Electric car: DIY!
- Thread starter Frank
- Start date
Yes, I know. Half the fun would be the lack of visual supports or other safeguards against terminal faillure.There are flying chairs alreadybut helicopter-like construction.
The main problem with driving electric is (and always has been) of course the size and the weight of the battery pack. For price/performance, nothing beats the ancient lead acid batteries. But they are very big and very heavy. If you use them to power the car and want decent endurance and power, you're looking at filling all available space (trunk, engine compartment and whatever other space you can find) with batteries, that in the end are just as heavy as everything else combined.
So, DIY electric cars are generally designed for an endurance of about 70 miles, with a top speed of around 100 km/h and a 0-100 km/h acceleration of less than 30 seconds. That makes it cheap and leaves most of the room in the car available for passengers and carrying stuff.
Then again, there are alternatives. A pack of the new Lithium Polymer batteries:
This is used in a converted Subaru Impreza to win races against ICE cars.
But, unfortunately, they're sill quite a way off for a home build EV.
So, DIY electric cars are generally designed for an endurance of about 70 miles, with a top speed of around 100 km/h and a 0-100 km/h acceleration of less than 30 seconds. That makes it cheap and leaves most of the room in the car available for passengers and carrying stuff.
Then again, there are alternatives. A pack of the new Lithium Polymer batteries:
This is used in a converted Subaru Impreza to win races against ICE cars.
And, as you can see, it's rather small and light. But it costs about $60,000. Mass production could and should take care of that, as there is nothing inherently expensive involved in making them.
But, unfortunately, they're sill quite a way off for a home build EV.
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About electric motors:
First, the power rating. While IC engines are rated for their maximum power, electromotors are rated for their sustained power. A 200 hp ICE is about equal to a 40 hp electromotor.
Second, while ICEs are generally rated in horsepower, electromotors are rated in KW. One hp = 0.75 KW. So, that electromotor will be rated 30 KW, while that ICE will be rated 200 hp.
Third, that electromotor has maximum torque from 0 rpm, and a linear increase of the power to the rpm, depending on the type. A DC motor has huge torque, but levels off at high RPM and needs a huge amount of current, an AC motor has great torque and levels off much more smoothly but needs an expensive controller, and a brushless motor has great torque and power over the whole range it is designed for, but only functions well in a rather narrow rpm range.
Fourth, depending on the type and configuration, that electromotor can have massive torque at low rpm (direct drive), or can reach very high rpm (15,000+) without problems. So, unless you only have a smallish energy source (few/small batteries) and don't want to lack power when it runs low, you don't need any transmission or gears (except for a fixed ratio when you use a high rpm motor).
Fifth, a 20 KW electromotor is generally not very much cheaper than a 50 KW one, and both will deliver up to 10 times the nominal power in bursts. So you can get a very beefy one, although it is a waste if your controller and batteries cannot deliver the needed electricity to power it.
Sixth, if you buy a great electromotor and controller, they should last pretty much indefinitely: you would probably replace the car around it and the batteries multiple times before you should see any wear on them. So if you are planning on going electric, they are a great investment into the future.
First, the power rating. While IC engines are rated for their maximum power, electromotors are rated for their sustained power. A 200 hp ICE is about equal to a 40 hp electromotor.
Second, while ICEs are generally rated in horsepower, electromotors are rated in KW. One hp = 0.75 KW. So, that electromotor will be rated 30 KW, while that ICE will be rated 200 hp.
Third, that electromotor has maximum torque from 0 rpm, and a linear increase of the power to the rpm, depending on the type. A DC motor has huge torque, but levels off at high RPM and needs a huge amount of current, an AC motor has great torque and levels off much more smoothly but needs an expensive controller, and a brushless motor has great torque and power over the whole range it is designed for, but only functions well in a rather narrow rpm range.
Fourth, depending on the type and configuration, that electromotor can have massive torque at low rpm (direct drive), or can reach very high rpm (15,000+) without problems. So, unless you only have a smallish energy source (few/small batteries) and don't want to lack power when it runs low, you don't need any transmission or gears (except for a fixed ratio when you use a high rpm motor).
Fifth, a 20 KW electromotor is generally not very much cheaper than a 50 KW one, and both will deliver up to 10 times the nominal power in bursts. So you can get a very beefy one, although it is a waste if your controller and batteries cannot deliver the needed electricity to power it.
Sixth, if you buy a great electromotor and controller, they should last pretty much indefinitely: you would probably replace the car around it and the batteries multiple times before you should see any wear on them. So if you are planning on going electric, they are a great investment into the future.
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I did some research, and a total conversion of a reasonably light car (up to 1200 kg) that would give you all the options, all the parts prebuild and matched, decent driving characteristics, 0-100 km/h in about 15 seconds, a top speed of ~ 150 km/h and a range of 200+ km with normal driving, would cost about 7000 Euro. It would use 18 8v lead-acid batteries, which is a lot of weight and room (ie: your whole trunk and engine compartment) you need to give up. If you use 12 12v batteries instead, you could save 1000 bucks and a third of the space, but your range would also go down with a third.
A minimal conversion would be about 4000 Euro (so yes, it can be done for that money), but you would have to do everything yourself, make some mechanical and other parts yourself as well, and it wouldn't be much fun to drive and have a rather low range (very dependent on the car and parts used). But it would be very cheap to drive, and excellent for daily commutes in and around the city.
For 12,000 Euro, you could buy a sweet kit, 250 hp, 500+ Nm, 24 KWh (with 5 35v Li-Ion batteries that are heavy (48 kg), but only a bit bigger than full-size lead acid batteries, very durable and can deliver over 1000 ampere sustained (!)), great acceleration and a range of 200+ km. It actually uses the favourite motor for this kind of projects: the Bulgarian Kostov motor. It's about the simplest and cheapest DC motor imaginable (originally build for forklifts), but you can easily run it at up to 10 (!) times the specified voltage of 32 volts for extended periods without any problems. It's quite famous. This is actually the best option for price/performance, but (like with the 4000 Euro one), you would have to do it all yourself.
If you want excellent performance in single-motor configuration, low weight and space requirements, 267 hp, 450 Nm, 29 KWh of "cheap" Lithium Polymer batteries (even better specs than the Tesla Roadster, but probably build into a heavier car), blistering acceleration, a top speed of over 200 km/h and a range of 2-3 hours / 200-300 km (depending on the car and driving style), you would pay 50,000 Euro.
And if you want the very best, a car that outperforms just about any other car in existence, with 4 hub motors, 428 hp, 2680 Nm torque (!!!) from 0 rpm, 50 KWh of high-performance Lithium Polymer batteries (So, up to 500 km / 5 hours range, but you will never make that in such a car), you would pay about 120,000 Euros. And the size of your wheels would determine the top speed you could reach, so bigger = better!
All this is excluding the car you use, so you would have to add the cost of that as well. For the two cheap options (4000 and 7000 Euro), you need a reasonably spacy car, as they use bulky lead acid batteries. The two expensive models both use a smallish stack of Li-Pol batteries, so they should fit any frame, and the 12,000 Euro kit is in between. And, of course: all ranges are for "light" driving. If you like to floor it and/or go fast, halve or even quarter those ranges, depending.
And, of course: the lighter the car, the better.
A minimal conversion would be about 4000 Euro (so yes, it can be done for that money), but you would have to do everything yourself, make some mechanical and other parts yourself as well, and it wouldn't be much fun to drive and have a rather low range (very dependent on the car and parts used). But it would be very cheap to drive, and excellent for daily commutes in and around the city.
For 12,000 Euro, you could buy a sweet kit, 250 hp, 500+ Nm, 24 KWh (with 5 35v Li-Ion batteries that are heavy (48 kg), but only a bit bigger than full-size lead acid batteries, very durable and can deliver over 1000 ampere sustained (!)), great acceleration and a range of 200+ km. It actually uses the favourite motor for this kind of projects: the Bulgarian Kostov motor. It's about the simplest and cheapest DC motor imaginable (originally build for forklifts), but you can easily run it at up to 10 (!) times the specified voltage of 32 volts for extended periods without any problems. It's quite famous. This is actually the best option for price/performance, but (like with the 4000 Euro one), you would have to do it all yourself.
If you want excellent performance in single-motor configuration, low weight and space requirements, 267 hp, 450 Nm, 29 KWh of "cheap" Lithium Polymer batteries (even better specs than the Tesla Roadster, but probably build into a heavier car), blistering acceleration, a top speed of over 200 km/h and a range of 2-3 hours / 200-300 km (depending on the car and driving style), you would pay 50,000 Euro.
And if you want the very best, a car that outperforms just about any other car in existence, with 4 hub motors, 428 hp, 2680 Nm torque (!!!) from 0 rpm, 50 KWh of high-performance Lithium Polymer batteries (So, up to 500 km / 5 hours range, but you will never make that in such a car), you would pay about 120,000 Euros. And the size of your wheels would determine the top speed you could reach, so bigger = better!
All this is excluding the car you use, so you would have to add the cost of that as well. For the two cheap options (4000 and 7000 Euro), you need a reasonably spacy car, as they use bulky lead acid batteries. The two expensive models both use a smallish stack of Li-Pol batteries, so they should fit any frame, and the 12,000 Euro kit is in between. And, of course: all ranges are for "light" driving. If you like to floor it and/or go fast, halve or even quarter those ranges, depending.
And, of course: the lighter the car, the better.
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Mintmaster
Veteran
It's not that small and light. Assuming a mediocre 25% thermal efficiency of an ICE, 25 lbs of gas will drive a car just as far as that 565 lb battery pack.
So the range of this battery pack is basically equivalent to the distance you can travel with 4.5 gallons of gas. Doesn't seem remotely good enough for mass adoption, but I guess some die hards will go for it. Bleeding edge battery tech has about 2.5 times the energy density, so maybe electric cars will be acceptable (in terms of practicality and economics) in a decade or two.
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That is just dumb. When you get to the end of that 4.5 gallons the gas is gone. Batteries don't simply disappear when the need to be recharged.
Mintmaster
Veteran
Uhh, did you notice the word "range" in my post?
I don't even know WTF you're trying to say. A fuel tank doesn't disappear either. When batteries empty, you can't go anywhere until your recharge again. When a fuel tank empties, you can't go anywhere until you refuel. Your analogy is completely bunk.
The gasoline is gone. You have to refill it with expensive fuel. Electricity if practically free in comparison. The expense is in the battery with an electric car and in the fuel for an ICE car. The point is energy density has absolutely nothing to do with it. Cost is orders of magnitude more important.
Why does driving electric sounds so compelling to some people?
1. After the initial investment, it's very cheap. Replacing the batteries is more expensive than filling it up, and cheaper than using gasoline.
2. No maintenance whatsoever, unless you use flooded lead acid batteries.
3. The sheer traction, power and acceleration an electric motor can deliver.
4. An electric motor and controller that puts just about all ICEs to shame isn't much more expensive than the economic option.
5. Your acceleration and range are mostly limited by your driving style, if your batteries can deliver.
6. It's Green!
7. It's almost solid-state and much neater and more high-tech than those silly ICEs.
And there are no problems mass production cannot fix that I can see. Sure, the range is lower, but how often do you want to drive more than 200 kilometers a day?
Even that can be fixed easily, by replacing the battery pack at the gas station. Hire the battery pack.
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I don't think that will pan out really. That is why I like PHEV's b/c you can use a small generator onboard to charge the battery as you drive if you are going a long ways, otherwise it is an EV. You may be right though Frank many people have postulated things about swapping batteries like propane tanks, but they are fairly heavy even the hi tech modules are like 50-75kg and that is for 40 miles. No way you are going to stop and swap cells every 40 miles.
Here is something, though not quite for you.
http://www.cnn.com/video/#/video/tech/2008/01/11/hunter.extreme.hybrid.cnn
I do not understand why people are leery that you need to plug a car in. (If you want it to run on batteries and not use an internal combustion engine). How do they expect the batteries to get charged without the engine turning on if they don't plug it in?
http://www.cnn.com/video/#/video/tech/2008/01/11/hunter.extreme.hybrid.cnn
I do not understand why people are leery that you need to plug a car in. (If you want it to run on batteries and not use an internal combustion engine). How do they expect the batteries to get charged without the engine turning on if they don't plug it in?
Mintmaster
Veteran
Maybe they want something like the wireless induction charging system that GM had with the EV-1. But yeah, I agree with you both. Plugging in the car is far less hassle than going to the gas station.
Still, it would be neat if they at least had a way to automatically pop out the plug if you buckled up and forgot to unplug it.
Still, it would be neat if they at least had a way to automatically pop out the plug if you buckled up and forgot to unplug it.
Wireless induction charging system? Wah? How long did that take, and what did it look like? Was it dangerous to people?
It wasn't wireless. It just had no contacts. It was a paddle system. You can transmit electricity over far greater distances wirelessly now though. MIT was doing something with it. Efficiency is crap though.
What is a good car to use as donor? I'm still looking around.
Low weight and aerodymanic (low drag) are preferrable, and it has to look nice. Simple (with as little electronics as possible) is best.
Well, actually, if I had the money, I would probably go for a De Lorean: I think that fits the bill perfectly. It isn't particulary light, aerodynamic or whatever, but can you imagine a better car to drive electric?
Low weight and aerodymanic (low drag) are preferrable, and it has to look nice. Simple (with as little electronics as possible) is best.
Well, actually, if I had the money, I would probably go for a De Lorean: I think that fits the bill perfectly. It isn't particulary light, aerodynamic or whatever, but can you imagine a better car to drive electric?
For an update:
First: batteries useable for electric vehicles are not the same as your run-off-the-mill car battery. They need to be able to deliver a lot of sustained power and to be drained regulary. A lot of abuse, so to say. That means that they are often bigger, or have a lower voltage. Batteries used in UPSes would work, but there are much better ones.
It seems, that flooded lead-acid is still one of the best options. Yes, the same batteries that powered those electric cars a century ago. Mostly because all the better ones are produced in rather small amounts. You might save half the weight and space by using better ones, but they would be much more than twice as expensive.
Those flooded lead acid batteries have the very bad property that you need to keep them filled all the time. Depending on your mileage, you would need to check all the cells about each month and top them up. That's a lot more maintenance than you would have to go through with your regular ICE car.
There are many sealed lead acid batteries, but they normally deliver a lot less amperage, and they degrade almost as fast when overused, without the means to refill them. Fine for a regular car, but not if you want to drain them regulary.
Still, sealed gel is quite useable for AC motors. Higher voltage (12 volt instead of 6 or 8 volt batteries) and less amperage. That also helps to keep the weigth and size of the other components (like cables) down.
An AC motor is about the simplest, most efficient and most durable motor imaginable, but it is more expensive to manufacture than a DC motor and needs a rather expensive controller that is tailored to it, to create and manage the multiple-phased AC voltages.
While you can get away with very simple and cheap pulse-width modulation (PWM, a high-speed switch) and a shunt (wire resistor) for direct current (DC) motors, you need to create three regulated (capped) sine waves for alternating current (AC) motors.
Then again, you can remove the gearbox when you use an AC motor.
So, sealed lead acid batteries are best if you don't want to do any maintenance, but that requires an AC motor and controller, which about make up the difference in price compared to a DC motor that uses a better kind of batteries. And of course, both solutions roughly double the price of the cheap solution.
Then again, both give you fast acceleration and a good range.
I normally never drive more than about 70 kilometer a day. 150 kilometer happens about four times a year, and 300-400 kilometer about twice a year. And that 150 kilometer is rarely in a single day, so recharging would work most of the time.
So, if I had a range of 80 kilometer when driving not too agressively, I would be fine. I could borrow a car for the two longer journeys. But if I wanted speedy acceleration, no maintenance and a roomy trunk, that would still require an AC motor or a better kind of batteries. About $7000 next to the cost of the donor car, $10,000 in all.
Still fairly expensive for a hobby project.
First: batteries useable for electric vehicles are not the same as your run-off-the-mill car battery. They need to be able to deliver a lot of sustained power and to be drained regulary. A lot of abuse, so to say. That means that they are often bigger, or have a lower voltage. Batteries used in UPSes would work, but there are much better ones.
It seems, that flooded lead-acid is still one of the best options. Yes, the same batteries that powered those electric cars a century ago. Mostly because all the better ones are produced in rather small amounts. You might save half the weight and space by using better ones, but they would be much more than twice as expensive.
Those flooded lead acid batteries have the very bad property that you need to keep them filled all the time. Depending on your mileage, you would need to check all the cells about each month and top them up. That's a lot more maintenance than you would have to go through with your regular ICE car.
There are many sealed lead acid batteries, but they normally deliver a lot less amperage, and they degrade almost as fast when overused, without the means to refill them. Fine for a regular car, but not if you want to drain them regulary.
Still, sealed gel is quite useable for AC motors. Higher voltage (12 volt instead of 6 or 8 volt batteries) and less amperage. That also helps to keep the weigth and size of the other components (like cables) down.
An AC motor is about the simplest, most efficient and most durable motor imaginable, but it is more expensive to manufacture than a DC motor and needs a rather expensive controller that is tailored to it, to create and manage the multiple-phased AC voltages.
While you can get away with very simple and cheap pulse-width modulation (PWM, a high-speed switch) and a shunt (wire resistor) for direct current (DC) motors, you need to create three regulated (capped) sine waves for alternating current (AC) motors.
Then again, you can remove the gearbox when you use an AC motor.
So, sealed lead acid batteries are best if you don't want to do any maintenance, but that requires an AC motor and controller, which about make up the difference in price compared to a DC motor that uses a better kind of batteries. And of course, both solutions roughly double the price of the cheap solution.
Then again, both give you fast acceleration and a good range.
I normally never drive more than about 70 kilometer a day. 150 kilometer happens about four times a year, and 300-400 kilometer about twice a year. And that 150 kilometer is rarely in a single day, so recharging would work most of the time.
So, if I had a range of 80 kilometer when driving not too agressively, I would be fine. I could borrow a car for the two longer journeys. But if I wanted speedy acceleration, no maintenance and a roomy trunk, that would still require an AC motor or a better kind of batteries. About $7000 next to the cost of the donor car, $10,000 in all.
Still fairly expensive for a hobby project.
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I'd think you'd be able to cut a lot on the $3000 you reserved for the donor car - after all you don't need one with a working engine.
Or if you do take one with a working engine, do you think it would be at all possible to create something like a simplified hybrid? I.e. one where you could use the old, existing engine solely for the purpose of recharging your batteries, or maybe even use the clutch to disengage the existing engine and make it drive electric only?
I'm not an expert here, just thinking out loud. I guess much depends on how important weight is for you, but there are small cars out there that weigh just under 800kg including an engine.
Or if you do take one with a working engine, do you think it would be at all possible to create something like a simplified hybrid? I.e. one where you could use the old, existing engine solely for the purpose of recharging your batteries, or maybe even use the clutch to disengage the existing engine and make it drive electric only?
I'm not an expert here, just thinking out loud. I guess much depends on how important weight is for you, but there are small cars out there that weigh just under 800kg including an engine.
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