3Ph AC motor question

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TropicalEV
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3Ph AC motor question

Post by TropicalEV » Mon, 05 Jan 2009, 21:01

Hi guys,
        in an effort to get my head around the power required to make things go I thought I would ask what likely to be a prety dumb question but I can't really find the answer anywhere. We have a couple of motors in the shed, the details are as follows:

Type kevmxx induction motor
volts 415
poles 4
cont rpm 1440
rotor c
hz 50
hp 2.5
code k
insulation j

These are pretty heavy for 2.5hp.( 20kg?) They look very much like your standard industrial motor. The pool pump 240ac motors we have are much smaller for the same power! My question is this...I read about you guys pulling as much as 3 times the rated output? are these the sort of motor you can do this with? How big would the controller be? I saw in one post the AC controller weighed 59kg!(Albeit for a small car) Is there an AC controller that will produce 3ph AC from 72v DC? (pie in the sky plan is 72v)
Are these motors suitable for a motorcycle? they are around the size I would expect to have to fit to a bike but they are no where near the power I would expect to need. Is industrial AC more suitable for a car given the extra weight due to industrial strength?
Any help would be appreciated Image

Thanks

Ken
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Johny
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3Ph AC motor question

Post by Johny » Mon, 05 Jan 2009, 21:53

You need about 600 VDC to produce 415 VAC for a typical Australian 3 phase AC induction motor. However, your 2.5HP will have the option for delta 250 VAC operation which only needs about 320 VDC. (Motors under 3Kw are 415 Star and 240 Delta - terminal box changable).
The controller wants to be about 3 times the motor power to get best performance from the motor. You would want a 5 to 6kW controller for your 2.5HP motor.
A single phase to 3 phase 240 VAC controller would be ideal and they come up on eBay a lot. Rewinding the motor is possible but lower voltage controllers are not readily available. Purpose built EV controllers are the only ones that come in lower voltage - maybe Chinese?

20Kg is on the heavy side - best motors are aluminium frame types. The 11kW I have in mind for mine weighs 59kKg but I notice that weight is not proportional - lower power motors are heavier than higher power (taken relatively). Then again my "toy" 2.2kW motor weighs 30Kg.

Bikes are difficult for industrial style AC due to the high VDC requirement as you will need about 25 to 26 of 12V batteries.

BTW. My 30Kw/44Kw Lenze controller (I bought another bigger one) only weighs 15Kg.

Last edited by Johny on Mon, 05 Jan 2009, 10:56, edited 1 time in total.

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3Ph AC motor question

Post by TropicalEV » Mon, 05 Jan 2009, 22:16

Thanks for that Johny,
                     Once again my ignorance of AC tells me I should stay away from it! Image I just thought I'd ask as we have them lying around. Maybe I should start looking around for an aircraft starter/generator. They can do 400amps! I'm sure with higher voltage they could do more..BUT...They are suposed to be overhauled after 2000hrs or so. This tells me they may not be robust enough for an EV Image
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3Ph AC motor question

Post by Johny » Mon, 05 Jan 2009, 23:32

You might check out www.evalbum.com and specifically search for motor cycles. Apologies if you have already done this.
Also post here but with a title more indicative of motor cycles rather than AC specifically that way your post will draw more of the right crowd.

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Richo
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3Ph AC motor question

Post by Richo » Tue, 06 Jan 2009, 04:56

Unless the motor is Aluminium is will be pretty heavy.
Cast iron motors are cheap and abundant but really heavy.
Here is a link to an industrial AC motor bike.

Your pool pump will be smaller due to the liquid cooling?
You will notice the AC induction motor has large fins to keep it cool.

A MARS AC motor might be more common for a motorbike.
Off the shelf controller and is lower DC voltage.

Maybe leave the industrial for the 2nd conversion unless your keen.
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3Ph AC motor question

Post by juk » Tue, 06 Jan 2009, 07:32

"Your pool pump will be smaller due to the liquid cooling? "

Pool pumps dont have liquid cooling. I don't know of any pumps with liquid cooling and i know pumps. Pool pumps are around 0.75-1.25kW that's why they don't have big fins. From memory they are an aluminium body mostly, with a plastic wet end. There'd be stuff all heat transfer from the motor to the liquid through the plastic or through the shaft. Can't help you much with motors, but i can with pumps.

edit.
my bad. car fuel pumps run liquid cooling.
Last edited by juk on Mon, 05 Jan 2009, 21:07, edited 1 time in total.

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3Ph AC motor question

Post by EVLearner » Wed, 21 Jan 2009, 03:44

I have been thinking on this topic for a few weeks and I am getting the opinion that the USA based 110 VAC 3 phase system may actually have merit as this works out as 190 V phase to phase, and they are sure to have plenty of motors over there as the USA population is always too ready to throw out perfectly good junk (in this case 3 phase motors)!!

My thinking goes along these lines: If you were to use a nominal 144 V DC battery pack (12*12), and use a DC to variable speed 3 phase convertor, then the 3 phase AC motors would be far cheaper to manufacture than DC series motors - and the controller should be rather simple compared to the DC equivalent version, then;

How would this approach compare to a DC driven motor?

I don't have the cost breakdown, (or where to store the batteries in a vehicle yet!) but it seems to me that the 3 phase AC motors should be very cheap in comparison, and the 3 phase controllers (if made as a small production run) could make the DC approach look rather expensive, if not, prohibitively expensive!

Has anybody played around with a DC to 3 phase controller attached to a 3 phase motor?


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3Ph AC motor question

Post by Electrocycle » Wed, 21 Jan 2009, 04:39

a 3 phase controller is always going to be much more expensive than a DC controller.
It needs to have six times the MOSFETs (or IGBTs) for the same current rating as a DC controller, and will have greater resistive losses.

The induction motors are simple and cheap to manufacture though, while giving good efficiency.
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3Ph AC motor question

Post by Johny » Wed, 21 Jan 2009, 05:03

EVLearner. In answer to your question - see:
This thread
Also check out www.evalbum.com\1149

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3Ph AC motor question

Post by antiscab » Wed, 21 Jan 2009, 05:35

Electrocycle wrote: a 3 phase controller is always going to be much more expensive than a DC controller.
It needs to have six times the MOSFETs (or IGBTs) for the same current rating as a DC controller, and will have greater resistive losses.
to give a little more information on this topic:
a 3ph controller will only have 6x switching devices if the comparable DC controller doesnt have any in parrallel.
This is rarely the case (i havent come across any, though that doesnt mean they dont exist).

having switching devices on independant phases means you dont run into any of the current sharing issues when running in parrallel.

you will of course have more gate drivers.

the extra losses encountered in the AC controller are actually switching losses.
The further you try and step the voltage down, the greater the losses.
with AC, even at full power at rated speed, the controller still has to create the lower voltage end of the wave.

a 3-phase controller is more expensive because they arent made in the same quantities as DC controlers (road going versions at least), and the development cost is higher.

back to the 208vac (120vac/phase) motors.
these require 300vdc at the controller, after accounting for voltage sag, to run at 3x torque at rated speed (actually slightly below rated speed).
ideally we want 3x torque at 3x rpm to be comparable (power density wise) to a DC motor.
so that means 900vdc on the DC bus.

so the motor you would really be looking for, is a 36vac motor for a 144vdc pack.
it just so happens, they make this voltage motor for the new AC forklifts. :D

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3Ph AC motor question

Post by EVLearner » Wed, 21 Jan 2009, 05:39

Yes, I agree with your sentiment about having 6 times the IGBTs, but I was thinking of using Gate Turn Off Thyristors (but I have not priced these yet), as these will handle hundreds of ampres and a couple of kV. I am aware that train controllers may use large GTOs, but at the smaller end (for cars), these devices should not be that expensive (as I would only need 6 GTOs, not 60 IGBTs).

There may be greater resistive losses, and I can't see any easy way around that except by minimising the overall current flow or using GTOs that have an inherently lower saturation voltage with equivalent current.   

It would need 3 extra floating (balanced) supplies to manage the biassing for the floating gates/cathodes, and a neg 12 V drive to work with the 3 gates with the existing pos 12 V to manage the grounded cathode. This could be a little ferrite cored converter with high voltage insulated floating outputs - very eaasy to make these days!!

If the GTO Thyristors cost about say $33 each then 6 would be about $200, and add another $400 in control and mounting and the controller would have a base cost of about $600 (all very 'round' figures).

How does that price compare wuth a fully made DC controller capable of say 150 A at say 90 V - or am I going for too large a voltage and/or current? I am asuming this 3 phase controller will produce about 150 A at 86 V rms (144 V p-p = 86 V rms between the phases.)

Agreed about the Induction motors, and that was the approach I had in mind, because in production these should be about 40% the cost of equavelent DC motors - and have no wearable parts (other than the bearings).


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3Ph AC motor question

Post by antiscab » Wed, 21 Jan 2009, 05:50

as far as the difference in wear goes,
its more of a matter of principal for me.

the brushes and comm last *ages*.

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Richo
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3Ph AC motor question

Post by Richo » Wed, 21 Jan 2009, 07:26

A 13kW controller sounds a bit light on for a motorbike.
Maybe double it Image
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3Ph AC motor question

Post by Richo » Wed, 21 Jan 2009, 07:33

Oh also once you get over a 100 sized motor it would need to be a Harley to fit the motor in. Image
And you have to change your name to Chopper Image
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3Ph AC motor question

Post by antiscab » Wed, 21 Jan 2009, 08:01

why stop at double?

and are you planning on having a gearbox?

direct drive requires a motor/controller combination capable of much more than the batteries can put out to make full use of them.
i usually go for at least 6x (so the constant power region is over much of the usable speed range).

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