Herm
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Re: Why AC motor and inverter?

Tue Mar 15, 2011 11:05 am

ENIAC wrote:Is there much innovation occurring in electric motors? If so, along what trajectories? Seems like they are already highly efficient and have excellent power to weight ratios. Anything revolutionary being researched in electric motor technology? Just curious.


Not really, its very old tech.. there is some work on switched reluctance motors but most of the improvements will be lower cost from mass production of the motors and advances in electronics for the inverters. The iron laminations used are expensive special alloys, that could be improved also.

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Nubo
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Re: Why AC motor and inverter?

Tue Mar 15, 2011 2:27 pm

mogur wrote:Actually, thus is true for most any motor. It will generally only pull as much power as is needed to do the job. Free spinning without a load, most motors pull very little as they only need to overcome parasitic losses.


Nubo wrote:The controller responds quite nicely; you can feel it respond with additional power when the blade starts encountering resistance (tall grass, etc). Only seems to use as much power as situation calls for. Gets quite a bit of work done for the amount of battery it has (2x12vx20Ah)


I'm familiar with brush motors drawing additional power under load, but having used both, it seems to me there is a difference. The brushless motor/controller seems more intent and able to maintain effective rpm, while the brushed motors I've used tend to bog down, even though they pull more power under load. They go slower and slower, drawing more and more power, getting less and less work done -- sort of a vicious spiral that ends up wasting power.
I noticed you're still working with polymers.

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EVDRIVER
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Re: Why AC motor and inverter?

Tue Mar 15, 2011 4:02 pm

Nubo wrote:
mogur wrote:Actually, thus is true for most any motor. It will generally only pull as much power as is needed to do the job. Free spinning without a load, most motors pull very little as they only need to overcome parasitic losses.


Nubo wrote:The controller responds quite nicely; you can feel it respond with additional power when the blade starts encountering resistance (tall grass, etc). Only seems to use as much power as situation calls for. Gets quite a bit of work done for the amount of battery it has (2x12vx20Ah)


I'm familiar with brush motors drawing additional power under load, but having used both, it seems to me there is a difference. The brushless motor/controller seems more intent and able to maintain effective rpm, while the brushed motors I've used tend to bog down, even though they pull more power under load. They go slower and slower, drawing more and more power, getting less and less work done -- sort of a vicious spiral that ends up wasting power.



Brushes do not have to equal DC motor.

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mgoleta
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Re: Why AC motor and inverter?

Tue Mar 15, 2011 8:01 pm

There is not a simple out of the box answer for this. Nissan had their reason we can only make guesses about the answer until Nissan or one of the design engineers to tells us what they were thinking. It could be as simple as the motor they picked overall cost $5 less in production or possibly their intellectual property ownership dictated which one it was. About the only thing we can safely say about the motor selection is they didn't want brushes. Overall a good question just not an easy answer without Nissan jumping in to answer it.
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Re: Why AC motor and inverter?

Wed Apr 06, 2011 6:04 am

As far as I can find, both the Tesla and the Volt use AC induction motors (no rare earth magnets) while the Leaf uses a "permanent magnet AC motor" (what I'm used to calling BLDC (brushless DC)). For a given power rating BLDC tends to be a tad more efficient and more expensive, mostly due to the rare earth magnets. Induction motors have been around since the dawn of time, or at least since Nikola's day.
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Re: Why AC motor and inverter?

Mon Apr 18, 2011 5:08 am

Wally Rippel from Tesla actually posted a blog discussing the difference between AC induction and BLDC and why they went with AC induction.
http://www.teslamotors.com/blog/induction-versus-dc-brushless-motors

daniel
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Re: Why AC motor and inverter?

Mon Apr 18, 2011 7:36 am

Herm wrote:... there is some work on switched reluctance motors ...

My Zap Xebra uses a "reluctance" motor: It is reluctant to go very fast, and it is reluctant to go up a really steep hill, and it is reluctant to get up to speed from a stop. :lol: I still like it, though, because it's enabled me to drive electric for four years while waiting for something better to come along. 8-) I will be glad to switch from a reluctance motor to one that is not so reluctant. :P
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Re: Why AC motor and inverter?

Mon Apr 18, 2011 7:45 am

daniel wrote:
Herm wrote:... there is some work on switched reluctance motors ...

My Zap Xebra uses a "reluctance" motor: It is reluctant to go very fast, and it is reluctant to go up a really steep hill, and it is reluctant to get up to speed from a stop. :lol: I still like it, though, because it's enabled me to drive electric for four years while waiting for something better to come along. 8-) I will be glad to switch from a reluctance motor to one that is not so reluctant. :P


Very well put, Daniel! :lol: :lol: :lol:
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Re: Why AC motor and inverter?

Mon Apr 18, 2011 7:57 am

Good one Daniel :)

An issue no one talks about is that permanent magnets sometimes go bad.. they will lose magnetism around 350° C or due to shock/vibration.. and if you chip the coatings they will rust easily. Also they are expensive.. but they are not really that rare. I'm very surprised Nissan chose them.

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Re: Why AC motor and inverter?

Mon Apr 18, 2011 10:41 am

I agree. I was a bit disappointed when I found out Nissan went with PM's instead of AC induction, which should be less expensive and not exposed to the rare earth element market fluctuations. I don't know how many anti EV articles I've see touting China's control of REE's causing the end of EV's.

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