Frequently asked questions about my homebuilt electric car project.
I get plenty of questions through YouTube, web forums, and other places asking specific questions about my car project. However, since many of them seem to be the same questions over and over, I am simply going to start a compilation of questions and answers right here to help everyone out.
What is the top speed?
Answer: On a DC motor system, speed is primarily based on VOLTAGE, which is mostly based on how many batteries you have hooked in a row (series connection.) The speed limit right outside my house is 45mph. In town, where I can find the bank, grocery store, library, etc., it’s all 25mph. So, I designed the car to go 45mph. This car, with a 72V battery pack will do the speed limit where I drive. I decided that I do not need to go interstate speeds to get to the grocery store. With more batteries in series, the car has a higher top speed. At 144V, the car can go over 70mph.
I have gotten a speeding ticket in this car.
Can the car easily cruise at 55mph for a range of 50 miles?
No. It was never designed to.
RANGE of an electric car is largely dependent on the CAPACITY of the battery pack, measured in Amp-Hours. The more bigger battery pack, the farther you can go. At some point, you just don’t have the room or weight-carrying ability to put more batteries in a car. In addition, the HEAVIER a car is, the more energy it takes to travel the same distance (you could say it gets worse fuel-economy.)
This car typically runs on six 12V batteries, each rated at 100AH. The math of multiplying all those together makes 7,200 watt-hours, or 7.2KWh. This car uses about 300 watt-hours per mile of travel. Dividing 7200 by 300 gets 24. 24 miles is the maximum theoretical distance that the car should be able to travel when fully using the batteries, all the way down to zero. Of course the batteries aren’t going to like that. Try using a number of half that (50% of battery discharge) to keep the batteries happy and long-lived. In this case, that’s only 12 miles, which doesn’t sound like much. However, my average trip to the library, grocery store, bank, hardware store, and post office, and back is just under 10 miles.
If I wanted to add more batteries to the car, there’s not much stopping me. As it is, the inside of the car looks pretty stock. I have a “normal” backseat and trunk. Adding more batteries might start cutting into my cargo space. I already have the range to go to the grocery store and back, AND I have the trunk space for groceries! It’s a win for me. That said, I would like to try to fit a few more batteries under the hood. That will give me a better range and top speed, without and real change to the rest of the car.
Some lead-acid battery cars can go 50 miles on a charge, but that’s on the high end. My car is definately on the minimal end. All of the major manufactured electric cars coming have some form of Lithium batteries. These batteries are smaller, lighter, and more expensive. Cars like the Leaf can go up to 100 miles on a charge. The Tesla Roadster can go over 200. It also cost more than my house. It’s very difficult to compare the performance of a $100,000+ carbon fiber sports car to a $1300 homebuilt economy car, but lets try…
The Tesla claims 240 miles percharge at a retail cost of $109,000. (We’ll ignore sales tax, etc. on buying one of these.) A little math tells us that it comes to about $445 per mile of range to buy this car. On the Electro-Metro, the complete cost of building the project was very close to $1300. Lets go with the 12 miles range just to be really conservative. That’s about $108 per mile of range for this vehicle. So, in terms of just plain miles you can go versus cost, the Electro-Metro is four times as cost efficient as the Tesla. (Granted, the Tesla IS a MUCH cooler car!) Keep in mind that the Metro was also built with off-the-shelf parts, and could be made by just about ANYBODY. And again, adding more batteries is always an option.
What do you think of installing solar panels on the roof?
I think it’s a great idea to install solar panels on the roof….. of my garage.
Referring back to the batteries answer earlier, the car uses about 300 watt-hours per mile. That is the amount of electricity used if you had five 60-watt lightbulbs on for an hour. A solar panel to create 80 watts in full sun will be larger than 3 feet long and 2 feet wide. You will need 4 of them to make at least 300 watts, and they will never be faced properly into the sun. (Except parked in full sun on the equinox…) So let’s say you now have the car with something like a ladder rack to support all these solar panels (and only drive on windless days…), You still have to be parked in the sun for an HOUR for every MILE you want to drive. If you live someplace VERY sunny, and ONLY drive short distances, and infrequently, this may actually work. You will have a very funny looking car, with the charging system that costs more than the vehicle, but it could work. You would also run into a problem in terms of WHEN you could charge the car. Lets say you go out for a drive in the evening. You can’t charge at night (no sun!) so charging doesn’t start until the next morning. Eight hours later, you now have enough charge to go 8 miles. And that’s only if it wasn’t cloudy that day.
A far better way to deal with all this is to put solar panels on the house, the garage, or mounted in the yard. Those panels can be bigger. You don’t have to worry about them getting ruined in a car accident. If they are grid-tied, you can sell extra power to your utility. At night, charge your electric car from the wall, at less expensive “off-peak” electric rates. It’s a win for everyone.
How many batteries did you finally put in?
Just six. (Seven if you are also including the original “accessory” battery, which runs the headlights, radio, etc.)
It’s enough to get me around with acceptable range and speed, while still keeping the full trunk and seating for four.
I am looking at adding some additional batteries under the hood for increased speed and range. This will require purchasing some batteries of a different size (just has to do with how they would fit) and some custom welding to build a rack to mount the batteries in.
I have experimentally run the car on up to 12 batteries. Boy was that fun! The car could go over 70 mph and do burnouts. The entire back of the car was full of batteries though!
I think that for the long run, a compromise of a 96 or 108 volt system will be ideal for this vehicle.
Why not just add an Alternator/Generator?
Running an alternator from the motor to make electricity to recharge the batteries is a bit like trying to fly by pickup yourself up by your own belt. Try all you want, you won’t come out ahead. Even if we completely ignore the cost and complexity of connecting a high-voltage alternator to an electric motor, the big question is ENERGY INPUT. In a typical gasoline car, the external energy source is the gasoline, filled into your tank at the gas station. On an electric car, the outside energy is electricity from the wall outlet, through the charger, into the battery pack.
An alternator does not ADD any outside energy into the system. It’s only a way to change mechanical energy into electrical energy. It can only lose energy in the form of heat and noise. It can NOT create energy. It also does NOT make any more efficient use of the battery’s electric energy. That going basically straight from the batteries to the electric motor is about as efficient as you can get. Adding more steps to the process only LOWERS efficiency.
On the other hand, if you added a gasoline generator, that WOULD add an outside source of energy to the system, in the form of the gasoline in the generator’s fuel tank. However, you also add complexity, an engine, a carbuerator, air filter, oil filter, exhaust system, noise, etc, etc. And you don’t really have an electric car any more. Now you have some sort of a “Plug-In Hybrid”. Not that there is anything wrong with that. That’s exactly what the Chevy Volt is, and when I saw it, I have to say it’s a pretty nice car. But you really can’t call it an EV.
(There are all sorts of discussions on the web right now about exactly how to describe the Volt. I guess I would simply call it “unique”, as there is no other car out there right now that uses the exact same setup. Love it or hate it, it IS in a class of it’s own.)
I DID do an experiment with my car adding a propane generator from an RV. The generator has a 250CC engine and could provide about half the energy needed for the car to cruise down the road. It also took up all the cargo space, and was louder than I care for. After some test drives, I decided that a better way for additional range would be one of two extremes – either a bunch more batteries and no generator OR a much bigger generator, better integrated into the car (under the hood, reusing original exhaust system, etc.) So, that gets us back to the Nissan Leaf vs Chevy Volt styles of building a car.
For me, I like it simple and not having to change the oil….. EVER AGAIN.
To me, that’s just a plain motor and batteries.
Question: What’s the CAPACITY of the battery pack?
The batteries are 100 AH, and I have typically been running with 6 of them.
12V x 100 = 1200WH x 6 = 7200.
So, it’s a 7.2KWh battery pack. However, it is all USED batteries, so I can’t expect them to perform like new.
300 Wh per mile is a common number to use as an estimate of how much energy a car like this uses. If you divide the number in half (because you only want to use half the battery pack, to keep them happy and give them a nice long life) that’s 3600 wh, divide that by watt-hours-per mile (estimated 300) and you get 12.
So, this car, running on only 6 used batteries, can regularly 12 miles per trip. That doesn’t sound like a lot, but I live 2 miles from town, 2.5 miles from the grocery, 3 miles from the hardware store. You get the point. My typical trip of running all my errands is about 10 miles. And that’s running the pack half-way down. If I want to take them down to about 80% discharge, that’s a nearly 20 mile range.
6 12-volt batteries is really bare minimum for an electric car. Recently, I removed one of the used batteries and added 4 new Die-Hard Platinum batteries. The car has much more ooomf! and better hill-climbing. (There’s two LARGE hills in my area)
Question: What car should I pick for my conversion?
Pick a car you like. If you don’t like it as a gas car, you won’t like it as an electric car. Make sure the body is sound. Don’t convert a rusty car. No sense putting in all that work only to have a rusty car when you are all done. On unibody passenger cars, the body is also holding the weight of the batteries. In general, you want a car with a manual transmission. Automatic transmissions can be converted, but are more complicated, more work, and yet less efficient. Pick a car that has enough cargo space and weight-carrying capabilities for the number of batteries you want. Station wagons and light trucks are popular.
Why did you use a forklift motor?
It was cheap and it works well. A series-wound electric forklift motor is powerful, very similar to what is sold commercially just for electric cars, and was very affordable. A used forklift motor can be found at a junk yard or other places (I found mine at a garage sale for $50!) It only really requires basic knowledge of electric motors to examine the motor, clean it up, inspect the bearings, and replace the brushes.
Can you tell me what power of motor I need for my project?
No, but you can figure it out. There are a number of on-line calculators that will assist you in figuring out speed, power, and other things about your project before you buy any parts. The EV CALCULATOR will help you figure out range and speed of your EV by entering what car, what batteries, etc. Over at EcoModder.com, they have a nice tool to figure out energy use of your car at various speeds.
Question: I want my car to go XX MPH/KPH for a distance of XX miles/km. How do I do that?
Using the tools listed just above, you should be able to ball-park your vehicle’s top speed and range. Please have realistic expectations. Remember that it takes MORE than twice as much energy to drive 75mph as it does to go 45mph. After you do the calculations, do a bit of a reality check. Can that many batteries physically FIT in a car? Can the car carry the weight of the batteries? Lead-acid batteries have diminishing returns when it comes to weight, space, and range. Lithium batteries are considerably better, but greatly increase the cost. Do your research to make sure you know what you are expecting before spending money on batteries and either spend too much on Lithium or are disappointed in the range on Lead.
Question: I’ve got a Geo Metro! Can you convert it to electric for me?
No, but I’d love to see you do it. I put a lot of time, energy, blood, sweat, and tears into my project. It was great fun and a fantastic learning experience. I did take time. For me, it was about 6 months. Of course I could do one faster now, but to charge somebody to convert a car for them, it would either cost them too much or I wouldn’t be able to make enough profit to make it worth my time. Instead, I strongly encourage you to purchase the BUILD YOUR OWN ELECTRIC CAR: CHEAP! instructional DVD set. In it, I take you through every step of converting my car from gas to electric.
Got more questions? Ask them in the comment space below! I’ll answer them, so everyone can benefit from learning more about this project!