# UltraCapacitor--Eye Candy



## major (Apr 4, 2008)

I thought some of you would like a look at something I worked on last month. Installed in a 20,000 pound hybrid shuttle bus.


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## reddwarf2956 (Dec 1, 2008)

major said:


> I thought some of you would like a look at something I worked on last month. Installed in a 20,000 pound hybrid shuttle bus.



Hmmmm looks like batteries. So, what kind are they? Stats?


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## dtbaker (Jan 5, 2008)

I can tell they are ultra-capacitors.... but what IS the capacity of each? cost? total system? and how are they suing them? as regen brake energy springs? complete charge instead of batteries?


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## major (Apr 4, 2008)

reddwarf2956 said:


> So, what kind are they? Stats?


 
http://www.maxwell.com/ultracapacitors/products/modules/bmod0165-48-6v.asp 

Total of 14 in series. Seven shown.

major


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## major (Apr 4, 2008)

dtbaker said:


> as regen brake energy springs? complete charge instead of batteries?


Yes and yes. Don't have time to go into it now.

Later,

major


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## dtbaker (Jan 5, 2008)

major said:


> Yes and yes. Don't have time to go into it now.


when you get a minute... I am sure LOTS of us would like to learn more about how ultra-cap (F) capacity translates into Watt-hrs for getting a handle on possible braking regen.

I don't know enough about how to compare the possible energy from regen braking, figure the ultra-cap needed, and get a price to compare to just adding more batteries....


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## major (Apr 4, 2008)

dtbaker said:


> I am sure LOTS of us would like to learn more about how ultra-cap (F) capacity translates into Watt-hrs for getting a handle on possible braking regen.


Hi Dan,

I have a minute or two. They just moved my office and I'm not unpacked yet. All references still in the box. But from memory......

Energy (E) in the capacitor E = (1/2)*C*V^2, where C = farads, V = volts.

Charging the capacitor happens during regeneration. The cap voltage is low to start and increases as energy is delivered to it.

The total energy for this event is E = E(high) - E(low).

Discharging the capacitor happens during the acceleration. The cap voltage is high at the start and decreases as energy is delivered from it.

The total energy for this event is E = E(high) - E(low).

Obviously E(high)max occurs at the maximum allowable voltage for the capacitor. And E(low)min occurs at the lower voltage limit for the system. V(max) and V(min), respectfully. For normal utilization which is compatible with the propulsion system, I use V(max) = 2*V(min). This is a 2 to 1 voltage swing. Or the working voltage window.

Put a little more math to it, and you'll see that a 2 to 1 voltage window allows you to effectively use 3/4 of the total energy stored in the capacitor, calculated from the manufacturer's specified maximum voltage and farad rating. So, E(usable) = (3/8)*C*V(max)^2. Using farads and volts yields the energy in units of Joules. A Joule = watt*second. J=Ws. You have 60 s/minute and 60 minutes/hour. So a Wh=3600Ws. And 1000W/kW, so 1kWh=3,600,000J.

1 Joule seems pretty small in the energy dimensions used for EVs. One watt second is like the energy from a 1 volt battery delivering 1 amp for 1 second. Wouldn't get the old EV down the road very far

Now, how to equate the energy needed for regen. For now, assume no elevation change. Where does the energy come from in the first place? It originally came from the source which was used to accelerate the vehicle to the speed (velocity) at which it is currently traveling. At this velocity, by virtue of the mass of the vehicle, it has a certain energy in and of itself, called kinetic energy (KE). From basic physics, KE = (1/2)*M*v^2. Use units of kilograms (kg) for mass (M) and meters/second (m/s) for velocity (v) and the KE units are Joules (J). Surprise!

In a loss free universe, one would set the capacitor energy E(usable) equal to the KE of the vehicle at the desired velocity. Which isn't too bad of way to go. But, the road losses (friction and aero) always play against you. Or in other words, subtract from the KE and cannot be converted into electrical energy to be stored in the cap. And also, the propulsion system losses work against you. More energy which will not make it into the cap. So, in reality, depending on a lot of factors, you might actually be able to put 50% of that KE into the energy storage device (capacitor) during the deceleration event. You could effectively size the capacitor to this energy.

Fifty percent is just a guess. A lot of factors play into this. A big one is how quickly you decelerate. For effective regeneration, the quicker the stop, the better. Less energy is lost to the imperfect universe in friction and windage. And then there is the system efficiency. I have seen overall energy recapture rates as high as 70%, but feel you could also see very low rates, 20 or 30%.

When it comes to electrical energy storage, you pay for every Joule. So one would attempt to choose the capacitor just large enough for the energy which can be effectively delivered to it during the regen event. Ultracapacitors are particularly well suited for this because when they are sized this way, they will likely have the needed power capability. Most batteries must be oversized in terms of energy capacity in order to provide the power capability for regeneration.

I mentioned elevation change above. I live in like the flattest county in the country, so don't pay much attention to elevation. However, hilly terrain can be a big factor for regeneration. In this case, one must take into consideration the change in potential energy (PE), which is added to the change in KE for the regeneration event. Say for a downhill travel, the regen brakes are used to maintain a constant speed. Then there is no change in kinetic energy. All the regen energy comes from the change in PE. It is calculated in a similar manner as above. See your local physics text book or web site for details.

Regards,

major


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## dtbaker (Jan 5, 2008)

super info, I think I can convert to metric units and come up with the total (aproximate) energy available in my minimal urban stop light example. Say.... stopping a 2500# vehicle going 45mph as the 'average' available energy.

Then sizing the ultra-cap system to twice that amount to allow for working voltage range and losses would give an aproximate cost to evaluate when considering the regen would probably extend range 20-30% for typical urban conditions; as compared to adding 20-30% more standard lead batteries for the same range.

THEN.... if the cost/benefit is acceptable, we'd have to learn a lot more about the wiring required to regulate the voltage so as not to blow up controller and motor, and how to pump energy in during braking, and use from capacitors first during accel until cap voltage drops to the floor, which would presumably be the satandard battery voltage.


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## major (Apr 4, 2008)

dtbaker said:


> Then sizing the ultra-cap system to twice that amount to allow for working voltage range and losses would give an aproximate cost to evaluate


Hi Dan,

Twice is too much. The losses always work against you. Even allowing for the working voltage range of 2 to 1, I'd use "equal" instead of "twice". Ultracaps ain't cheap. No need to buy and carry more than you'll need. But then again, when it comes to energy, more is better. Having more energy in the cap than you'll use allows you to move the voltage window up and therefore get more power at your current limit. It all comes down to design choices.



> when considering the regen would probably extend range 20-30% for typical urban conditions; as compared to adding 20-30% more standard lead batteries for the same range.


To get above 20% extended range from regen, you'd need a very efficient system and be making like 10 stops per mile, every mile. Your expectations may be inflated. But you can define a drive cycle and do an energy spreadsheet analysis and see if it is in the ballpark.

Using regen to extend range compared to adding batteries is a tough nut to justify. But, consider brake wear saving and the fact the regen system and caps will last the life of the vehicle whereas extra batteries will eventually need replacement, and it looks better. Also, regen is fun. It is a good feeling when you come to a regen stop and know that energy wasn't wasted warming the atmosphere.

Good luck.

major


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## Technologic (Jul 20, 2008)

major said:


> Yes and yes. Don't have time to go into it now.
> 
> Later,
> 
> major


 
Considering their largest capacitor they make of that model (165 farads at 48v) is 213,000 joules roughly, or 0.059kwh, why didn't they just use lithium ion batteries?

I assume one of those caps was in the $1000 range a piece... for a mere 0.06kwh, they'd be hard pressed to have the bus functioning by the time lithium dies, let alone make the added durability of caps worth it.

Am I missing something on the cost effectiveness table here?

A small 1 cell lithium ion battery could replace 5 of these batteries, let alone what a prismatic batt could do.

Ice engine won't last 1,000,000 battery cycles, 50 ice engines probably wouldn't

I assume this system cost 15k-20k in caps. Whereas the 0.84 KWH in this pack would cost roughly $200 in lithium form.

Maybe I'm missing something here on energy densities/price, but usually ultracaps are freaking expensive


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## major (Apr 4, 2008)

Technologic said:


> Considering their largest capacitor they make of that model (165 farads at 48v) is 213,000 joules roughly, or 0.059kwh, why didn't they just use lithium ion batteries?


What would the total cost be for a lithium battery system capable of the 160 kW required to stop the bus in 7 seconds for a couple million cycles?



> I assume one of those caps was in the $1000 range a piece... for a mere 0.05kwh, they'd be hard pressed to have the bus functioning by the time lithium dies, let alone make the added durability of caps worth it.
> Am I missing something on the cost effectiveness table here?


Bus has been running for 4 years. This was a capacitor up-grade. It is a parallel hybrid, energy recovery/launch assist. It increases fuel economy about 25% on stop intensive routes. The ultracapacitors will last the life of the vehicle whereas any battery available will not. Total life cycle cost is better with capacitors than batteries.

Yes, energy density for batteries is much higher than ultracapacitors. But that is not the only factor when choosing the energy storage system. This application required little energy and lots of power, high efficiency and durability. Ultracaps made sense.

Regards,

major


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## major (Apr 4, 2008)

Technologic said:


> Ice engine won't last 1,000,000 battery cycles, 50 ice engines probably wouldn't


The Cummins ISB should do several million accelerations, maybe with a little maintenance. What does a battery cycle have to do with it?


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## Technologic (Jul 20, 2008)

major said:


> What would the total cost be for a lithium battery system capable of the 160 kW required to stop the bus in 7 seconds for a couple million cycles?


low voltage high amperage cylindrical cells would work fine as they could be charged at a 10-15C rating in bursts for a lot of short cycles.



> Bus has been running for 4 years. This was a capacitor up-grade. It is a parallel hybrid, energy recovery/launch assist. It increases fuel economy about 25% on stop intensive routes. The ultracapacitors will last the life of the vehicle whereas any battery available will not. Total life cycle cost is better with capacitors than batteries.


You're correct it will last the life of the vehicle, no doubt about it. The question is if 2 lithium cell replacements is cheaper than 1 set of those, my guess is yes since you're upgrading after 4 short years.



> Yes, energy density for batteries is much higher than ultracapacitors. But that is not the only factor when choosing the energy storage system. This application required little energy and lots of power, high efficiency and durability. Ultracaps made sense.


I don't disagree with the choice per se, I'm just curious on the cost effectiveness or if the government should have been going with different engineering standards. Ultracaps are well and good but the weight addition, cost addition likely will be more damaging to overall performance per dollar than batteries or dropping the hybrid design completely. Granted I lack the political "prowess" to do much else besides cost benefit schema, clearly there is other motivations out there.

Buses are a decent application for hybrid designs because of the constant stopping/going in short distances. I don't doubt you will see the 25% figure for efficiency increase. I simply don't know if ultracaps are doing something lithium can't here. How much amperage for a 30mph stop are you REALLY dumping into these caps? I can't imagine it's over 1500A.

Anywho it's definitely an interesting project 



If you're dumping 160kw for say 10-15 seconds at a time (which would be indeed a hard stop and a speedy one), you'd need something like a 20-30C charging rating for bursts... I'm sure Li-ion could supply you with something like that, might be able to extend range too with the large pack you'd want (say 4kwh of lithium) 

According to my sources the 165F 48v verison is 1372 Euros, or 842 Euros in quantities over 100, so 1130USD/ea at the cheapest from this particular source. 

There's always the option of having a high power DC-DC converter to transform the amperage to something useable and the voltage sky high on the recharge cycle.

Cheers


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## major (Apr 4, 2008)

Technologic said:


> How much amperage for a 30mph stop are you REALLY dumping into these caps? I can't imagine it's over 1500A.


Hi Technologic,

It is fused at 300 amps. 680 volts max.

I looked into batteries for this application. Still am. Basically anything that is actually available, with the required support (BMS), cost more than a single set of UCs. And the up-grade was to the best UC available because the original UC (sourced from Russia 5 yrs ago) was not an option for continued development and commercialization.

If you can add a component (or system in this case) to an existing vehicle which can recover cost in the life of the vehicle and reduce fuel consumption and emissions, what's wrong with that?

Hey, give me a battery which will do the job, or a fuel cell, or a rubber band. I really don't care. I'm just trying to make this place a little easier to live in.

Regards,

major


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## Technologic (Jul 20, 2008)

major said:


> It is fused at 300 amps. 680 volts max.
> 
> I looked into batteries for this application. Still am. Basically anything that is actually available, with the required support (BMS), cost more than a single set of UCs. And the up-grade was to the best UC available because the original UC (sourced from Russia 5 yrs ago) was not an option for continued development and commercialization.
> 
> If you can add a component (or system in this case) to an existing vehicle which can recover cost in the life of the vehicle and reduce fuel consumption and emissions, what's wrong with that?


The BMS for such a system would have to be custom I'd imagine, but in reality that voltage/amperage would be a simple thing to find in a fast charging lithium component... 

It's an interesting project...


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## dtbaker (Jan 5, 2008)

major said:


> KE = (1/2)*M*v^2. Use units of kilograms (kg) for mass (M) and meters/second (m/s) for velocity (v) and the KE units are Joules (J). Surprise!


ok, I am trying to work my way thru this...

so, energy available from stopping a 2500# car going 45mph is....

KE = (1/2)mv^2
(1/2) * 2500#* 1kg/2.2# * (45miles/hr*(1609 m/mile) * (1hr/3600 sec))^2

229837 Joules available from a single typical stop, 

...now, since Joule = W*s, and an average stop is maybe 10 seconds of braking, that means it would come in at about 23000 watts for 10 seconds. WOW. so at 96 volts, thats a max of about 240 amps. Obviously more than (any kind) batteries can absorb... 

...right?
so the next step, to figure number of caps required requires knowing the voltage. My EV happens to be a 96v system, so I am assuming I could build a bank of ultracaps in series or parallel to provide a matching 'low voltage' of 96 v, and a max of double that, right?

my question is which voltage to use in looking at the ultra cap specs to match this all up. and then, if the 'charged' ultracaps are at 2*96 volts, how would I bleed energy back out to my system without frying controller and motor?


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## JeffPritchard (Jun 10, 2008)

Technologic said:


> Considering their largest capacitor they make of that model (165 farads at 48v) is 213,000 joules roughly, or 0.059kwh, why didn't they just use lithium ion batteries?
> ...
> I assume this system cost 15k-20k in caps. Whereas the 0.84 KWH in this pack would cost roughly $200 in lithium form.
> 
> Maybe I'm missing something here on energy densities/price, but usually ultracaps are freaking expensive


I think it probably has a lot to do with charge/discharge rate. The "deceleration event" would typically happen over the course of maybe 5 to 10 seconds, and the acceleration event is similarly short. While the total energy may seem small from an EV perspective, the Power is massive, because the time is very short.

You would need to grossly over size your lithium pack in order to accept the charge in the short time it is being generated by the slowing vehicle. Likewise, you need to be able to use that power very quickly. (very high discharge rate compared to the total capacity).

Ultra caps have very low internal resistance, and are able to accept and deliver charge at a much higher rate than any kind of battery.

jp


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## JeffPritchard (Jun 10, 2008)

oops, didn't notice there was another page of comments. Mine was redundant.

jp


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## Qmavam (Aug 17, 2008)

JeffPritchard said:


> oops, didn't notice there was another page of comments. Mine was redundant.
> 
> jp


Redundancy is good, for rockets, nuclear power plants
and especially for human memory retention.
Now, where did I put my glasses and what did I want to see
after I found them?








Mike


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## major (Apr 4, 2008)

dtbaker said:


> 229837 Joules available from a single typical stop, since Joule = W*s, and an average stop is maybe 10 seconds of braking, that means it would come in at about 23000 watts for 10 seconds. WOW. so at 96 volts, thats a max of about 240 amps. Obviously more than (any kind) batteries can absorb...
> ...right?


Yeah, I guess. Still haven't found my calculator, so trust your math. Now the 230kJ was just the kinetic energy. So you'd subtract losses from that and really need only like maybe 160 or 170kJ of usable energy storage. And the current profile for a complete decel will resemble a triangle. So, the maximum current will probably be on the order for 400 amps. Just kinda guessing. But it looks like you got the right idea going there.



> so the next step, to figure number of caps required requires knowing the voltage. My EV happens to be a 96v system, so I am assuming I could build a bank of ultracaps in series or parallel to provide a matching 'low voltage' of 96 v, and a max of double that, right?
> 
> my question is which voltage to use in looking at the ultra cap specs to match this all up. and then, if the 'charged' ultracaps are at 2*96 volts, how would I bleed energy back out to my system without frying controller and motor


This all gets into the system design. You have to keep the maximum capacitor voltage where the manufacturer has set it. And you have to keep max voltage below the limit of your motor controller. So, you either live with half voltage when the caps are discharged, or look at some type of voltage controller between the caps and the rest of the propulsion system. Such a device is often called a buck-boost DC/DC converter. Not something you can buy off the shelf. And would be on the order of power and size of the motor controller. Maybe you can steal one from a Prius. Or just design the system around a 2 to 1 voltage swing.

Regards,

major


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## dtbaker (Jan 5, 2008)

major said:


> ...You have to keep the maximum capacitor voltage where the manufacturer has set it. And you have to keep max voltage below the limit of your motor controller.


ok, I want to ask just a little more about this... I want to be sure I understand the parameters for sizing. Let's say my EV battery pack is a 96 v nominal system; motor and controller obviously can handle a 'little' more than that as the pack at full charge is more, and the 96v would be the floor when the batteries are 80%-90% DOD.

When I go look at the ultracap site, there are some 'rated' at 48.6 v. My question was whether that is the MAX, and from your comment, it sounds like yes. So, if I went with three in series my max would be 3*48.6 = 145.8 v with the
http://www.maxwell.com/ultracapacitors/products/modules/bmod0165-48-6v.asp

...assuming that my controller could handle the 146v ultracap pack until it 'discharged' back down to 96-ish volts, then the usable energy is the difference right? Or, is there a way to more completely 'drain' the ultracaps before switching back to the battery pack which is at 96+volts?

The part I am not getting is how this switching s handled, and what the actual usable energy is calculated so that the system could be designed to suck up all the typically available regen energy.


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## major (Apr 4, 2008)

dtbaker said:


> ...assuming that my controller could handle the 146v ultracap pack until it 'discharged' back down to 96-ish volts, then the usable energy is the difference right?


Hi Dan,

Yes, 146 to 96 would be your "working voltage window". Usable energy = (1/2)*C*(146^2-96^2). I think I did that right



> Or, is there a way to more completely 'drain' the ultracaps before switching back to the battery pack which is at 96+volts?


Run a lower voltage battery. Or if you have the cap isolated from the battery when it is operational, run it down to a lower voltage. Or put an electronic voltage conditioner in front of the cap. At some point it becomes uneconomic to keep going lower on cap voltage to get that last Joule out. Afterall, how high a current will it take to get usable power at 0ne or two or 10 or 20 volts from a 146 volt cap? You just have to decide where that lower limit is for your design. Like I said, I tend to use 2 to 1. 146 to 96 isn't too far from that.



> The part I am not getting is how this switching s handle


A number a ways. I have done it by just wiring the battery and the cap in parallel. And let the impedance difference handle the current sharing. Works, but does not do a good job in regards to energy utilization. But can't get much simpler. Tried a diode system. Not too bad. Contactors. Haven't done that. But it'd work. And then, the buck-boost electronic converter. Or, dream up some new way.



> and what the actual usable energy is calculated so that the system could be designed to suck up all the typically available regen energy


I thought you did a pretty good job at it. 

Regards,

major


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## dtbaker (Jan 5, 2008)

ok, good to know I am on the right track... In the meantime I was crunching numbers at my end, and poking around the ultracap site. I want to work this example all the way thru to get a good idea of what it would actually take to pull this off....

Turns out that with aprox 229837 J or *(3^-7 kWhr/Joule) = .07 kWhr available in my typical braking model, using three of the big boys is overkill. Looks like a better match is the http://www.maxwell.com/ultracapacitors/products/modules/bmod0063-125v.asp
where the ratings are different. Usable energy would be

E = (1/2) 63 (135^2-96^2) = 283784 joules .... perfect

so... how big is it and what does it cost?
60 kg , 762mm x 425 x 265
132#, 30" x 16.7 x 10.4 ...wow, big and heavy!

I am still waiting to hear back what it would cost.


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## her0 (Jul 8, 2009)

Hi I would like to ask, if I have a battery of 36V connected in parallel with a 48V Capacitor, during regeneration, how is it possible that the motor will charge up the capacitor since E<V unless there is a Boost convertor added.


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## major (Apr 4, 2008)

her0 said:


> Hi I would like to ask, if I have a battery of 36V connected in parallel with a 48V Capacitor, during regeneration, how is it possible that the motor will charge up the capacitor since E<V unless there is a Boost convertor added.


Hi her0,

If the battery and cap are connected in parallel, the voltage is the same on each. If you want a different voltage on the battery and cap, then you need an electronic converter between the two.

Regards,

major


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## her0 (Jul 8, 2009)

major said:


> Hi Dan,
> 
> Yes, 146 to 96 would be your "working voltage window". Usable energy = (1/2)*C*(146^2-96^2). I think I did that right
> 
> ...


If I take the above as an example. A 96V battery in parallel with a 146V capacitor (Am I correct?). During regeneration, voltage would not be able to flow back to the capacitor right? The battery would charge up the capacitor to 96 Volts. Would the regenerated power be able to charge up the capacitor higher than 96V?


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## major (Apr 4, 2008)

her0 said:


> If I take the above as an example. A 96V battery in parallel with a 146V capacitor (Am I correct?). During regeneration, voltage would not be able to flow back to the capacitor right? The battery would charge up the capacitor to 96 Volts.


Hi her0,

Now that is the point of it. To effectively utilize the cap, you need some type of "capacitor controller". Some have tried an electronic buck-boost converter and others some simpler diode-contactor circuits. No cookbook answers for you. Sorry  Something you'll have to search out or design on your own.



> Would the regenerated power be able to charge up the capacitor higher than 96V?


That depends on the motor/controller you have.

Regards,

major


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## her0 (Jul 8, 2009)

Alright thanks.


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## JohnMogs (Dec 2, 2009)

If batteries and ultra caps are in parrellel, on say a 96v system, Would the ultracaps absorb the regen quicker than the batteries, so that the voltage for a short time would be higher in the ultra caps until that energy was balanced between the battery and ultra caps?

Also, fyi a friend of mine has used 48 of the 2.7v 650F ultra caps for a "booster" pack of 130v ultra cap Max, and his battery pack & controller are rated for 96v on a DC system.... thus this is NOT used for re-gen, but he claims that it helps reduce the current demanded from the batteries on acceleration, and it helps balance the batteries... said the key is that the ultra caps max voltage must be higher than the batteries will ever get, otherwise they might need a balance system. This is about all I know on his system, but here is a link with photo:
http://www.zenn35.com/Progress/Progress.html


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## Guest (Dec 30, 2009)

Vague info and two images is all that site has! 

Thought there'd be more than that!


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## gor (Nov 25, 2009)

major said:


> Hi Dan,
> ...
> A number a ways. I have done it by just wiring the battery and the cap in parallel. And let the impedance difference handle the current sharing. Works, but does not do a good job in regards to energy utilization. But can't get much simpler. Tried a diode system. Not too bad. Contactors. Haven't done that. But it'd work. And then, the buck-boost electronic converter. Or, dream up some new way.
> ...
> ...


...yeaa... heard it 20 years ago... nothing changed : (((((((((((
LOL
my idea (in school) was - since caps can charge and discharge quickly -use it as energy storage instead of heavy batteries;
diode (lamp ) would release, say 60 shots per sec in 110v - creating AC...
...
never got to try it ...

but they did:http://www.treehugger.com/files/2005/09/philadelphia_hi.php


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## gor (Nov 25, 2009)

same principle: energy storage (regen energy) effectiveness, flywheel 

http://www.blueprintenergy.com/


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## gor (Nov 25, 2009)

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ElectrodeSize ___________ 100x100mm ---//- _ 60x100mm
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----- 

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## gor (Nov 25, 2009)

Technologic said:


> Considering their largest capacitor they make of that model (165 farads at 48v) is 213,000 joules roughly, or 0.059kwh, why didn't they just use lithium ion batteries?
> 
> I assume one of those caps was in the $1000 range a piece... for a mere 0.06kwh, they'd be hard pressed to have the bus functioning by the time lithium dies, let alone make the added durability of caps worth it.
> 
> ...


how about this calc:

1C=1A*1sec
1C=1F*1V

1A*1sec=1F*1V

amount of electric charge transported in one second by a steady current of one ampere
=
amount of charge stored by a capacitance of one farad charged to a potential difference of one volt:



A*hour=F*V/3600
A*V*hour=F*V^2/3600
wh=F*V^2/3600

"(165 farads at 48v) is 213,000 joules roughly, or 0.059kwh"
165*48=7920 A sec or 132 A min or 2.2 A h

wh=2.2*48 or 165*48*48/3600= 105.6 wh or 0.1056 kwh
0.1056 kwh *14 batt = 1.4784 kwh total 14batt


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## jlind (Dec 2, 2009)

When designing a regen system with both ultra capacitors and batteries do we really need to try to keep the capacitors to a certain voltage related to the batteries?

As a DC/DC system has losses I'm thinking that you could do it like this:
All controllers (that I know) use PWM to reduce the voltage from the batteries to what is needed for the moment. Normally that switches between battery voltage and ground. now we have two situations:

1) We want lower voltage than what is stored in the cap.
Run PWM between cap and ground.
2) We want higher voltage than what is stored in the cap. 
Run PWM between Battery and cap until it's discharged.

As I see it this would utilize the caps to the maximum with a minimum of losses.


/Johan


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## gwartnet (Feb 4, 2010)

major - 

Do you know if in running a capacitor bank that is larger than the battery in parallel, say 128V nominal and a 96V battery, the voltage sag out of the capacitors would reduce the advantage of having the current divider there?

In other words, you have a capacitor bank running at 96V, but is rated for 128V. Is the drop off in voltage less in 10 secs, maybe 96V to 80V than if you ran a system rated for 96V where in 10 secs the voltage sag might go from 96V to 48V?

Just trying to figure out if using a system with overhead would be worth it.

Not sure if I'm relaying my question clearly though.


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## major (Apr 4, 2008)

gwartnet said:


> major -
> 
> Do you know if in running a capacitor bank that is larger than the battery in parallel, say 128V nominal and a 96V battery, the voltage sag out of the capacitors would reduce the advantage of having the current divider there?
> 
> ...


Hi gwart,

I think I see what you're asking. Answer is no. Keep your upper working voltage limit equal to the rated Vmax of the cap. The only value I see in maintaining voltage headroom would be cycle life extension. Since good UCs can have like a 1,000,000 cycle rated life, what's the point? Unless you want you descendants to be able to use the ultracaps 

Regards,

major


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## JohnMogs (Dec 2, 2009)

I'm told that Maxwell technologies 
suggest a balance circuit if using
multiple smaller cells in series.

The overhead 120v caps for a 96v pack
allows you to avoid a BMS for your caps.

I don't know much about caps so 
I might not have this correct


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## GerhardRP (Nov 17, 2009)

gor said:


> Premlis®Supercapacitors
> 
> http://www.jeol.com/NEWSEVENTS/PressReleases/tabid/521/articleType/ArticleView/articleId/109/Premlisreg-
> 
> ...


This "supercapacitor" actually looks like a very fast lithium cell.. discharges in 1/2 minute so 120C.
Where is the boundary between an electrochemical capacitor and a battery?
Gerhard


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## dtbaker (Jan 5, 2008)

a capacitor is VERY different than a battery. cycle duty close to a million, but much less energy density (i.e. physically large, and heavy compared to the amount of usable energy). The voltage also drops like crazy between full and empty, which would require different design for several major components.

I think an ultra cap MIGHT be a good 'spring' for braking energy, but not the main battery pack.


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## major (Apr 4, 2008)

GerhardRP said:


> This "supercapacitor" actually looks like a very fast lithium cell.. discharges in 1/2 minute so 120C.
> Where is the boundary between an electrochemical capacitor and a battery?
> Gerhard


Hi Gerh,

When I was testing ultracaps, IIRC, I was discharging (or charging) 75% of the total energy in time periods of 6 to 8 seconds. And could have actually been faster, but limited by test equipment.

Ultracaps are high power density devices, not energy dense. And have a number of advantages over batteries as dt pointed out like cycle life. But the relatively low energy density prevents them from being primary energy storage for vehicles. 

As far as a boundary, look for a Ragone Chart which shows batteries and ultracaps on a grid of specific power vs specific energy. If I come across one, I'll post it up here.

Regards,

major


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## Guest (Dec 5, 2010)

Major,

I think some who are following this thread may be thinking that the caps are for main power. I gather that they are for regenerative braking and acceleration only and that the buses are diesel powered for the main power. Since stopping and starting are energy hogs the supercaps can help in this matter. Allowing a better use of energy saving loads of money in this stop and go situation. I like the idea. We should be using this even on gasoline cars. A step in the right direction. 

Pete


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## major (Apr 4, 2008)

gottdi said:


> Major,
> 
> I think some who are following this thread may be thinking that the caps are for main power. I gather that they are for regenerative braking and acceleration only and that the buses are diesel powered for the main power. Since stopping and starting are energy hogs the supercaps can help in this matter. Allowing a better use of energy saving loads of money in this stop and go situation. I like the idea. We should be using this even on gasoline cars. A step in the right direction.
> 
> Pete


Yeah, Pete, that's was the idea. Launch assist and energy recovery braking. Parallel hybrid, induction motor coupled thru gear box post transmission. Diesel engine and OE transmission intact. Electric only engaged below 40 mph. Saved about 25% of fuel on urban duty cycle (7 stops/mile). Also reduced emissions about the same amount.

Too bad nobody bought into the idea 

major


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## EVfun (Mar 14, 2010)

GerhardRP said:


> This "supercapacitor" actually looks like a very fast lithium cell.. discharges in 1/2 minute so 120C.
> Where is the boundary between an electrochemical capacitor and a battery?
> Gerhard


Electrochemistry is the boundary. A capacitor stores electrons, not the chemical potential to release electrons. The chemical potential is what gives a cell its nominal cell voltage. The voltage of a capacitor varies based on state of charge. At 50% charge remaining a capacitor's voltage will be 71% of the full charge voltage. At a 50% SOC a lead acid cell is down to about 2.07 from 2.14 volts at a full charge (about 97% of the starting voltage.)


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## ElectriCar (Jun 15, 2008)

I've worked the formula with my capacitor bank and I'm not sure what I have. Trying to see how much this will assist me during cycles when the controller is off. When the controller is off, the cap charges, when on it discharges. So I want to calculate what sort of boost this thing is giving me at various frequencies or at various % throttle.

*I have 10,000uf bank (10x1000) in parallel. So I figure usable energy based on Major's formula = .375*.01*156*156=91.26w correct?* 

91.26/3600=.02535wh=.00002535kwh? Not really a factor in extending range but that isn't what I'm looking for here. I'm looking to reduce the peukert effect by charging the cap bank when the controller is cycling off.

So instead of drawing 500A burst for 50% of the time giving me 250A average at 50% throttle, I could theoretically draw 250A continuous and get the same amount of power while drastically reducing the P effects, or at least it seems that way due to cutting the amp draw in half.

Anyway if my calculation is correct, 91.26w/156v=.608

So that would give me 1A at 156V for .608 seconds at full throttle where the controller is on 100% right? That's basically nothing at WOT.

But at 50% throttle, assuming a 50% cycle time that will give me a boost but I'm just not sure how much. I know it depends on the frequency of the controller (Curtis 1231 500A) and the charge time of the 1000uf caps. 

Edited below: 
The time constant of a cap to charge to 63.2% of capacity is: RxC where R is resistance and C is capacitor value. *I'm not sure of what the resistance value would be. Is it the total resistance of the loop from the controller through the batteries including the batteries, contactor, wire and connections resistance?*

Just looked up the frequency of the controller, it's 15khz at WOT and 1.5khz at minimum throttle. So that's a cycle time of .000075 or .075ms at 15khz and .75ms at minimum throttle. Therefore the time allowed for the bank to charge/discharge would be half of the cycle time.

Any thoughts on all of this?


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## major (Apr 4, 2008)

ElectriCar said:


> Just looked up the frequency of the controller, it's 15khz at WOT and 1.5khz at minimum throttle. So that's a cycle time of .000075 or .075ms at 15khz and .75ms at minimum throttle. Therefore the time allowed for the bank to charge/discharge would be half of the cycle time.
> 
> Any thoughts on all of this?


Hey Electri,

The motor controller already has DC bus caps inside of it. Adding extra fast acting caps, like electrolytics, outside the controller may get you into trouble. There is more to it than meets the eye. I think Tesseract put up some comments relating to this but can't recall where. 

Beware of unintended consequences.

major


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## ElectriCar (Jun 15, 2008)

I have had them running for about a year now. Think I put up photos but made a busbar from aluminum and used 2/0 from the contactor to the controller. They precharge through a resistive load so as to not weld the contacts. 

So now that that's out of the way, got any input on the calculations above? 

And if you have a link to Tesseract's thread I'd like to see it. I have read a lot on here about this but don't recall him doing that.


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## major (Apr 4, 2008)

ElectriCar said:


> So now that that's out of the way, got any input on the calculations above?


More info would be required, like ESR of the caps, the inductance of the external circuit, the specs on the internal caps, diodes, mosfets, gate drives, bus inductance, and likely a thing or two I haven't thought of. Oh, a guy like Tesser to calculate it 

Me? I'd get a good scope and snap a waveform picture with and without those external caps. I got to wonder if they are doing anything, helping or hurting you 

And after all that, what actually is your objective? And how would added capacitance help? Is it really improving sometime tangible, or just in your mind? Certainly that much energy storage isn't going to help get you up a hill. And does a smoother discharge waveform help a Pb-acid battery? Some guys sell add-on devices to put spikes in the charge waveform to "improve" the battery. 

Hey, I don't know. Good for. You're trying something  Sorry I can't help much more. Good luck and keep us informed. Oh yeah, send Tesser a PM and ask him to chime in on this thread 

major


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## michaeljayclark (Apr 3, 2008)

I have a project I am working on involving UCs.

I have access to 52 3000F Maxwell 2.7 Boostcaps or 100 2600 farad 2.5v maxwell boostcaps for the same price. the caps will be wired in series.

I want to accelerate a 5000 lb vehicle to 55 in 5 seconds with a soliton jr controller. using a netgain 9 inch motor. if not 5 seconds what could i expect? just looking to have some good merging power lol.

there will be a battery pack to cruise on, the caps to accelerate with. reading the voltage size of pack compared to the voltage of the caps it would have to be half the cap pack I think?

my question would be which one would be best for this project? i am getting a really good deal on these caps so the cost factor isnt an object here.


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## major (Apr 4, 2008)

michaeljayclark said:


> I have a project I am working on involving UCs.
> 
> I have access to 52 3000F Maxwell 2.7 Boostcaps or 100 2600 farad 2.5v maxwell boostcaps for the same price. the caps will be wired in series.
> 
> ...


Hi mic,

Start by doing some energy calcs. Basic equations are E = ½CV² for the caps' stored energy and E = ½mv² for the vehicle's kinetic energy. You also must supply energy to overcome losses.

It is very hard to use cap energy near zero cap voltage, so use a 2 to 1 range. Like charge caps up to 300V and discharge them down to 150 or there abouts. That uses 75% of the total energy possible to store in the cap. I think that may be doable with the SolJr controller. 

The 3000F product is more energy dense and therefore the better choice, if there are enough of them.

There have been a couple of guys post up EV calculators like FrankyEV and ?? Run some calculations and post them up, maybe in a new thread. I and hopefully some others will chime in. Interesting project. Look up BYU ultracap powered EV1 drag race car. I know they did some white papers which might give you some insight.

Regards,

major


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## michaeljayclark (Apr 3, 2008)

the calculator from franky ev is 

http://www.diyelectriccar.com/forums/showthread.php/yes-another-ev-calculator-45278.html

doesnt allow much change. Id need a calculator because im a math dunce.

the 52 3000 farad caps are on their way. I have an s-10 that was made 5 years ago and the batterys have voltage and can move the truck but the range is less than a mile.

would be a good test bed to parallel up the 52 caps in series and see what happens. the pack voltage is 144 so the caps in series would be 140 so i better order a few more caps to get it more than the battery voltage.. do not want to see a big light show!


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## major (Apr 4, 2008)

michaeljayclark said:


> the 52 3000 farad caps are on their way.


Hi mic,

Here is a picture of an ultracapacitor install I did a few years back:










It consisted of 156 2600F Maxwell cells. On the left side of the photo. It was just under 1 MJ of useable energy. It was sufficient to launch the 15,000 lb step van to about 40-45mph.

You had better read up on these things. A discharged cap looks essentially like a short circuit when you connect it to a battery 

Regards,

major


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## michaeljayclark (Apr 3, 2008)

yes to the short circuit! have to figure out about the voltage window you were talking about on another thread.

i may need more than 52 caps at this point.


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## Tesseract (Sep 27, 2008)

michaeljayclark said:


> I have access to 52 3000F Maxwell 2.7 Boostcaps or 100 2600 farad 2.5v maxwell boostcaps for the same price. the caps will be wired in series.
> 
> _I want to accelerate a 5000 lb vehicle to 55 in 5 seconds with a soliton jr controller._ using a netgain 9 inch motor. if not 5 seconds what could i expect? just looking to have some good merging power lol.


First off, you will need a lot more power to accelerate a 5000lb vehicle to 55mph in 5 seconds than you can get from a SolJr. Indeed, it will take more power than you can get from a Soliton1. Try out this handy 0-60 calculator to see just how painful it is to move 5000lb quickly. Hint: you need to keep the weight under 2200lbs (aka 1000kg) to accelerate to 60mph in 5 seconds with a SolJr).

52 2.7V x 3000F caps in series are equivalent to a single capacitor rated at 140V and 57.7F. The maximum energy stored is 0.5 * 57.5 * 140 * 140, or 565,460J (aka watt-seconds). As maj points out, you can use 75% of that energy if you allow the caps to discharge from 140V down to 70V which gives you ~424kW-s of energy). With this amount of energy you could power a 100kW load for 4.24 seconds. Making sense so far?

There is a twist, here, because you are supplying a power converter - ie, a motor controller - which has fixed current and voltage ratings which must be respected. Fortunately I have a spreadsheet with common calculations (for my line of work anyway) and one of them is "power supply holdup time"). I had to modify it a little bit for the scale involved here but the end result is that you can draw 100A for 40.4 seconds. Current and time trade off exactly proportionally, so you could pull 500A for 8.08 seconds.

Now, the final caveat is whether or not these capacitors have a low enough ESR to withstand the reflected ripple from the controller. The worst case ripple current from the SolJr is 300A. Much of that is absorbed by the internal capacitor - that's its job, after all - but some of it will be presented to anything else that is connected to the battery terminals. In general, you want to locate dc/dc converters, chargers, additional capacitors, etc., as far from the controller's battery terminals as possible, and/or insert additional inductance in series with said devices to isolate them from the ripple. Depending on how sensitive they are, 10-100uH will generally be sufficient.

This is unavoidably technical and "mathy"... sorry, but that's what happens when you want to do something different with an EV


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## michaeljayclark (Apr 3, 2008)

I appreciate the response, it helps get a better picture of whats I am trying to do. Dont worry about the math, it helps to see things. It does take a few times looking at the formulas, I am a math idiot!

I learned in series would require a BMS to make sure the caps play nice to each other so Ill need to arrange them in a different way then just a string in series. Major, your cap array in the truck, were they all in series?

the soliton has a wide voltage window from 8 volts to 300+ volts. the junior has the same voltaghe window. either way I think ill look at the soliton in this situation. the soliton jr was a hope to use.

to get to 60 in 6.8 secs requires 300 HP to get a 5000 vehicle to 60mph. I looked up horsepower to watts, and that is 1 HP = 745 Watts. Watts is a measure of power as is Horsepower so I can see how those relate. So to get the 6.8 seconds you would need 300(745) =223500 watts.

that gives me a good idea of what I need to build in order to get that number. Ill need to increase the power in the caps to get the 223500 watts. That may be more caps. That i dont mind it just adds to the "wow" factor from those that will ask me how many caps I have.

ESR DC is mohm .29, ESR AC @ 1khz is .24. energy available 3038 Wh, continuous amps is 150, Emax is 5.96, Pmax is 14800, Ic mA

Jeff pointed out the ripple effect. he was talking about a series hybrid project were they just used caps with a genset behind them and the gen and the soliton didnt play nice at first.


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## major (Apr 4, 2008)

michaeljayclark said:


> Major, your cap array in the truck, were they all in series?


Yep. Working voltage approx 180 to 390.

And I tested these caps to 500A. I have no doubt they will do 1000.


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## nimblemotors (Oct 1, 2010)

major said:


> Yep. Working voltage approx 180 to 390.
> 
> And I tested these caps to 500A. I have no doubt they will do 1000.


Major, who do you work for? very impressive work on the Bus.
Can you get some of the trash trucks setup too? They are constantly 10-20ft stop-n-go, and their roaring engines and squelling brakes are LOUD AS HELL. 

So do you have any kind of per-cell control on the caps? Or just serial connected and charge/discharge the string?

I just acquired a Porsche Boxster, and want it to accel fast and brake fast for road racing, and am thinking I might try a bank of ultra caps with the AC motor. I want 0-60 in 5 seconds for a 3000lb car, the formula indicates I need 300hp, which is 223 Kw. What caps do you suggest?

Jack Murray
Nimble Motorsports


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## major (Apr 4, 2008)

nimblemotors said:


> So do you have any kind of per-cell control on the caps?


Hi nimb,

Each cell did have a small circuit board attached which would protect to some degree excess voltage due to imbalance. Not near as complex as a BMS.

Refuse collection vehicles are indeed prime candidates. HTUF (Hybrid Truck Users Forum), branch of CalStart/Weststart, was working in that direction several years ago when I was active in the field.

Battery/UC combinations are tricky to say the least. I have my doubts UC can be justified for non commercial applications. But WTH, give it a go, or at least a look. Like I said, been a few years back, but at that time, Maxwell had the best product although there were others close like Ness, Panasonic, Nipon, etc.

Regards,

major


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## nimblemotors (Oct 1, 2010)

Looking at the prices of the caps, I don't think they are going to work.
There is a 120v 64F maxwell module on ebay for $3300, 200lbs.
Mouser has the 48v 56F modules at $2400. 30lbs. Quite expensive.

So I think you are right, the value of handling 1-million cycles with essentially no degradation is something that is mostly valued by
commerical installations that appreciate the long-term value and can make the investment. For racing, just like when we did R/C racing, guys would consider worn-out batteries as an expense of racing.

For a DIY, going with a battery that costs 1/3 and weighs much less but wears out 100x faster looks like the way to go.

So I think my plan is to use some A123 cells as the "capacitor",
and use another pack, probably thundersky, or even some lead,
for range.



major said:


> Hi nimb,
> 
> Each cell did have a small circuit board attached which would protect to some degree excess voltage due to imbalance. Not near as complex as a BMS.
> 
> ...


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## michaeljayclark (Apr 3, 2008)

The cost is an important factor however I am getting the 52 3000 FARAD maxwell ultracaps for 2060.00 shipping included. 

I can get more at a low cost as well.

as far as a semi BMS to handle the series string I am reading about using diodes simliar to zener diodes that are used sometimes in toyota prius add on battery packs. 

if one cap in the string fails it brings down the whole string and maybe destroy some caps. 

i see repeatedly that the use of caps in parallel with increase the lifespan of the batteries. Just how long is the debate. Id like to see if i can make a low cost lead pack last longer to the point it makes lead even cheaper than it is today for standard non lithium conversions


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