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Just starting out

6906 Views 14 Replies 8 Participants Last post by  Duncan
I have been doing some research for about two months now just trying to get a ground of where to start a new EV and could use some help. I am going to make an EV from scratch. I am expecting this project to take about 3 to 5 years or so, thus I am in no rush at all. I still have tons to learn about a variety of things for this undertaking and I am pretty optimistic about it. I have been thinking about a good place to start, and after much deliberation I have decided to start with a motor and plan on from there. I definitely want to go with an AC motor. My budget that I plan on spending for the whole car is about 50,000, give or take 20,000 if need be for everything that i want in it. So back to starting with the motor I would like something around 250-300kw. Anyone have any suggestions? Again, I am just starting out, thanks for any help!

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With the budget you have and the performance you want, I think your best AC option would be to get a motor and controller from Bob Simpson. His motors are very well built, with liquid cooling and even with cooling of the rotor. So it has a very high continuous power rating (much higher than any DC motor which are very good for peak power but bad for continuous since it is difficult to do liquid cooling). His controllers are made by Rinehart, which for my money is the best AC controller available to DIY. It won't be cheap, but it will be a monster. He has just one that sounds like it is just what you want for 37k. You'll need probably a 30kwh pack to run it. That would put you back another 15k if you bought it today...probably cheaper when you are ready for that part. Another 10k for a donor worthy of these components, and another 5-10k for charger, dc-dc and odds and ends, and you will be pushing the upper limits of your budget. But if you do a good job it would be worth way more.

Interested to see what you have in mind for a donor. Me, I'd see if I could cram it in an Audi TT Quattro...that kind of power would like 4wd. I don't have your budget though :)

You'll get plenty of pressure on here to do it cheaper. You could have similar peak power for 20k less if you went DC. But I say if you have the money, go for the gold.
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Wow...I fail at life. But yeah that is the link. Thanks zsnemeth.
I think you just about have my idea pegged! I'm not exactly trying to build a Tesla, but something similar to it where i have all the control over the design. I have been thinking about my requirements and two things come to mind. Range being the first. I live in Austin, TX and would like to have the ability to travel to some of the major cities on a single charge. That being said 250 to 300 miles would be ideal. Secondly i would like a good deal of power to be able to get up and go. I do a considerable amount of interstate driving, so being able to get up and around people would be nice if needed. I assume that the 250 kw that i stated would be peak power, only used when say going uphill or to pass someone. I will have to figure out specific figures later, but are electric motors rated by their peak power? I read the amount of kw produced depends on your controller and if your motor and batteries can handle the load. I think i need to buy a book and do more research on this matter as I feel so lost! Any suggestions?

There's certainly nothing wrong with buying books and doing research, but you will probably learn more from here than from any given book.

As far as power requirements go, you need a lot less than you might think to cruise around at interstate speeds. But I'm guessing you don't want a weenie car that's barely powerful enough.
Electric motors are in fact measured in peak power as well as continuous power rating. But you have to be careful comparing electric power ratings with ICE power ratings. With an ICE, the peak power is a point on a narrow power band that falls off rapidly to each side. On an electric motor, you have a wide flat power band. The maximum power rating is a point at the high side of the flat part (since power is torque times speed) but that same torque extends all the way back to zero RPM instead of falling off. So you get a lot more out of an electric motor than you do out of an ICE for a given power rating. With an electric motor, when we talk about peak power, that's referring to how long of a time the motor can output that power before it has to pull back due to temperature issues. For a brushed DC motor, the difference between peak and continuous ratings is huge. A DC motor can briefly handle mindblowingly high amounts of power for brief periods of time, as long as you have a controller that can throw the current at it. But, since they are pretty much always air cooled (the heat is generated primarily in the rotor, which is hard to liquid cool) the continous ratings are actually quite low. With a liquid cooled AC motor, the peak values tend to be lower while the continuous values are much higher. With an undersized DC motor, you can run into temperature problems with normal driving. With a liquid cooled AC motor, a motor that is powerful enough to accelerate you will probably have enough power to drive around at decent speeds. The motors you will want for quickness will much more continuous power than you ever need.

For the range you are wanting, that's going to cost a good 30 grand, so that will eat up a lot of your budget. On the other hand you probably don't really need as much power as you initially said. I still would say go with if you go down to a single controller option, you can get a 180kW peak system for under 20 grand. It won't be as powerful as a Tesla but it will be very quick and fast.

One thing that going overboard on power gets you is the opportunity to go single speed. I don't know if that is important to you or not, but if you went for the ~180kW peak option, I would probably retain multiple gears.

What do you have in mind for a "glider" or donor car? It kind of sounds like you want to make your own. While that is not impossible, it does suddenly make the project at least an order of magnitude more difficult and expensive. Keep in mind that even Tesla didn't make their own glider their first go around. There are a lot great donor car options out there...I'm guessing you might find one that suits you well. Do consider using one with all wheel drive. That way you won't just use all that power to convert your tires into smoke.

Sounds like a really fun project! I wish you lived in Portland so I could help you with it. Ah...maybe some day I'll have a decent budget available :)
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