# EV Conversion mileage eqns 180sx/300zx **NEED HELP**



## Stiive (Nov 22, 2008)

Hi guys this is my first post, I’ve been interested in EV's for quite a while. Just landed a new job so will hopefully now have the funds to build my dream EV. I am a Mechatronics & Robotics engineer (mechanical and electronic engineer). Ive got a few requirements for my EV as I plan on keeping it for awhile.
a) I want something that i like the look of. Something sporty
b) needs to have good/decent acceleration as Im a bit of a rev head
c) Needs a range of above 80kms (50 miles) (I plan on using lithium batteries).

Anyway I have always been fond of Nissan 180sx's and plan on using one of them but have recently come across a cheap 300zx I am considering. The problem with 300zx’s are is that they are heavy ~1450kgs (3196lbs) compared with 1200kgs (2645 lbs)

So I have been looking through the EV Wiki and been applying some formula’s to get an approximate range etc, but just need to make sure im doing them right.


Firstly the specs of the car and information of parts

Car: 300zx
Weight: 1450kg
Cd (coefficient of drag): .33 
m^2 (frontal Area): 1.82


It’s a non turbo and the engine weighs about ~300kgs
I thinking of a 120Volt system using Thunder-sky *TS-**LFP**9**0AHA **batteries which have the following the specs*

*Nominal Voltage: 3.2V*
*Nominal Capacity: 90Ah*
*Max Discharge Cont: 270A*
*Weight: 3.2kg*

*To make 120v I will need 37.5 batteries – round up to 38 batteries = 121.6 V*


*Calculations:*

*Estimated weight of car after conversion*
*1450kg (stock car) – 300kgs (engine) – 100kgs (exhaust, petrol tank, misc) + 100kgs (electric motor) + 38*3.2kg (batteries) + 100kgs (misc) *
*= ~1370 kgs*

*Considering an average driving speed of 80km/h (= 49.7mph, = 22.22 m/s)*

*From EV Wiki – *
Power in Watts = ((Mass in kg) (9.8m/s²) (Velocity in m/s) (Rolling Resistance)) + ((0.6465) (Coefficient of Drag) (Area in m²) (Velocity^3))

I don’t really know what value to use for rolling resistance so I’m going to use .03 for asphalt, can someone confirm this is correct

Therefore* amount of watts to sustain 80km/h is*
*W = 1370 * 9.8 * 22.22 * .03 + .6465*.33*1.82 * 22.22^3*
*W = 8950 + 4260*
*W = 13210 Watts = 13.2 kW*

*From EV Wiki –*
Efficiency in Wh/mile = ((Power in Watts)(1 hour))/(velocity in mph)

I think this formula is incorrect, you don’t need to multiply the top by 1 hour as the hour denominator (the hours) in m/h (mph) comes to the top to produce Wh/m. Using the formula previously stated would generate units of wh^2/m

*Wh/mile = 13210/49.7 = 265.8 Wh/mile*

*Therefore using the thundersky 90Ah batteries*

*miles = Wh/265.8 = (V * Ah)/265.8 = (121.6 * 90)/265.8 = 41.17miles*
*which is 9miles less than I had originally wanted.*

*I estimate an 180sx will have a converted weight of 1100kgs*
*It has a coef of drag of .3 and similar frontal area*
*Therefore the watts required to sustain 80km/h is*

*W = 1100*9.8*22.22*.03 + .6465*.3*1.8*22.22^3*
*W = 7186 + 3830 = 11016W = 11kW*

*Wh/mile = 11016/49.7 = 221.65 Wh/mile*
*miles = Wh/221.65 = (V * Ah)/221.65 = (121.6 * 90)/221.65 = 49.4miles*
*which only just gives me my minimum distance requirement. And that’s not even dividing the amp hour rating by 1.32 as suggested by the sizing your battery pack wiki!*


*Anyway my question is what can I do to improve the range? I am already coughing up a heap for the batteries and don’t really want to upgrade to the 160Ah as they are almost double the price. I can up the voltage to 144 but then that limits the type of motor and controller I can get. If using low resistance tyres I saw a website which claimed the rolling resistance of about .018 but I think that might be on concrete or something. Using this figure with the 180sx will yield a mileage of:*

*W = 1100*9.8*22.22*.018 + .6465*.3*1.8*22.22^3*
*W = 4311.6 + 3830 = 8141.6 W*
*Wh/mile = 8141.6/49.7 = 163.8 Wh/mile*
*miles = Wh/163.8 = (V * Ah)/ 163.8 = (121.6 * 90)/ 163.8 = 66.8 miles which would be great!*

*It seems like the rolling resistance is the key for better mileage. A decrease of 200kgs in weight only improves the mileage by 8miles but changing the rolling resistance increases the mileage by 17.4miles. Does anyone know if this rolling resistance is obtainable?*


*The next thing I gotta do is chose my motor and controller, like I said earlier I want it to be reasonably quick, top speed needs to be about 110km/h (70mph) with reasonable acceleration. Will I be able to reach 70mph on 120V? or will I need to up it to 144V? also for the acceleration I was looking at either 2 warp 9’s in series or a warp 13 or something, suggestions? *
*Can someone tell me if any of my workings are incorrect. I’m finding it hard to find any good DC conversions with a lithium battery pack to get an estimate of my mileage.*
*Any comments/suggestions would be greatly appreciated! thanks*


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## bblocher (Jul 30, 2008)

Sounds like you've already done more math than most. http://www.evconvert.com/tools/evcalc/ uses .015 for rolling resistance default but I recall from my research that was for standard inefficient tires and of the few tires I could find with better rolling resistence you could bring that down to .010. I just assumed this was on aspault.

As for your batteries and range I just ordered the 160s myself. I thought about the 90s too but went for the 160s for a couple of reason. The easier you are on them the longer they are going to last. The 90s can handle 3C continuous (270 amps) and anything over that shouldn't happen for too long. However any acceleration you will be pushing those limits. So for the 160 batteries your 3C limit being 480 is much better. Also trying to keep your DOD (depth of discharge) as small as possible increases the life of the cells (you can get more cycles out of them).

I wish my build was done so I could give you some better info on actual range but sounds like we are wanting the exact same type of build.


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## madderscience (Jun 28, 2008)

My god Jim, a mathemetician!

With the amount of money you are going to be throwing around anyway and the result of your calculations, it seems like you should find yourself a 180SX that is lighter and thus more efficient to start with and thus a better conversion candidate. Like you said, you are gonna keep the car awhile, right?

ABSOLUTELY get the low rolling resistance tires. Thats probably the biggest bang for the buck you can get in increasing range. Budget for a 4-wheel alignment job too after the car is completed (cheap!). Of course, low rolling resistance tires aren't also sticky drag strip tires. You can't have it all.

Removing external trim, spoilers, blocking the radiator air inlet, etc. and adding a good front air dam or belly pan with help aerodynamics too.

Even with all that if you really need a 50 mile drive on a daily basis without recharging, seems like the 160AH thunder skys would be better, plus the 3C maximum current on the 90AH ones is a bit low as previously stated.

No reason not to do 144v. At least with curtis controllers, there is no cost difference of any significance between their 120v, 550A controller and their 144v, 500A controller. The former will give a bit more low end torque, the latter better top speed. Plus higher voltage means less amps for the same power and thus less strain on the batteries. Don't worry about using 144v with a 120V rated motor. It will be a very rare case that you have full battery voltage across the motor anyway. DO get a controller/fuses/breaker that is rated for your full battery voltage.

A single warp 9" should be just fine. Siamese motor setups greatly increase cost and complexity and are usually used with much higher voltage battery packs. A 13" motor will be an absolute torque monster but bigger motors don't rev as well (lower peak RPM, etc). It would be like putting a diesel bus engine in your car. Lots of power but not the power band you want.

With zilla controllers off the market for now there really aren't any tire-screeching controllers out there that I know of, but a controller is fairly easy to upgrade so you can keep your eye out for a used raptor or zilla controller while you are actually able to drive the car. Stay away from kelly controllers, a lot of people seem to be having trouble with those.

Good luck.


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## Stiive (Nov 22, 2008)

Thankyou both for you replies and help.
i will start with a reply to bblocher

thanks for the link, i had seen that before but am unsure about how to use it! I am unsure what to do with the battery part, i select the thundersky batteries, it tells me its nominal voltage is 24v? and weighs 52kg? This sounds more like a lead acid battery but then the puekerts effect is only 1.056 which sounds more like lithium based. # battery strings? I’m guessing this is batteries in parallel not serial? Anyway I know im doing something wrong because I only get a mileage of 20miles.

As for the rolling resistance http://en.wikipedia.org/wiki/Low-rolling_resistance_tires gives the low rolling resistance tyres a value between .007 to .014 but never says on what surface. Whereas this wiki http://en.wikipedia.org/wiki/Rolling_resistance gives a table of tire rolling resistance but then underneath gives an example of a car on asphalt and uses a value of .03
“For example on the earth a car of 1000 kg on asphalt will need a force of around 300 newtons for rolling (1000 × 9.81 N/kg × 0.03 = 294.30 N).”

The value of .02 was used for normal tires on concrete, everyone knows concrete is smoother than asphalt, (that’s why tires screech so much in underground car parks) so I just assumed .03 was right. I always think its better to use a higher value and be surprised/happy with the actuals rather than be expecting too much and be disappointed, but im thinking super low resistance tires is the way to go. One thing that concerns me is using super low resistance tires with an everyday ICE car only gives 5-15% increase, but working out from an EV P.O.V the increase in range is enormous! (in my example almost double).

Yeh I think your right about the 160Ah’s, how about lowering the voltage to ~100V and then using 2 parrallel strings of 90Ah’s. That would give 180Ah and 540A 3C. Where did you get your batteries from? I am looking at this guys website for a generic price but havn’t shopped around.
http://www.everspring.net/txt/product-battery-pricing.htm
According to those prices 2 strings of 90Ah’s would be
100v/3.2 = 31 batteries
31 * 180 * 2 = $11,160
Continous Amps: 540A
Total weight = 3.2*31*2 = 198.4kgs

1 string of 120V 160Ah’s
38 * 320 = $12,160
Continous Amps: 320A
5.6 * 38 = 212.8kgs

Which seems like a pretty viable option! The range might be slightly less, but the acceleration should be better as the continous draw is increased from 320A to 540A! I would need to be sure though that my top speed of 70mph (110km/h) could be reached on the lower voltage! Is there a formula for getting an estimate for that? Either way though, upping my battery budget from 6,000 to 12,000 is a big kick in the teeth! Especially now because the Australian dollar has dropped so much! (yes I live in Aus) We are now down to 60cents US for some unknown reason!! Stupid US, its your financial crisis anyway, but that’s another story 


And now a note to madderscience:
I think Mathlete is the appropriate term 
Yeh I think 180sx is the way to go, although I was hoping for a far greater improvment in mileage for the 200kgs less it weighs! Ohwel, but like I said earlier, I cant believe that low rolling resistance plays such a big role in increasing mileage in EV’s but not in ICE’s. maybe its because I was using a ridiculously high coefficient? 
Interesting point you raise about the Warp13, never thought of it that way, but I will have a five speed gearbox, wouldn’t that eliminate the low revving problem? I am thinking of keeping my clutch as I want to be able to accelerate quickly. This is only going to be useful I guess if first gear is still useable with a DC electric motor as they have a tendency of not being high revving. How many seconds of full throttle do you think ill be able to get out of first before needing to shift? Is starting from first really going to make my acceleration time faster? I know electric motors have higher torque at low RPM, does this mean that the car will accelerate faster in 2nd as the speed will be lower and thus producing higher torque? I guess it really depends on the gearing ratio’s between 1st and 2nd and if the torque difference between them outweighs the torque droop of the motor. Unless I’ve got things completely wrong!
Its such a shame about Zilla controllers, that is really the key to my whole EV, I really need to plead with someone to sell me theirs! Will the car be fast enough with just one warp9 motor, can i expect good accelaeration? Say I did get the 160Ah batteries or the 2 strings of 90Ah’s what type of acceleration am I looking at? Anyone got a similar build that can comment?

Thanks both for you input and help! I have had a brief look at your builds and they are both looking VERY good! Your blogs are very comprehensive aswel, I think ill have to have a complete read of them. 
Bblocher, I couldn’t find what motor you are using? What type of mileage are you expecting from this build and acceleration. what percentage are you at in your build? im very interested because your using lithiums. BTW nice car, I love s2000’s, did you buy it as a wreck or you’ve just got plenty of money? Hope you sold the engine for a bit if you didn’t!  lol. You’ll be enjoying that car for many a year.

anyway thanks again for your replies! got a big learning curve ahead of me... gotta think of what im going to do about the money situation, im going to europe next year which is going to eat up about 15k minimum. I was happy to spend about 15-20k AU on the car, but now i think ill have to rethink my budget or expectations.


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## madderscience (Jun 28, 2008)

Mathlete... hmm.

One thing that did occur to me that you don't appear to be taking into account in your calculations though is the conversion efficiency for the energy powering the car. Your calculation for energy needed to move the car from aerodynamic and rolling resistance is energy at the wheels. There is a loss of around 20% going from the batteries through the controller, motor, and drivetrain. When I did my math, I modeled it as so:

Batteries/wiring: 98%
Controller: 98%
Motor: 89% (advanced DC 9" at the peak of its efficiency curve)
Drivetrain: 95% (RWD transaxle)

Multiply all those terms together and you get about 80% efficiency. So you need to factor that into your calculation too.

For what its worth, when trying to figure out what factor to use for LRR tires, I actually measured my rolling resistance before and after various steps to improve it. In all cases I measured it on the same strip of flat concrete roadway, with multiple measurements taken in each direction and averaged.
Knowing CdA, and the coast-down time from 40mph to 30mph, I can work backward to rolling resistance.

Anyway, at last measurement my car had a rolling resistance coefficent of 0.01 even. that is with bridgestone B381 LRR tires, 4 wheel alignment, tweaks to the brakes. Before I started, it was 0.014. (but the tires that were on it were better than most in rolling resistance, and they were almost bald)

So I suspect you can safely use a lower number in your calculations if you plan on using LRR. No more than 0.015 at the most conservative.

Motor size is really secondary to the controller in EV performance. "Its the watts, Stupid" would be a good way of putting it. A kelly, curtis, etc. all can put out at most around 500A at around 150V. That means a peak of about 100HP. Now just for comparison the top-of-the-line zilla I mentioned earlier can do 2000A at about 300V (assuming it had the battery to match). That is 800HP!!!!. The size of the motor is going to affect the ratio of RPM to torque for a given amount of power (HP) and it will affect efficiency, and how long you can sustain the peak HP. It doesn't matter whether you have a 6.7" prestolite or a siamese warp 9", you can't get any more power out of the motor than the controller can put into it. A single Warp 9" can take pretty much anything a 150V or lower controller can dish out from what I understand. No need to go bigger. 

I would not go below 120V in your conversion. You will not have any power at higher speeds. Try (hard) to stick with 144V if you can.

Good luck.


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## Stiive (Nov 22, 2008)

Bblocher, been reading your convert and im such a fan! I can see your taking alot of time with making everything you do perfect and it will really pay off. Top build, i love the fact that you have knowledge of sensors and microcontrollers, i intend to do alot similiar to what you have done. One thing i was scared of with converting a more modern car is the electronics (ESP, ABS etc) but i see you've found a way to handle these problems extremely well. You've provided me with much motivation, thanks.
It doesnt state in your blog however, that you intend on using lithium based batteries, have you already bought them? 
Ill be really interested to know what type of acceleration and range you are expecting.


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## Stiive (Nov 22, 2008)

Wow madderscience, thanks for the info...
considering what you have said, lets see how well my proposed 180sx will go.

*W = 1100*9.8*22.22*.01 + .6465*.3*1.8*22.22^3*
*W = 2395.3 + 3830 = 6225W = 6.2kW*
*considering efficiency of 80%*
*W = 6225 * 1.25 = 7781W = 7.8kW*

*Wh/mile = 7781/49.7 = 156.6 Wh/mile*

*Factoring in the amp hour rating by 1.32 as suggested by the sizing your battery pack wiki and 144V*
*miles = (V * (Ah/1.32))/165.6 = (144 * (90/1.32))/165.6 = 59miles using a 90Ah pack*

*miles = (144 * (160/1.32))/165.6 = 105.4miles using a 160Ah pack!!*


therefore 90Ah pack should be okay for me, and that's including 80% DOD, i will normally only travel about 50kms in a day (30miles) therefore i should stay above 50% DOD. Im happy again!

thanks madderscience! its all in the low resistance tires, and like you said earlier; adding a belly pan, blocking the air intakes etc should all add up to even more mileage! now to find a donar car


Added:
oh yeh forgot about the problem of 3C rating. hows about a bunch of capacitors, on a switch, when you think you will want to accelerate heavily in the near future, set them charging then when the battery drain next increases dramatically they take over to deliver the needed amps.
Could maybe hook them up in parrallel with the battery pack to give massive amperage, but then im guessing the voltage would have to be the same as the pack or would possibly screw something up. Anyone have any examples of using capaictors in EV's?
dont really want to upgrade to the 160Ah's as i think i should have enough juice for my mileage needs.... what are some other ways to increase the continous draw ratings? Is it possible to put just some batteries in parrallel? ie have 2 strings of 15 batteries in parrallel in series with 1 string of another 15? is anyone an electrician here? lol


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## bblocher (Jul 30, 2008)

Sorry for the delay I don't seem to be getting any emails from this thread like I normally do. 

That site is a little confusing but you can plug in all the data from your car to get some pretty cool results. I'm assuming all the math is correct. I'm not so sure on that strange lithium pack they have in there for the TS90 but it's a series pack. However, TS cells are 3.2 volt so nothing works out to exactly 24v. I'm assuming it's 8 cells in series and still the range didn't make sense with the capacity of those cells. I used the Valence pack which is 100Ah and just did some rough math to figure what the 160Ah would give. Hopefully it's close but what I also recommend is looking at what watt/hr rating is at different speeds and then figure out your range from there based on the pack. You can find this value hidden in one of the lower sections. Just click details to open it up after you calculate.

The other cool thing about the site is if you open the bottom sections it will break down what your top speed is for each gear. The lower gears will say it's limited by motor RPMs and the higher gears at some point will say limited by voltage so you can get an idea of your top speed this way.

I keep reading it's a really bad idea to put the lithium cells in parallel unless there is a balancing system. When you put them in parallel they self balance so I'm not sure what the problem would be if both cells where equal to start with. If not I could see a huge amperage draw the first time you hooked them up and that would be bad. Considering the price and to not void my warranty I'll just stick with the distributors recommendations for now 

I found Everspring first as well and their prices are pretty good with the quantity discounts they offer. However, you can get an even better deal from Elite Power Solutions. I have a "Which Batteries?" thread in the batteries secion you can check out for details on my purchase. I originally was planning on lead acid but over time realized that for my commute and to make the car practical for my needs I needed to go Lithium. I haven't updated my blog on that purchase yet. I was a tough one to make!


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## Stiive (Nov 22, 2008)

Hey thanks for the reply, i have been playing around with the calc, kinda getting it to work. Is there a reason why you went for the ADC 9" motor over a warp9? on the calc it says the warp9 gives more mileage per charge and is also more powerful. Therefore it must be quite a bit more efficient.
Im still concerned that i dont want to upgrade to the 160Ah pack because of the price as the 90Ah's will give me mileage i require, the only problem is the 3C rating. Still looking whether or not a bunch of capacitors can give me the extra AMP draw i will need for good acceleration....


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## bblocher (Jul 30, 2008)

Stiive said:


> Hey thanks for the reply, i have been playing around with the calc, kinda getting it to work. Is there a reason why you went for the ADC 9" motor over a warp9? on the calc it says the warp9 gives more mileage per charge and is also more powerful. Therefore it must be quite a bit more efficient.
> Im still concerned that i dont want to upgrade to the 160Ah pack because of the price as the 90Ah's will give me mileage i require, the only problem is the 3C rating. Still looking whether or not a bunch of capacitors can give me the extra AMP draw i will need for good acceleration....


If I remember correctly when I was researching the ADC motors have been around a lot longer and are proven reliable. Same with my controller I choose the Curtis 1231C because they have been around forever and most would agree they too are very reliable while not the most powerful controller available.

I hear you on the batteries. I've been debating what to buy since I started this project 5 months ago. Capacitors hold a rediculously small amount of power I can't imagine how many you would need and more importantly I'm willing to bet you would spend more money on high end capacitors than the lithium cells to get a decent reserve. You'll have to research that and prove it out  Other than exceeding the 3C continuous limit you will in general be pushing those cells harder than if you had 160Ah. If you check the documentation you'll see another number .3C which is over the cycle life. Not only do you need to try and discharge only down to 70% DOD to get the 3000 cycles but also try to average only .3C discharge rates (which won't happen). Go higher here and that also reduces battery life. So it might cost less in the beginning but if your cells are dead after a 1000 cycles or less then you're spending more in the long run. So in theory, the larger batteries should last longer too.


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## Stiive (Nov 22, 2008)

bblocher said:


> I keep reading it's a really bad idea to put the lithium cells in parallel unless there is a balancing system. When you put them in parallel they self balance so I'm not sure what the problem would be if both cells where equal to start with. If not I could see a huge amperage draw the first time you hooked them up and that would be bad. Considering the price and to not void my warranty I'll just stick with the distributors recommendations for now
> quote]
> 
> Surely you would be using a BMS anyway? but in order to only make half your string in parrallel im guessing you would then require 2 BMS's which will be expensive. Well i guess your right about the 160Ah's then, definetly eats into my budget though! when do you think you will have your installed by? maybe i should wait and see how your goes before i run off and order mine. BTW how much did you pay? did you get 45 to make 144V?
> ...


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## bblocher (Jul 30, 2008)

Stiive said:


> Surely you would be using a BMS anyway? but in order to only make half your string in parrallel im guessing you would then require 2 BMS's which will be expensive. Well i guess your right about the 160Ah's then, definetly eats into my budget though! when do you think you will have your installed by? maybe i should wait and see how your goes before i run off and order mine. BTW how much did you pay? did you get 45 to make 144V?


The system they recommend doesn't limit current or low voltage. You could do it with one BMS but it must be able to limit current to safely put batteries in parallel (from what I'm told).

I'm not sure when I'll be done but it'll be 3 or 4 months still I'm guessing. I ordered the litium cells $264 a piece times 45 for the 144v. The bad part is after ordering it's a minimum of 5 weeks they say. I may have missed the ordering window which means I could be looking at 2 months turn around  Elite doesn't keep the cells in stock (too damn expensive I'm guessing) and the time for China to perhaps make, ship them through customs, etc and get them to me takes awhile. You can get other cells quicker but if the sticker price of the TS cells scares you then don't bother looking around. They are cheapest out there that are still considered a good cell.


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## Stiive (Nov 22, 2008)

bblocher said:


> The system they recommend doesn't limit current or low voltage. You could do it with one BMS but it must be able to limit current to safely put batteries in parallel (from what I'm told).
> quote]
> 
> Why wouldnt the BMS limit low voltage and cap the current draw? what else are you using it for? just to charge? They are the 2 main things that kill a battery. Which BMS are you reffering to, is this the one you got? Im confused unless your talking about its parrallel BMS qualities.
> ...


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## bblocher (Jul 30, 2008)

Stiive said:


> bblocher said:
> 
> 
> > The system they recommend doesn't limit current or low voltage. You could do it with one BMS but it must be able to limit current to safely put batteries in parallel (from what I'm told).
> ...


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## Stiive (Nov 22, 2008)

drainer.... i wonder if you can upgrade and get a BMS that also monitors current draw and critical voltage and keep warranty. Although it probably wouldnt be too hard to make your own. Homemade volt meter over each cell and a microcontroller with a built in ADC. Can either use a MUX to continually check through the cells or get a microchip big enough with 45 ADC's in it. If voltage starts to drop warn the passenger with a couple of LED's and if its critical shut the power through a relay. 
I was wondering are you displaying the values from your sensors anywhere? An LCD on the dash or anything or are you just feeding the ECU? Maybe your going to inbed that laptop into your glovebox 
I plan on converting this car for my 5th year project so i plan on doing some cool stuff with MC's


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## bblocher (Jul 30, 2008)

They probably would honor the waranty but I never found a complete BMS system. I kept finding bits and pieces you could buy from different people/companies. Let me know if you run across any full systems that look good.

I haven't finished my electronics yet for the build, just done some prototyping so I don't have anything showing on the dash yet but do plan to add something. I have a giant lcd touchscreen to put somewhere now from the BMS system as well. As you mentioned there are some easy ways that I can add my own low voltage and even current limiters so that'll probably be another fun project after I get things up and going


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