# How many batteries for my project?



## dimitri (May 16, 2008)

First of all, you do not want to parallel multiple series connected cells, you want to parallel individual cells and then connect those parallel sub-packs in one series string.

Pack AH sizing depends on 2 factors:

1. Max and continuous C rate, so you don't ruin your cells.
2. Providing you with enough range, which is function of C rate over time.

For example, A123 may be OK with 10C continuous ( I don't know real C rate, I just use 10C for illustration ) , but it means your EV will drive for 6 minutes at 10C ( 1C equals 60 minutes of discharge at 1C rate ). So, your desired range and typical cruising speed will tell you how long your pack should supply current to meet your needs. Then , based on calculated time and current you will know your AH figure.

For example, if your cruising current is 100Amp at 50mph and you want 50 mile range, then you need 100AH pack at 100% DOD, but since we want to keep our packs to 80% DoD or better, you'd need 120AH pack at minimum. Then, if your 1C is 120Amp, then your max accelration C rate should still be within max C rate of your cells. Of course if you parallel multiple cells, then you divide the C rate among them. So if you have 10 cells in parallel, each will see 12Amp as 1C rate in above example.

Hope this makes sense.


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## rickeolis (Aug 13, 2009)

Thanks Dimitri,
I wasn't aware that I should be paralleling first and then putting those packs in series. I will go that route. I'm sure this helps with charging the cells, right?
 So, from what you said, it looks like I would need to know how much amperage I typically use on a given drive based on the spec's of my car and do the math from there. That's catch-22 in that I can't drive the car until I buy batteries!
 I'm sure there is a reasonable guess I can make based on input from others that have similar setups and know what they do.
I really appreciate the input!

Rick


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## dimitri (May 16, 2008)

There are a few rules of thumb to determine required energy, which then divided by voltage will give you required amperage.

You can get MPG for comparable ICE car, use gasoline energy density and ICE efficiency ( or inefficiency  ) to see how much energy is actually used to spin wheels. You can look at comparable EV conversions on EV Album and check with people how they like performance.

You can also go by your motor and/or controller's max rates (whichever is smaller), keep in mind that controller is rated for motor current, not battery current. Battery current is always less, except brief acceleration bursts at low RPM. 

For example your Netgain controller 1200Amp figure is mostly just a number on paper, since that much current would melt your Warp9 motor.

Look for realistic max and continuous motor and controller ratings, which don't cause thermal meltdown, that might hint you toward max C rate you need from your cells.

There are many angles to look from, then try to find a common area, then see how much it would cost and whether it would fit in the car. Its definitely a multiple variable equation, but that makes it fun, doesn't it?


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## rickeolis (Aug 13, 2009)

Back again on this:
I have decided to go with A123's.
I am using the 26650 style (M1) and have figured on paper that I need about 350 of them for this project. (3300 watts at 3.3 volts each according to spec sheets)
I currently have acquired nearly 100 so far and am working on the rest.
They come to me as eight in series as 28.8 volts and I am trying to find the best configuration to make them up as mounted packs for the car.
dimitri suggests wiring each battery in parallel for the amperage I need and then doing voltage by putting those packs in series.
I want 1000 amps and 165 volts, so how will that work?
Thanks-


Rick


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## rickeolis (Aug 13, 2009)

OK, I am now questioning the 3300 watts...


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## rickeolis (Aug 13, 2009)

Spec sheet from A123 website for these M1 style batteries:










*ANR26650M1A:* The ANR26650M1A is A123 Systems’ pioneering product, originally designed for a new class of power tools. Applicable to a wide variety of system designs and currently in mass production, the 26650 cell offers excellent price-performance. 

*Power:* Over 3000 W/kg and 5800 W/L
*Safety:* Excellent abuse tolerance and environmentally friendly
*Life:* Excellent calendar life, 10X cycle life vs. conventional lithium ion
Our batteries use a new type of cell construction based on a dual plate tubular design optimized to deliver very high power with high efficiency. This new design does not use crimp seals and instead opts for a more advanced “all laser welded” construction optimized for very low humidity penetration over the life of the battery as well as stronger, thicker dual plate headers.

Download Specs
For high volume orders, customized energy solutions, or OEM pricing only, please contact us at 617-778-5575 or email:

[email protected] 

Nominal voltage: 3.3V
Nominal capacity: 2.3Ah
Core cell weight: 70 grams
Internal impedance: (1kHz AC) 8 mΩ typical
Typical fast charge current: 10A to 3.6V CCCV
70A continuous discharge
120A, 10 sec pulse discharge
Cycle life at 10C discharge, 100% DOD: over 1,000 cycles


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## rickeolis (Aug 13, 2009)

Again, I am still trying to find the best manner in which to build these up in packs for my race car.
(TransWarp 9"; Netgain 1200 amp controller; Mazda RX7 direct drive)
Thanks everyone!


Rick


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## dexion (Aug 22, 2009)

The numbers are way off. You are mixing up the stored power with the ability to deliver max power.

Stored power is 2.3ah (or 2.3 amps for 1 hour ie 1c) 

Lets play with the numbers and assume 300wh a mile. 

Ok so 165V = 50 cells
75 miles = 22.5KW at 300wh a mile

so 50 series sells
Now for the BAD news

Lets use 160ah (its really about 137 ah to get to 75 miles but you need to get to 80% not 100% discharge.)

So 160ah/2.3= 70 strings of 50.

Ergo you need 3500 cells (at 2.3ah) to get you your 75 miles.

I wouldnt worry about power they will be able to give out more than you could use. Its the 75 miles that is your determining factor. 

With 350 cells you would be able to get 5 miles but you would REALLY be stressing the cells.


so, 70 strings of 50 cells in series. Sorry.


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## dimitri (May 16, 2008)

Your power and energy requirements are about half of Tesla. Tesla uses 6800 cells of similar size, so you would need about half of those cells compared to Tesla, which is 3400. This is very approximate of course, but it would be north of 3000 no matter how you slice it.

If Tesla could go on 700 cells, we would all be driving one and not bother converting anything.


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## rickeolis (Aug 13, 2009)

That's more like it, thanks Dexionm and Dimitri,
It never did look right, and the 350 cells did seem way off.
So, 70 strings of 50 cells in series is the answer I was in search of. 

OK, so 50 times 3.3v is the 165 volts I am after, and 70 packs of that in series gives me the amperage I want for long lasting mileage such as my goal of 75 miles.


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## toddshotrods (Feb 10, 2009)

dexion said:


> ...so, 70 strings of 50 cells in series. Sorry.


I was wondering about that. I am planning on 1800 26650s for my 1200lb race rod, but I don't care about range. Granted I am planning to run much higher voltage (330), but I still couldn't see how you could get anything useful out of 350 cells (what you mentioned in your other thread). I'm planning to run 18 parallel strings of 100 cells in series.


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## dexion (Aug 22, 2009)

One thing to note for both of you (70x50) and (100x18) is a friggn LOT of connections. I have 48x100ah cells and I worry about my connections. 
Id go insane with all those connections and wires. Throw a bms in it and my head would explode like in scanners 
Any reason you dont want to consider prismatic cells?

You could get 50x 160ah cells that pull 4c for a short time thats 640battery amps thats about 90KW assuming they sag to 2.8v.
.

Not sure about 100x18 however. Thats about 40ah so 100 40 ah cells wouldnt pull much over 160amps. But 18 strings of 123's would be able to for a short time do gagzillions.


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## rickeolis (Aug 13, 2009)

Yeah, I see my mistake, in that I once saw a spec of 3200 watts per cell. That would be nearly a 1000 amps per cell and I know better.
This is why I needed to post this query here!
Thanks guys!!


Rick


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## rickeolis (Aug 13, 2009)

Hi Dexion,
Actually I am still open to Thundersklys but don't know if it will perform like I want.
I've watched the threads for guys who use them and they seem very happy, but they don't race (the one's I've read.)



Rick


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## MN Driver (Sep 29, 2009)

It's a tough call because with cells that perform very well, they end up being overkill for performance with a 75 mile range target, yet 75 miles of lower performing batteries is extra weight for racing and also less capable at the track.

The highest performance option is to use cells that most people here would have issues if I mentioned them and suggested their use in a car but there are cells capable of pumping out 50C without much voltage sag and have less weight per wh than even A123s. If I was racing, I would use them but only if I was looking for a 1/4 mile range with a dedicated racecar and was planning on pulling 2000 amps. ...but it only makes sense for a dedicated racecar to do that.

For what it is worth, if you go the prismatic LiFePO4 route, CALB(formally Sky Energy) cells look better than the Thunder Sky cells in every discharge graph I've seen and their specsheets have been improving and it seem pretty much everyone is getting more Ah for a given cell than its spec too, they increase the energy density of the cells and the cells are the same size but they don't change the Ah specs. The discharge graph posted for the 40Ah cell used to show 40Ah at 40 amps in the past, now if you look at their site it looks like it has another 5Ah or so in the spec graph and 10C for 10 seconds with cell in the specsheet when it used to say 4C for 30 seconds. Of course it's not exactly apples to apples with the different time periods though.


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## dimitri (May 16, 2008)

rickeolis said:


> I want 1000 amps and 165 volts, so how will that work?
> Thanks-
> 
> 
> Rick


How are you going to apply 1000 amps and 165 volts to a Warp9 motor? 

Please video tape it and buy a spare motor so you can replace the one you zorch 

Did you read my comment earlier about realistic sustainable power levels? Have you done any math or research of how much power Warp9 can actually absorb without melting or zorching?

I almost burned my Warp9 by testing limits of Soliton1 and still can't go over 800Amps at 128V.

Especially with direct drive, you will end up turning Warp9 into an electric heater instead of the electric motor 

Do you have a solid grasp on the concept of battery amps/volts vs. motor amps/volts and how controller does the conversion from one to another?

Sorry for all the basic questions, but you will thank me later when you save your $1700 motor from bursting in flames.


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## toddshotrods (Feb 10, 2009)

dexion said:


> One thing to note for both of you (70x50) and (100x18) is a friggn LOT of connections...


Well, in my case as much as possible will be done with CNC'd plates. The 100 cell strings are going in CAD/CNC cases, with copper plates in them for the main connections. As for BMS, I haven't made it that far yet, to decide how it will all be wired, but I'll deal with whatever I have to to go fast.



dexion said:


> ...Any reason you dont want to consider prismatic cells?... You could get 50x 160ah cells that pull 4c for a short time thats 640battery amps...


Not even in the ballpark for my goals.



dexion said:


> ...But 18 strings of 123's would be able to for a short time do gagzillions.








dimitri said:


> How are you going to apply 1000 amps and 165 volts to a Warp9 motor?
> 
> Please video tape it and buy a spare motor so you can replace the one you zorch
> 
> ...


They are good questions, but the answer is using the same methods all the fast NEDRA guys are using, and knowing that eventually you are going to destroy something. If you're not prepared for that consequence, you have no business racing. Rickeolis is building an autocrosser, which means he stands good chance of hurting something eventually if he plans to race competitively. I am building a sick drag/autocross racer that I know will mean lots of abuse on the components. The White Zombie's owner isn't named Plasma Boy because he likes to donate blood.  It comes with the territory...


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## rickeolis (Aug 13, 2009)

MN driver: It's hard to know whether or not Thundersky's would give me what I want, but I know the A123's will... Thanks.

Todd: We're doing similar things, and since I am going into unknown territory, I try to use this board for things like this. I love the rod you're building!

Dimitri: I don't plan to push 1000 amps right from the start, probably half that at first. As for the voltage, I have read several accounts claiming that the Warp can handle 176 volts before having issues, and that's why I chose 165 as my goal, but there is no reason I could not begin testing at a lower voltage as well, thanks!



Rick


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## dimitri (May 16, 2008)

rickeolis said:


> Dimitri: I don't plan to push 1000 amps right from the start, probably half that at first. As for the voltage, I have read several accounts claiming that the Warp can handle 176 volts before having issues, and that's why I chose 165 as my goal, but there is no reason I could not begin testing at a lower voltage as well, thanks!


You are missing my point. Voltage is your friend, not the enemy. High current is the enemy since it creates heat. If you want to start lower, you'd be better off starting with lower current, but still your planned high voltage. You can always add more cells in parallel, its easier than adding cells in series afterwards ( charger changes, controller config changes, DC-DC changes, etc etc ).

With a good controller ( Soliton or Zilla ) you can have max pack voltage, but still set motor voltage limits to whatever you want, since controller converts power in to power out, it can keep the voltage at whatever level you want. Higher pack voltage is always better than lower pack voltage, until certain practical limits.


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## toddshotrods (Feb 10, 2009)

rickeolis said:


> ...Todd: We're doing similar things, and since I am going into unknown territory, I try to use this board for things like this. I love the rod you're building!...


Thanks Rick!  Ditto for me, I am still pretty _green _(pun intended ) to the whole EV thing. Unless you have an unlimited budget to experiment, the best way to go fast is to do what the fast people are doing. I am trying to lay the basic foundation others like the White Zombie have developed, and build on it. Even when someone has already proven it, there will always be internet "experts" who will tell you it can't or shouldn't be done - just follow the yellow brick road... 

Dimitri is right - don't limit your pack, let the controller set the limits. That monster pack I am planning to build will be exploited over time, as experience dictates. The fast guys also tend to always have more voltage than they need to allow for sag. Lithium-based batteries don't sag like lead, but they all run pretty high voltage anyway.

I have to read up on this parallel-stringed-cells-then-series thing. This is the first I have heard of it. A lot of commuter-style EV stuff is still foreign to me because all I care about is going fast. That means most of what I do has no practical application for a daily driver either.


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## rickeolis (Aug 13, 2009)

Exactly-
I'm new to the EV thing, so these boards really help, but so often when I ask something I get 5 differing opinions from 8 different people.
That's where using a few different web boards can come in handy, though rarely do I get a correct answer right away.
I tend to do the same thing in learning what other successful builders have done and try emulating those ideas. White Zombie sure has been helpful in that manner!



Rick


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## toddshotrods (Feb 10, 2009)

I consider all viewpoints, but normally follow the ones presented by, or taken from the efforts of, those who have successfully accomplished something at least similar to what I have in mind. The one thing that can't be disputed is success. People can debate what led to the success, but if it works consistently I would rather figure that out through experience, rather than debate.

I was told not to run direct-drive, and seriously considered all the evidence why a transmission was supposedly better. The whole time though I was watching these guys fly with direct drive! Case closed. Their argument in favor of a transmission was so convincing that I actually tried to present it to you, when you said you planned to run direct drive. Then I remembered that the White Zombie was between 2400 & 3000lbs, depending on what battery pack was in the car. I realized that you could, indeed, go direct drive with your project and eventually shut my mouth. 

You just have to consider the source - meaning what the person's experiences are, that shaped their view. There can still be a lot of valuable information in opposing views. For instance, I saw all the reasons a transmission was critical for certain applications through those debates, and worked to eliminate those reasons from my project!


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## rickeolis (Aug 13, 2009)

I too have two very specific desires for this car in mind: Low weight and direct drive. They can benefit each other. This will help the racing aspect in that not having to shift cuts down on lap times, and the low weight is much easier to race with.
The Tesla has done both as well. The advantage to it is the big price tag which allows for the best of everything put in it. (Variable A\C drive system, LARGE bank of batteries, low car weight, etc.)
Most of the quick drag racing EV's do it too. They have plenty of power way past the speeds I desire (up to about 100 mph.)
I truly figure that rear-end gearing and tire diameter will give me what I want as long as I have EXTREMELY low vehicle weight.
Quickness will come from: Electrical power to the motor, car weight, and gearing; Whereas longer distances (75 miles between charges) will be based upon battery charge length and gearing.
I have determined that this will cause me to have to have two different diameters of wheels and tires for the rear axle of the car; One smaller set for racing and a normal size set for street driving.
That's not an issue for me though because I race often and usually change all 4 tires from street to racing slicks when at the track on the Vette.


Rick


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## rickeolis (Aug 13, 2009)

Mark this 4th of July the official date I got my EV running!
 I mounted the controller onto the firewall in the engine bay along with the big relay I got from the vendor too.
 I ran all the 4\0 cabling first from the motor to the controller and then to the back of my Mazda in the hatchback area. I then wired in the 12 volt control wiring as needed, and then mounted a small 12 volt battery under the hood as well.
 I then got everything set and slowly pushed the (hall-effect) throttle pedal and viola! I was moving!
 Quite happy to get this far. Now to continue buying and building up a set of battery packs to make it work well.
 More to follow-

Rick


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## DavidDymaxion (Dec 1, 2008)

Just food for thought: You might want the smaller diameter tires for the street and the larger diameter for racing. The smaller set might be good for 0 to 85 mph, and be a bit easier on the motor and controller for stop-and-go driving. The larger set (maybe 0 to 100 mph) would then be great for the drag strip.

This assumes you have a lot of power, like White Zombie.

Of course, the easier way to do this is to keep the tranny and move the lever from 3 to 4. 


rickeolis said:


> ... I have determined that this will cause me to have to have two different diameters of wheels and tires for the rear axle of the car; One smaller set for racing and a normal size set for street driving. ...


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## vpoppv (Jul 27, 2009)

Congrats! Where's the pictures? Where's the video? Inquiring minds want to know!


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## EVfun (Mar 14, 2010)

DavidDymaxion said:


> Just food for thought: You might want the smaller diameter tires for the street and the larger diameter for racing. The smaller set might be good for 0 to 85 mph, and be a bit easier on the motor and controller for stop-and-go driving. The larger set (maybe 0 to 100 mph) would then be great for the drag strip.
> 
> This assumes you have a lot of power, like White Zombie.


Oh man, I thought the small tires where on the front to save power by making the entire trip slightly downhill


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## rickeolis (Aug 13, 2009)

Hi guys!

David, interesting suggestion. I guess the only way to find out what works best would be to try both ways and see. Thanks!

vpoppv, The car looks like crap and that's why I haven't posted pic's yet. A video might be a great idea though just to show that it really does run! Thanks-

EvFun, funny!



Rick


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