# Ultracapacitors & Supercapacitors



## rmay635703 (Oct 23, 2008)

IanJames said:


> Has anybody actually utilized these?
> 
> ultracapacitors—have an energy density thousands of times greater than conventional capacitors and a power density hundreds of times greater than lithium-ion batteries.


I disagree with that statement to some extent, ultracapacitors volumentrically with packaging (real world) have very poor density which is why they aren't used in place of batteries alone. They do however have to ability to dump energy very rapidly (what little they have)

However a few here have tried them on the end of their controllers to improve the switching efficiency and reduce peukert (maybe) by smoothing pulses



IanJames said:


> In an electric vehicle drivetrain, energy density provides sustained speed, while power density facilitates acceleration. “Energy density is what allows you to run a marathon; power density is what enables you to sprint,” said Ted Bohn, an automotive engineer in Argonne’s Center for Transportation Research.
> 
> “Ultracapacitors aren’t of much use just by themselves,” he added, “but when you couple them with lithium batteries, they dramatically boost the performance of the entire vehicle.”


 I agree that a cap could discharge quickly but dramatically boosting the performance of an EV would require a dramatically large ultracap and a specialized system to actually fully use the caps linear discharge along side a battery.



IanJames said:


> When an electric vehicle merely needs to maintain a particular speed, it requires little of the battery’s power density. However, when the car needs to accelerate from a standstill to a cruising velocity, today’s lithium-ion batteries must strain to provide the necessary “oomph.”
> 
> “Ultracapacitors give an electric vehicle the initial boost it needs to get going,” Bohn said.


 Again probably not unless you have a specialized management system to fully utilize the caps, unless you have a very very very large cap bank (which costs more than lithium) Since a cap likely can't deliver high amps for 15 seconds to accellerate hard from stop to 60mph.


IanJames said:


> A PHEV or pure electric vehicle needs a battery with sufficient power density to accelerate the vehicle quickly. A vehicle that uses an energy-dense battery that lacks sufficient power density will fail prematurely, possibly in a matter of months if driven aggressively.


Assuming you are a moron, buy an undersized pack and then procede to exceed the amp rating.



IanJames said:


> By using the same potentially lower cost energy-dense battery, in combination with ultracapacitors, the vehicle will have sufficient performance and the batteries should last 10 years or more.


They should anyway if not abused



IanJames said:


> Today’s hybrid cars recharge their batteries by transforming kinetic energy from the wheels into potential electrical energy as the driver brakes. Conventional lithium-ion batteries, however, absorb this energy slowly and inefficiently. By contrast, ultracapacitors, because of their immense internal surface area, sort of soaking up reclaimed energy like a sponge.
> 
> “By integrating the entire system,” Bohn said, “we can drive down the cost. When we can put these various electronic elements together, we’ll transform an $8,000 battery into a $4,000 allelectric drivetrain system.”
> 
> ...


I believe what he says is possible at some point but at the cost of caps right now I don't really think its feasable to be able to store cap only the energy required to accelerate to 60mph and back. Unless you are driving a ultralightweight vehicle.


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## ElectriCar (Jun 15, 2008)

I put a cap bank on mine in part to help reduce losses from the internal resistance of the batteries. Not sure how much it helps but I did it anyway hoping for more oomph on take off to get the sled off and moving. Didn't notice anything to speak of there. 

My batteries are getting some miles and recharges on them now and I was told by an experienced EVer/engineer that on a vehicle with near worthless batteries it doubled his range but I think his range was less than 5 miles to begin with. 

I think I put 10 10K caps on for a total of 100,000 uf bank. I'm soon going to be driving it about 11.5 miles each way of my commute so my pack needs any help it can get before it gets destroyed...

Correction, just checked and I have 10 1000uf installed.


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## dtbaker (Jan 5, 2008)

I think that to capture one typical 'braking event' you need an ultracap like this
http://www.maxwell.com/ultracapacitors/products/modules/bmod0063-125v.asp

...too big, heavy, and expensive compared to a little extra capacity in a battery as far as I can see.


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## DavidDymaxion (Dec 1, 2008)

BYU had an EV-1 converted to run on supercapacitors. The supercapacitors took up the passenger area. They would push it to the starting line to conserve power. It had enough energy to do one 1/4 mile run. If you look at a several second number, A123 batteries have more power per kg!


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## Duncan (Dec 8, 2008)

Hi Guys

I had done some numbers on super/ultra caps and they looked OK

This was because I had stuffed up

Electricar - you have 10 off 1000uF capacitors installed if they are of high enough voltage so that they are in parallel you have a whopping 1/100th of a Farad

Ultracaps are measured in tens or hundreds of Farads

I looked at using the Maxwell 350 Farad "d Cell" caps
These have a voltage limit of 2.7v
for my 150v system I would need 63 in series
63 off 350 Farad ultracaps in series have a string capacitance of 5,5 Farads
(this was where I stuffed up)(I thought it would be 350F)
The string can store 1/2 x 150v x 150v x 5.5F = that is 6,187 Joules or 17 watt hours

This is enough to get a 1000kg car to a massive 8 mph!
note 80 mph would need 100 times as much

A hundred times as much would be 1.7 Kwhours - and would weigh about 300Kg - without packaging!

Electricar if you have a 150v system you would have 

1/2 x 150 x 150 x 0.01 = 112 joules - this is the energy of lifting a 11 kg weight 1 meter!


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## Guest (May 5, 2010)

We did some experiments a couple of years ago with Maxwell's 3000 farad Supercaps on a GEM platform. I could actually switch in the lead acid cell bank, the LiFePo4 cell bank, or the cap bank, in any combination, or each singly. 

I drove about 1/4 mile on the charged caps alone. They are truly amazing devices.

Used with batteries, they provide a huge boost to instantaneous current through the controller.

I am convinced they would extend the life of the batteries to essentially "lifetime guarantee."

Here's the problem. They do extremely little to extend range, you get about the 1/4 mile I was talking about.

And here's the second problem. Their weight and volume are not much different from the batteries. Whenever I have enough room for a cap bank, I can buy batteries at less expense, and get more range. Range is a little more of an imminent benefit that cell longevity. Ergo, the caps sit on a bench in the garage.

It comes out the same way every time. They are fantastic devices and should by rights be married to these cells. I'm convinced they should make a cell with 3 plates, instead of two, and alternate a supercap with each pair of plates in a cell. But it would come out the same way, fantastic performance, infinite life, but a third bigger with no more range.

Jack Rickard


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## Wirecutter (Jul 26, 2007)

IanJames said:


> From the ARGONNE NATIONAL LAB:
> 
> Charging Ahead: Taking PHEVs Farther on a Single Battery Charge
> 
> Fortunately, researchers at Argonne may have found a way to *exponentially* increase the calendar and cycle lifetimes of lithium-ion batteries. Electric double-layer capacitors— typically referred to as ultracapacitors—have an energy density thousands of times greater than conventional capacitors and a power density hundreds of times greater than lithium-ion batteries.


*BULLSHIT ALERT!*


Ok, stop, hold it. Again with the misuse of *"exponential"* increase. Someone is using a word they don't understand, and you shouldn't do that. Exponential change is *big*. Really big. An _exponential_ increase in cycle and lifetime would quickly mean that the battery would outlast you, and then the planet. (Ok, it's plausible if the exponent is a really small fraction, but be real. When it's exponential, the convention is that you're talking about whole integer exponents, not tiny fractions.)

Stupidity like this really casts a shadow over the credibility of the rest of the article. Or as stated in a Dilbert comic once: "Welcome to Marketing. Two drink minimum."

-M


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## major (Apr 4, 2008)

Wirecutter said:


> *BS ALERT!*
> 
> Ok, stop, hold it. Again with the misuse of *"exponential"* increase. Someone is using a word they don't understand, and you shouldn't do that. Exponential change is *big*. Really big. An _exponential_ increase in cycle and lifetime would quickly mean that the battery would outlast you, and then the planet. (Ok, it's plausible if the exponent is a really small fraction, but be real. When it's exponential, the convention is that you're talking about whole integer exponents, not tiny fractions.)


Hi Wirecutter,

The quote from ARGONNE NATIONAL LAB also says: 


> A PHEV or pure electric vehicle needs a battery with sufficient power density to accelerate the vehicle quickly. A vehicle that uses an energy-dense battery that lacks sufficient power density will fail prematurely, possibly in a matter of months if driven aggressively. By using the same potentially lower cost energy-dense battery, in combination with ultracapacitors, the vehicle will have sufficient performance and the batteries should last 10 years or more.


An increase from a few months to 10 years or more could be considered exponential, I think. And Argonne National Lab isn't trying to sell you anything, except maybe their research and testing services. And I don't think they have a 2 martini marketing department. 

There may be value in this approach. The battery design can be altered (optimized) for power or energy, but usually not both. Certain Ultracapacitors have been validated to over a million deep cycles. The combination of a battery specifically designed for energy and an ultracapacitor could result in a substantially improved system. 

Worth taking a look at, IMO.

major


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## MN Driver (Sep 29, 2009)

There is some missing information here. Do we know if Argonne National Lab is discussing lead-acid though? Lead acid is picky about discharge rates, especially when it comes to what kind of Ah you can pull out of it because of the peukert effect. As long as LiFePO4 doesn't get too hot in its discharge it isn't going to fall flat on its face in a matter of months. A cycle still remains a cycle and there are only so many a battery can do no matter how gentle you make the discharges, making them gentle will help them last longer but if you are driving 1C down the road the capacitors aren't going to help that, they might help if you are planning on drawing 10C on a battery that specs 3C(as a rough example), but they won't help much beyond that because it isn't going to magically bring a 1C discharge into .5C territory for the fairly constant current of maintaining a constant speed. I don't think that the impact is going to make sense in terms of cost or size/weight of adding the capacitors to Lithium. It makes sense for lead-acid since they are so picky when it comes to high discharge rates but, IMO it negates some things versus just going with lithium capable for the job. Got a drag racer, sure go with it, otherwise I don't see the benefit being that great for lithium in most EV applications unless they are exceeding the performance of a standard passenger vehicle or have an undersized pack.


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## major (Apr 4, 2008)

MN Driver said:


> There is some missing information here. Do we know if Argonne National Lab is discussing lead-acid though?


Hi MN,

The first sentence of the article says "Lithium Ion". And those can come in different flavors, so to speak. I get the impression that the "energy" type of Li Ion is what is being considered in this research. This is not what is available to the EV crowd. Give the guys up there a break. If they can reduce the energy storage system for your EV from $8000 to $4000, wouldn't you like that? I doubt you'll see it next week, or next year, but maybe not so far off as Tesseract's Mr. Fusion.

major


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## dtbaker (Jan 5, 2008)

MN Driver said:


> ... I don't see the benefit being that great for lithium in most EV applications unless they are exceeding the performance of a standard passenger vehicle or have an undersized pack.


even current LiFePO4 is a clear winner over Lead today... sure it costs 2x, but lasts 3x or maybe 4x, so the cost per cycle is lower AND you get better performance with less voltage sag and lower weight affecting suspension and braking. I'm convinced, and transitioning as soon as my batteries arrive... 

my FLA are still 'ok' with a range of around 25-30 miles (down from the original 40). But I have a feeling they are headed downhill by the end of summer. perhaps I will sell FLA, watering system, charger, dc-dc to someone local looking to get something rolling that doesn't need much range.... and then they can replace/upgrade as they want.


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## MN Driver (Sep 29, 2009)

dtbaker said:


> even current LiFePO4 is a clear winner over Lead today... sure it costs 2x, but lasts 3x or maybe 4x, so the cost per cycle is lower AND you get better performance with less voltage sag and lower weight affecting suspension and braking. I'm convinced, and transitioning as soon as my batteries arrive...
> 
> my FLA are still 'ok' with a range of around 25-30 miles (down from the original 40). But I have a feeling they are headed downhill by the end of summer. perhaps I will sell FLA, watering system, charger, dc-dc to someone local looking to get something rolling that doesn't need much range.... and then they can replace/upgrade as they want.


What I was saying was that I don't see the benefit being that great -when being used with capacitors- for Lithium. I understand the advantages of using lithium and was trying to say that we have capable lithium battery chemistries that allow for us to skip the use of capacitors and still maintain battery life over the long haul.


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## MN Driver (Sep 29, 2009)

major said:


> Hi MN,
> 
> The first sentence of the article says "Lithium Ion". And those can come in different flavors, so to speak. I get the impression that the "energy" type of Li Ion is what is being considered in this research. This is not what is available to the EV crowd. Give the guys up there a break. If they can reduce the energy storage system for your EV from $8000 to $4000, wouldn't you like that? I doubt you'll see it next week, or next year, but maybe not so far off as Tesseract's Mr. Fusion.
> 
> major


Sorry, I didn't see a link for the article so I wasn't sure.

Most of the time people use Lithium Ion and are speaking about Lithium Cobalt and usually if people mention other chemistries in the family they mention the specific chemistry. I hear what you are saying, using the energy type would allow us to use less battery space and weight and still pull high amperage acceleration discharges. The cost of large capacitors seems to be outside the realm of the advantage though but maybe I'm not looking in the right places. I'll keep my eyes open.


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## dtbaker (Jan 5, 2008)

MN Driver said:


> What I was saying was that I don't see the benefit being that great -when being used with capacitors- for Lithium. I understand the advantages of using lithium and was trying to say that we have capable lithium battery chemistries that allow for us to skip the use of capacitors and still maintain battery life over the long haul.



oooohhhh, RIGHT. 

I do think that caps will be a great way to capture and return regen energy, but not until they are smaller/lighter/cheaper. Even under the best of circumstances regen capture may add 20% to around town range, but would probably (more beneficially) assist 'restart' high-C amp draw and extend life of (any) battery.

but... caps are not there yet as far as I know.


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## PhaseShift (Oct 12, 2009)

Wirecutter said:


> *BULLSHIT ALERT!*
> 
> 
> Ok, stop, hold it. Again with the misuse of *"exponential"* increase. Someone is using a word they don't understand, and you shouldn't do that. Exponential change is *big*. Really big. An _exponential_ increase in cycle and lifetime would quickly mean that the battery would outlast you, and then the planet. (Ok, it's plausible if the exponent is a really small fraction, but be real. When it's exponential, the convention is that you're talking about whole integer exponents, not tiny fractions.)
> ...


Amen on the BS alert. The only exponential here is the amount of hooey coming out of them now as compared to times past. 

Phase


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## MN Driver (Sep 29, 2009)

dtbaker said:


> but... caps are not there yet as far as I know.


A high density solution other than caps(and cheaper today) would be to use smaller cells that have very high power density, on the lines of A123, SAFT for LiFePO4. ...or for those of us who aren't scared of the Lithium Cobalt chemistry, use high-density Lithium Polymer cells in a separate parallel string to the standard pack since we have ones available that are capable of 40C draw constant and 50C for a 10 second burst. Max charge rate of 5C, so not quite regen enabling without the right amount of capacity. 5Ah cells providing 200 amps with a 22.2v nominal 6 pack weighing 836 grams. They aren't built for the EV community as they are used by the plane and helicopter R/C crowd(where power density, light weight, and small size are required) but the e-bike users use them, usually the cheaper versions with 2 or 3 in parallel and it works for them.

I wouldn't recommend mating the LiPo's with a LiFePO4 pack due to the very different discharge curves between the chemistries but if Lithium Cobalt cells came at the right price and ideally in a larger format, using LiPo's in a string parallel to the standard pack to ward off voltage sag and make their lives easier might not be a bad idea. Might even help to ward off the increased internal resistance that comes with calendar aging, which would be the reason I would want packs with the least internal resistance(and higher price) to begin with.


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## GerhardRP (Nov 17, 2009)

jrickard said:


> We did some experiments a couple of years ago with Maxwell's 3000 farad Supercaps on a GEM platform. I could actually switch in the lead acid cell bank, the LiFePo4 cell bank, or the cap bank, in any combination, or each singly.
> 
> I drove about 1/4 mile on the charged caps alone. They are truly amazing devices.
> 
> ...


Hi Jack.
In your many battery measurements, have you used a scope to observe the current and voltage pulse shapes at the batteries? And in this case, with battery and supercap in parallel?
Gerhard


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## mmw109 (May 28, 2010)

Sorry as this is a bit of a newbie question.
I'm spec'ing up a build using some new 'carbon fibre' agm batteries which seem better than FLA, but still have quite a wide gap between their 20hr Capacity and 30 minutes capacity. Anyway, I think I can build a pack that would give me 30-40 mile range at constant speed, but I think a power spike (e.g. starting ) would drain them considerably.

How would you wire up a capacitor bank to smooth this out ? if they were just arranged in parallel to the battery pack how do you actually ensure that they take the load first ?

Additionally can a similar arrangement be done with a second pack of (small) FLA batteries (so I'd have one small set just to handle power spikes and one big set to give me decent range).


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## major (Apr 4, 2008)

mmw109 said:


> I'm spec'ing up a build using some new 'carbon fibre' agm batteries which seem better than FLA, but still have quite a wide gap between their 20hr Capacity and 30 minutes capacity. Anyway, I think I can build a pack that would give me 30-40 mile range at constant speed, but I think a power spike (e.g. starting ) would drain them considerably.
> 
> How would you wire up a capacitor bank to smooth this out ? if they were just arranged in parallel to the battery pack how do you actually ensure that they take the load first ?


Hi mmw,

See http://www.diyelectriccar.com/forums/showthread.php?t=25994&highlight=candy Has some info for ya. Also a search on this site might turn up more. I remember a post with a link to a project showing a simple circuit.

Just wiring the UC in parallel with the battery will work to some degree due to the lower impedance of the UC, but will not take full advantage of the UC. For that you need a "controller" of sorts.

There are no cookbook answers for you. Just have to do your own thing. 

Good luck,

major


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## Harlan (May 29, 2010)

I'm experimenting with a bank of ultracaps on my motorcycle project. The traction battery consists of twenty 20Ah (ironically named) HiPower LiFePO4 cells. I have a few things in mind with the cap bank. I hoped they would act as "stiffening capacitors" to keep the voltage from sagging as much while reducing the stress on the battery pack. The short bursts of power would be an added bonus.

The caps I chose were the PBL-25/16.2 from Tecate Group:
http://www.tecategroup.com/store/index.php?main_page=product_info&cPath=26_30_73&products_id=1225

Five of them in series gives me a 5F bank.

A little more info on my setup, I'm running a 300A Alltrax with an Etek-R motor. I have the cap bank wired directly to the B+ and B- of the Alltrax so it is disconnected from the battery during charging but directly in parallel when the contactor is engaged.

My expectations have not been met at all as my battery still sags 10-15V within a second of full throttle and very little current appears to be coming from my cap bank as observed on my inductive ammeter. I'm only getting 10-15A of current from the caps when according to my calculations a 10V sag within a second should give 50A of current.

Any idea on what I am doing wrong here?


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## major (Apr 4, 2008)

Harlan said:


> Any idea on what I am doing wrong here?


My first guess would be instrumentation. Can you get a low resistance shunt in there and use a scope?

major


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## Harlan (May 29, 2010)

I do have a shunt with a Cycle Analyst hooked up to it but the batteries and caps are both across it. The max current I'm seeing is around 100A.


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## major (Apr 4, 2008)

Harlan said:


> I do have a shunt with a Cycle Analyst hooked up to it but the batteries and caps are both across it. The max current I'm seeing is around 100A.


Another thing. The DC internal resistance per spec is 430 milliohms for the 5 cap modules in series. Not counting interconnects. At 50A, that is 21.5 volt drop inside the caps. 

The E=½CV² relates to the theoretical internal voltage and does not account for the internal resistance. Due to the high internal resistance, it may not be possible to get that energy out at that rate. In other words, the caps are not powerful enough.

What is the internal resistance of your battery pack? 

Not 100% sure about this, but thought I'd share some ideas.

major


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## major (Apr 4, 2008)

major said:


> Another thing. The DC internal resistance per spec is 430 milliohms for the 5 cap modules in series. Not counting interconnects.


Hi Harlan,

Another thing to look at is the time constant of the capacitor. RC = 2.15 seconds. It is difficult to find a reference for this, but I believe you want this time constant to be at least 5 times smaller than the period in which you are attempting to draw from or deliver energy to the capacitor. But that may be for a complete charge. Still, the resistance looks awfully high for the cap.

major


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## Harlan (May 29, 2010)

Major,

Thanks for your insightful comments. You've certainly given me a couple of things to look into and I'll post my progress.


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## Automcdonough (Sep 1, 2010)

Any update on this? I'm toying with the idea of a HV ultracap w/ boost converter off lower v batts..


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## tomofreno (Mar 3, 2009)

> Another thing to look at is the time constant of the capacitor. RC = 2.15 seconds. It is difficult to find a reference for this, but I believe you want this time constant to be at least 5 times smaller than the period in which you are attempting to draw from or deliver energy to the capacitor.


 The voltage drops to 1/e of its initial value, or by about 63% in one time constant. Seems like time constant ~ period ought to be enough, no?


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## major (Apr 4, 2008)

tomofreno said:


> The voltage drops to 1/e of its initial value, or by about 63% in one time constant. Seems like time constant ~ period ought to be enough, no?


Hi tomo,

If you look back at post #21 you'll see what he was attempting. To reduce voltage sag when cap is parallel with battery. Then seeing only 10-15A from cap in 1 second with a 10V drop. To reduce the 10V drop, he needs to get more current from the cap and less from the battery. Since the energy from the cap depends on the voltage change, he needs to increase the C. And the power from the cap depends on R, he needs to decrease the cap circuit time constant.

I have tried this set-up. And it really is not effective. You end up using very little of the cap energy if you are successful in maintaining the voltage. In my case, I was using Pb-Acid near the maximum power of the battery (sag to near 1/2 voltage) and found the cap just marginally effective. In fact, it could not be justified due to the additional mass on the vehicle 

To make such a system work for you, you need to decouple the cap and battery voltage. Meaning some type of buck-boost voltage controller.

Regards,

major


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## Automcdonough (Sep 1, 2010)

major said:


> Hi tomo,
> To make such a system work for you, you need to decouple the cap and battery voltage. Meaning some type of buck-boost voltage controller.


this about sums up what I am considering.. Seems like it would be a powerful setup but these things are just too expensive.. just packing more lithium would be cheaper. What I like about the caps is much less impact from temp and much longer life (a million cycles compared to 6k). Also when dealing with dynamics such as regen they are more efficient.


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## valerun (Nov 12, 2010)

anybody tried to use a separate pack of 20Ah high-discharge cells wired into a separate controller to augment currents at wide-open-throttle? Or maybe some other way to wire this would be better? Not sure what the discharge curves are for LiPo vs. LiPoFe4 but if the LiPo is 'stiffer' (i.e. less voltage sag at high load), could you wire a 144V pack of LiPo in parallel with 144V pack of LiPoFe4 and effectively use LiPo as high-burst buffer which would predominantly discharge during open-throttle and recharge back from LiPoFe4 at light loads?


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## major (Apr 4, 2008)

valerun said:


> anybody tried to use a separate pack of 20Ah high-discharge cells wired into a separate controller to augment currents at wide-open-throttle? Or maybe some other way to wire this would be better? Not sure what the discharge curves are for LiPo vs. LiPoFe4 but if the LiPo is 'stiffer' (i.e. less voltage sag at high load), could you wire a 144V pack of LiPo in parallel with 144V pack of LiPoFe4 and effectively use LiPo as high-burst buffer which would predominantly discharge during open-throttle and recharge back from LiPoFe4 at light loads?


Not that I know about. I tried a hybrid battery pack of large Pb-acid and smaller Nicad. Seemed to work well in the lab, but never got onto a vehicle.

If you think it will get your mission accomplished, go for it


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