# LiFePo4 Continuous Current



## dimitri (May 16, 2008)

octagondd said:


> Has anyone been drawing 1.5C to 2C continuously(more than 5 minutes) on a consistent basis(daily) with the TS LiFePo4 batts? I am curious if there is any hard data on how it affects the number of charge cycles.
> 
> Thanks,
> Dave


Many people draw 1.5C - 2C for several minutes at a time, myself included, but we don't know how it effects lifecycle since we haven't had our cells long enough to find out.


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## octagondd (Jan 27, 2010)

Thanks Dimitri. I emailed Thundersky but they just sent the same data sheet that is on their website which only shows cycle life at 0.5C. I replied to them to try to clarify what I was asking, so we'll see what the response is. It's tough to put down $5-$10K on a pack and not know how long it will last because the only data out is at 0.5C. If I were to get a pack matching that spec, my humble little freeway speed CRX would have a $17000 battery pack of (47) 300AH batteries. Yikes! 

I guess there is some risk involved with trying new product. btw, what kind of C rating can you continuously pull from most lead acids?


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## FalconEV (Aug 21, 2007)

Generally speaking, it takes a greater # of low discharge rated cells to equal the discharge rate of higher quality / rated cell to avoid voltage sag under load.
So, you have to buy more cells to get the performance your after.
more weight, less space...
stressing the cells to their limit and creating heat leads to a shorter cycle life.
right ?
But then, TS cells are cheap, cheap , cheap..
and thats the only thing that matters.


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## dtbaker (Jan 5, 2008)

octagondd said:


> btw, what kind of C rating can you continuously pull from most lead acids?


even the various forms of lead-acid vary in what they can delivery and how much they sag.  My floodies for instance have a 20hr rating of 185ah or so, but only about 100ah at a 1 hr discharge rate. This type of FLA has been used for years in Evs at typical draw rates of 1.5-2C (150-200amps) without hurting their expected 500-700 cycle life. What kills'em though is repeat use more than 70% DOD.... similar to curves you'll see for Li; big difference in cycles with 60% DOD, 70% DOD, 80%DOD 

But with Li the cycle life is all conjecture anyway since none of them have been in use 3000 cycles yet in EV use.


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## favguy (May 2, 2008)

Falcon EV,

TS cells may seem "cheap" to you, but to most DIY'ers they are still very expensive. Even using the "cheap" TS/SE cells to build a half decent range car (using a low cost and older donor) brings the total conversion cost to more than what we here in the UK can buy a brand new Diesel supermini style car for and get 70mpg from. Needless to say, an EV built on a new car platform comes in at twice the cost, any savings in fuel cost will never be recouped over the life of the vehicle (even assuming most owners would want to keep the same car for 10 years or so, which is almost unheard of here!!)

This means for the general public, an EV will never be cost effective compared to an economical ICE car, until battery prices drop much further. 

Allowing for this, there are, surprisingly, still a few of us who will build an EV for other than cost reasons. So I for one say thank goodness for "cheap" TS/SE cells.

If all we had was your superior product, there would be virtually no DIY builds at all, other than by a few more wealthy individuals or those prepared to use very range limiting lead acid!

I suspect in fact, if truth be told, you are just a little worried that the latest TS/SE cells are not quite as naff as you would have us all think, and if time proves this... well your market may be threatened a little by this perhaps? 

Paul


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## octagondd (Jan 27, 2010)

FalconEV said:


> Generally speaking, it takes a greater # of low discharge rated cells to equal the discharge rate of higher quality / rated cell to avoid voltage sag under load.
> So, you have to buy more cells to get the performance your after.
> more weight, less space...
> *stressing the cells to their limit and creating heat leads to a shorter cycle life.*
> ...


By how much? That is what I want to know. The TS graph shows that if I discharge at 2C I will get less DOD, so instead of 90AH from a 90AH battery I will only get like 81. But what it doesn't show is how it affects cycle life. I just want some data, either from TS, independent testers, or real world EVers to know what kind affect discharging at 2C will have. 

Most people I have read about recommend discharging at 1C, but the TS spec sheet shows 3000 cycles with 80%DOD at only 0.5C, so is there anyone who has been running at approx. 1C that have any significant amount of cycles on their batteries yet? Has there been any performance degradation? Anyone running at a higher C rating with some decent cycles on their setup?


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## Sunking (Aug 10, 2009)

dtbaker said:


> What kills'em though is repeat use more than 70% DOD.... similar to curves you'll see for Li; big difference in cycles with 60% DOD, 70% DOD, 80%DOD


Well DOD is quite important when we talk about FLA batteries. Here is the published stats from one of the better Deep Cycle battery manufactures Surrette.

5000 cycles @ 10% DOD
3300 cycles @ 30% DOD
2500 cycles @ 50% DOD
750 cycles @ 60% DOD

In Renewable Energy applications involving stand alone battery systems the lowest we shoot for is no more than 20% DOD in any given 24 hour time period, and prefer 10% for longevity because if you go beyond 20% DOD per day, the cycle life falls sharply, and past 50% it falls off the cliff. So good battery like a Surrette can last up to 13 years @ 10% DOD, or 7 years at 50% DOD. Sweat spot economically is 10 years @ 20% DOD.


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## yarross (Jan 7, 2009)

Sunking said:


> 5000 cycles @ 10% DOD
> 3300 cycles @ 30% DOD
> 2500 cycles @ 50% DOD
> 750 cycles @ 60% DOD


Quite interesting to compare total charge flown through the battery for those cases:
500C
990C
1250C
450C
Looks like adding more batts to go below 50%DoD is counterproductive when considering total battery cost in vehicle lifetime.


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## dtbaker (Jan 5, 2008)

yarross said:


> Quite interesting to compare total charge flown through the battery for those cases:
> 500C
> 990C
> 1250C
> ...


thats the diff between EV and PV..... especially when with EV we have limited space and weight to work with. also the big seller for Li when you can get the same 2000-3000 cycle life at 70% DOD that you got with lead at 20% and many times the space and mass....


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## Sunking (Aug 10, 2009)

dtbaker said:


> thats the diff between EV and PV..... especially when with EV we have limited space and weight to work with. also the big seller for Li when you can get the same 2000-3000 cycle life at 70% DOD that you got with lead at 20% and many times the space and mass....


Well that was kind of my point. It is counter productive to use FLA batteries in an EV. 

With an energy density of 40 to 50 wh/kg and can only use up to 50% of the stored capacity sacrificing a few years of life doing so is insane economically and technically.

I think eventually Lithium Ion technology wil fill the bill. But from the numbers I have ran Li is only half way there as it will take at least 300 to 400 wh/kg, a minimum 5C discharge, and 10 C charge rate, 10,000 charge cycles to 80% capacity, at a price point of $150 per Kwh storage to become appealing to the mass public.


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## dtbaker (Jan 5, 2008)

well.... I still think that FLA serves a purpose in cases where the lowest possible entry cost is the hurdle, and a 30 to 40 mile range is adequate. For the 'Masses', the technical and/or absolute financial justifications are sometimes not as important as the monthly payment....

Even FLA is now comparable $/mile with gasoline as close as I can figure it in terms of operational cost including electricity and amortized replacement of batteries versus gas, oil and ICE maintenance... and the current LIFEPO4 is even better over its (projected) life per cycle. so, I'd say it makes sense NOW, for people that can live with the range and we work to develop solar/hydro/wind power to provide the extra energy.


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## tomofreno (Mar 3, 2009)

> but the TS spec sheet shows 3000 cycles with 80%DOD at only 0.5C


 The spec sheet for my SE cells states that standard charge and discharge current is 0.3C. They don't specifically say what current the cycle life is based on, but it seems reasonable to assume the standard current, 0.3C.


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## favguy (May 2, 2008)

Tomofreno,
You can bet the quoted cycle life is based on the .5C or .3C figure, if it was based on 1C, they'd be shouting it from the rooftops!

We won't know what the real expected cycle life is for a year or two yet, until the early users have put some mileage on them, although I very much hope they can run to thousands of cycles at a 1C or higher average current pull, I expect they'll probably not get anywhere near the 3000 to 5000 cycles bieng bandied about. Still, if they can last 8 years and do over 1000 cycles, they'll be more cost effective than lead, plus half the weight and knocking on twice the range for a given Ah. 

Paul


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## tomofreno (Mar 3, 2009)

> Still, if they can last 8 years and do over 1000 cycles


 Huh? If you charge roughly 300 times per year 1000 cycles is about 3 1/3 years.


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## JRP3 (Mar 7, 2008)

But if you charge every other day....


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## Sunking (Aug 10, 2009)

dtbaker said:


> well.... I still think that FLA serves a purpose in cases where the lowest possible entry cost is the hurdle, and a 30 to 40 mile range is adequate.


I understand your point, and will not disagree with you from the POV of a hobby or DIY.

However from a commercial POV all market studies indicate the public is going to demand a 200 to 300 mile range, a recharge time of a few minutes like 10 to 15 minutes, have all the same bells and whistles as ICE, at a competitive price. For me personally I am not going to buy a EV with a limited range of 40 to 60 miles, and be forced to buy another ICE vehicle for longer trips. The 200 to 300 mile range is about the sweatspot as that is about as far as one can sit and drive in a vehicle before needing a pit stop and recharge. Maybe that is just me, but market studies seem to draw the same conclusion. 

There are two things preventing that right now, the battery tech and the infrastructure. I am however confident the battery technology will be here in within 5 years, and once that is in place the infrastructure will soon follow at an accelerated pace.


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## JRP3 (Mar 7, 2008)

Sunking said:


> However from a commercial POV all market studies indicate the public is going to demand a 200 to 300 mile range, a recharge time of a few minutes like 10 to 15 minutes, have all the same bells and whistles as ICE, at a competitive price...
> There are two things preventing that right now, the battery tech and the infrastructure. I am however confident the battery technology will be here in within 5 years, and once that is in place the infrastructure will soon follow at an accelerated pace.


I disagree slightly. The only thing preventing 200-300 mile range right now is cost, not technology. Same thing with fast charging, the technology exists and is proven. Once battery costs come down so that 200-300 mile range is affordable two things will happen:
1. Fast charge stations will start popping up at businesses looking to attract customers
2. People will realize that leaving your house every day with a "full tank" at a low price means they really don't need or want more expensive fast charging 99% of the time.


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## dtbaker (Jan 5, 2008)

...and more people will realize that their in-town car really doesn't NEED to go 200-300 miles. Perhaps its more cost effective to rent a long distance vehicle for vacations just when needed?! Its a perception thing as we make the shift in the way we travel, take vacations, live far from work, etc.... not overnight.


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## Sunking (Aug 10, 2009)

JRP3 said:


> I disagree slightly. The only thing preventing 200-300 mile range right now is cost, not technology. Same thing with fast charging, the technology exists and is proven. Once battery costs come down so that 200-300 mile range is affordable two things will happen:


Well I understand, and the technology almost exist IMO as the Tesla proves that but the Tesla is a small two passenger coupe. I am thinking something more practical and marketable like the size of a Toyota Camry or a Honda Accord size vehicle. As for Tesla they get the range but everything I have read reported the batteries cycle life falls way short of their claims. You will need a truly 10,000 cycle 10 year battery that cost around $100 per Kwh with a density of around 400 wh/kg to pull it off. Those do not exist yet. I do think they are not to far off in the future if not already in the proto type stage.

I mean how many cars could you sell if you could guarantee 250 mile range with all the bells and whistles, 3 to 5 cents per mile fuel cost depending on your electric rates, 10 year battery, almost no maintenance cost except tires and windshield wiper blades, great acceleration and performance, family sized, and priced about the same as an ICE vehicle. I don't know about you but I think you would have one hot potato that you could not keep in stock. I could be wrong, but I don't think so.


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## Ioku (Sep 27, 2007)

dtbaker said:


> ...and more people will realize that their in-town car really doesn't NEED to go 200-300 miles. Perhaps its more cost effective to rent a long distance vehicle for vacations just when needed?! Its a perception thing as we make the shift in the way we travel, take vacations, live far from work, etc.... not overnight.


The thing is nobody cares that they only need a car that has a range of 50 miles for 99% of there driving they they still wont want it. The reason people love cars is because a car gives you freedom people like the idea that at any time they want you car jump in you car fill up at a fuel station and in 10 mins be able drive 300 to 500 miles with out stopping, even if that may only do this once in 5 years they still don't want to give it up because to do so means giving up that freedom. And unless people are forced to do so by a fuel prices becoming too high nothing will change, its the same as buying a big truck or suv to tow the boat you use once or twice a year and now get only 15mpg all the time, it doesn't matter how little sense it makes people will keep on doing it unless forced to change. 
And I include my self in all this its only about a 15 mile round trip for me to get to school or work but I'm not giving up the ability to drive 300 miles on a whim if I want to. So thats why when I convert my car I'll be adding a on board gas generator.


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## octagondd (Jan 27, 2010)

Let me steer the Tesla off the race circuit and back into the school zone for a minute.

I just saw a graph of a test at different C ratings that I thought was interesting. It doesn't say anything about cycle life, but does show some differences between SE and TS batts. Granted it was only a 1 unit test and probably not all that scientific, but interesting to look at none the less. Maybe you all have seen this one already.

If you were trying not to break the bank and needed 150amps continuous, but would only use 50%DOD, would you get the TS 90AH that claim longer cycle life but lower C rating or the SE 100AH that have a higher C rating but shorter cycle life? My guess is most will answer neither, but I would like you to pick one for the sake of the argument.


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## dimitri (May 16, 2008)

octagondd said:


> If you were trying not to break the bank and needed 150amps continuous, but would only use 50%DOD, would you get the TS 90AH that claim longer cycle life but lower C rating or the SE 100AH that have a higher C rating but shorter cycle life? My guess is most will answer neither, but I would like you to pick one for the sake of the argument.


You are making a big assumption that stated cycle life on TS sheet is true 

As those tests are proving, SE is superior quality and I believe their published cycle life to be closer to the truth than baloney published by TS.

After paying arm and a leg for TS cells a year ago and using them every day since then, I would always pick SE cells given a choice between the two.

I hope to get some test results from new Hipower 200AH cells soon, they make fantastic claims, I hope they aren't too far from the truth. I should be getting my 4 cells in a couple of weeks.


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## JRP3 (Mar 7, 2008)

Ioku said:


> The thing is nobody cares that they only need a car that has a range of 50 miles for 99% of there driving they they still wont want it. The reason people love cars is because a car gives you freedom people like the idea that at any time they want you car jump in you car fill up at a fuel station and in 10 mins be able drive 300 to 500 miles with out stopping, even if that may only do this once in 5 years they still don't want to give it up because to do so means giving up that freedom. And unless people are forced to do so by a fuel prices becoming too high nothing will change, its the same as buying a big truck or suv to tow the boat you use once or twice a year and now get only 15mpg all the time, it doesn't matter how little sense it makes people will keep on doing it unless forced to change.
> And I include my self in all this its only about a 15 mile round trip for me to get to school or work but I'm not giving up the ability to drive 300 miles on a whim if I want to. So thats why when I convert my car I'll be adding a on board gas generator.


The problem is this attitude has grown out of a world with cheap energy for transport, (oil). Very likely that era is over, coupled with a sinking economy people's expectations will have to change. I think there is going to be a time lag before people can afford long range EV's, for various reasons, and if oil prices climb once again, which seems likely, they'll have to change expectations. Hybrids, ICE rentals, tow behind gen set rentals, and just accepting the fact that they don't really need to travel hundreds of miles on a whim, are all different ways of dealing with range anxiety.
A reliable low maintenance EV that gets you to and from work cheaply becomes very attractive even if it only has 100 miles of range when your expectations are more realistic. A lot of people realize this and if the price were right would jump on board.


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## JRP3 (Mar 7, 2008)

Sunking said:


> Well I understand, and the technology almost exist IMO as the Tesla proves that but the Tesla is a small two passenger coupe. I am thinking something more practical and marketable like the size of a Toyota Camry or a Honda Accord size vehicle. As for Tesla they get the range but everything I have read reported the batteries cycle life falls way short of their claims. You will need a truly 10,000 cycle 10 year battery that cost around $100 per Kwh with a density of around 400 wh/kg to pull it off. Those do not exist yet. I do think they are not to far off in the future if not already in the proto type stage.


The Tesla isn't the most efficient platform for range. You could build a more aerodynamic shape, carrying more batteries underneath the vehicle, (skateboard concept), and use longer cycle life cells such as A123, which could easily hit 300 miles range. That was done 10 or so years ago with NiMH cells in a Solectria.



> I mean how many cars could you sell if you could guarantee 250 mile range with all the bells and whistles, 3 to 5 cents per mile fuel cost depending on your electric rates, 10 year battery, almost no maintenance cost except tires and windshield wiper blades, great acceleration and performance, family sized, and priced about the same as an ICE vehicle. I don't know about you but I think you would have one hot potato that you could not keep in stock. I could be wrong, but I don't think so.


I think you're right, but it all comes down to price, not technology. The technology exists, you can buy it, it just costs too much, for now. Remember, a car with a 250 mile range means the pack will be shallow cycled most of the time, which means the pack should last a very long time. A123 cells shallow cycled have show over 100K cycles.


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## Sunking (Aug 10, 2009)

JRP3 said:


> The Tesla isn't the most efficient platform for range.


Not sure I can agree with you there as their efficiency is around 130 wh/mile. Benchmark is 400 wh/mile. I mean heck my golf cart does not get 130 wh / mile


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## Sunking (Aug 10, 2009)

JRP3 said:


> I think you're right, but it all comes down to price, not technology.


IMO price is a technology issue. FLA is about $100 per Kwh, LI is around $400 and up. Get the density up to 300 or 400 wh/kg and price down to $100 per Kwh and you have a monster of an industry. I se it just like a VCR, PC, DVD Player, etc.. We just are not their yet.


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## favguy (May 2, 2008)

Sunking,

The eventual mass take up of EV's (if it ever happens!) will most likely not offer lower cost motoring (even when the initial car purchase cost becomes comparable to current gas cars) based on the low cost of electricity, at least not here in the UK unfortunately.

At present, running an EV from the fuel cost point of view can be much cheaper than gas, especially as our fuel is around $8 for a US sized gallon.

However, the majority of that cost is tax, the UK government is pulling untold billions in revenue from gas sales to spend/waste on services and bank bailouts etc... In the event of mass EV take up, they will certainly tax electricity used from a charge station heavily to replace the lost gas revenues. Further to this, they are unlikely to want cheap overnight recharging at home on mass without tax due,therefore it follows, at least where possible in the control computers that will inevitably be in future mass production EV's, that they will insist on some sort of tamperproof system that differentiates home charging from station charging, and can bill you for the additional tax due. That, or the car will only be chargeable via a meter you'd have to fit at home or some such, probably utilising the same technology used in immobilisers presently.

Maybe I'm cynical, in fact certainly I am, but well get screwed financially, you can bet on it! 

Paul


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## JRP3 (Mar 7, 2008)

Sunking said:


> Not sure I can agree with you there as their efficiency is around 130 wh/mile. Benchmark is 400 wh/mile. I mean heck my golf cart does not get 130 wh / mile


At 130 wh/mi and Tesla's 53kwh pack, times 90%, would give 360 miles of range. You can build a much more aerodynamic vehicle than a Tesla. What benchmark is 400 wh/mile? I consider that pretty bad actually. I do most of my calculations with 300 wh/mile and hope for better.


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## JRP3 (Mar 7, 2008)

Sunking said:


> IMO price is a technology issue. FLA is about $100 per Kwh, LI is around $400 and up. Get the density up to 300 or 400 wh/kg and price down to $100 per Kwh and you have a monster of an industry. I se it just like a VCR, PC, DVD Player, etc.. We just are not their yet.


I see it more of a production volume issue. VCR, PC, DVD didn't get cheap until production volume increased enough. The first expensive VCR wasn't that technologically different from the last cheap one. Sure technological advancements will help, but if the best batteries we have right now were truly mass produced, along with motors and controllers, economies of scale would give us all affordable 200+ mile range EVs. I consider an affordable EV to be around $30K because of the cheaper operating costs.


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## BMI/LiFeTech (Aug 12, 2009)

favguy said:


> Sunking,
> 
> The eventual mass take up of EV's (if it ever happens!) will most likely not offer lower cost motoring (even when the initial car purchase cost becomes comparable to current gas cars) based on the low cost of electricity, at least not here in the UK unfortunately.
> 
> ...


You only get screwed if you let the government screw you. If you install solar panels and/or a wind generator so you become self sufficient with power you can tell the government to go to hell with their wasting of taxes! It is all about becoming independent of government controls (taxes).


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## JRP3 (Mar 7, 2008)

JRP3 said:


> At 130 wh/mi and Tesla's 53kwh pack, times 90%, would give 360 miles of range. You can build a much more aerodynamic vehicle than a Tesla. What benchmark is 400 wh/mile? I consider that pretty bad actually. I do most of my calculations with 300 wh/mile and hope for better.


Here's a not particularly aerodynamic vehicle that beat the Tesla 311 range record with a 345 mile run at around 190 wh/mile:
http://green.autoblog.com/2009/11/1...s-tesla-range-record-with-tokyo-to-osaka-run/
Look what was done 15 years ago, no reason this couldn't be done better with lithium right now:
http://www.megawattmotorworks.com/display.asp?dismode=article&artid=305


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## favguy (May 2, 2008)

I agree, but only if you can access whatever source of electricity and not have to account for its use to the government...if the car will only recognise an authorized source, or report other sources to said government, they'll want their tax per Kwh!!

An example here in the UK is Diesel, you can buy and run a lot of cars on heating oil (a form of diesel) that is much lower in cost due to lower taxes, if they catch you using it without paying them the difference in tax, they destroy your vehicle and fine you a hefty lump on top!

The mass market will get EV's when the powers that be want them to, and not before, when that happens, they'll make us pay as much as we did for gas. So enjoy your DIY EV's whilst we're still a small minority. 

What will be interesting to see will be what bullcrap they use as an exuse for heavy tax, presently, it's for our own good to make us drive less and emit less Co2, no doubt they'll think up some crap about power station emmissions to justify the green stick to hit us with when we have EV's.

Oh dear, I'm a bit soapboxy today... 

PS, In this shitty little country of ours, most people live in crappy little over priced terrace housing, there will be no option for most to fit solar, or have wind generators, to buy a place where you could utilise these would cost far more than 90% plus of the population could ever afford.


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## JRP3 (Mar 7, 2008)

favguy said:


> PS, In this shitty little country of ours, most people live in crappy little over priced terrace housing, there will be no option for most to fit solar, or have wind generators, to buy a place where you could utilise these would cost far more than 90% plus of the population could ever afford.


You paint such a pretty picture, can't wait to visit


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## Sunking (Aug 10, 2009)

JRP3 said:


> At 130 wh/mi and Tesla's 53kwh pack, times 90%, would give 360 miles of range. You can build a much more aerodynamic vehicle than a Tesla. What benchmark is 400 wh/mile? I consider that pretty bad actually. I do most of my calculations with 300 wh/mile and hope for better.


I get the 130 wh/mile from Tesla and other independent sources claims. As for Tesla having a 53 Kwh pack I do not know for sure I have not worked out the math based on the number of cells used something like 6831 or something like like. I was under the impression it is more like 39 Kwh? 

As for 400 wh/mile benchmark I here touted here mostly, and gave it credence because that is what the Engineering underachievement award winning Chevy Volt boast. . Personally I am thinking 200 wh/mile is a good number to shoot for in the compact line, but perhaps 400 is realistic for the mid size line with all the bells and whistles. Key is going to be that elusive 300 to 400 wh/kg battery.


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## Tesseract (Sep 27, 2008)

JRP3 said:


> At 130 wh/mi and Tesla's 53kwh pack, times 90%, would give 360 miles of range. You can build a much more aerodynamic vehicle than a Tesla. What benchmark is 400 wh/mile? I consider that pretty bad actually. I do most of my calculations with 300 wh/mile and hope for better.


Example - the 2004 New Beetle Rebirth Auto just converted needs 21kW to drive at 60mph on level ground and no or light wind. That works out to 350Wh/mi, and it is what we consider to be a more realistic power usage rate than the oft-quoted 250Wh/mi.

Kick the speed up to keep up with traffic on the highway and that rate goes up dramatically, of course.

Back on topic - the LFP pack in the above vehicle consisted of 65 TS-160Ah cells, so the nominal current draw at 60mph was 100A, or about 0.63C. During high speed range testing (uh... completely legal speeds, of course!  ) we drove the New Beetle flat out up and down the interstate at a rev-limited 5000 rpm drawing an average of 55kW while stuck in 1 gear (the ECU was in limp-home mode - a code scanner was complaining that the engine was missing or something crazy like that ) and afterwards we found 3 cells had swollen up like dead fish... That was an average draw from the pack of 264A, or 1.65C. We aren't sure if it was the high current that did them in, or inconsistent charging (FrankenCharger was pressed into service for charging while the Zivan was off being reprogrammed) but regardless, I would say pulling more than 2C from the TS cells for more than a few minutes at a time is just asking for trouble.


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## JRP3 (Mar 7, 2008)

Sunking said:


> I get the 130 wh/mile from Tesla and other independent sources claims. As for Tesla having a 53 Kwh pack I do not know for sure I have not worked out the math based on the number of cells used something like 6831 or something like like. I was under the impression it is more like 39 Kwh?


 Pretty sure it's 53 Kwh, though they limit the amount used to preserve the pack life. LiCo doesn't have the cycle life that LiFePO4 does.



> As for 400 wh/mile benchmark I here touted here mostly, and gave it credence because that is what the Engineering underachievement award winning Chevy Volt boast. . Personally I am thinking 200 wh/mile is a good number to shoot for in the compact line, but perhaps 400 is realistic for the mid size line with all the bells and whistles. Key is going to be that elusive 300 to 400 wh/kg battery.


Sure that would be nice, but some attention to efficient vehicle design gets us 300 mile range as the technology stands right now. I expect the technology will continue to improve, but the only thing holding us back from 300 mile EV's right now is cost. No matter what battery technology brings us, improving the efficiency of the base vehicle is important in the long run. It will always be better to go farther with less.


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## JRP3 (Mar 7, 2008)

Tesseract said:


> Example - the 2004 New Beetle Rebirth Auto just converted needs 21kW to drive at 60mph on level ground and no or light wind. That works out to 350Wh/mi, and it is what we consider to be a more realistic power usage rate than the oft-quoted 250Wh/mi.
> 
> Kick the speed up to keep up with traffic on the highway and that rate goes up dramatically, of course.


It all depends on what you consider normal use, and changes things considerably. I rarely spend any time on a highway, my average speed is 45 for 95% of my trips. I don't think the new Beetle is all that aerodynamic and obviously at higher speeds aero becomes more important.


> Back on topic - the LFP pack in the above vehicle consisted of 65 TS-160Ah cells, so the nominal current draw at 60mph was 100A, or about 0.63C. During high speed range testing (uh... completely legal speeds, of course!  ) we drove the New Beetle flat out up and down the interstate at a rev-limited 5000 rpm drawing an average of 55kW while stuck in 1 gear (the ECU was in limp-home mode - a code scanner was complaining that the engine was missing or something crazy like that ) and afterwards we found 3 cells had swollen up like dead fish... That was an average draw from the pack of 264A, or 1.65C. We aren't sure if it was the high current that did them in, or inconsistent charging (FrankenCharger was pressed into service for charging while the Zivan was off being reprogrammed) but regardless, I would say pulling more than 2C from the TS cells for more than a few minutes at a time is just asking for trouble.


Well since you don't know if it was the discharge or the charge that caused the problem that's a pretty large jump to a conclusion.


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## tomofreno (Mar 3, 2009)

> Look what was done 15 years ago, no reason this couldn't be done better with lithium right now


 Damn, why can't you buy one of these?


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## JRP3 (Mar 7, 2008)

tomofreno said:


> Damn, why can't you buy one of these?


You might be able to at some point: http://www.sunrise-ev.com/


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