# LiFePO4 Prismatic vs. Cylindrical



## Jacob Riskin (Jun 10, 2008)

So has anyone actually had any real practical experience with the prismatic cells? I'm reading conflicting data on whether or not they will take the punishment of a full EV.

Companies like tradewin list specs. that I would imagine would work great. 3C continuous (90AH cell) and 10C impulse current for a 144V pack is 135amp continuous and 450AMP impulse current. Bump that to a 192V pack and its 180AMP continuous and 600AMP impulse. 

Is there something wrong with my reasoning? At $1.2/AH even if they aren't the highest quality packs, you could buy 20% more and still save a bundle.


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## joseph3354 (Apr 2, 2008)

most of the prismatics i have seen listed 1- 1.5c continuous discharge.i haven't tested any that were claiming 3c continuous.specs are easy to print out but often hard to achieve in real life.most dc systems will need more than 180 amps continuous discharge( especially on hills).the cylindrical cells seem to have better discharge rates but are usually smaller in capacity(can be paralleled for more).a 5c continuous discharge for a 10ah cylindrical cell is 50 amps and 10c for 15 seconds is 100 amps.now package that for a 100 ah battery and you've got some kick! 500 amps continuous and 1000 amps for 15 seconds! i am ordering some samples of the cylindrical cells and will be posting results as soon as i have them!


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## Jacob Riskin (Jun 10, 2008)

So is the problem manufactures not being so honest about specs?

The batteries I'm looking at are here...

http://www.tradwinhk.com/sj.asp?ArticleID=13

And I've been quoted $1.20/ah which is by far the cheapest I've seen (followed by Thundersky, then Headway, then Phet, then maybe Valence...).

They seem entirely suitable, maybe with a bank of Ultracaps to back them up to increase batt life and instantaneous speed. I'm not an EE but my napkin calculations say you could probably put together a reasonably priced pack ($1000ish) to give you an extra 20seconds of 1000amps at 144v.


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## frodus (Apr 12, 2008)

Those are thundersky cells...

http://www.thunder-sky.com/products_en.asp?fid=66&fid2=70

might be worth picking up a few


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## joseph3354 (Apr 2, 2008)

have to agree with frodus,they look like thundersky.maybe thundersky has improved their batteries a bit.their old specs(2 months ago?) were 2c continuous and 8c burst.be careful of buying on specs alone.get some samples and do some tests.$1.20/amp hour is a great price,but if they don't perform to spec it's not too good of a deal. check thundersky's homepage for specs and see if they match up.


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## Jacob Riskin (Jun 10, 2008)

The question is, how much out of spec makes a battery that is like half the cost not worth it? I'm in the early stages (lots of research) of starting up a small EV shop in LA. We would like to build brand new vehicles based on existing cars, again with my napkin calculations I'm estimating we can build full EV's with reasonable ranges (70-100miles) in the $28-32k range (given a base cost of $15k for a new honda fit/civic, etc...).


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## joseph3354 (Apr 2, 2008)

we had a huge thread on that very subject(new car conversion company).if you can get your batteries for low enough price(6-8k/car) you could possibly meet your projected sales price.but to do that your going to need a better deal than $1.20/amp hour.thundersky will sell at $1/ah if you purchase $500k worth of batteries.that would make your 144v pack a little more affordable.but it depends on the range you truly want.


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## Jacob Riskin (Jun 10, 2008)

If you could find that thread i would love to check it out, I can't find it from a few quick searches...

I would really like to see 100miles. $500k might be doable if they would come down to $1/ah. But we would need to do a lot of testing beforehand to make that sort of investment. For a 20kW pack that would equate to about $6200 and 440lbs. Assuming we save about 500lbs for engine/cat/exhaust/etc... we might even be able to stay at or around the original weight. So with 20kwh 2500lbs, a cd of about .3, low resistance tires, maybe some capacitors to decrease the instantaneous load, a good efficient controller, a series DC motor and going to about 10%(?) DOD...could we get there?


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## joseph3354 (Apr 2, 2008)

if you're looking for 100 mile range at 144 volts you're gonna need about 200 amp hours maybe a little more.here's the thread,there is a calculation in there for that kind of range. enjoy! 

http://www.diyelectriccar.com/forums/showthread.php?t=13851


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## Jacob Riskin (Jun 10, 2008)

So i just read that entire thread, did it die out? No one has posted since may! I found the extension to it but it was only a few pages. 

We don't have a specific target voltage, AH, etc...we have performance targets like...

1. 0-60 in a reasonable amount of time (10-12 seconds?)
2. Range 80-100miles
3. Cost ~$15-$20k for the conversion

I'll keep trolling the forums for information. Thanks for the help!


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## joseph3354 (Apr 2, 2008)

yeah ,it kinda died off there didn't it? if a fella had $1 mil to invest in bulk parts and battery buys you could probably average the conversions out at about $20k,maybe get a few cars for fleet deals around $10k each.profit margin is definitely low.but i think it could be done.good luck in your venture and keep researching!


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## Jacob Riskin (Jun 10, 2008)

Interesting, $1M isn't really that much as far as raising money. Especially considering how fairly low risk it is. Most of your expenses are in capitol equipment costs that could be recouped in case of failure. In fact if you were up and running you could probably get SBA loans for a sizable portion of the expenses.

What I need is someone who has had real world experience building these things. I can research until I'm blue in the face, but I'd like to see some concrete examples.


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## NobleTruths (Jan 14, 2008)

That was an interesting, and lengthy, read....my question is why focus your project on the middle class? Sure, I understand the desire to mass produce for the masses, but I think a start up company might fare better by focusing on the rich at first. Someone made the comment that if they had $100,000 to spend, they might not care too much about the price of gasoline. That is not quite accurate. I, and others I know, would find owning an EV speedster that out-performs an ICE very exciting...if convenience was not compromised. 

Take a FactoryFiveRacing or LoneStarClassics kit, and install a powerful drive system. A select clientele will show up to purchase them. As your revenue builds, THEN you can focus on cheaper productions for the masses. Focus intially on those who WONT quibble over the extra money.


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## joseph3354 (Apr 2, 2008)

not to hijack this thread but,if you have a 100k to spend,google predator performance.they built 2 ford ranger ev's for a nasty company that shall remain nameless.they are in process of designing and building porsche replicas for a california company.might even be less than 100k.check them out if you like.


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## Jacob Riskin (Jun 10, 2008)

*Middle vs. high end*

I agree that the high end is an easier market. But really at that point, you're competing with Tesla and the like. While there may be a decent amount of profit in doing these on custom basis. The real money comes in as you can mass produce. I mean if you making 1-5 cars/month and making $10-20k/car thats $10k-100k/month. If you are building in quantity like a factory you can make 15-30/month at $5k each and that's $75-$150k/month. 

I'm not necessarily against it, but it seems more like the thing you do when the major manufactures take over. You scale back in to a performance/custom shop, but while the window for making a reasonably priced vehicle is there, why not take the opportunity?


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## joseph3354 (Apr 2, 2008)

*Re: Middle vs. high end*



Jacob Riskin said:


> ..... but while the window for making a reasonably priced vehicle is there, why not take the opportunity?


i agree with that 100 percent.if you can get the initial costs down it is viable.wish i had the kind of money that it will take....hopefully someone does!


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## Jacob Riskin (Jun 10, 2008)

Well, if I can get the right team together I'm sure I can raise the money. There are a lot more details than I would have preferred and that will cause a lot more complications in manufacturing them.

Know any good EV engineers in LA? I'm meeting with a couple people next week, and I'll see how it goes.


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## joseph3354 (Apr 2, 2008)

i'm on the east coast,don't know anyone in l.a.,maybe post a thread in here? wish you all the luck in your endeavor!


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## saab96 (Mar 19, 2008)

Jacob Riskin said:


> Know any good EV engineers in LA? I'm meeting with a couple people next week, and I'll see how it goes.


http://leftcoastelectric.com/


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## NobleTruths (Jan 14, 2008)

*Re: Middle vs. high end*



Jacob Riskin said:


> I agree that the high end is an easier market. But really at that point, you're competing with Tesla and the like. While there may be a decent amount of profit in doing these on custom basis. The real money comes in as you can mass produce. I mean if you making 1-5 cars/month and making $10-20k/car thats $10k-100k/month. If you are building in quantity like a factory you can make 15-30/month at $5k each and that's $75-$150k/month.
> 
> I'm not necessarily against it, but it seems more like the thing you do when the major manufactures take over. You scale back in to a performance/custom shop, but while the window for making a reasonably priced vehicle is there, why not take the opportunity?


Yes and no to some of these points. There are not too many Telsa-like companies to compete against, so I dont see this as an issue. I do agree that mass production is where the money is in the long run. 5 cars/month @ 20k profit = 100k vs 30 cars/month @ 5k profit = 150k might kind of nice with the 50% increase, but I'm not convinced that the current battery/motor options are quite in place (taking into account price, weight, size, power and travel distance) to appease the masses. 

I dont know about the rest of the world, but in Texas, driving 40+miles/day seems pretty typical. If your vehicle only holds a (let's say) 50 mile range, you will be chewing your fingernails daily wondering if you can get around town.

If you focus on high-end production initially, as your capital-base builds, your reputation grows, and your number of units/purchase increases, THEN you will have the ability to negotiate lower prices on the better quality items to make them more affordable to the masses. Not only that, greater advances in the future will be available at a time when you can IMMEDIATELY implement them into your existing structure, instead of trying to initiate a new company at a time when many others might be jumping into the fray.

Joseph, I looked at predator preformance, thank you. They have an idea similar to mine, although I want to focus exclusively on EV. But I dont just want to own that vehicle, I would like to own the company. They may be positioning themselves in just the way I was outlining above.


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## Jacob Riskin (Jun 10, 2008)

It's definitely a very fine line right now. I think 80 miles would be the bare minimum for consumer car. My dad loves is RAV4 EV which gets around 80-120miles. If you can build a reasonably priced LiFePO4 pack to do that, I think everything else could fall in to place. Its all about the batteries (technology wise). The motors and the controllers can all come down in price with quantity. Component costs drop dramatically as you increase voltage and decrease amperage. That's probably why most of the major manufacturers engineer solutions at 300v and up. The motors are only expensive because of the limited quantities.

Coincidently I'm having dinner with the guy from LeftCoast next week. We'll see how that meeting goes.


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## OldElectronicsGuy (Sep 17, 2013)

When placing batteries in series as is necessary to achieve higher voltages than a single battery can produce, you must realize that the amperage output actually decreases. This is because the maximum amperage rating is dependent on the capability of the individual cells, unless they are connected in parallel. That's why the total resistance of the battery pack must be taken into consideration.

Going from a 50 cell to a 100 cell series battery will increase the total power of the battery, but not the amperage. The voltage will approximately double but the maximum current will go down slightly due to total pack resistance.

Each link that connects one cell to the next has a small resistance, as does the connection itself. Each battery has internal resistance also. Although these resistances are very small individually, they are additive. Consider 100 lithium cells in series, providing about 350 volts (depending on state of charge, current draw, temperature, etc.). (I won't give specific resistance values because of the many, many variables!)

Though cell resistance is very low, you have 100 X cell resistance, plus
100 X individual resistance of battery links, plus
200 X individual cell connections, and this is just for the pack itself.

This resistance is in series with the motor, controller and cabling, all having their own resistance, along with all their connections.

This is why the size of your battery links, along with proper torque of the individual nuts/screws, proper washers, largest possible gauges of wire, etc. are so important. A few dollars spent on larger wiring, better connectors and so on can give huge improvements in performance. (And don't forget, all that resistance is dissipated as HEAT!)

The highest possible battery voltage in a given situation will provide less loss due to resistance, because as voltage goes up current goes down for any given power output. Higher voltage = less current and lower I squared losses, but of course higher voltage = higher cost. 

The 'devil' is always in the details, and now you understand the engineers' dilemma!


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