DIY Electric Car Forums banner

the answer to if ultracaps really help or not

23K views 112 replies 21 participants last post by  major 
#1 ·
#2 ·
I like the part that says:

"[without capacitors] The resulting current surges in and out of the
battery tend to generate extensive heat inside the battery,
which leads to increased battery internal resistance – thus
lower efficiency and ultimately premature failure"

... and yet almost every EV that has ever pulled into my driveway had either no capacitor bank, or a very tiny one. Then they wonder why you have to change your pack every two years. Gee, maybe that's why?

- Paul
 
#4 · (Edited)
I like the part that says:

"[without capacitors] The resulting current surges in and out of the
battery tend to generate extensive heat inside the battery,
which leads to increased battery internal resistance – thus
lower efficiency and ultimately premature failure"

- Paul
I wonder how much of an effect this really has, by the way that reads it should be beneficial for FLA in the winter?

Also $20 a pop for a 2.5volt cap would mean for me at least about $700 in caps for a slight margin of safety above my max bat pack voltage, that seems, well rather high, if my battery life doubled, I could see it but it would take a while for that to be recovered.

And my pack isn't even a HV pack.
 
#3 ·
I liked the idea of using caps when i first heard it almost 2 years ago. back then ultracaps where hundreds of dollars.

goldmine electronics has 2600 farad 2.5 volt maxwell caps for 20 dollars each. they are the older white label but cheap enough to put a nice pack in your car to help save battery life.
 
#5 ·
Look at what these caps are being used for, filtering high speed ripple. That will only happen if the equivalent series resistance of the caps is very low. Most of the very high capacity caps have high equivalent series resistance. I would suggest looking toward capacitor used for for car stereo system. Not the overpriced offerings in the pretty packaging but the guts that makes up the inside of them.
 
#9 ·
Judging by the heading that paper is pre 2003 and most of the reference material is pre 1999, do you think it's relevant to present day battery technology? Maybe if the EV is using flooded cells but then the cost of ultra caps may be better spent off setting the cost of LiFeP04 batteries that can accept rapid charge and discharge. Will a paper dated more than 8 yrs ago help me make a valid decision regarding the use of ultracaps with lithium batteries? Not really.

T1 Terry
 
#11 ·
Hi,I am new here so be gentle.

It would seem any transient on an electronic device will have an effect. How much can be debated.

The continued heating and cooling of the metal in the batteries has got to have an effect. Even in the newer batteries.
I like the idea that the caps are not affected by temperature. It may be worth it if they allow your batteries to age longer and they allow you to have fewer batteries.
 
#12 ·
Hi Michael

144v x 160Ah TS = $10,800 energy = 23Kwhrs

52 off 3000F capacitors

at 144 v - energy = capacitance (3000/52) x 144v x 144v x 0.5 = 589,153 Joules
589,000 joules = 166whrs = 0.166Kwhrs

That is if you can use the power all the way down to zero volts - SAAAG!!!

If you use a second voltage booster you could use down to 100v

energy = 3000/52 x 144 x 44 x 0,5 /3600 = 50Whrs

23Kwhrs = $10,800 for TS = $469/Kwhr

50 whrs = $2,000 for caps = $40,000/Kwhr

Sounds a little more expensive to me!

Way back in 2003 the batteries available had much higher internal resistances most were only capable of a 0.5C discharge - a supercap pack stiffener was a good idea then

Now? No
An idea that is past its time
 
#13 ·
Hi Michael

144v x 160Ah TS = $10,800 energy = 23Kwhrs

52 off 3000F capacitors

at 144 v - energy = capacitance (3000/52) x 144v x 144v x 0.5 = 589,153 Joules
589,000 joules = 166whrs = 0.166Kwhrs

That is if you can use the power all the way down to zero volts - SAAAG!!!

If you use a second voltage booster you could use down to 100v

energy = 3000/52 x 144 x 44 x 0,5 /3600 = 50Whrs

23Kwhrs = $10,800 for TS = $469/Kwhr

50 whrs = $2,000 for caps = $40,000/Kwhr

Sounds a little more expensive to me!

Way back in 2003 the batteries available had much higher internal resistances most were only capable of a 0.5C discharge - a supercap pack stiffener was a good idea then

Now? No
An idea that is past its time
Thanks for that Duncan, saved me having to ask how to convert capacitance to ah. Stuff must be meg a cheap in the states, 3000f Maxwell caps to buy here AU$2,123 for 26 units. At 48v not quite 0.5ah. With a motor looking for 650amp peak that's not much of a buffer.
AU$2,160 will buy another 16 100ah Thundersky cells. Min 200ah rate at 3C max charge/discharge = 600amps, another 100ah at 3C gives me 900amps, sounds far more logical to me. Am I missing something?

T1 Terry
 
#14 ·
Hi Ti

AU$2,160 will buy another 16 100ah Thundersky cells. Min 200ah rate at 3C max charge/discharge = 600amps, another 100ah at 3C gives me 900amps, sounds far more logical to me. Am I missing something?

I must be getting old - did not understand - can you explain a bit further what you are planning?
 
#15 ·
Hi Ti

AU$2,160 will buy another 16 100ah Thundersky cells. Min 200ah rate at 3C max charge/discharge = 600amps, another 100ah at 3C gives me 900amps, sounds far more logical to me. Am I missing something?

I must be getting old - did not understand - can you explain a bit further what you are planning?
The motor I'm looking at using at the moment is the 48v Green Motorsport that is matched to a 650amp controller. I plan to use this as a hybrid drive for my motorhome conversion so it's other function is regen braking, with the bus weighing around the 10 tonne mark there will be lots of regen. If the ultra caps could soften the impact the Thundersky batteries would cop from that amount of regen then they would be a viable proposition but simply adding an additional 100ah to the battery bank for around the same cost it looks to me to a better way to spend the money. If the ultracaps could absorb the regen load and release it slowly into the batteries I would get a better cycle life but they don't have the capacity to absorb more than a few seconds from what I can see. I may have got that all wrong, I'm very green at this stuff.

T1 Terry
 
#16 ·
http://web.mit.edu/first/kart/everpres.pdf

this is a study by MIT in 2009. yes its a go-cart but Im sure the parts could be sized up because a dc to dc converter between the batteries and the motor controller would need to be 144 volt and 600 amps in the case with an ev.

regen recapture by ultracaps is very acceptible and makes sense. when regen happens trying to put back into the batteries is fighting internal resistance of the batteries.

putting that regen power into ultracaps would be much more efficient.

lets remove the cost factor from this discussion. yes, ultracaps are expensive but the price is dropping. the case for showing a quick ROI would be a huge debate and thats not my intention. I am just trying to see how this would all work. the AFS trinity implements such a system.

http://afstrinity.com/

they were issued a patent for their system using ultracapacitors to recapture regen in an AC system.

regen is possible in a dc system buy placing a generator next to the motor with a clutch system where when the brakes are applied the clutch engages and regen is happening and the vehicle slows.

yes these ideas have a pricetag but lets discuss it without dollars involved.
 
#17 ·
If $$ aren't in the equation then replacing the batteries with ultra caps would be the way to go, a million plus cycles with no BMS issues and unlimited charging speed.
In reality $$ need to be in the equation, not many could afford an ultracap only power pack and I thought the whole thread was about the prospect of using ultracaps to extend battery cell life and save frequent replacement $$.

T1 Terry
 
#18 ·
this thread is meant to discuss how ultracapacitors can extend the life of batteries.

the afs trinity testing showed:

AFS Trinity claims a 150,000-mile useful life for its battery/ultracap system. What is this based on? The claimed 150,000 miles useful life is based on ten months of extensive and continuous physical testing by America's leading independent battery testing laboratory, Mobile Power Solutions of Beaverton, Oregon. This laboratory subjected AFS Trinity's dual energy storage system of lithium ion batteries and ultracapacitors to a demanding duty cycle simulating an urban/highway driving cycle with strong and frequent high current demands. Such a driving cycle was meant to subject the batteries to the kind of strong and frequent loads that the energy storage system would be subjected to by an aggressive driver— think New York or Paris cabby or your teenager. The AFS Trinity system delivered more than 3,800 duty cycles before the batteries reached end-of-life. Each cycle represents a full charge and discharge. Assuming that each charge can deliver sufficient power to propel a vehicle for 40 miles, this represents 152,000 miles, which we rounded down to 150,000.


I can compare the costs to how much it even costs to build an EV. Batteries are very expensive and will fall in price but in the meantime EVers still buy them even with the cost being so high. The production EVs are expensive, yet people still buy them. The ROI is WAY out for an EV right now. So the cost is a factor however under an early adopter label, the cost is high and ROI is low until the cost is low and the ROI high.

so, back to the discussion..........

as far as a balancing system there is already an active balancing system sold by maxwell for their caps. the kit costs 95 dollars for 5 circuit boards. 89 if you buy more than 5 kits.

I found an article laying out the diagram of this active balancing system.

http://electronicdesign.com/article...racapacitor-strings-from-overvoltage-yet.aspx

I am wondering if I can have them made cheaper than buying them from maxwell distributors.

and.. can this active balancing circuit designed for 2.7 vdc be used for lipo 2.7 vdc cells?
 
#19 ·
Hi Ti

If you set up a voltage booster system so that you could get all of the power out of the ultracaps

589,000 joules at 144v and 650 amps is 6 seconds - not a lot!

2 x 100ah TS can be charged at 3C so 600amps - I don't think your controller can actually pump as much as 600 amps so you should be sweet

Hi Michael
Modern batteries have much lower internal resistances - as long as you are not exceeding their limits I don't see any way that the ultracaps can increase battery life
 
#20 ·
I don't see a control here -- how would those same cells have done without the capacitor bank?

Several types of Lithium-chemistry cells, including most LiFePO cell structures, have significant charge storage (as opposed to only chemical potential energy as in lead-acid cells). Effectively they are already a combination of chemical battery and capacitor.
 
#21 ·
battery lifetimes are dramatically shortened when they are discharged at high rates. even the "continous" rating reduces their life, most cells specify their cycle lifetime at 1C rates.
But if you have a large enough pack, you can discharge at low rates and still have pretty high power. So the key is having a large battery pack.
For 650amps, at 1C you need 650Ah battery, at 3C 216 AH.
That is a very large pack. The larger the pack, the heavier the vehicle, and thus more power needed to get to 60mph.

Most just live with a slow EV and/or are killing their batteries.

I don't see a control here -- how would those same cells have done without the capacitor bank?

Several types of Lithium-chemistry cells, including most LiFePO cell structures, have significant charge storage (as opposed to only chemical potential energy as in lead-acid cells). Effectively they are already a combination of chemical battery and capacitor.
 
#22 ·
The cycle life for CALB and Thundersky batteries of 3,000 to 5,000 cycle @ 70% DoD is at the nominated 0.3C charge/discharge rate, it says this quite clearly in the specs, how many people don't want to read that bit :lol: I have put the question to each of the battery companies (there is a lot of them producing LiFeP04 batteries now) asking what the cycle life is at the max rated discharge. Either I receive no reply or some obscure specs from a completely different type and capacity battery that doesn't answer the question at all. They try the "no understand question" tactic rather than giving an honest answer.
Ultracaps could extend the cycle life but the number required relates to the max charge or discharge rate the motor will produce. At the max rated 650amps @ 48v in the case of my chosen motor would be a lot of caps, simply financially a non viable proposition. With a small light vehicle where minimal room for batteries is available and weight is everything but $$ are secondary then some gain could be achieved but I can't see it being enough to warrant the cost. A better deal $$ wise would be to sell the tired batteries at a reduced cost to someone looking for electrical energy storage generated via solar or wind or even using them yourself to make a solar home charging pack and using that value to offset the price of a new battery pack. With the cost of electricity continually rising and the cost of lithium batteries continually falling the self storage system makes a lot of sense and would save more $$ than cents

T1 Terry
 
#23 ·
Thundersky only show .3C ? Scary how long they will last at 3C,
Someone needs to just simply test them and publish the results,
I'm probably going to build such a tester to truly find out.
For a 40AH, 24 cycles a day is 750 cycles a month, so it would take 3-6 months to truly find out, but I'd bet after 1 month you'd see some results.
I'd rather find out with one cell that a whole pack of them.

The caps don't have to supply all the current, if they can just reduce it by half during acceleration when the batteries are taxed, then it might double the life of the batteries, and for a $10k or $15k pack, that is a lot of cost savings. I'm more interested in building a really fast car using caps.

The cycle life for CALB and Thundersky batteries of 3,000 to 5,000 cycle @ 70% DoD is at the nominated 0.3C charge/discharge rate, it says this quite clearly in the specs, how many people don't want to read that bit :lol: I have put the question to each of the battery companies (there is a lot of them producing LiFeP04 batteries now) asking what the cycle life is at the max rated discharge. Either I receive no reply or some obscure specs from a completely different type and capacity battery that doesn't answer the question at all. They try the "no understand question" tactic rather than giving an honest answer.
Ultracaps could extend the cycle life but the number required relates to the max charge or discharge rate the motor will produce. At the max rated 650amps @ 48v in the case of my chosen motor would be a lot of caps, simply financially a non viable proposition. With a small light vehicle where minimal room for batteries is available and weight is everything but $$ are secondary then some gain could be achieved but I can't see it being enough to warrant the cost. A better deal $$ wise would be to sell the tired batteries at a reduced cost to someone looking for electrical energy storage generated via solar or wind or even using them yourself to make a solar home charging pack and using that value to offset the price of a new battery pack. With the cost of electricity continually rising and the cost of lithium batteries continually falling the self storage system makes a lot of sense and would save more $$ than cents

T1 Terry
 
#24 ·
Hi Nimble

battery lifetimes are dramatically shortened when they are discharged at high rates. even the "continous" rating reduces their life, most cells specify their cycle lifetime at 1C rates.



Not what the Carnegie guy said in his lecture - he talked about the amount (amp-hours) of charge and discharge and the temperature

As long as you keep within limits with cool cells - no big deal!

If you go over the limits and heat the cells -----
 
#26 ·
well that is just it, isn't it, at 3C, the batteries generate heat.
How much does 3C reduce life? I don't know, but if they won't tell you, the results can't be good.

Hi Nimble

battery lifetimes are dramatically shortened when they are discharged at high rates. even the "continous" rating reduces their life, most cells specify their cycle lifetime at 1C rates.



Not what the Carnegie guy said in his lecture - he talked about the amount (amp-hours) of charge and discharge and the temperature

As long as you keep within limits with cool cells - no big deal!

If you go over the limits and heat the cells -----
 
#25 ·
I'm more interested in building a really fast car using caps.
Would ultracaps or headway cells be a better deal? Headways are cheap and rated at 10C. very high maintenance regularly checking for dead cells or high techo gadget dependant for cell checking but $$ wise? What a bout a bank of Headway cells buffering the main TS or CALB cells in place of the ultracaps?

T1 Terry
 
#27 ·
Hi Nimble

Range from lecture was 0.5 - 5 milliOhms

The only data I can find for TS says 1milliOhms internal resistance at 5C
(TS 60Ah sag to 2.9v at 5C)

The resistance will be less at lower C ratings

so a 100Ah cell at 3C , 300A is 0.3v and 90 watts - so for a 45 cell pack you need to dissipate 4Kw and keep your temperatures below 60C
Does not sound too difficult to me - probably get more cooling that that simply by having the cells on the chassis of your car
 
#28 ·
http://batteryuniversity.com/learn/article/modern_lead_battery_systems
according to this site

EEStor

This is the mystery battery/ultracapacitor that receives much media attention. The battery is based on modified barium titanate ceramic powder. EEStor claims that the battery has a specific energy of up to 280Wh/kg. The company is very secretive about their invention and only limited information is available. Financial Post, 26 June 2008 compares EEStor with specifications of NiMH and customary lead acid systems.
There are other batteries listed. which also use ultracapcitors. so it seems they do help but the battery manufacturers are starting to put them in their batteries
 
#29 ·
http://batteryuniversity.com/learn/article/modern_lead_battery_systems
according to this site

There are other batteries listed. which also use ultracapcitors. so it seems they do help but the battery manufacturers are starting to put them in their batteries
That seems to be a lot of capacity, which makes a lot of people think that this may be a battery/capacitor hybrid, not just a supercap. Has anybody seen any proof that this is strictly a capacitor???

- Paul
 
#30 ·
http://www.tecategroup.com/white_papers/200904_WhitePaper_EngineColdStarting.pdf

Here are some white papers on the subject. Seems in cold starting they can cut the total batteries in half in an ICE required for cold weather starting.

from another white paper
http://www.tecategroup.com/white_papers/200904_WhitePaper_AutomotiveElectronics_ASchneuwly.pdf
Ultracapacitors are best suited to perform in those applications that require short bursts of power, interspersed with longer durations of low power requirements. Engineers continue to learn how to design systems that use two different components to achieve an optimal solution for both power and energy. One model is that of a cache of power; the ultracapacitor is sized for maximum peak power, while the primary energy storage is a large device sized for maximum continuous power (Figure 2). The primary energy storage can be a fuel engine, high-energy batteries, or a fuel cell. System designers size the ultracapacitor for the difference between maximum continuous and maximum peak power, to take full advantage of both components.
 
#31 ·
speaking with the DEKA rep for the southeast he indicated that DEKA is designing a battery that has capacitors built into them... so the idea of how caps help bats I think is a yes.

the car stereo world is going to them... diesel truck battery companies are doing it. Ive seen a car stereo bat that was half caps and half bat.. a hybrid battery!

I have all 52 of my ultracaps in and I cannot wait to try them. As far as power only for 6 seconds? that is enough to get my jimmy up to 50 mph from a dead stop.

now I havent seen anyone talk about the peukert effect. regardless of what the china battery companies say they cannot beat the PE. The higher the C rate of discharge the lower the amp hours in the battery goes. discharge a lipo 160ah cell at the highest rated discharge C and you take away amp hours from the cell prematurely.

I will be happy to be the guinea pig here and put the system together and publish the results from real world testing. The test bed will be driving on US 19 between hudson, florida and st petersburg, fl. cant get any more real world than that. lots of stop and go track mixed in with a few miles of 55 mph semi-highway.

afterall, I am the one who stated this thread ;)
 
#32 ·
Michael

As far as power only for 6 seconds? that is enough to get my jimmy up to 50 mph from a dead stop.

That was assuming that you could get all of the power from the ultracaps - if you are just using them to stiffen your pack you will get about5/144 of that

0.2 seconds worth of power!
Still worth $2,000? - you must be a lot richer than I am!
 
#33 ·
Don't you hate it when half the post vanishes into the ether I'll try again.
Looking forward to the results. Not sure just how much regen you can expect from a Jimny, not much weight to keep the wheels turning. The Peukert’s factor with lithium batteries is only around 5% @ 3C going by the TS charts (if you can believe them) so if you plan to get a decent life out of the battery pack it wouldn't be pulled much below 80% DoD anyway so it doesn't seem to be a factor to me. In my case the discharge loads will be big and long as will the regen so to make any sort of an impact I think I'd need a lot of ultracaps, not $$ viable as I see it.

T1 Terry
 
#34 ·
well, the whole idea of electric cars was too much money to begin with, yet we are here.

the volt was too expensive, yet they are selling..

the leaf is too expensive, yet there is a LLOONNGG list to get one.

overall ownership of an electric car is 3 cents per mile, a gas car is 25 cents just for gas then goes up from there...

yet people tell me $10,000 to build an EV is wwwaayyy too much...


I think $2000 for a cap back to make a smaller pack of batteries go further and last longer is worth it..

look at the long run here. not just the first initial cost.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top