AC motors, multipoles, torque

AC, DC, amps, volts and kilowatt. It's all discussed in here
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woody
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Post by woody » Thu, 15 Jan 2009, 19:18

Mesuge wrote: Did anybody (apart from Kermit's experiments) perform this hack on any (smaller output) VFD and motor combo? Will the efficiency map for this emotor plotted against RPM remain essentially the same or there might be 1-2x efficiency gaps? Improved forced air cooling, water cooling, heatpipes, peltier, ... Image
Which hack?

240V motor with 415V controller - I think Johny is in the best position to do this (he has a small motor for playing with which I assume is 415 star / 240 delta) But he has no load...

As for dyno-ing: acmotor has the only road-registered industrial AC EV in Australia that I know of :-) a4x4kiwi is getting really close.

I suspect the efficiency may go down a bit switching from 415V to 240V, the I^2R will be higher, I'm not sure how much of the (in)efficiency is due to those though, R is pretty damn small.

I think overstating the V/F ratio will get more performance with more heat (magnetic losses) and less efficiency. The difference between 75% load efficiency and 100% load efficiency isn't that huge (<1%).

The losses from memory come from:
bearings
fan
I^2R windings
I^2R stator
Air gap
I^2R motor cable

I think the fan would be significant, especially at higher speeds.

I am a fan of acmotor's computer fan mod :-)

cheers,
Woody
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Post by Nevilleh » Thu, 15 Jan 2009, 19:37

I've been reading through all this stuff with great interest as I am completely new to many of these ideas, particularly the VFD. I am puzzled as to how an 11 kw motor can be persuaded to produce so much more power! What am I missing here? There's obviously a lot of expertise amongst the people on this forum and I hope someone will be patient!
Also, I notice that 4-pole motors seem to be preferred. I have an 11 kw 2-pole motor and I wonder why that wouldn't be better? It could be persuaded to spin twice as fast as a 4-pole.
I became interested in the electric car idea when I read about the Tesla Motors thing and coincidentally "found" this motor, and I have been reading the forums on this site for quite some time. Inspiration!

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Post by Mesuge » Thu, 15 Jan 2009, 19:49

Yes, I meant mainly the first 2pages of this thread and the basic idea rewinding for 230V delta on 415VAC vfd, no torque boost magic (ordinary vfd), "~5.3x overclocking," seems too good to be true. Woody thanks for the reply.

btw. I'm worried will this hackenstein work out of the box in all the modern vfd glory, i.e. automatic config. of the newly rewinded motor, closed loop (w. sensor), accel./deaccel. ramps,..., etc. ?
Last edited by Mesuge on Thu, 15 Jan 2009, 09:03, edited 1 time in total.
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Post by antiscab » Thu, 15 Jan 2009, 20:22

Hi Nevilleh,

an induction motor can be pushed to 3x (or so) its rated torque at slightly below rated speed at rated voltage and frequency.
because we run with a *much* high voltage, and the vfd can create a higher frequency, we can run this 3x rated torque at 3x rated speed.
so this gives 9x rated power.

industrial motors (dpending on size, the bigger the slower) have an upper limit of around 4500rpm.
so thats 3x rated speed for a 4-pole (for 9x power) or 1.5x rated speed for a 2-pole (4.5x).

what we are really looking for is a motor with high rpm potential, and high peak torque/kg.
on one of the previous pages, tuarn posted a chart showing peak torque/kg for a range of motors, and the 4-pole units consistently had a higher rating.

Matt
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Post by acmotor » Thu, 15 Jan 2009, 20:28

Nevilleh,

That 2 pole 11kW will work with the right gear ratio, i.e. retain the gearbox and it will be fine.

The interest in 4 pole is that it presents the right torque and speed for direct (or near direct) drive. i.e. 73Nm at 1500 RPM in 11kW.
2 pole will be 36Nm at 1500 RPM (and up to 3000RPM). A gearbox can fix that though. (all nominal numbers)

In reality, the 2 pole with gearbox will be much the same as a 4 pole without (or in a higher gear). Efficiency and weight may be the only difference.

How many kg does your motor weigh ?

Mesuge, I think that if we can demonstrate a combination that works even if parts are world sourced, then it will end up 'out of the box'.
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Post by woody » Thu, 15 Jan 2009, 20:54

Hi Nevilleh, welcome!

Industrial motors are rated at their 50 Hz all day / every day for 20 years in a poorly ventilated factory. Using one in an EV is quite different - you only want the high power for less than a minute, since after that you're speeding :-) Also you get a bit better cooling in an EV than a factory, since the air is whizzing past at 80kph plus...

The motor's nominal torque rating is about 1/3rd of it's maximum torque - the motor specs give this ratio as a "breakdown ratio" or "pullout". So even plugged into the wall @ 50Hz, an 11kW motor will probably do 33kW before it stalls.

Introduce a VFD with higher voltage than the motor, then you can have this performance at a higher frequency as well. So say double voltage and 3 x breakdown gives you 3 times torque @ double speed = 6 times nominal power.

I think the 4 poles are prefered since they have a torque and speed range more suitable for a conversion using direct drive to the diff. A 2 pole is probably more suitable if you want/need/are happy to keep the gearbox.

4 poles are about the sweet spot for torque/kg. The pole count doesn't really matter if you have a VFD and you're going to rewind the motor for the voltage that suits you anyway.

Rewinding for lower voltage does increase the current proportionally, so your VFD has to handle the higher current.

cheers,
Woody
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Post by Nevilleh » Thu, 15 Jan 2009, 21:52

Thanks for the replies. I am getting a better understanding of it all as I read more.
I checked with Danfoss here and they have a single 5042 in stock (obsolete now, apparently) which they have offered to me at the "keen" price of $NZ3900! That's about 3200 Australian and I seem to recall reading that acmotor only paid about $2000 for the one in his Suzuki. Can you still buy these controllers in Australia?
I am getting pretty keen to have a go now and I had thought a BMW 318 might make a good candidate and Lo! I see on one of the other forums that someone else had the same idea. Great minds etc.
I have some experience with LiFeP04 batteries and saw a neat idea for a BMS that uses a switcing regulator controlled by a micro to do the balancing. Basis is a flyback transformer with a single primary across the whole bank and a winding for each cell. The micro measures each cell's voltage and if one reaches the charge limit, the micro turns on that cell's winding and dumps a current pulse back into the primary, so it takes current from the "full" cell and applies to all the others. Very efficient, no energy wastaed. Also, when a cell reaches the lowest voltage, the micro takes a current pulse from the rest of the string and dumps it back into the low cell.
I've built a transformer to manage a 4-cell battery but still have to progarm the micro (Atmel Tiny 25) to drive it all, but if it works as well as I think it will be easily extendable to more cells. Has anyone else played around with this idea?

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Post by woody » Thu, 15 Jan 2009, 22:24

Woah, must be a slow work day, 3 of us pounced at once!
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Post by woody » Thu, 15 Jan 2009, 22:34

Hi Nevilleh again.

I think that price is great for a new 5042 with warranty + factory support etc. About the same as a Curtis DC controller is now.

acmotor and a4x4kiwi bought their danfosses on eBay I think about $2k.

I'm yet to see a big 5000 series on ebay in australia the last 6 months. Hopefully danfoss australia will have a fire sale soon :-)

I'm not in a huge hurry (more time than money), I'm waiting for a bargain on ebay still.

Richo on this forum is going for a 318 BMW AC conversion, great minds think alike.

cheers,
Woody
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Post by bga » Thu, 15 Jan 2009, 23:57

AC11KW 4 Pole
One of the reasons that this is preferred over 2Pole is that is sizes 11Kw and above, 2 Pole motors are difficult or impossible to obtain.

When I checked last week, a Crompton Parkinson Aluminium 11Kw motor was available off the shelf in Perth, probably easy in NZ. The price has gone up to over $1K AUD now. Most come out of europe and are linked to the Euro Image.

If anybody finds a good chinese motor, I'd like know. They are likely to be configurable for 240V operation in the US Market.
   
There is a family of sizes that are relatively easy to obtain 11, 15, 18.5, 22 kW that vary from about 80 to 125 kg in weight, but the larger sizes will need a huge controller to obtain their potential (100 kW, probably). The smaller ones more likely to be stocked and well priced.

I'd avoid a 2-pole in 11kW and above because of the significantly lower maximum torque at low speed and supply issues. The VFD can allow a 4 pole motor to be run to approximately 150 Hz for about 4000 RPM.
Regardless of the number of poles, the motor will have a mechanical and durability limiting speed not from this, above which, bearings or flying metal will become problems.

(ABB 2Pole 160MLA frame 11kW Tn=36Nm Tmax=93Nm) << very low
(ABB 4Pole 160MLA frame 11kW Tn=71Nm TMax=205Nm)

The result being that a 4 pole motor is a better match for an ICE conversion and may allow direct drive operation or much reduced gear use.

While ACIMs are designed to be operated in servere conditions, their operating limits may be exceeded by a long steep hill climb. Retaining the gearbox maye be needed so that the climb can be done at a lower gear, keeping the torque within the motor's capability.

Say, 10% grade, 3.9:1 diff, 600mm dia wheels, 1500kg vehicle requires 125Nm before losses, drag and acceleration, so about 200Nm needed. This will probably require 2nd gear to keep an 11kW 4P motor within its 5 minute limit of approximately 100Nm. Driveways may be 15% grade.
Last edited by bga on Thu, 15 Jan 2009, 13:02, edited 1 time in total.

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Post by Johny » Fri, 16 Jan 2009, 00:16

Well over thar in Perth you must might long driveways - why, in Melbourne ours don't exceed 1km. Image

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Post by Johny » Fri, 16 Jan 2009, 00:20

Sorry, finger slipped before I could stop myself.
Seriously, I have been using this tool to check out my normal driving routes with rear-wheel NM in mind.
http://www.heywhatsthat.com/profiler.html
Remember to use multiple clicks...

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Post by acmotor » Fri, 16 Jan 2009, 02:04

Hey bga, the 11kW 2 pole would be OK with gearbox !

Nevilleh,
The fancy BMS options have wasted quite a bit of my time over the last 2 years !

I have built simple zener units for SLA and picaxe PWM charge shufflers with opto isolation and now programable zener lithium BMS units.
I programed in a charge profile for SLA but came back to the lead acid favourite.... slow charging voltage limited !
The reason being that there are 6 cells in the SLA and you are not eq ing at the cell level.

There are a number of factors....
If I have 220 TS lithium to fit BMS to, the cost of parts and time to assemble is a problem e.g. $40 for micro based in parts and PCB and a day each to make is not on. This was using $5 pic08m with their 10bit ADC and PWM to fet / transformer with serial streamed data out.

Charge shuffling is a waste of time IMHO having played with it and PWM shunting. The amount of eq required is so small for a series battery pack and charge transfer efficiency of <60% that it is not worth the expense. Potential power saving becomes lip service not reality.
e.g. The 40Ah TS lithium I am setting up for my Rodeo seem to only require 100mA of eq in my test module.


The other factor I find is that in a conversion with regen that there needs to be an actual 'power waste to heat' type eq. once the cells are fully charged and the shuffler system can't get rid of the kW anywhere.

I am now making up (analogue) programable zener shunts with opto isolated hi/lo voltage indication. The cost is more like a few dollars per cell. They don't read out digitzed voltages for each cell, they just sit there and WORK and you only hear from them when there is a problem ! Rather than 220 must read voltage numbers.
OK full battery data is interesting to have, but at what expense ?
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Post by Mesuge » Fri, 16 Jan 2009, 04:33

bga wrote: While ACIMs are designed to be operated in servere conditions, their operating limits may be exceeded by a long steep hill climb. Retaining the gearbox maye be needed so that the climb can be done at a lower gear, keeping the torque within the motor's capability.

Say, 10% grade, 3.9:1 diff, 600mm dia wheels, 1500kg vehicle requires 125Nm before losses, drag and acceleration, so about 200Nm needed. This will probably require 2nd gear to keep an 11kW 4P motor within its 5 minute limit of approximately 100Nm. Driveways may be 15% grade.


Another angle, VFD spec. often mentions max overload: Imax. for ~120sec every 20min. Presumably the relationship isn't linear, for example lets have 10sec accel. run at max overload => 120/10 = 12x => 20min/12x => 100sec => so each 1min 40sec the VFD allows for this top output?

In reality this should be more complex also because of cooling/residual heat build up in the engine/vfd area etc., any idea how to compute/guesstimate these relationships? Possibly, a little additional circuitry (output current, time, temp sensors) should keep floating watch on the recent history (20-30min) of overload and put limit on another attempted run..
Last edited by Mesuge on Thu, 15 Jan 2009, 17:47, edited 1 time in total.
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Post by acmotor » Fri, 16 Jan 2009, 05:35

Danfoss overloads are dependent on...

A) what user settings have been made about overload. e.g. trip delay on overtorque can be set to 'off' or 0-60 sec par 409
If off is slected then C (below) applies.

B) If VFD is 30kW and motor is 11kW then inverter never considers IT is in overload anyway.

C) what the heatsink temperature <90 degC or the measured (thermistor) or calculated motor temperature (called motor time) par 128/129 are.

Overloads of the inverter itself e.g. max current are user selectable timed. e.g. par 410 trip delay inverter 0-35 seconds.

Mesuge, the duty cycle you mention does not seem to be a timed thing, that I have seen, just a temperature limited function.

The VFD in an EV is most unlikely to be at 100% duty cycle, even as an average over 5 minutes (unless Andrew is driving). Likewise, the emotor is not really stressed, unless I can get more voltage into it ! Image
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Post by Mesuge » Fri, 16 Jan 2009, 06:12

Ok, but the context we are talking here is about 230V delta (rewound) on 415VAC VFD:
<6x overload (kW) and <3x overload (Nm) on aircooled thingy..

Be it just for a few seconds in the top overclock range, the temps and overload peaks will be an issue to some degree (hopefully manageable) in the real world. Just imagine urban concrete jungle/summer conditions and pushy driver, and/or >10-15% grades for long distance therefore resulting in prematurely reaching the Nm ceiling as just posted above by BGA. Also among other things VFDs suffer from is high alt. sickness (reduced power), low 0.5-1G vibration rating, .., etc. Otherwise such a setup would be more common by now. I'm all for it but we also have to address the weak points openly.

EVs should mimic the utility-performance of ICEs as much as possible, i.e. disregarding weather, hills, crazy drivers, it must work dependably at all imaginable regimes.

My impression is that historically the top EV drivetrain manufs. deviated from this main branch by adopting liquid cooling and even higher factors of overload applied, ..
Last edited by Mesuge on Thu, 15 Jan 2009, 20:24, edited 1 time in total.
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Post by acmotor » Fri, 16 Jan 2009, 07:20

Not certain I'm with you ?
I run >3x overload in kW and >4x in Nm it is all cool !

Liquid cooling means the cooling fins are located elsewhere, not that they are smaller.
In fact copper and aluminium are still far better thermal conductors than water when it comes to removing heat from a motor or controller and passing it on to the air around via fins / fans.

Water can have a storage tank associated with it but then there is weight and complexity and risk of failure.
Remember, the single most common cause of ICE failure is the water cooling system.

In an EV, the location of cooling fins is not a big issue.
Water cooling may seem to provide for a small, light weight motor but don't forget to add in the cost / size / weight / reliability concerns of the cooling system.

The best way to reduce heat in motors / controllers is by going for maximum efficiency. i.e. a 95% efficient motor needs a lot less cooling than a 75% efficient one. There are plenty of both around.
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Post by Mesuge » Fri, 16 Jan 2009, 07:37

Yes, sorry, it gets a bit confusing here, I'm talking about the rewind setup - in fact THE topic of this thread as nicely summarized in Woody's second post from the top on this page - you are now talking about your current stock unmodded 415V motor and Dan VFD combo, right?

But as mentioned before on this thread, the rewind mod will decrease efficiency hence more heat to deal with, especially in conditions I tried to list, which there are perhaps many more. Btw. the Tesla boys go liquid cooling in the new revision of their drivetrain as other major brands have done decade/s ago..
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Post by acmotor » Fri, 16 Jan 2009, 08:50

Yes, I long for a 220V delta wound.

Remind me again why the rewind would reduce efficiency ?
Is that from iron lossses at increased frequency ?
I thought we covered that with double a small number is still a small number.

Re liquid cooling. If you are serious then super cool, otherwise leave me out. I detest liquid cooling particularly since the liquid is water.
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Post by Mesuge » Fri, 16 Jan 2009, 09:39

Re: air v. water cooling preferences, fair enough. But we're the creatures from the water planet afterall Image

Re: rewind induced losses, yes this is likely the less prominent parameter among the other listed (gradebility, several consequtive stop&run cycles to Imax, ..)

Re: availability of >100kW inverters for this mod, I think that Danfoss and possibly other brands usually produce per specific order only, so no big warehouses exist - only few items left in the corner at dealerships or alternatively used ones from factories, therefore the supply of discounted drives is rather shallow.. I'm hunting in my neck of the woods for large VLT 5000 or alternative.
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Post by Johny » Fri, 16 Jan 2009, 17:17

The only way I can see a lower voltage ACIM increasing losses is increased current in the VFD causing higher IGBT losses - the motor efficiency surely stays the same.

acmotor - does this look similar to your simple BMS - low voltage dual comparator and I use an LED for reference. Temperature range was no good for a diode but the higher voltage for a LED swamps the temp. effect. Just have to choose the right colour. The opto conducts for too low or too high voltage - I figure I'll know which one is causing it.
Image

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Post by woody » Fri, 16 Jan 2009, 17:58

Johny wrote: Image
Someone else who doesn't like Visio! Image
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Post by Johny » Fri, 16 Jan 2009, 18:23

I actually scribbled it in Excel while I was doing an automatic calculator for the high, medium and low resistors so I could check the effect off different voltage references and temperature effect. The drawing was so I didn't forget what the calculations were about (scuttling to explain self).
That being said, I installed Dia for my future schematics and it looks good. No more word drawings.

They want me to buy my motor now - it was being held till mid-Jan. 11kW ABB 132 frame - now that I have 2 controllers I guess I should commit to the motor that they/it will drive.

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Post by acmotor » Fri, 16 Jan 2009, 21:22

First,
Most of the water on earth is sea (salt). Does the admission that we are water creatures mean we should use salt water for cooling ? Image

Danfoss make a 1MW VFD. I'd order one if I could find enough batteries !

There are plenty of manufacturers out there. I think the issue with the second hand large drives is making the contacts. They must be out there in the millions. Just not standard consumer items reaching ebay.

Johny,
Basically your circuit looks OK.
Love the drawing ! It is all about the content !

Not certain about the accuracy or stability of the LED as a reference !
You will at least need to use one or two trimmers to set it up.
I would avoid trimmers for cost / vibration tollerance and the need to set them. (220 x 2 = 440 adjustments)

Two points...

The opto needs to be running in NC i.e. failsafe mode so all BMS can be daisy chained and loop is closed when all is well. This means use low current opto so it can stay on.
You need to watch the Vce max and Von when multiple optos are in series. May need to group them and pass on to another opto.
I am working in groups of 22 cells (my module size).

The other point.
The shunt (I think) needs to occur before the overvoltage signal.
You don't want an OV signal when shunt is jusy sitting there doing its job. The OV will mean stop charging NOW. Shunt means eq is occuring.
I use a third prog.zener for shunt.

The alternative is to use 3 optos (OV UV shunt) but where do you stop.

I'm working with...

UV 2.5V
OV 4.2V
shunt 3.8V
shunt current determined by shunt res value, I'm using 2A
This gives me 3.8 x 2 x 220 = 1672W of shunt total to absorb regen if cells are full.

What were you temp corr thoughts ?

This is my circuit...
Sorry the software I used wouldn't output a jpeg, pdf or anything so I printed it and scanned to jpeg !
Image


I think we are hyjacking the topic ! Image
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Post by Johny » Fri, 16 Jan 2009, 21:34

We should put a DIY (or low cost) BMS topic under batteries. I was just idly trying to determine the price and effort besides the cell price for Lithium. I hadn't considered fail safe - good point. It's really a big topic by itself - anyone care to start the thread?

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