# What I have discovered while building an EV



## sirwattsalot (Aug 27, 2012)

I am certainly not the last word on building an electric car. What I can tell you is that my own experience so far has brought me to some conclusions about motors, transmissions and other components that are required. I have never seen a really good electric car that was cheap to build, or cheap to buy ready made. I really would like to buy one from a local dealer at a price that I could afford. Dream on right!
First, lets talk about the motor. If the motor is too small for the job, it will overheat and the top speed and overall performance will disapoint.
While it is tempting to use cheap motors intended for industrial use, you will find that these are usually built much too heavy, and are difficult to fit into a small car. There are a few really good motors that are built specifically for use in electric cars. They are all expensive, but they are well worth the price if you are looking for speed and reliability that has been proven on the road. I was considering the Warp 9, DC series wound and the AC50, 3 phase motor. Weight, Range, and top speed, are everything to me so naturally I picked the AC50 which is an excellent fit, it is reasonably light, it is really effecient and good at climbing the hills. I wanted at least 75 mph and a car that could get me to work and home again on the highway without a drop of gasoline. Who would not want to drive a car like that? So, I will not attempt to install an old forklift motor, or something out of a washing machine because it just won't give me what I want.
I wondered why I needed a transmission at all. I found that I would really miss having all those gears in city traffic. Every time the car stops and starts rolling again it would put a huge load on the motor, controller and batteries without the lower gears, so I will keep the transmission and make certain that it is a manual 5 speed.
Then there are Issues of getting guages to work like a fuel guage. Of course, if I had a volt meter, an amp meter, and if I used the old speedometer, that would do just fine. I made up my oun sending unit for the old fuel gauge so that it would detect full, empty and all points inbetween. But, the kit that I purchased had this cool little digital display that shows the RPMs, temp, current, battery charge, etc. What could be more perfect?
Power brakes? Yep, all I needed was a vacuum pump. I choose a really noisy electric pump which works great. I just had to run some hose off the output of the pump into a muffler to quiet it. An electric car with a muffler, can you imagine that?
The kit had the relay and main contactor so that was no big deal. The hardest part has been installing batteries in the car. 
Yep batteries. How about 18, 6 volt, 70 lb, sulfuric acid filled, lead batteries? Yep, the kind that some companies recommend to me over the phone. Nope not really, I don't think so. The last thing I wanted was 1260 lbs of tire poping, car crushing weight. I could see myself swiming in a bath of sulfuric acid after a bad accident. I have installed 9, 12 volt, premium, non-spillable, lead drycell batteries which weigh 49 lb each. If they are good enough for race cars, they are good enough for my car. I really can't afford lithium ion batteries either so these will do.
this is only my second try to build an electric car. I will be honest. The first attempt was a really fun go-cart that looked like a car with a top speed of 48 mph and a range of about 40 miles. The motor was built for motorcycle use, not for a car. The motor got very hot and produced some smoke. It was fun, it was cheap, and it was far less than what I wanted a car to be. So, now I am trying to do it right with a budget of only $15000. and components that are actually rated for electric car use. I hope it will be rewarding in the end. It sure was cheaper when I was a kid and I could build a spaceship out of a cardboard box. I have not finished my car yet so if you will excuse me I am going to sit in it and make electric car noises. Brrrrrrrr, woosh, wiz-zoom.


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## PStechPaul (May 1, 2012)

I don't know how much you are paying for the SLAs but I found a good deal on 12V 12Ah SLAs for about $23 each including free shipping. They are 10 pounds each, so for the same weight as your 450 lb of SLAs you could get 45 of these for about $1000 and have 6.5 kWh. They would also provide 540 volts so it would be possible to run a 480V VFD. Probably best to add 5 more batteries to get 600 VDC which is a perfect DC link voltage, and that would be 7.2 kWh. When I got my batteries I got a coupon for 10% off, and you can probably get an even bigger discount for a large order. So for under $1000 you can have 7.2 kWh although if you run near 1C Peukert will bite you and you might get only half that. If you have a really good car you might go 4 miles on 1 kWh so you'll have a range of 16 miles or so. If you can accept twice the weight, for a total of about $2000 you can get at least 32 miles range and perhaps 40.

The batteries came from: http://stores.ebay.com/Ecomelectronics

Specs: http://www.batterysolutionsinc.com/ub12120-12-volt-1200-amp-hour-p-7530.html

They were delivered within a few days and seem to be good, but only time and use will tell. However, I have a 12V 17Ah SLA I bought probably 8 years ago with a 1999 date code and even though I had left it outside for several years it still held a charge and still seems pretty good, so perhaps SLAs are better than flooded batteries. 

The best price I've found for flooded batteries is about $80 for 120 Ah, or about $0.055/Wh. The SLAs are about $0.16/Wh. And Lithium cells seem to be about $0.50/Wh. 

Good luck with your build.


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## sirwattsalot (Aug 27, 2012)

The batteries that you have were a good deal for many projects however, 16 kw is about the minimum required for a long range car. The SLAs that I purchased deliver 3100 short circuit amps and the bank of 9 batteries provide approx. 16 kw. The total battery weight is 441 lbs.
I need to exceed a range of 60 miles to make it practical to drive. Each battery was $240. but it was still a fraction of the price of lithium ion. The power to weight ratio is about the same as 6 volt golf cart batteries but the advantage is lower curb weight, drag and less space required to fit them in.


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## major (Apr 4, 2008)

sirwattsalot said:


> The batteries that you have were a good deal for many projects however, 16 kw is about the minimum required for a long range car. The SLAs that I purchased deliver 1500 short circuit amps and the bank of 9 batteries provide approx. 16 kw. The total battery weight is 441 lbs.
> I need to exceed a range of 60 miles to make it practical to drive. Each battery was $240. but it was still a fraction of the price of lithium ion. The power to weight ratio is about the same as 6 volt golf cart batteries but the advantage is lower curb weight, drag and less space required to fit them in.


Hi sirwatt,

Are you confusing power (kW) and energy (kWh)? You say 16 kw is required for long range. That is 21 hp for long range???? 

Assuming you meant 16 kWh, then each of your 9 batteries would need to store 1.78 kWh of energy. Each battery is 441 lbs / 9 = 49 lb. For a nominal calculation: 1780 Wh / 12 V = 148.3 Ah.

I do not think it is possible for you to get a 49 lb lead acid battery rated anywhere near 148 Ah. If so, please let us in on your source.

Regards,

major


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## PStechPaul (May 1, 2012)

As I have been reminded of previously, there is also the Peukert factor. Typically, lead-acid batteries pulling 1C deliver about 1/2 their rated 20 hour capacity. So a nominal 16 kWh pack will only provide 8 kWh if using a full 16 kW for cruising. I think it's more likely that only about 8 kW will be needed at moderate speeds, but even then, at 1/2C, Peukert of 1.2 still gives only 63% of rated capacity, so about 10 kWh usable (and that's probably to a very deep discharge, which shortens battery life). Using standard 250-350 Wh/mile, you might get a range of 30-40 miles with new batteries, and it goes downhill from there. 

Using my EVcalculator http://www.enginuitysystems.com/EVCalculator.htm, a 1000 kG (2200 lb) car will take about 5.5 kW at 62 MPH on a flat road. But with 500 pounds of lead, it goes up to almost 7 kW. And for the usual weight of an SLA 16 kW battery pack (0.069 lb/kWh or 1100 lb), the power goes up to 8.3 kW. This works out to 134 Wh/mile, which is only achievable for purpose-built EVs. At the more generally accepted (and optimistic) 250 Wh/mile, you get the more realistic estimate given above. 

The reason for the lowball estimate of the EV calculator may be the zero slope (zero acceleration). his would be true if 100% regen were possible, or on a perfectly flat road. But since regen might only account for 10-20% recovery, you can figure an average slope of 2% for normal terrain, which is 0.02G or about 0.2 m/s/s. Plugging that in, I get 16 kW average power, and thus 268 Wh/mile, and with Peukert the battery pack is now only 8 kWh, and your range will be only about 30 miles. 

"Sorry, Charlie." It's not going to work as well as you expect.


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## sirwattsalot (Aug 27, 2012)

PStechPaul said:


> As I have been reminded of previously, there is also the Peukert factor...and your range will be only about 30 miles.
> 
> "Sorry, Charlie." It's not going to work as well as you expect.


OK, but here is the thing- I have had this car on the road for a real world test drive with only six of these same 1500 series batteries. I drove the car 10 miles with my foot to the floor and the small electric PM motor (too small but 90% effecient) smokeing hot, up and down hills and lots of starts and stops. The top speed was only 48 mph except for one downhill stretch, but I expended only 1/4 of the battery charge. When a battery such as these have been discharged to 10 volts under load, it should be considered empty. Fully charged, a good battery may read from 13.3 to 14 volts. Each battery quickly charged back up to full on a 10 amp charger within 40 minuets. I feel certain that I could exceed 30 miles with as few batteries at the car's best speed. Calculations only work well when all the numbers are exact and true. If you take out everything that you do not need that is heavier than a paper clip, you will improve the power to weight ratio, the range, and acceleration. Different types of batteries behave very differently and temperature has a huge effect on most. Lithium for example will loose energy in the cold of Winter but will perform well in Summer. Not all batteries are created equal but the calculators treat them as such.
In the end, the results will tell the tale.


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## sirwattsalot (Aug 27, 2012)

I have not been able to find an amp hour rateing for the Oddessy 1500 series batteries. I have used them to power my house during power outages and one of these has run a full size fridge and a TV for 7 hours. Most batteries have a 5 minuet reserve. These have a 40 minuet reserve and a short circuit current of 3100 amps.
My first test drive with six of them proved that batteries perform well. They are not the largest battery, they weigh only 49 lbs, they work in the cold of winter.
We will just have to see what the car can really do when finished. To be honest, anything else is just a guess. I am always interested in what other people have been able to do to exceed 100 miles on a charge. I know what batteries they used but I can't afford them.


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## major (Apr 4, 2008)

sirwattsalot said:


> I have not been able to find an amp hour rateing for the Oddessy 1500 series batteries. I have used them to power my house during power outages and one of these has run a full size fridge and a TV for 7 hours. Most batteries have a 5 minuet reserve. These have a 40 minuet reserve and a short circuit current of 1500 amps.
> My first test drive with six of them proved that batteries perform well. They are not the largest battery, they weigh only 49 lbs, they work in the cold of winter.
> We will just have to see what the car can really do when finished. To be honest, anything else is just a guess. I am always interested in what other people have been able to do to exceed 100 miles on a charge. I know what batteries they used but I can't afford them.


http://www.odysseybatteries.com/battery/pc1500series.htm 

Chart at bottom of page: One hour, 47.3A (47.3 Ah), 556 Wh. And that is a discharge to 10.02 V. So pretty much 100% DoD. You'll cut your cycle life way down if you do this often.

note.... that comes out to 5.0 kWh for your 9 batteries.


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## PStechPaul (May 1, 2012)

I've followed some of your videos, and from what I can tell you are using these 1500 series batteries:
http://www.odysseybattery.com/autospecs.html

They are 68 Ah at 20 hr rate and 62 Ah at 10 hr rate. From this I calculate a Peukert number of 1.15, which is better than most batteries. But using six of them you will have a total of 4900 Wh. According to your video you are using a Mars/ETek 19 HP (probably peak) motor. Probably about 10HP continuous rating. If it overheated then it shows that you were running probably 15-20 HP for a long time, so we'll say 10 kW. That's a 140 amp draw on 68 Ah batteries so even with the good Peukert number the effective capacity will be 38 Ah and a run time of only 16 minutes. 

Since the motor overheated it was obviously not very efficient at that power level. Maybe 50%. So your actual power delivered for moving the car may have been only 5 kW, which is about right according to my calculator. A true 90% efficient motor might have given you 30-40% more range. 

As I had suggested before, it would be very helpful to run a data logger for a typical run of your car, and maybe it can be done with what you have now. I know you believe you can "beat the odds" and challenge the doubts of the EV community, and I admire your efforts and optimism. But something does not quite add up. For one thing, you said your 9 batteries would provide 16 kWh, but 68*12*9=7.3 kWh. Perhaps you used the 135 *minutes* reserve capacity per the specs as Ah, and the full 13.2 volts which gives 135*13.2*9=16.0. 

Again, I don't mean to be critical. But I think you have made some erroneous assumptions. If your budget is $15,000 you can probably spend $12,000 on batteries and that should buy you about 24 kWh of LiFePO4 which will give you an honest 70+ mile range. I'm sure you can find a motor and controller for about $3000.


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## sirwattsalot (Aug 27, 2012)

I have been trying hard to determine what the speed and range might be however I think that now we will just have to wait and see. None of the calculations have come close to the test results so far. The ten miles that I drove did not run the batteries down very much. I could have gone close to 40 miles if I had continued to drive with the motor smokeing, at a lower speed and on a straight and level road without all the stops and starts. The lighter I make the car, the less energy it will take to move it down the road. But, there are too many variables. In the end, it will go as far as it does and as fast as it does.


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## PStechPaul (May 1, 2012)

I can see that you are determined to proceed as planned and then just accept the results, being optimistic but resigned to whatever the end result may be. There is some virtue in that, and "more power" to you. But one other thing confuses me. You say that you drove 10 miles with the motor overheating and purposely starting and stopping to maximize the power used, and the batteries were depleted to about 10V (under load). So you used 68*12*6=4.9 kWh or about 500 watt-hours per mile. About twice what "good" EVs use but you were purposely pushing it and your motor was inefficient, so that seems just about right. 

But then you say you fully charged the batteries in 40 minutes at 10 amps. That's only about 6 Ah. They may have reached a voltage of close to 14V after 40 minutes but they were probably still accepting charge current, so could not have been fully charged even if they were "perfect" batteries. I think it would be wise to invest in a datalogger and determine just how much power and energy you need for the performance and range you want, and then determine the components that will come close to fulfilling your dream. 

These batteries do seem to be much better than the usual deep cycle batteries or SLAs. But that comes at a hefty cost. Flooded batteries are about $0.06/kWh, SLAs are about $0.16/kWh, and these are about $0.30/kWh. If you are pushing them to 1C the effective cost will be about $0.50/kWh. For the same cost you can get LiFePO4! 

Check out http://www.electriccarinternational.com/Lithium-Prismatic-Batteries.php. They have genuine Calb 40 Ah 3.2V cells for $54 each. That's $0.42/Wh. So for the 108 volt system you plan with your nine batteries you can get about the same for 34 of these at $1836. I say about the same because this pack would have a true capacity of 4352 Wh while your pack would be 9*12*68*0.6=4400 kWh with the Peukert factor. And the LiFePO4 cells would weigh only about 120 lb compared to your 450 lb of lead. 

Think about it!


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## sirwattsalot (Aug 27, 2012)

Thanks for the information on the lithium batteries. I am certain that they would work better and reduce the weight. The one thing that I must clarify is that I did drive a total of 10 miles but the six batteries were not discharged each to 10 volts. 10 volts per batt would have been fully discharged. They dropped less than one volt each or about 25% of the full charge. 
Yes, I did purposly press the motor to it's limits and I tried my best to discharge the batteries with my foot pressed to the floor all the way. I really wanted to see how far it would really go but I quit before I ruined the motor.
Here is a new video of the progress on the car which was made just this afternoon.
http://youtu.be/Fub9TIr57Y8


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