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Discussion Starter #1
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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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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Discussion Starter #3
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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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
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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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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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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Discussion Starter #7
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.
Awesome! I will be in touch with the owner...
thanks
 

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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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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

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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Discussion Starter #10
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?

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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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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Discussion Starter #12
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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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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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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Discussion Starter #16
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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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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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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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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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.

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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