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.
Fast car: higher C rating or more volts?
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.
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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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.
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.
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.
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.I'm perfectly in accord with you.... it's why I choose 38120S 10 Ah for my smart fortwo project..
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.
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?
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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