# I have a question....



## rfengineers (Jun 2, 2008)

Hampton said:


> I think my math is right, with these batteries I'll have (144V * 200A) 28,800 W (or 28.8 kW) for my power.
> For my energy I'll have 28,800W * 60 min= 1,728,000 Wh or 1,728 kWh (did I do that part right?)


Hi Hampton,

That sounds like an ambitious project, bet of luck with it.

The power in your proposed battery is 144-Volts x 200-AmpHours or 28.8-kWh. How much of that is usable depends on how deeply and how quickly you discharge the battery. The battery manufacturer should be able to provide the information necessary to make that determination.

Just for argument's sake let's say that you only want to discharge the battery to 75% (depth of discharge) and that you must derate the capacity by 20% due to your rate of discharge. That would leave you with about 17.3kWh of usable power. Next assume that your vehicle uses, on average, 250Whr per mile. Then your range would be 17.3/0.25 or 69 miles.

Remember, the above is simply a thought-experiment with arbitrarily selected parameters. Your actual range could be very different.

Top speed is more complex to determine and requires information about your motor, gear ratio and rolling/wind resistance.


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## ClintK (Apr 27, 2008)

Hampton said:


> hey everybody, I'm going to attempt to form a project at my high school with some physics teachers to make an EV.
> 
> I've done some research, and i want to try a setup with:
> 2 fb1-4001 engines
> ...


You may have messed up the units a bit. Your batteries are probably rated with 200 Ah, not 200 A. The Ah being the capacity. Your batteries will also have a discharge rating (something like 3C, 10C, etc...). So 200 Ah capacity is 600 Amp maximum discharge for 3C rating.

You were correct in your max power being Volts * Amps, but the Zilla 2k controller can provide 2000 amps (144V * 2000 = 288kW). Now with that said, your batteries won't be able to provide that many amps for long at all. Going with the 3C 200 Ah batteries you'll have (144V * 600 = 86.4kW) max power.

Any reason you're going with 2x 9" motors? You could look into getting a single 11" instead.

Your range will be based on how many amps your pulling. If you know what kind of vehicle you'll convert you can play around with the EV calculator http://www.evconvert.com/tools/evcalc/ to get an estimate of top speed / range.


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## TX_Dj (Jul 25, 2008)

EDIT: I got this topic confused with another that was asking about sand rails... so please disregard my mention of sand rails below. 

For the record, a sand rail with 500 lbs of batteries and one 9" motor will weigh something like 1700 lbs or less. Two motors or a larger motor would be overkill, imho... The 9" will make far more torque than the engine that would have powered it in the first place, and is capable of making continuous horsepower enough to push the thing down the road at freeway speeds with very little problem.

However, a sand rail is not very aerodynamic ... so it will burn a lot of energy at higher speeds unless you put a body over the tubing that makes up the vehicle.

Also, rfengineers says you'll have to de-rate the capacity by 20%, which I guess was suggested due to how Peukert's Law applies to a Lead Acid battery, but these are LiFePO4, not PbH2SO4... so I'm not so certain it applies... but then again, I'm No Expert!(TM)

I think it's a great idea for a project... now, who's donating $50k to the school to make it happen?


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## Hampton (Mar 10, 2008)

thanks for the info you guys,
and ClintK:
I found out about using two motors and thought it would be a cool thing to try, also i heard that you can get good performance from using two. And if this school project turns out nice, then i'll use a similar setup in a 79' z28 camaro! 
so i want to use this project as a way to test how my own personal car will turn out to be in the future.

but, would a single 11' motor be more efficient and better performance wise than two 9's?


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## skullbearer (Jul 9, 2008)

Hampton said:


> would a single 11' motor be more efficient and better performance wise than two 9's?


Not necessarily from what I've been able to learn. In fact, two motors give you the advantage of having 2 electrical gears, and possibly eliminating the transmission altogether.

You could still do that with a single 11" but you can't eliminate the diff or have the electrical gearing.


It seems to me that two Warp 9s would have a much higher power capability than any single 11", but more power means higher draw and less range (if you are smacking that throttle). So in the end it is really going to depend on your driving, and what you would like to be _able_ to do.


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## Hampton (Mar 10, 2008)

hmmm okay.

oh and since with that battery pack for the project won't supply enough amps wired in a series, how would one wire them parallel?


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## skullbearer (Jul 9, 2008)

Hampton said:


> hmmm okay.
> 
> oh and since with that battery pack for the project won't supply enough amps wired in a series, how would one wire them parallel?


If you mean, 'how do I wire things in parallel', then allow me to explain.

To wire in series you connect the (-) terminal of one battery back to the (+) terminal of the next battery pack to make one long 'series' of batteries, right?


To wire in _parallel_ you connect the (+)s to each other, and the (-)s to each other, so that the wires will run 'parallel' to each other.


Lets see if I can ASCII up a diagram...

+ source
|
|
+batt1 (+)
._
|.|
._

.- batt1 (-)
|
|
+ batt2 (+)
._
|.|
._

.- batt2 (-) That's series, and you can continue it until you build up so many volts you become a desirable ground and it stops your heart.


+ source
|
|

+ batt1 (+) ---- (+) batt2 +
._................................._
|.|...............................|.|
._................................._

.- batt1 (-) ----- (-) batt2 .- Parallel. Ignore the periods!


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## rfengineers (Jun 2, 2008)

TX_Dj said:


> Also, rfengineers says you'll have to de-rate the capacity by 20%, which I guess was suggested due to how Peukert's Law applies to a Lead Acid battery


No no no, that's not what I said. Those were made up numbers simply to illustrate the point that the manufacturer's data would be needed to determine the amount of usable power.


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## Hampton (Mar 10, 2008)

ahhh i see,
that's actually what i thought it would be, i just wanted to check with someone to make sure I'm on the right track.

oh wait, would it be possible to do half of the pack in series and the other half parallel?


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## bblocher (Jul 30, 2008)

rfengineers said:


> No no no, that's not what I said. Those were made up numbers simply to illustrate the point that the manufacturer's data would be needed to determine the amount of usable power.


From what I read you don't have the Peukert's effect with the lithiums and can get their full, or close to it, capacity as long as you stay within the rated discharge rates (usually 3C).

Even the 600 amps you could safely draw from those batteries is nuts and would be awesome performance for just street driving


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## rfengineers (Jun 2, 2008)

Hampton said:


> ...would it be possible to do half of the pack in series and the other half parallel?


I think that would be a very bad idea.


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## Hampton (Mar 10, 2008)

really? can you explain why please?


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## TX_Dj (Jul 25, 2008)

Let's say you have 12 batteries, 12v & 50 Ah each. The total series voltage is 144vdc with a capacity of 50 Ah.

If you then do what you're asking, you will have one pack in series with a voltage of 72vdc and a capacity of 50Ah, and another pack in parallel with a voltage of 12vdc with a capacity of 300 Ah. First of all, the voltages are not compatible. Second, the higher voltage source will attempt to charge the lower voltage source.


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## bblocher (Jul 30, 2008)

TX_Dj said:


> Let's say you have 12 batteries, 12v & 50 Ah each. The total series voltage is 144vdc with a capacity of 50 Ah.
> 
> If you then do what you're asking, you will have one pack in series with a voltage of 72vdc and a capacity of 50Ah, and another pack in parallel with a voltage of 12vdc with a capacity of 300 Ah. First of all, the voltages are not compatible. Second, the higher voltage source will attempt to charge the lower voltage source.


I think he means series and parallel together. So for example you would have 24 12v batteries. You'd create two 144v series packs and then put those in parallel to each other increasing your amps by double, but also your weight and need for room for these by double as well. There are many other variations of how you could do these in parallel/series to get the same configuration too. It's usually just better to buy larger batteries with more amp/hr rating which usually mean they can handle the larger loads too.


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## rfengineers (Jun 2, 2008)

Here is 1000 words on the subject:

The leftmost configuration shows 4 12V batteries connected in series. Each battery is rated at 100 Amp-hours. The resulting battery (remember, two batteries connected together makes one battery) is 48 Volts at 100 Ahr. Voltage adds in series.

The center configuration shows two of these 48V 100Ahr batteries connected in parallel. The resulting battery is 48 volts at 200 Ahr. Current capacity (Ahr) add in parallel.

The rightmost configuration shows 4 pairs of 12V 100Ahr batteries connected in series. Each pair of 12V 100Ahr batteries are connected in parallel, making four 12V 200Ahr batteries. The four batteries are connected in series, making one 48V 200Ahr battery.

Questions?


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## bblocher (Jul 30, 2008)

Yes pictures! It's always hard to explain it without a good picture. That should make it very clear.


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## Hampton (Mar 10, 2008)

so rfengineers, there is a safe way to do it?
the one you listed. And btw, those pics really helped! thanks!


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## rfengineers (Jun 2, 2008)

Hampton said:


> so rfengineers, there is a safe way to do it?
> the one you listed.


The original question on this thread was how fast you could go, but I think we are now talking about stringing together batteries.
This is an area I know about, but I am not the "all-knowing battery wizzard" so if someone out there knows better please feel free to contradict me.

Rules-of-thumb:
In Parallel:
Battery Voltages MUST be equal. 
Amp-hours SHOULD be equal.
Voltage does not change.
Current capacity (Amp-hours) add.

In Series:
Battery Voltages SHOULD be equal. 
Amp-hours SHOULD be equal.
Current capacity does not change.
Voltages add.

Hampton, If this does not answer your question please ask it again a little differently.

Joe


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## Hampton (Mar 10, 2008)

well, my original question was if it was possible to have a battery pack with both in series and in parallel at points so you can increase both the voltage and current. 

And I think that your post with stringing together batteries answered it. where you can put two batteries in series (which will make it one battery) and do this in pairs, but then string all of these pairs in parallel. But, i have another question... 
can someone make a pair with something more than two batteries (like maybe five or something), and then string up these bigger pairs parallel like you said previously?


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## rfengineers (Jun 2, 2008)

Hampton said:


> can someone make a pair with something more than two batteries (like maybe five or something), and then string up these bigger pairs parallel like you said previously?


Yes, this is a valid configuration.


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## rfengineers (Jun 2, 2008)

ACTUALLY, Hooking it up like this would be better. Think Balance.


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## bblocher (Jul 30, 2008)

Hampton said:


> well, my original question was if it was possible to have a battery pack with both in series and in parallel at points so you can increase both the voltage and current.
> 
> And I think that your post with stringing together batteries answered it. where you can put two batteries in series (which will make it one battery) and do this in pairs, but then string all of these pairs in parallel. But, i have another question...
> can someone make a pair with something more than two batteries (like maybe five or something), and then string up these bigger pairs parallel like you said previously?


Look back at Joe's first diagram. That shows pairs of two that are in a string of four if I recall. Any combination is possible but you need to apply the rules that were mentioned to prevent battery death  The first diagram he posted should be all you will need for this application.


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## TX_Dj (Jul 25, 2008)

The key thing to understand though, is that regardless of the configuration of the batteries, the Watt-hour energy stored is still the same.

For example, Joe's diagrams show 12v bricks rated at 50Ah. This represents about 600 Watt-hours (Wh) of energy stored per brick. 

If I take 10 of these bricks and wire them in series, I have 120v, 50Ah, 6 kWh.
If I take 10 of these bricks and wire them in parallel, I have 12v, 500Ah, 6 kWh.

In the series pack, every battery supplies exactly the same amperage as the load requires. In the parallel pack, in this instance (with 10 batteries) each battery only supplies 10% of the overall amperage requirement of the load.

However... amps are not the whole picture. Work is done with watts. Lets run a 100W light bulb with these two packs.

100W / 120v = 0.8333 Amps
100W / 12v = 8.3333 Amps

In the higher voltage series-pack scenario, all 10 batteries are supplying 0.8333 Amps each. In the lower voltage parallel-pack scenario, each of the batteries are providing... guess what... 0.8333 Amps.

That's all fine and dandy... but we're talking about moving a hunk of steel and lead down the road, and we all want to get to light speed, or at least some reasonable fraction thereof.

12v isn't going to get you there.
120v is going to get you closer.

Motor speed is dependent on the voltages supplied to it. At 12v, the motor may be able to spin a few hundred RPM and take hundreds of Amps to get the vehicle moving. At 120v, the motor may be able to spin 10x as fast, and possibly use 10x fewer Amps.

Does this make sense?


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## rfengineers (Jun 2, 2008)

TX_Dj said:


> However... amps are not the whole picture. Work is done with watts. Lets run a 100W light bulb with these two packs.
> 
> 100W / 120v = 0.8333 Amps
> 100W / 12v = 8.3333 Amps


True True True. AND there is another thing to consider: The above only considers Volts and Amps, Watts = Volts x Amps.

BUT Watts also equals Amps squared times Ohms. That means that system losses due to resistive heating increases with the Square of Current!

Higher Voltage means lower current (in the system between the battery and the controller) If the resistance stays the same the high Voltage-low Current system will loose less power to heat.

So the 120V 50Ah system will deliver more power to the motor over time than the 12V 500Ah system.

Joe


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## dtbaker (Jan 5, 2008)

I think you are missing the point on experimenting with EV, unless you have money to burn, in building a 'go fast' vehicle just for grins. considering dual motors in a lunky heavy old z car and such like that is maybe not where you want to go to offer an example of how to convert to post-fossil fuel future.

Instead, I would suggest you set your PRIMARY goal on range for a 'commuter car'. This would be a socially responsible experiment offering the same learning experience, although with the borng reality that the days of the muscle car are over. Which means minimal weight, and MINIMAL power to maintain target speed. If you've got lots of money go for the LiFeSO4 and AC with regen, but if you want to approach an average guy stick with an 8" DC motor and a reasonably small light donor car.

The contest should not be max HP, it should be to see minimum kWhr per mile at your target speeds.... say 35 or 45 for a city commute, or 70mph for a highway commute (which eats batteries pretty quick).


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## rctous (Jun 18, 2008)

here is the way I would wire it up, I do not see the need to join together the inside + and - wires what is important here is that the out side wires I have marked at 14" are the same length. If they are not the draw will not be even throughout the individual cells. You could connect the inner + and - to help keep each cell of the 3 in balance with each other and this could even be a small gauge wire like a 12 ga or so, there will never ( should never) be any huge current drawn at this part of the cells/ pack.

The 14" was for reference only the important factor here is they are the same length and as short as possible, this is all about KISS ( keep it simple )

Brian


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## booksix (Aug 26, 2008)

dtbaker said:


> I think you are missing the point on experimenting with EV, unless you have money to burn, in building a 'go fast' vehicle just for grins. considering dual motors in a lunky heavy old z car and such like that is maybe not where you want to go to offer an example of how to convert to post-fossil fuel future.
> 
> Instead, I would suggest you set your PRIMARY goal on range for a 'commuter car'. This would be a socially responsible experiment offering the same learning experience, although with the borng reality that the days of the muscle car are over. Which means minimal weight, and MINIMAL power to maintain target speed. If you've got lots of money go for the LiFeSO4 and AC with regen, but if you want to approach an average guy stick with an 8" DC motor and a reasonably small light donor car.
> 
> The contest should not be max HP, it should be to see minimum kWhr per mile at your target speeds.... say 35 or 45 for a city commute, or 70mph for a highway commute (which eats batteries pretty quick).


Saying the days of the muscle-car are over is kind of ignorant. Yes, muscle-cars as a auto historian would define them are no longer in production, but auto sports are bigger than ever. And what about the Ronaele electric mustang (huge rage with 'real' car people) and of course the Tesla Roadstar; a car currently in production as _you_ speak which would absolutely waste 90% of 'muscle-cars' on the street today.

To the OP: it's awesome to see someone converting their hobby! I am in the same boat. I love cars enough to where I was going to build a 600 hp twin turbo, gas gussling V8 despite gas prices. But electric has attracted me to a cleaner source of fuel that can provide massive amounts of power and that will only grow from here. It's not just for your little clown cars that can barely carry your briefcase...


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## brywisco (Aug 18, 2008)

Just curious here, but have you priced out the LiFePO4 batteries. I am not trying to discourage this at all but wow, those are pricey!


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## Hampton (Mar 10, 2008)

yes i did find the prices for the Li batteries.
at first i was gonna use 45 3.2 V 60 Ah batteries in series. this would cost me about $4600. which was relatively cheap compared to some others. i found this battery at www.cloudelectric.com. it would be a 144 V 180 ah pack. but i found out that i need more ahrs than that so i made a new plan


this pack will have 135 batteries! there will be 45 batteries in series (one 144 V baterry). Then these three big batteries will be connected in parallel so i can get 540 ah. which will be plenty for me (i wanna be able to go 3 hrs of driving) however, this pack costs $13,770. 
so the conversion will probably be somewhere around $20,000.


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## dimitri (May 16, 2008)

> yes i did find the prices for the Li batteries.
> at first i was gonna use 45 3.2 V 60 Ah batteries in series. this would cost me about $4600. which was relatively cheap compared to some others. i found this battery at www.cloudelectric.com. it would be a 144 V 180 ah pack


how did you figure this? smallest batt they sell is $200, so its $9000 for 100 Ah pack. 

how did you turn 60 Ah batts into 144V 180 Ah pack with only 45 batts 

you need 3 strings of 45 each to make 180 ah, that's 135 batts

in reality you can get away with a single 100 Ah string for a small car, but that is still pricey at 9 grand


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## bblocher (Jul 30, 2008)

Hampton said:


> yes i did find the prices for the Li batteries.
> at first i was gonna use 45 3.2 V 60 Ah batteries in series. this would cost me about $4600. which was relatively cheap compared to some others. i found this battery at www.cloudelectric.com. it would be a 144 V 180 ah pack. but i found out that i need more ahrs than that so i made a new plan
> 
> 
> ...


Yeah your math is incorrect here. With 60Ah batteries you would need 3x as many batteries for the Ah you are talking about. This is also like 1500-2000 lbs of battery. You'd need 9 seperate parallel packs with the 45 cells in each.

Each series of 45 batteries is 144 volts and 60 Ah. Each series that you create and add in parallel will add that many more Ah to the full system. So three strings is 180 Ah using 135 batteries.


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## Hampton (Mar 10, 2008)

oh guys i'm sorry i gave the wrong website. its www.elitepowersolutions.com 

and i should be right with the math. here's how i figured it.
with 45 batteries in series that'll give me 144V since each one is 3.2V.
also, each battery has 60ah, BUT it can carry out that current at 3C. 
So 3*60=180 ah with the 144V. 
if i had the 135 batteries strung together parallel that'll give me 540ah.


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## dimitri (May 16, 2008)

Wrong. 3C just means you can discharge those 60 Ah faster, it doesn't make it 180 Ah


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## Hampton (Mar 10, 2008)

what, really? man someone on here told me that previously, oh well.
back to the writing boards! haha


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## bblocher (Jul 30, 2008)

Yeah you can discharge those at 3C 3*60 = 180 amps continuous (10C pulsed)....but that's just a discharge rate. The overall capacity is not in amps, it's amp hours that they are rated in.

It's confusing to figure it all out but you're getting there


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