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#11
09-03-2008, 11:38 AM
 booksix Senior Member Join Date: Aug 2008 Location: San Diego Posts: 248
Re: Choosing a motor(s) and effects on range

Well, the fact is I don't even know the difference (between AC and DC - whether it's series, shunt, perm, etc..) I like DC because there is a lot of parts available. But then I see a vehicle like Tesla's running AC and I wonder what I should REALLY do. Is there a big cost difference between the two? How about performance and range differences?

edit: ok, looks like AC is roughly twice the cost!! I'll have to go DC until I can afford a bigger system...

Last edited by booksix; 09-03-2008 at 11:50 AM.
#12
09-03-2008, 11:54 AM
 1clue Senior Member Join Date: Jul 2008 Location: Chicago area Posts: 504
Re: Choosing a motor(s) and effects on range

Quote:
 Originally Posted by booksix Well, the fact is I don't even know the difference (between AC and DC - whether it's series, shunt, perm, etc..) I like DC because there is a lot of parts available. But then I see a vehicle like Tesla's running AC and I wonder what I should REALLY do. Is there a big cost difference between the two? How about performance and range differences?
Keep in mind I'm still just reading up on it, I knew a bit about motors before but I don't have practical experience yet.

Based on the introductory information on this site and my use of a search engine to expand on some topics, here's what I can give you for a short tutorial:
1. AC is alternating current, like you get in your house. Only the motor and controller and any incidental circuitry (if any) are going to change for this, the batteries and charger etc. are always DC.
2. DC is direct current, which is what you have in your car right now. One wire is always + and the other is always -.
3. Most conversions are still DC conversions because the equipment is easier to deal with and is much cheaper if you are buying components.
4. AC can be higher performance in every way than DC, unless I missed something somewhere. Building your own AC components, if you are qualified or willing, can be cheaper money-wise than buying DC components. Not including your labor!
5. AC gives you a lot more features and gives you potentially better efficiency. Also, the torque curve for an AC motor looks WAY better than the torque curve on a typical DC conversion.
Check out this site: http://www.metricmind.com/ac_honda/main2.htm

Before you go much further, I strongly recommend that you read the wiki (click on NuWiki in the upper left corner of the page) and start reading. Also, look at my first thread here: http://www.diyelectriccar.com/forums...t-17468p2.html

and then start using the search engine. People responding to your posts is easier for you, but once you get started you can much more effectively research things on your own. Everybody who answers your question colors it with their own preferences, and they are less likely to be accurate or complete when it's a response to a post than they are when it's a tutorial or wiki page.

I'm not trying to make you stop asking questions, I certainly haven't stopped asking and I'm very glad people are still answering! I'm just saying you can get a more complete idea of what's going on by looking at what's already out there, and then ask questions to clarify what you found.

Good luck and have fun.
__________________
No conversions yet. Still learning before I jump in.
#13
09-03-2008, 01:05 PM
 booksix Senior Member Join Date: Aug 2008 Location: San Diego Posts: 248
Re: Choosing a motor(s) and effects on range

Yeah, i always search first... its choosing the right keywords that is hard.

Anyway, that page you linked was crazy! That AC setup is sick but that's a lot of room and MONEY in batteries and caps. Have you come across any information detailing how much range can be increased by AC regen braking? I downshift a lot when i drive my car so I'm sure switching over to doing a lot of regen braking wouldn't be hard for me. What I'm getting at is: can I save money in batteries (less Ah) by relying more on AC regen?
#14
09-03-2008, 01:32 PM
 1clue Senior Member Join Date: Jul 2008 Location: Chicago area Posts: 504
Re: Choosing a motor(s) and effects on range

Usually around 10%. More if you use a huge bank of capacitors, but that costs even more yet, like over 10G.

That link was a no-holds-barred conversion. It's possible to use some not-so-good components and get the same sorts of things done, but it will be more work. If you like working on cars and aren't afraid to experiment, you might be able to do it the hard way.

Here's the place to start on a lot of these questions:
http://www.diyelectriccar.com/forums...redir_from=668

From what I gather from all this, if you're doing a conversion to save dollars then you need to stop right now. It's possible, but not for the type of car you're looking at, with the capabilities you're looking at. If, on the other hand, you're a gear head who wants a really cool car, then go right on ahead.

The caps will give you two things: More power from Regenerative Braking, and a huge kick in the seat when the light turns green, assuming your controller can handle it. Batteries don't like being run at full current rating. The less current you draw from them, the longer they last. That goes both for that charge and for the overall life of your batteries. Start doing brake torques and you will trash your batteries unless you have a capacitor bank that can handle it and still protect the batteries.

Regenerative Braking is only one of the features you get with AC, and for some reason it's what everyone focuses on. For me, it's the potential higher efficiency and a torque curve that is literally flat from zero until it gets over half of red line. I would have thought you would have grabbed that right away with your particular car.

I gave you that link because his stated intent was similar to your stated intent. I would look closely at what he did, and try to figure out why he made that particular choice. Then decide if that particular choice is compatible with your situation. You could still go with AC motors and spend a whole lot less than he did. You could use lead-acid batteries for now, and still use a capacitor bank. Your performance will be less than his, but you would still get a car that can break the speed limit when you want to, even though it won't go as far on a charge and won't set you quite so far back in the seat.

Whatever you do though, remember that batteries WILL wear out, and no matter how much or how little you spend on them, the charger and battery management system will either make the most out of them or trash them in a few cycles, depending on how well you paid attention.
__________________
No conversions yet. Still learning before I jump in.
#15
09-03-2008, 01:42 PM
 booksix Senior Member Join Date: Aug 2008 Location: San Diego Posts: 248
Re: Choosing a motor(s) and effects on range

Well, it is to save money, but my calculations have me paying the entire conversion off (\$8-10k) in about 3 years (this is money saved in gas - including charging costs).

My main thing is to do a 'budget build' for 8-10k but that is scaleable without a full rebuild. So, I want to plan on a motor that I can buy a matched 2nd in a few years and link it up. I also don't want to have to rewire everything (i'll already have 4/0). Also, I really like having control of my car, which means I like shifting. So, if I have to use gears to keep in the power band of a DC setup rather than using no gears and having constant torque with AC it's no big difference for me...
#16
09-03-2008, 01:48 PM
 1clue Senior Member Join Date: Jul 2008 Location: Chicago area Posts: 504
Re: Choosing a motor(s) and effects on range

Just be sure you know what the power band is on a DC motor. Generally, it gets good torque right around zero RPM and not much higher. Definitely NOT the same as an ICE.

I'm definitely injecting my preference for AC into this discussion. You need to make your own decision, just make sure you cover all the bases before you start tearing your car apart.
__________________
No conversions yet. Still learning before I jump in.
#17
09-03-2008, 01:55 PM
 booksix Senior Member Join Date: Aug 2008 Location: San Diego Posts: 248
Re: Choosing a motor(s) and effects on range

From what I understand it's a lot of torque from 0 to about 4000 rpm. Yes it's much different than an ICE but so is an AC. And I'm all about hearing you thoughts, but I'm not seeing the gain for the cost yet... what am I missing?
#18
09-03-2008, 02:06 PM
 1clue Senior Member Join Date: Jul 2008 Location: Chicago area Posts: 504
Re: Choosing a motor(s) and effects on range

Well, I wouldn't have nearly enough money to put together a car like that Honda.

On the other hand, I'm not afraid to try building my own motor and/or controller. That would increase the work several times, but cut down the money cost toward what I would spend on a DC system. I am interested in how the process works as well as in the end result. Building my own gear fits that goal nicely.

Another data point for me is that I've always had a fascination with 3-phase AC motors. Can't explain why. All the weak points of DC seem to be addressed in AC. I'm not going to try to rationalize this, I'm just not very interested in a DC conversion.

My goal is not your goal. I'm not after making a hot rod. I want a commuter that's not totally nutless. This again shifts my end goal away from yours because to make a hot rod with this technology is WAY more expensive. You might want to see what the drag racers do, because your project is more akin to a drag racer than to a commuter.
__________________
No conversions yet. Still learning before I jump in.
#19
09-03-2008, 02:25 PM
 booksix Senior Member Join Date: Aug 2008 Location: San Diego Posts: 248
Re: Choosing a motor(s) and effects on range

Yeah, it's kind of a drag/street car yet a daily commuter. Seems DC is popular in drag but then again, that's only an acceleration similarity with me. I still need to get 25 miles to work each day (where I can charge).

Anyway, aside from that, I dig your interest! Any chance you're in San diego? LOL, I'd SO love to be involved in what you want to do with building components. I actually would like to get into this stuff as a career somehow but im just starting my first build with already made/proven components.
#20
09-03-2008, 02:27 PM
 booksix Senior Member Join Date: Aug 2008 Location: San Diego Posts: 248
Re: Choosing a motor(s) and effects on range

nm: I see your in Chicago... I'm from WI

Oh,and btw, I'm way more fasicnated with AC as well. Wish I could get the price down!

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