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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
 

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Discussion Starter · #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.
 

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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.
 

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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.
 

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Discussion Starter · #6 ·
I am using boostcap 3000 farad maxwell 2.7vdc.

the DC ESR for these caps is .23 m ohms.

ill have 52 in series.. would the .23 ESR for each cap simply be added? 11.96 m ohms?
 

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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
 

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Discussion Starter · #10 ·
considering that thundersky lipo is at about $1.25 an amp hour, a 160 amp hour cell would cost $200.

for a 144 volt pack would be 54 cells.

thats $10800.

52 capos cost me $2000.

I think its worth a try.
 

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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.
 

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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
 

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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
 

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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?
 

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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
 

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Discussion Starter · #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.
 

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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
 

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Discussion Starter · #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?
 

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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
 

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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.
 
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