you experience sag you need to solve the sag. i am 100% sure that adding the money those supercaps cost into increasing the battery you will get far better results. i know this because of simple mathz.

try buying 50 caps and see what they cost and comare that the performace gains you would get if you were to put that money in simply building a bigger battery.
The main issue is the voltage sag in li-ion batteries. Like the chart is showing supercaps have 10x the power density so there are applications that need this power. Like the tesla Roadster. It needs to have high power with low weight.

Conversion efficiency of boost converters are usually 90%>

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Re: Super Capacitors for "Burst Mode"?

Post by rg12 » Nov 08 2019 7:21am

flippy wrote:
Nov 08 2019 4:30am
CryB4Die wrote:
Nov 08 2019 4:20am
What do you think? And ofcourse this is only for cars or larger vehicles because the super caps take alot of space.
space is not the issue, its a massive conversion losses and weight issue.

also you dont gain anything with it.

if you just make a 400V battery you dont need the conversion in the first place and that diode will do nothing but generate heat.

there is nothing to gain, or do people forget your controller is crammed with (usually) high quality low ESR caps on every stage that do exactly what you are trying to do with external caps?

if you experience sag you need to solve the sag. i am 100% sure that adding the money those supercaps cost into increasing the battery you will get far better results. i know this because of simple mathz.

try buying 50 caps and see what they cost and comare that the performace gains you would get if you were to put that money in simply building a bigger battery.
I always encourage using a higher capacity pack to solve that but I was thinking of doing that in applications where you don't have the physical space for a large enough battery but if you say that the caps bank needs to be big even though it will need to give only a few seconds of "burst mode" then I guess it is a bad idea.

BUT, why did Tesla buy that super capacitor company recently?
I bet they do see the gain in something like that maybe used a different way...

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Re: Super Capacitors for "Burst Mode"?

Post by spinningmagnets » Nov 08 2019 7:54am

Maxwell has some patents that would be useful for Tesla batteries. If another company bought them, Tesla and others would be locked out. Since Tesla makes their EV patents open to the world, this was a very good thing.

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Re: Super Capacitors for "Burst Mode"?

Post by rg12 » Nov 08 2019 10:49am

spinningmagnets wrote:
Nov 08 2019 7:54am
Maxwell has some patents that would be useful for Tesla batteries. If another company bought them, Tesla and others would be locked out. Since Tesla makes their EV patents open to the world, this was a very good thing.
Hmm so nice to have so much money...

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Re: Super Capacitors for "Burst Mode"?

Post by neptronix » Nov 08 2019 11:06am

CryB4Die wrote:
Nov 08 2019 4:20am
There can be a way to have an advantage of the power density of supercapacitors:

Have your normal Li-ion battery pack to keep it simple 100V nominal.

Get a motor controller that can handle a higher voltage let's say 400V

Get a super capacitor bank that that is 400V Max charged.
That's an electrical engineering and efficiency loss nightmare in the making.
You will also have a wild fluctuation in the speed your bike goes if your voltage goes from 400v to 100v. You'll need to design a custom controller to deal with that, with very high resistance and very expensive FETs that will perpetually eat away at your efficiency.

Seriously, just get a battery pack that can deliver the amperage you need. It'll be the cheapest, lowest weight, most compact, highest range, most efficient option possible.

Super caps are expensive. They have weird voltage curves. They're insanely bulky compared to lithium. They have a tiny storage capacity for the power they put out. You'll need a few pounds of them and only get a few seconds of current out of them. Another few pounds of lithium will give you more range AND more power.

Lithium batteries can be so powerful in the right formulation that you can start a diesel truck with one the size of your fist that weighs 2-3lbs.

Here's a tiny 2010 era turnigy nanotech starting a car with a 1.8L engine, kicking out 50-100 amps. There are lithium batteries on the market that are twice as powerful as that now.

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Re: Super Capacitors for "Burst Mode"?

Post by stan.distortion » Nov 08 2019 11:28am

Kind of makes sense for regen, most lithium batteries have a much higher discharge rate than charge rate but there are exceptions, there are extremely durable (10k cycle or more) batteries on the market now with very high values for both charge and discharge. Power density isn't great but they're ideal for the same roll, burst current for acceleration and braking.

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Re: Super Capacitors for "Burst Mode"?

Post by methods » Nov 08 2019 11:30am

Who has performed the following experiment and recorded the results?

100V 10Ah of 1C or otherwise low quality lithium
parallel with
100V 1Ah of 50C lithium
parallel with
Extended capacitor bank external to the controller

There is zero doubt that you can stiffen up the leading edge of your power curve by supplementing a low C pack with some high C lipo. It is the same principle as adding a large capacitor bank to an audio system .. . only the frequency is more like .3hz instead of 30hz

This sort of stuff will take off when the market is flooded with upcycled and EOL can cells. You are going to be able to buy truckloads of cells that have 40% of their original capacity.

But...
I am not going to argue with flippy on that front again. It was made clear to me that all packs will be built from brand new cells at all times now and in the future... and the recycle fairy is going to magically make all those old packs disassemble themselves and fall into a 100% efficient recycling process. It is highly improbable that we will see a market for up-cycled (NOT RECYCLED) can cells.

(I will return to this thread in 10 years)

-methods
Increasing battery voltage and controller current limit will result in a non linear experience

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Re: Super Capacitors for "Burst Mode"?

Post by neptronix » Nov 08 2019 11:50am

methods wrote:
Nov 08 2019 11:30am
It was made clear to me that all packs will be built from brand new cells at all times now and in the future... and the recycle fairy is going to magically make all those old packs disassemble themselves and fall into a 100% efficient recycling process. It is highly improbable that we will see a market for up-cycled (NOT RECYCLED) can cells.
:lol:

Yeah there's a shit ton of lithium cells that are thrown away because they have increased IR and cannot provide the current their application needs. These cells still have 80-90% of the capacity and can be reused. But they're not, they just get thrown away and turned into e-waste as we've not figured out how to economically recycle any of this.

Another way of stretching an old pack is to double the amp hours, cutting the resulting pack's internal resistance in half, doubling the amps it can deliver.

Or be smart and design your pack with double or preferably quadruple the amp output you need to start, and suck every cycle out of it possible.

It's frocking nuts because EVs are supposed to save us from climate change, pollution etc but here we are building them and throwing them away at 2-3x the rate we should be.

I once had a camera with a very well designed lithium battery. The battery lasted 12 years. The output was hugely overspecced. That's how a pack should be designed.

There is a direct relation to amp output and long term longevity of a pack.

Throwing supercaps at a weak pack is not the answer.
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Re: Super Capacitors for "Burst Mode"?

Post by Balmorhea » Nov 08 2019 1:11pm

I like to use supercapacitors to add a standlight feature to LED bike lights that run on a dynamo. They work well for that, because LEDs draw logarithmically less power as they drop below their rated voltage.

As part of a traction motor pack, supercapacitors are not useful. Not only is their energy density inadequate for the job, but their range of discharge voltage makes them a poor match for batteries.
Without some complicated and inefficient voltage conversion, you can't even use most of the inadequate amount of energy they contain.

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Re: Super Capacitors for "Burst Mode"?

Post by neptronix » Nov 08 2019 1:15pm

^--- yup.
Capacitors or supercapacitors have some applications but traction power is not one of them..

it's nice to have a tiny battery with a wide voltage range sometimes. In times when a series string of lithium cells with a BMS and all that complicated stuff would be to expensive or complex. A dynamo light is a really good application.
"Love and compassion are necessities, not luxuries. Without them, humanity cannot survive." - Dalai Lama

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Re: Super Capacitors for "Burst Mode"?

Post by sleepy_tired » Nov 08 2019 1:28pm

If you combine capacitors with batteries what will happen is that the capacitors will increase the load on the battery, not reduce it.

Imagine you accelerate hard and notice that the battery cannot keep up due to the high voltage drop. So you add a capacitor bank to 'fix' it.

Now you accelerate hard and the voltage drops in BOTH the battery and capacitor bank. The battery now has to struggle with not only providing enough current to keep the motor happy, but also the capacitor bank. Capacitors are greedy. They will draw as much current as possible. This is NOT a win-win. It's a lose-lose.


The whole capacitor thing is a big snake-oil scam from the high-end car audio industry. They try to sell these expensive big capacitors to 'make up for' the inability for the car's battery and alternator to keep up with the current demands of large subwoofer amplifiers. The end result is slightly worse performance, overheating amplifiers and more cocaine money for the owner of the car audio shop. It doesn't work for them and it's not going to work for ebikes.

The solution to inadequate battery is to replace it with a adequate one.

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Re: Super Capacitors for "Burst Mode"?

Post by neptronix » Nov 08 2019 1:42pm

It actually makes sense for car stereos. Just think of it like this, a car audio system's load can rapidly fluctuate from 10-100%, based on when a bass drum is hitting, or not. Reproducing low frequencies takes a lot of electricity, and the low frequency hits are intermittent in most music.

An ebike is not really like that. When you're accelerating, climbing a hill, or fighting a wind, the load is constant and that can go for a long time.. it could be for miles. No capacitor will help you here, because the capacity in watt-hours is so low.

A supercapacitor and battery will regulate their own voltages like water seeking it's own level, but yeah there is a minor efficiency loss from one transferring power to another. And you'd have to regulate the charge current the capacitor would take because it will try to draw 1000000000a at once and trip the BMS or blow a fuse etc.

Well now we've got even more reasons why this would be a bad idea.
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Re: Super Capacitors for "Burst Mode"?

Post by sleepy_tired » Nov 08 2019 7:06pm

It actually makes sense for car stereos. Just think of it like this, a car audio system's load can rapidly fluctuate from 10-100%, based on when a bass drum is hitting, or not. Reproducing low frequencies takes a lot of electricity, and the low frequency hits are intermittent in most music.
So you have a car with the the amp is hooked up to a 12v system that can't generate enough current to keep the amplifier happy. This includes both the alternator (primary) and battery (secondary) hooked up to a amp in your trunk with wiring that is much too thin. Between the sub amp and the rest of the system you have a gigantic capacitor. So you start up the car and turn on the receiver and the amp is happy and sees 12-13 volts from a happy system... until you turn the volume up.

The first beat hits and immediately afterwards the amplifier sees a massive voltage drop as it's competing with the capacitor for current. Every beat followed by voltage drop. If the music is loud and the wiring and/or alternator is particularly inadequate then the amplifier that is designed for a 12 volt system is going to see as sort of pulsating voltage that, I am guessing, could range between 6 and 10 volts.

So all you accomplished was to trade a short duration voltage drop for a much longer duration voltage drop.

Sure, the capacitor 'smooths things out', but it smooths things out to a lower level that causes the amp to overheat, or protection circuits to kick in (or whatever other terrible things happen) due to having the amplifier hooked up to a a power supply that is, on average, running at a lower voltage system then it was designed to operate at. :)

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Re: Super Capacitors for "Burst Mode"?

Post by CryB4Die » Nov 09 2019 5:09am

What about using supercaps with a hydrogen fuel cell?

The fuel cell is rated at a low power but with capacitors the car can accelerate like a normal car.


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