[nimblemotors]

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.

Originally Posted by DJBecker

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.

[T1 Terry]

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

[nimblemotors]

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.

Originally Posted by T1 Terry

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

[Duncan]

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 -----

[T1 Terry]

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

[nimblemotors]

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.

Originally Posted by Duncan

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 -----

[Duncan]

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

[idarusskie]

http://batteryuniversity.com/learn/a...attery_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

[PZigouras]

Originally Posted by idarusskie

http://batteryuniversity.com/learn/a...attery_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

[idarusskie]

http://www.tecategroup.com/white_pap...ldStarting.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_pap...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.