Author Topic: Electric cars  (Read 64067 times)

MartinJG

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Re: Electric cars
« Reply #1065 on: October 28, 2018, 01:27:44 PM »

I'm OK with this bit.

Electric motors work on a magnetic rotor ( capable of rotating)  following a rotating magnetic field generated by a wound copper coils in a stator ( stationary ). Most electric  cars use the squirrel cage  motor used for so long as a power source in industry, it has a rotor that needs no electrical contacts as it is a laminated iron with a solid ' cage ' of aluminium conductors - it is an induction motor, so called because the rotating field from the stator ' induces ' currents in the 'cage) and magnetized the rotor without and electrical supply to the rotor.  This lack of moving electrical contacts ( sliprings or brushes ) means motors are very trouble free and reliable.

This is where it gets interesting.

The problem with induction motors is they develop maximum torque when they are not rotating, as the rotor catches up with the rotating field the amount of 'slippage ' decreases and the torque drops, if the rotor speed ever caught up with the rotating field the torque would drop to zero.  With modern electronics the frequency of the rotating field can be changed to the optimum for every situation, think of this as ' electrical / electronic CVT ' if you like - no need for a heavy gearbox that would absorb power in the drive train.

This explains the fall off in performance of an electric versus combustion at higher MPH which was the reason for my thinking along the lines of compensating performance with the use of a CVT. Fair enough. I'll shelve that idea then.

That's my thought for the day.

Thanks.
« Last Edit: October 28, 2018, 01:31:17 PM by MartinJG »

richardfrost

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Re: Electric cars
« Reply #1066 on: October 28, 2018, 05:18:27 PM »
Tesla Model 3 doesnít use an induction motor. It uses an advanced reluctance machine design.

culzean

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Re: Electric cars
« Reply #1067 on: October 28, 2018, 05:44:06 PM »
Tesla Model 3 doesn’t use an induction motor. It uses an advanced reluctance machine design.

Basically the same rotor as an squirrel cage induction motor inasmuch as it does not use permanent magnets ( which are expensive ) but the stator induces magnetism in the rotor just the same. Switched reluctance motors use salient poles on the rotor ( stick out like gear teeth ) and it works like a stepper motor, which does not rely on slippage to develop torque but pulls the rotor around in a series of definite steps. All the clever stuff is in the electronics which supply the square wave pulses, electronics is cheap and lightweight compared to permanent magnets. I would like to know if this motor is capable of acting as a generator as well though, as this kind of motor normally not suitable for regenerative purposes like a wound rotor or permanent magnet motor.

https://en.m.wikipedia.org/wiki/Switched_reluctance_motor
« Last Edit: October 28, 2018, 05:50:48 PM by culzean »
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richardfrost

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Re: Electric cars
« Reply #1068 on: October 28, 2018, 08:38:37 PM »
From what I have read, it does regenerate power from braking in the Tesla design but not right down to zero mph like the other Tesla motors.

culzean

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Re: Electric cars
« Reply #1069 on: October 28, 2018, 09:03:21 PM »
All the carmakers are  avoiding using rare earth permanent magnets because the Chinese have control of the raw materials and they are rare and expensive.
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richardfrost

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Re: Electric cars
« Reply #1070 on: October 28, 2018, 10:00:10 PM »
Most of what I have been reading is drawn together here..

https://cleantechnica.com/2018/03/11/tesla-model-3-motor-in-depth/

Small amounts of rare earth are used to smooth out the performance of the new motor design.

culzean

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Re: Electric cars
« Reply #1071 on: October 29, 2018, 08:33:34 AM »
Most of what I have been reading is drawn together here..

https://cleantechnica.com/2018/03/11/tesla-model-3-motor-in-depth/

Small amounts of rare earth are used to smooth out the performance of the new motor design.

Good article, the problem with switched reluctance motors has always been 'torque ripple' or cogging,  where the output especially at lower speeds is 'lumpy' as the rotor gets tugged around from one magnetic field to the next. The small permanent magnets in the stator seem to cure that, other motor designs used permanent magnets in the rotor,  which left them open to becoming loose or even breaking up as the rotor spun.
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richardfrost

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Re: Electric cars
« Reply #1072 on: October 29, 2018, 11:56:38 AM »
The small permanent magnets in the stator seem to cure that, other motor designs used permanent magnets in the rotor,  which left them open to becoming loose or even breaking up as the rotor spun.

I think this design was only possible with the rare earth magnets and also with the modern regulating electronics.

I think Musk is a great innovator, but he really needs strong engineers and production designers around him to modify his 'reality distortion field', in the same way wthat Steve Jobs had Steve Wozniak to moderate him.

culzean

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Re: Electric cars
« Reply #1073 on: November 14, 2018, 02:18:49 PM »
Oops,  another Tesla fire, the list of spontaneously combusting Tesla cars mounts .. was it the collapsing of the suspension that triggered the problem (maybe the weak suspension was the reason why the Tesla was written off and put in the junkyard,  or had the owner parked it there because they couldn't find a charger ? )

https://electrek.co/2018/09/10/tesla-vehicle-fire-junkyard/
« Last Edit: November 14, 2018, 03:32:17 PM by culzean »
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culzean

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Re: Electric cars
« Reply #1074 on: November 15, 2018, 09:07:54 AM »
All is not what it seems in the murky world of BEV. Latest bombshell is that on Nissan Leaf fast charge can only be used a certain number of times in a journey - then the car says 'no' and switches over to slow charge ( hint - fast charging damages the battery a bit every time you use it).  It is a bit like having an ICE car that slows down the fuel filling to a snails pace after the first fill up of the day and your have to spend an hour or two at the service station pump trickling fuel in.

https://www.bbc.co.uk/news/business-44575399

Another problem, ( extract from article in link)

"But Mr Pitcairn was also disappointed by the range of the new Leaf, which he bought specifically for long journeys.

His marketing brochure claimed the car could do 235 miles on a single charge.

But having bought the car, he found the range was actually 155 miles.
"
« Last Edit: November 15, 2018, 09:11:50 AM by culzean »
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John Ratsey

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Re: Electric cars
« Reply #1075 on: November 15, 2018, 12:08:19 PM »
And while it's in slow charge mode it's hogging one of the charging points.

Jeangenie

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Re: Electric cars
« Reply #1076 on: November 16, 2018, 06:05:34 PM »
Just found this thread. Havenít read it all but had a trawl through the recent stuff. Quite interesting reading.

peteo48

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Re: Electric cars
« Reply #1077 on: November 16, 2018, 09:38:55 PM »
Some good stuff on YouTube Jeangenie. A guy whose channel is called EV Opinion is worth a look in. He has lived with a 24 kwh Nissan Leaf for 3 years. Another channel is "James and Kate" - check some of their earlier stuff including a journey from Leicestershire to Orkney in late 2015.

sparky Paul

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« Last Edit: November 17, 2018, 09:25:54 AM by sparky Paul »

culzean

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Re: Electric cars
« Reply #1079 on: November 25, 2018, 10:52:39 AM »
« Last Edit: November 25, 2018, 10:56:49 AM by culzean »
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