# Fast car: higher C rating or more volts?



## notailpipe (May 25, 2010)

Hi All,

I'm getting closer to buying some parts for my build. It's a 1990 Honda CRX (base), so it's a quite light two-seater. 

Here are my design goals:
1. Range: I don't need to go far. My work is only 5 miles away, but I want it to have a 25 mile range, assuming 80% DOD for LiFePO4, because the town I live is about 5 miles x 5 miles, so I figure 20 miles is safe to let me run errands after work if I need to drive the whole perimeter (plus 5 miles margin plus the 80% DOD margin).

2. Acceleration: My main goal with the car is to replicate the performance that I had with my Pontiac G8 GT that I sold <sniff>. In other words, I'd really like sub-5 seconds for 0-60mph. Granted, RWD would be better, but I got the CRX so it can be a year-round car in cold climates. I plan to put as much weight up front over the drive wheels. I am currently thinking since the car is light and with Li-ion, that a DC9 should be able to do it, but would consider an 11inch. I talked to a guy with a Civic and he only has an 8" motor but his tires just spin in 1st gear, so I'm not sure if the motor is the limiter anyway (versus grip).

3. Budget: I can probably afford to spend $6k-7k on the battery portion (before BMS/chargers)

So my question is, assuming price and range is fixed, would it be better to build a 144V system and put more money into a higher Ah cell, or would it be better to shoot for 192V and a lower Ah cell? 

My thoughts are that I read that you can hit higher speeds and better performance with more volts, because even with significant drop over the controller, you've got more volts in reserve. And V=RPM. The problem there is that to get 0-60 times like I want, I'm probably talking 800-1000A for a short burst. Even the Hi-Power 100Ah batteries are 5-8C burst, which is pushing the lifetime at 1000A. So I could buy fewer of the higher Ah cells and it'd probably be easier on the battery life, but only 144V which means I'm not sure if I can go 80mph if I ever need the highway (this is not too limiting, with only 25mile range, but I'd like to be able to).

144V system:
45 cells --> 160Ah cell --> @ safer 5C = 800A burst --> $7920 at $1.1/Ah (pushing the budget pretty hard) and a 23kWh pack.

192V system:
60 cells --> 100Ah cell --> @ 5C = 500A burst --> $6600, better for budget, 19.2kWh pack

So the other thing I read here (Dmitri, I think you said it?), was that at higher voltage there is just plain less current draw needed, so maybe 500A is enough?

I guess how do I know if higher voltage pack with lower Ah cells or lower voltage pack with higher Ah cells is better for battery life and acceleration?

Since my car is quite light stock, do you think this setup (even worst-case with an 11" motor) could be at 250Wh/mile? If so, then my range is like at least 75 miles, which is way more than I need. 

Now I'm just rambling, time to wrap it up...
Thanks everyone.


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## Bellistner (Dec 12, 2010)

For battery life, lower Amp draw is better. For range, there's no difference (assuming two packs of the same kWh). For performance, again, not much difference, as the controller will limit how much you draw from the batteries and how much you feed to the motor.


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## notailpipe (May 25, 2010)

I mean, when you look at specs for some fast cars they're talking about being able to handle 1000-2000A for a short period (at least, that's what the controllers are spec'ed for).

So lets say they're running at the max (that I've found anyway) of an 8C discharge rating... an 125Ah cell could get you the 1000A but pushing the battery lifetime, but you'd need 250Ah to hit the 2000A and I don't think anyone even sells that. 

Or are those numbers less of "this is the max current they can source" and more "this is the most you'd want to do without hurting the battery"? Maybe they even have an 100Ah cell for all I know and are just killing its lifetime but they don't care if they're racing(?)

I need to know if a 100Ah cell can put out 1000A or so for very short bursts, and what that might do to overall lifetime. Anyone with experience care to comment? Thanks


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## rwaudio (May 22, 2008)

notailpipe said:


> I mean, when you look at specs for some fast cars they're talking about being able to handle 1000-2000A for a short period (at least, that's what the controllers are spec'ed for).
> 
> So lets say they're running at the max (that I've found anyway) of an 8C discharge rating... an 125Ah cell could get you the 1000A but pushing the battery lifetime, but you'd need 250Ah to hit the 2000A and I don't think anyone even sells that.
> 
> ...


Personally I would choose the motor first, a warp 9 or the new kostov 9" 220v should do the trick in a light car. THEN pick a controller that matches the motor, THEN build a battery pack that suits the controller.

I don't know how well the prismatics handle high C rates, but for long term life I would try to stick with their continuous ratings for daily use and only hit the "burst" rating when you are playing around or want to drive a bit faster.

If the prismatics won't do it, there are headways and other small cells that will do 10-20C bursts.


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## efan (Aug 27, 2009)

Hey,
I dont have experience building an ev and am not very knowledgeable but looking at evalbum.com I spotted this build:

http://www.evalbum.com/1991

assuming that your car is similar in weight to this civic you can achieve 0 to 60 in less than 5 sec with the lower voltage pack assuming that you have a controller that can handle 1000A...I am sure you can also achieve similar performance with higher voltage too.

hope this helps.


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## Bellistner (Dec 12, 2010)

notailpipe said:


> I mean, when you look at specs for some fast cars they're talking about being able to handle 1000-2000A for a short period (at least, that's what the controllers are spec'ed for).


They do this by stringing together a lot of small batteries, usually in Series, but also in 'buddy packs' (several cells in parallel) in a series string.

For an all-out performance vehicle, you're not going to be using Prisimatics (like CALB, ThunderSky, etc). You'd be using Headway's, K2's, A123's, some Kokams, etc). These smaller calls are able to handle being pushed harder, but may have shorter lifetimes, we just don't know yet.

For a 'cruiser' or around-town car, prisimatics are the best bang-for buck.


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## notailpipe (May 25, 2010)

efan said:


> Hey,
> I dont have experience building an ev and am not very knowledgeable but looking at evalbum.com I spotted this build:
> 
> http://www.evalbum.com/1991
> ...


Awesome!  I will be in touch with the owner...
thanks


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## Yabert (Feb 7, 2010)

Hi notailpipe

Because you only need a short range (25 miles) and great performance, you don't need to hesitate and lost your money on large prismatic cells...... Go with high C discharge cells.

The voltage depend of your motor / controller choise.

A Warp 9 with 1000A controller can give 210 lb-pi of torque and around 150 hp at 4000 rpm

Or the new Kostov 9" 220v with appropriate controller can probably give the same peak power because of his higher rpm (6500) (we expect the motor curves) but less torque. 

So, between both, loose the front wheel will be not a problem. Start in 3e gear with Warp 9 and in second with Kostov 9 can give the same torque at wheel. With electric you are able to have the peak torque from 0 rpm.

And concerning battery, if 150 hp peak is ok, you need a battery pack able to give 150 hp (112 Kw).

Well Headway 38120P 8Ah are rated at 1500w / Kg and weight 0.33Kg.
112 Kw + 24 Kw (for motor/ controller inefficiency) = 136Kw / 1.5Kw x 3cells = 272 cells @ 20$ each = 5440$
But you need a bit more cells to don't push it to the limit (350 cells = 7000$).

So, a Warp9 and 1000A give you a battery pack of 50S 7P (160v and 56Ah) and a Kostov9 give you a battery pack of 70S 5P (224v and 40Ah)

You can plug different values into this great calculator: http://www.diyelectriccar.com/forum...-charts-ev-performance-spreadsheet-41565.html


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## rwaudio (May 22, 2008)

Yabert said:


> Hi notailpipe
> 
> Because you only need a short range (25 miles) and great performance, you don't need to hesitate and lost your money on large prismatic cells...... Go with high C discharge cells.
> 
> ...


 
When I was looking at cells last year Crodriver recommended the 10AH 15C cells over the 8AH 20C cells for a street car. (160A vs 150A peak current) You get more capacity and almost the same peak current for the same price and same weight. Using the 10AH cells at a lower continuous and peak C rate could increase the cycle life of the cells. 

Also if you do some digging you can get the cells for less than $20 a piece in your hands (it just make take a bit longer).


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## notailpipe (May 25, 2010)

Yabert said:


> Because you only need a short range (25 miles) and great performance, you don't need to hesitate and lost your money on large prismatic cells...... Go with high C discharge cells.
> 
> Well Headway 38120P 8Ah are rated at 1500w / Kg and weight 0.33Kg.
> 112 Kw + 24 Kw (for motor/ controller inefficiency) = 136Kw / 1.5Kw x 3cells = 272 cells @ 20$ each = 5440$
> But you need a bit more cells to don't push it to the limit (350 cells = 7000$).


Hi Yabert, thanks for the reply. The Headway's are intriguing, I'll have to read more about them, but how much amperage can they put out? My first search result yielded about 160A peak for a cell... so to get 1000A are you connecting bundles in parallel and then stacking those bundles in series? How is this for long-term balance of the battery pack? And would a pack like the one you're describing, with small high-discharge cells, be able to give me the range I want at my budget, or is it better for drag racers?



Yabert said:


> You can plug different values into this great calculator: http://www.diyelectriccar.com/forum...-charts-ev-performance-spreadsheet-41565.html


That calculator looks great but I could never get the drop-down menus to work to change any of the battery or motor selections. How do you do that? I'm using Excel and I enabled Macros. Thanks


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## jeremyjs (Sep 22, 2010)

With a good controller wouldn't it be better to just go by Kw/h; since the controller isn't necessarily feeding the motor pack voltage wouldn't it be easier to go with the highest voltage the controller can handle than figure out the max draw that way. Say a solution 1 can go to 300ish volts. just build a 300v pack with whatever ah rating you need to achieve your power output goals; since 150v 100 a/h id the same as 300v 50 a/h?


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## notailpipe (May 25, 2010)

jeremyjs said:


> With a good controller wouldn't it be better to just go by Kw/h; since the controller isn't necessarily feeding the motor pack voltage wouldn't it be easier to go with the highest voltage the controller can handle than figure out the max draw that way. Say a solution 1 can go to 300ish volts. just build a 300v pack with whatever ah rating you need to achieve your power output goals; since 150v 100 a/h id the same as 300v 50 a/h?


Well they are equal in total energy in the pack, but not equal in discharge capacity. For the cells I've been looking at, they are all 5-8C peak discharge rating. So say they're all 5C just to be consistent. That means the first pack can put out 500A without harming the battery and the second one is 250A limited. So even if the controller can handle 1000A, I'd think it'd be destroying both battery packs (moreso the smaller Ah ones) to demand that much current.

I'm curious about these high-C discharge cells others are talking about, but apparently teh internets is devoid of any information on them.. (?) 

RWAudio, your Oct 3rd posting about your electric Porsche (sweet ride and blog, btw!) mentions you went to a Headway 90s7p 10ah pack, but I don't see any earlier posts detailing that decision to switch from Calb. Why did you change it? And can you explain how you get so much amperage from a 10Ah cell? Are those Headways rated at like 100C unlike prismatic cells?


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## Yabert (Feb 7, 2010)

rwaudio said:


> When I was looking at cells last year Crodriver recommended the 10AH 15C cells over the 8AH 20C cells for a street car. (160A vs 150A peak current)


I'm perfectly in accord with you.... it's why I choose 38120S 10 Ah for my smart fortwo project.. Especially with 0.00035 Ohm results of my test.



> And can you explain how you get so much amperage from a 10Ah cell? Are those Headways rated at like 100C unlike prismatic cells?


It is rated at 15C peak discharge, but I push it to 20C (200A) for 1-2 sec. in my motorcycle (30Ah (3x 10Ah cells) @ 600A)
They are able to take this discharge because of her small inductance and with her great ability to dissipate heat.


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## notailpipe (May 25, 2010)

It looks like this might be what people are talking about.

With 5 of these in parallel, it has 1000A CONTINUOUS rating, for $100!  Compare that to $110 for a Hi-Power 100Ah prismatic cell, and that would be limited to 500-800A _peak_, not continuous! 

I just want to say, I love everybody today.


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## efan (Aug 27, 2009)

notailpipe said:


> Are those Headways rated at like 100C unlike prismatic cells?


no they are not...they are rated @10C continuous discharge, and something like 15C max...but if you notice there are 7 cells wired in parallel meaning 70ah, multiply this by 10 and you have 700 amps continuous or ~1050 max


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## notailpipe (May 25, 2010)

Yabert said:


> I'm perfectly in accord with you.... it's why I choose 38120S 10 Ah for my smart fortwo project.. Especially with 0.00035 Ohm results of my test.
> 
> It is rated at 15C peak discharge, but I push it to 20C (200A) for 1-2 sec. in my motorcycle (30Ah (3x 10Ah cells) @ 600A)
> They are able to take this discharge because of her small inductance and with her great ability to dissipate heat.


Thanks for the reply, Yabert. Looks like we keep posting at the same time and missing some of your posts. Well I will probably get a Zilla1K which is limited to 1000A, hence my target, so I'm not sure if the 10Ah is better for me. 

What are the caveats/things to watch out for when building a series stack of parallel bundles? I read once this isn't good to do because of cell-to-cell voltage mismatch in the parallel bundle will cause internal shorting and shorten lifetimes... what is your experience with that?


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## jeremyjs (Sep 22, 2010)

notailpipe said:


> Well they are equal in total energy in the pack, but not equal in discharge capacity. For the cells I've been looking at, they are all 5-8C peak discharge rating. So say they're all 5C just to be consistent. That means the first pack can put out 500A without harming the battery and the second one is 250A limited. So even if the controller can handle 1000A, I'd think it'd be destroying both battery packs (moreso the smaller Ah ones) to demand that much current.
> 
> I'm curious about these high-C discharge cells others are talking about, but apparently teh internets is devoid of any information on them.. (?)
> 
> RWAudio, your Oct 3rd posting about your electric Porsche (sweet ride and blog, btw!) mentions you went to a Headway 90s7p 10ah pack, but I don't see any earlier posts detailing that decision to switch from Calb. Why did you change it? And can you explain how you get so much amperage from a 10Ah cell? Are those Headways rated at like 100C unlike prismatic cells?


Right, but 1000 amps is at the motor side not the battery side and I just used those particular numbers as an example. You can either go higher voltage than you're going to use at a lower a/h or lower voltage and a higher a/h. I was under the assumption you usually wanted to go with the higher voltage; because it reduced wire size and reduced the effects of voltage sag. The actual power available to the controller is still the same.


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## rwaudio (May 22, 2008)

notailpipe said:


> Hi Yabert, thanks for the reply. The Headway's are intriguing, I'll have to read more about them, but how much amperage can they put out? My first search result yielded about 160A peak for a cell... so to get 1000A are you connecting bundles in parallel and then stacking those bundles in series? How is this for long-term balance of the battery pack? And would a pack like the one you're describing, with small high-discharge cells, be able to give me the range I want at my budget, or is it better for drag racers?
> 
> 
> 
> That calculator looks great but I could never get the drop-down menus to work to change any of the battery or motor selections. How do you do that? I'm using Excel and I enabled Macros. Thanks


To get the power and the range you are looking for without pushing the cells too hard, Headways are probably cheaper than prismatics.
I will be using them in my street car, I believe Yabert already has them in his street car, Jackbauer on this forum also has them in his street car.

This is a simple 4S3P pack that I created for testing. Because they are in parallel the 3P portion of the pack can't drift, and the 4S part of the pack acts like four 30AH cells in series.


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## Yabert (Feb 7, 2010)

rwaudio said:


> Headways are probably cheaper than prismatics.


Cheaper for same power, but at 1.75$ to 2.00$ per Ah is not really cheap vs 1.30$ for prismatic!
But less cells cost less money and it perfect for short range/high power EV.

Another great advantage vs large prismatique cells is the weight....
Large prismatic weight around 7-8 lbs for 100Ah and it's similar for 10x 10Ah Headway cells.
But because you only need 1/2 to 1/3 of headway cells to have same peak power you can save 1/2 to 1/3 of the weight.

Also, It take less place in the car.


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## rwaudio (May 22, 2008)

Yabert said:


> rwaudio said:
> 
> 
> > Headways are probably cheaper than prismatics.
> ...



Lol, without the sentence before, my quote looks pretty "false" but within context peak power is cheaper but with less range, and it's the reason I'm going headways. To get 1000 battery amps near a safe C rate with TS/CALB I would require a massive/expensive pack. The rate from China for headways with ocean shipping and only brokerage+tax (no duty which is valid with the right customs classification) is much less than $1.75-2.00 per AH based on my last quote (800-1000cells)


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## efan (Aug 27, 2009)

Yabert said:


> 1.75$ to 2.00$ per Ah


they sell for $1.6/Ah for the 10Ah cells 

http://www.evassemble.com/index.php?main_page=index&cPath=2&zenid=nqbsm9s0b722po6m4pnflc8mv5


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## rwaudio (May 22, 2008)

efan said:


> they sell for $1.6/Ah for the 10Ah cells
> 
> http://www.evassemble.com/index.php?main_page=index&cPath=2&zenid=nqbsm9s0b722po6m4pnflc8mv5


If you are going to buy from China, direct from headway is much cheaper than that as well.


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## efan (Aug 27, 2009)

rwaudio said:


> If you are going to buy from China, direct from headway is much cheaper than that as well.


do you have any information on how much it costs to import batteries? import duties etc. ?


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## Yabert (Feb 7, 2010)

efan said:


> they sell for $1.6/Ah for the 10Ah cells


Do not be innocent...
When you add the shipping price for 100 cells, the price go to 1.92$/Ah...... and you need to add taxe, duty, credit or bank payment. 

But RWaudio he's right, you can buy it cells for a bit less money when you buy it directly from Headway. 
The 338 10Ah cells I have buy few month ago (when $ CAN has lower value..) was at 1.7$/Ah (USD) including air shipping, bank transfert and taxes.


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## rwaudio (May 22, 2008)

efan said:


> do you have any information on how much it costs to import batteries? import duties etc. ?


To bring them into Canada there is no duty, but there is a brokerage fee as well as GST (5% tax) however the brokerage fee and tax would also apply to ordering them from the USA as well so then it comes down to price + shipping.

Batteries are just heavy enough that air shipping gets really expensive on the type of quantities that an individual would order. (In the range of $1000 - 2000US) so for the best price you really have to be patient and do the slow boat from China. My specific quote was $2000 for air or $200 for ocean. I'm not in that big a hurry so $200 for ocean is the way I will go, you have to be careful though, sometimes that only includes shipping to your nearest port. You may have to arrange extra shipping to your door (ask in advance). There will also be a brokerage charge, it's basically for someone to look at your import paperwork and file the customs entry, this is often based on the value of the shipment, for my broker it looks like it would be around $82CAD for this service based on 8000-10000US worth of batteries, then 5% tax on the value of the batteries. Another important thing is make sure the shipper uses the HS code that you want the batteries to be classified under. A LiFePO4 cell could fall under quite a few different categories, EV parts, batteries, UPS parts, you name it. The key is finding a classification that is honest, but is also duty free. China is bad for proper paperwork, just like the USA (sorry guys) Most people simply aren't familiar with the requirement for a commercial invoice/customs invoice to ship something to Canada, it's also a legal document so don't lie! I make a dozen shipments a week to the USA, and they very seldom get stuck in customs, I've gotten half a dozen shipments from the USA this week and every single one got stuck because it had no paperwork on incomplete paperwork.

I became a dealer for Evnetics recently because there was no Canadian dealer, (great people to work with, probably the most down to earth and honest company I have ever delt with) but I took it upon myself to make sure the documents would be in order when I buy something from them. I asked about the build and where the parts come from and the Soliton1 qualifies for NAFTA (meaning no duty when shipped to Canada or Mexico) I'm sure the Jr. will qualify as well, in short I created the documents, got them to check them over and sign them and all should be good (first order should be in transit I'll have to see how well I did). To make a long story short, it doesn't matter who you buy from, you have to do your homework and make sure you know all the details of the deal and all of the costs involved.

For me it will be a better deal ordering directly from Headway, however the quantity you order will ultimatially deterimine if it's better to buy domestic or import them yourself. I'm not sure what quantity draws the line where it is cheaper to do one than the other.

Just like everything else in EV's you have to do your own homework and make your own decisions based on your findings not just the advice/experience/opinion of others.

If someone had the motivation to do a group buy with headway I'm sure the costs would come down a little bit more.


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## jk1981 (Nov 12, 2010)

Bellistner said:


> For an all-out performance vehicle, you're not going to be using Prisimatics (like CALB, ThunderSky, etc). You'd be using Headway's, K2's, A123's, some Kokams, etc). These smaller calls are able to handle being pushed harder, but may have shorter lifetimes, we just don't know yet.
> For a 'cruiser' or around-town car, prisimatics are the best bang-for buck.


I don't understand this, there must be something I'm missing. If you build a spreadsheet to compare cells/packs and build two cost-equal (figures from one of the advertisers >), roughly voltage equal packs then prismatic 100AH Calb cells actually come out better than 18AH (5P) Headway on paper at least for: (~$7.5k pack)

Continuous Power (75 vs 68 kW)
Peak power (224 vs 204 kW)
Capacity (18.7 vs 13.6 kWH)

On the other hand the headway are ~50kG lighter, something that's not too important when you're looking at a 1000kg+ build, significantly more so for a lightweight racer.

Ok, the power/$ and power/kg capacity of LiPO is obvious but the capacity/$ is rubbish, there's also the whole bursting into flames thing.

Is it that the Headways cope better with near or above rated continuous discharge?


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## rwaudio (May 22, 2008)

jk1981 said:


> I don't understand this, there must be something I'm missing. If you build a spreadsheet to compare cells/packs and build two cost-equal (figures from one of the advertisers >), roughly voltage equal packs then prismatic 100AH Calb cells actually come out better than 18AH (5P) Headway on paper at least for: (~$7.5k pack)
> 
> Continuous Power (75 vs 68 kW)
> Peak power (224 vs 204 kW)
> ...


What specs are you using? And probably more importantly what pricing? Headway 10AH cells are all over the place at $20 per cell in single quantities (this is the for the electric bike market) however when you buy from China in the quantities required for an EV the price is quite a bit different. I get:

Calb 130ah vs Headway 70AH 307.2v nominal (96S) this is the pack I will most likely be building.
Weight: 929lbs vs 487lbs (plus some extra for the headway due to more buss bars required)
Peak power: ~260kw for both considering voltage sag at 1000A (On the data sheet for CALB, 15C for headway)
Continuous power: ~143kw vs ~192kw (4C for CALB, 10C for headway)
Capacity: 40kwh vs 21.5kwh
Cost: $13,728US vs $8601US

This is based on $1.1 per AH for CALB (this was mentioned in the forum a few times correct me if I'm wrong, higher or lower)

This is a real world comparison... MY build.
The cell sizes were chosen to get a peak 1000 battery amps. Cell count was chosen to get close to the Soliton1's 340v maximum when the cells are charged to 3.5v.

If the goal is power on a budget, Headway is the winner, that's about the only time Headway is the winner. Prismatics win for just about every other goal in EV conversions. Or for racing the it goes to the A123's Kokam's Turnigy Nanotech's etc.
Building for equal range, headway would cost more.
Buying at the listed single cell prices would cost a small fortune, even those that sell at $20 for one would probably give you a better price on 600-1000 cells.

I don't think Headways are the best choice for everyone, but they do have their place. It's the middle ground between the more cost effective prismatics and the higher cost Kokam/A123 or other hard to get cells.


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## jk1981 (Nov 12, 2010)

rwaudio said:


> What specs are you using? And probably more importantly what pricing?


http://www.currentevtech.com/ purely as a quick single click way of comparing spec and price.

Interesting they quote the Headways at 5C continuous as opposed to your figure of 10C. If they'll source 10C continuous then I can totally see why they're popular for short range medium/high power builds, at 5C they don't appear to make much sense over the 4C Calb or the 3C TS cells.

I've no budget for a build so I've not looked into pricing direct from China, I was merely trying to understand what's available battery wise and how they measure up against each other and whether it's remotely cost effective (and practical in range/performance terms) to switch to a battery EV yet. It looks like it might just be if you get the right deal.


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## notailpipe (May 25, 2010)

jk1981 said:


> Ok, the power/$ and power/kg capacity of LiPO is obvious but the capacity/$ is rubbish, there's also the whole bursting into flames thing.


Please elaborate. As far as I know, both TS/CALB and Headways are LiFePO4 chemistry, which is inherently safe. Are you suggesting that the Headways are of the other Li-ion chemistry that was flammable?


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## notailpipe (May 25, 2010)

Actually, not sure about the 10Ah cells, but for the 8Ah cells which I'm considering, they are rated 15C continuous, and 25C burst!


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## jk1981 (Nov 12, 2010)

notailpipe said:


> Please elaborate. As far as I know, both TS/CALB and Headways are LiFePO4 chemistry, which is inherently safe. Are you suggesting that the Headways are of the other Li-ion chemistry that was flammable?


I've no idea about the LiFePO4 batteries besides they store an awful lot of energy so have the potential at least to get very hot should they fail. I'd hope/presume they have some protective measures built in to control this though I'd check before building around them.

LiPO (Lithium Polymer) batteries have a tendency when damaged mechanically or by overload/charge to heat, swell and burst into flames. The power output for the size/weight/cost when they work right is astonishing!

jk


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## rwaudio (May 22, 2008)

notailpipe said:


> Please elaborate. As far as I know, both TS/CALB and Headways are LiFePO4 chemistry, which is inherently safe. Are you suggesting that the Headways are of the other Li-ion chemistry that was flammable?


Headways ARE LiFePO4, however Li-PO are sometimes cheaper and/or higher power density which is good for racing. And since racing is pushing the limits, a more volitile chemistry isn't out of the question. Lithiumaniacs is building a Turnigy Nanotech Li-PO pack for is drag racing Camaro.


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## rwaudio (May 22, 2008)

I'm not sure why there is all the different data regarding continuous and peak discharge rates of Headway cells. Perhaps a reseller is hoping to avoid any responsibility with regard to warranty if they state more conservative numbers. The info I got from headway directly states:
38120S 10AH = 10C continuous and 15C peak
38120P 8AH = 20C continuous (no peak listed)
38140S 12AH = 10C continuous (no peak listed)
40160S 16AH = 10C continuous (no peak listed)

This is simply info for other cells that was included with material I requested for the 38120S 10AH cells.
I have discharge curves at 1C/3C/5C/10C/15C as well as low temperature discharge curves.

These are Headway supplied so there is no 3rd party verification, however they look reasonable based on other peoples experience with them.


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## notailpipe (May 25, 2010)

I have been thinking the same thing. I'm seeing different numbers from everyone. 

Note the 8Ah cells are available in "P" (power) rating, vs "S" for... "something else" basically the S are better capacity and P are for dumping current. That's why I've only been looking at the 38120P (8Ah) cells. So it's possible some numbers we've seen are for the 38120S cells instead.

For the *P* cells:

From ManzanitaMicro.com:
200A (25C-rate) max _CONTINUOUS_ discharge

Headway-Headquarters.com (is this a legit site?):
120A (15C) max continuous discharge
160A (20C) max discharge (peak)

Powerscaner.com:
120A (15C) max continuous discharge
160A (20C) max discharge (peak)

Zeva.com.au:
80A (10C) continuous
160A (20C) peak

I have been talking to someone at Manzanita, because their data is clearly outlier compared to the other sites. But he says they are going straight from manufacturer specs and sent me a data sheet from Headway and it says "200A continues[sic] discharge" 

/SIGH
so... who knows? Even the other retailers can't agree.


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## Batterypoweredtoad (Feb 5, 2008)

http://www.evcomponents.com/forum/viewtopic.php?f=13&t=15


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## ewert (Sep 5, 2009)

Don't forget that even though you are pushing say 1000 amps to the motor, the controller is drawing only Umotor/Upack worth of amps from the pack. Of course if you intend to have the gearbox in place, forget this. Though grip may give you problems even with high gears, and then you prolly should calculate this before you decide. Considering ev dragsters seem to be going the no gear changes route definitely a thing to look at beforehand.

You will severely overshoot your needed range if you buy a pack that can push for 1000 amps at max volts. CRX is low CdA car, and light. That Civic linked earlier mentions 80Wh/mile at 60kph (city speeds), that sounds like a miscalculation and he probably meant 125Wh/mile, but still and the CRX is even more economic I think. So the packs discussed here are like x3 or more the range you estimated.

So, what will be your top speed wanted? 80mph? 90mph? Lets say 80mph. To maintain that 1000 motor amps, at 60mph meaning only in the very end of 0-60 you will pull 750amps from batteries. That means you could have a quarter less of battery pack and still maintain full acceleration in "single gear mode" from start to finish of 0-60. If the motor at 1000 amps provides torque enough even at start to spin tires when in a gear for 80mph top speed, then you won't need to go past that 750 amp pack amperage. Even less if you aim for 90mph, but will need torque/grip calculations then.

Nevertheless, you'll definitely be power limited before range limited, and 25 miles is so little ... Check the Ev dragster thread and wait if the HobbyKing nanotech LiPo option works, because with those you could do a pack for $3k that could blow the controller/motor to kingdom come and have enough range for your needs.


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## notailpipe (May 25, 2010)

ewert said:


> Don't forget that even though you are pushing say 1000 amps to the motor, the controller is drawing only Umotor/Upack worth of amps from the pack. Of course if you intend to have the gearbox in place, forget this. Though grip may give you problems even with high gears, and then you prolly should calculate this before you decide. Considering ev dragsters seem to be going the no gear changes route definitely a thing to look at beforehand.
> 
> You will severely overshoot your needed range if you buy a pack that can push for 1000 amps at max volts. CRX is low CdA car, and light. That Civic linked earlier mentions 80Wh/mile at 60kph (city speeds), that sounds like a miscalculation and he probably meant 125Wh/mile, but still and the CRX is even more economic I think. So the packs discussed here are like x3 or more the range you estimated.


Thanks, ewert. I go back and forth. I want to design a pack that can handle (without shortening the overall lifetime of the battery) 1000A peak, but for most of the driving won't be drawing nearly this much. I am tending to overenginer the pack a little since it sounds like battery manufacturer numbers are like ideal condition tests, so accounting for cold weather, or once I'm 1000 recharge cycles in...

I talked to the Honda owner and yeah he misprinted his 0-60mph times as really 0-100kph, oops.  But as you mention, it is a CRX, is lighter and a hair more aerodynamic. And I also have five actually do-able ideas for improving my aerodynamics:

1. underbody belly pan
2. remove whip antenna, replace with sharkfin antenna at rear of roof
3. vortex generators at the lip of the rear hatch (where a spoiler would go)
4. moving the rear-view mirrors inside the vehicle (google "Aero Civic")
5. damming up the front scoop and radiator openings

And I'm thinking of removing the rear windshield wiper, which the HF version does to cut down Cd by 0.01. So I think 175-200Wh/mile is likely. 



ewert said:


> So, what will be your top speed wanted? 80mph? 90mph? Lets say 80mph. To maintain that 1000 motor amps, at 60mph meaning only in the very end of 0-60 you will pull 750amps from batteries. That means you could have a quarter less of battery pack and still maintain full acceleration in "single gear mode" from start to finish of 0-60. If the motor at 1000 amps provides torque enough even at start to spin tires when in a gear for 80mph top speed, then you won't need to go past that 750 amp pack amperage. Even less if you aim for 90mph, but will need torque/grip calculations then.


I guess this is the next step, but I don't know how to really calculate this. I'm planning on the Zilla1k-LV, but not sure of the motor yet. How do I know where peak amps are drawn? I'd have guessed at low RPM because my speed differential is greatest. Basically I need to calculate the actual motor amps and volts at that speed, and then see (using powerIn=powerOut) what the peak battery amps drawn will be, right?



ewert said:


> Nevertheless, you'll definitely be power limited before range limited, and 25 miles is so little ... Check the Ev dragster thread and wait if the HobbyKing nanotech LiPo option works, because with those you could do a pack for $3k that could blow the controller/motor to kingdom come and have enough range for your needs.


I am really intrigued by this! I'll check it out. Hopefully when you say LiPo you still mean LiFePO4...


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## rwaudio (May 22, 2008)

notailpipe said:


> I am really intrigued by this! I'll check it out. Hopefully when you say LiPo you still mean LiFePO4...


LiPo is Lithium Polymer, or the stuff that tends to catch on fire easily if abused. I wouldn't put it in a street car.


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## ewert (Sep 5, 2009)

rwaudio said:


> LiPo is Lithium Polymer, or the stuff that tends to catch on fire easily if abused. I wouldn't put it in a street car.


If you mean tended to caught fire if abused stupidly, I guess that's right. Can't remember right which all techs a guy on endless-sphere abused intentionally to high heaven, but old tech is old tech and new is new. Being stupid of course remains the same.  Those nanotech LiPos are currently the cheapest $/W route.

Now I just remembered this guy and website:
http://www.emissions-free.com/catalog/i8.html

Say 8 parallel, 58 series, that gives bout 191 volts nominal, 960 amp peak 10sec burst for a cell price (query for a prebuilt pack I would suggest) of just about $2800. Actually it also hits your range requirement pretty well too, getting maybe 28miles at 100% DoD with city speeds on a CRX (calculated with 125Wh/mile). Sounds like a smack dab right on the spot power/capacity pack for you! And price seems "okay" compared to others shown here.


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## notailpipe (May 25, 2010)

ewert said:


> If you mean tended to caught fire if abused stupidly, I guess that's right. Can't remember right which all techs a guy on endless-sphere abused intentionally to high heaven, but old tech is old tech and new is new. Being stupid of course remains the same.  Those nanotech LiPos are currently the cheapest $/W route.


Interesting, very interesting. My controller is limited to about 160V, so I'll spend more money on making it capable of the high amperage bursts. If I were to go this route, I'd still be cautious about pushing the pack too hard to avoid any fires, so I would design it for 1000A continuous, even though I will only be pushing 1000A peak for about 5 seconds (by then I will be going 60mph... or at least that's the point!)  That should be plenty of safety margin.

So based on that, 14cells/bundle gives me 1000A continuous so it should be safe (I need to research this more still, I obviously really do not want my car going up in flames), and 50 bundles gives me 160V. That's a total of $4200, nice! It's only a 5.15kWh pack, but if I even got 175Wh/mile, that's still about 25 miles with 80% DOD. And 175Wh/mile seems realistic in a light two-seater car, especially since this pack would only weigh 112 pounds!

Has anyone ever used that site before? It sounds like Chinese distributors owned by a British dude... isn't A123 an American company (Michigan, I thought..) Anyway, anyone have any experience with www.emissions-free.com?


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## dtbaker (Jan 5, 2008)

problem with assembling a pack from little cells.... is assembly, and then attempting to balance. Instead of 30-40 cells, you're talking LOTS of potential failure points. The other thing to keep in mind is that unless you are racing ,and have deep pockets, you really want to design to use no more than 70% range to get max life cycles and prevent killing any cells that have slightly less capacity than all the others.


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## ewert (Sep 5, 2009)

dtbaker said:


> problem with assembling a pack from little cells.... is assembly, and then attempting to balance. Instead of 30-40 cells, you're talking LOTS of potential failure points. The other thing to keep in mind is that unless you are racing ,and have deep pockets, you really want to design to use no more than 70% range to get max life cycles and prevent killing any cells that have slightly less capacity than all the others.


Thing is though, the op is kinda in the "racing" territory, wanting a fast 0-60 with minimal range requirements. The difference being 8k for a huge pack weighing down the car with way too much range, or 3-4k for a pack that fits his needs weighing a lot less ...

Oh and those cells on the emissions-free seem to be not the "LiPo that brings fire from stupid use" but LiFePO4 with high specs. The guy has sold as far as I know good quality cellpouches before on endless-sphere. Atleast his rep has been good there, and still is. No, I can't vouch for him, am not him, have not bought (yet) from him ... but his rep seems to be solid on endless-sphere.


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## notailpipe (May 25, 2010)

ewert said:


> Thing is though, the op is kinda in the "racing" territory, wanting a fast 0-60 with minimal range requirements. The difference being 8k for a huge pack weighing down the car with way too much range, or 3-4k for a pack that fits his needs weighing a lot less ...


Right, I don't need prismatics since they can't handle the high current than I need without a super low voltage (for a fixed budget). They should give me about 25 miles on a 80% DOD, and most days my commute is more like 12-15 miles so more like 50% DOD.



ewert said:


> Oh and those cells on the emissions-free seem to be not the "LiPo that brings fire from stupid use" but LiFePO4 with high specs. The guy has sold as far as I know good quality cellpouches before on endless-sphere. Atleast his rep has been good there, and still is. No, I can't vouch for him, am not him, have not bought (yet) from him ... but his rep seems to be solid on endless-sphere.


Ewert, where do you see that? I can't find any specs on the cells on that site, just the text "Safety: Excellent abuse tolerance and environmentally friendly" Additionally I see this on the site: "Initially we have specialized in bringing possibly the very best LiFePO4 cells currently available to the end user at great prices" but I'm gonna need more than that.

I'm still waiting to hear back from them, but it's only been a day so I need to give them a bit more time than that.


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## notailpipe (May 25, 2010)

Looks like emissions-free.com took the info straight from A123's website. 
A couple other websites are claiming they are LiFePO4, but I'm skeptical of anyone selling anything except the direct manufacturer's claims. 

I contacted A123, will post here to confirm/deny when I hear back.


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## ewert (Sep 5, 2009)

notailpipe said:


> Ewert, where do you see that? I can't find any specs on the cells on that site, just the text "Safety: Excellent abuse tolerance and environmentally friendly" Additionally I see this on the site: "Initially we have specialized in bringing possibly the very best LiFePO4 cells currently available to the end user at great prices" but I'm gonna need more than that.


Based on the specs it's LiFePO4.

Anyways: http://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=14820

That's his endless-sphere account. He has atleast a couple of sale threads, so can look him up there.


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## rwaudio (May 22, 2008)

I don't know about the cycle life of the new Turnigy Nanotech batteries, but I have a bunch of the different series of Turnigy batteries for my electric RC helicopter and they don't seem to have great cycle life.

Capacity seemed to increase for the first 15ish cycles, then started to decrease very slightly after about 50. My oldest battereries probably have 175-200 cycles on them and they are down to a hair below 90% of rated capacity, at their peak they were about 105% rated capacity. So in the past 125-150 cycles they have lost 15% roughly.

So you might get lead acid type cycle life, out of the RC grade Li-Po's.
And I have no idea what you might get out of fake A123's


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## algea07 (Oct 1, 2010)

rwaudio said:


> I don't know about the cycle life of the new Turnigy Nanotech batteries, but I have a bunch of the different series of Turnigy batteries for my electric RC helicopter and they don't seem to have great cycle life.


but remember the life cycle relates to the charge and discharge rate, for example thundersky have a discharge rate of .5c for 3000 cycles or headway have a discharge of 1c for 2000.

the batteries in your helicopter probably only last for 15 minuets, so that's a discharge of at least 4c for 15 minuets to 100% DOD, which is a petty hard life for a battery. 

the harder you push the batteries the quicker they will fail.

quality will also have a fair bit to do with it as well i imagine


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## notailpipe (May 25, 2010)

rwaudio said:


> And I have no idea what you might get out of fake A123's


What makes you think the ones for sale on emissions-free.com are fake A123's?


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## rwaudio (May 22, 2008)

notailpipe said:


> What makes you think the ones for sale on emissions-free.com are fake A123's?


There are tons of fake A123 cells out there, and those who really want them have resorted to cracking open dewalt battery packs. I've seen lots of test where people compare the output of a dewalt sourced A123 (real) battery vs an ebay/internet sourced A123 (fake) battery and although the fakes acutally perform fairly well they simply don't compare to the real thing.

http://www.diyelectriccar.com/forums/showthread.php/proud-owner-fake-a123-cells-not-54169.html

I would say unless you can confirm with A123 directly that a company is an official distributor/reseller of their batteries it's safe to assume they are fake.

If they were that easy to come across and not stupidly expensive don't you think everyone would be using them? The Chinese are experts at taking items that are in high demand (expensive) and making a working, less expensive copy that can't match the performance of the real thing. And we are so cheap that we keep the cycle going and buy their fakes. It goes for anything and everything, from sunglasses, and hand bags, to headphones, cameras, phones and our batteries.


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