woody wrote: ......Nominal ratings go about 10% into this "over-magnetising" area, but you can go a lot further and get more magnetism at the expense of higher loss.
So I reckon a certain weight of ali in the stator can take a certain amount of magnetism assuming it's in a good motor design. Magnetism creates torque - so weight limits the amount of efficient torque.
If you run the motor at half volts, you'll get half the current / magnetism and 1/4 the torque...
Do you mean magnetic saturation ? Normal ratings seem to be something like 1/3 of the magnetic saturation (not 10% into it) otherwise you couldn't get Tmax 3x Tn with linear current to torque ratio up to at least 70% or more of Tmax.
Sorry I was talking stators - I thought you get Tmax 3x Tn by increasing the slip, not the stator magnetism - i.e. the rotor bars cut more magnetic field => current goes up and hence the rotor magnetism goes up.
DOL implies same stator magnetism for all loads, but you still get Tmax / Tn.
But true, this is not a brick wall, just a case of diminishing returns. i.e. 400% or more Tn is there for the taking. I do this already.
Yes I think increasing V/F overmagnetises the stator to a higher degree.
I take 'ali' as a new type of iron !
Aluminium is the stator in an aluminium motor? But you can't permanently magnetise aluminium, so how can you over-magnetize it.
I'm not certain that I follow '1/2 the volts' woody.
Is this 1/2 volts while maintaining the v/f ratio i.e. half the frequency as well ? In that case the torque is still exactly the same = Tn, without question.
Yes, I can be vague at times. I meant 1/2 the volts that the nominal V/F ratio suggests.
If you mean 1/2 voltage / same frequency then I would have thought you have half the torque available if current was half since current == torque.
Nah, I think it's 1/4. It's the same as operating in the higher frequency ("field weakening zone" - after run out of voltage to keep up with VF) : double frequency = quarter breakdown torque. Also Star/Delta starting gives 1/3 the starting torque/current despite being only sqrt(3) * the voltage.
Still examining the pole number topic .... perhaps I can throw in the original thinking I had when chosing 4 pole 11kW for the Suzi.
My first experiment with ACIM was a very small (1.1kW) 2 pole and a 20:1 gearbox. This was enough to tell me that stall torque (zero RPM torque) was all important with AC. You must have a minimum torque available to take off up a slope in the EV. 11kW is cruise power at 80kmph.
As it happened Tn of 72Nm 11kW 4 pole emotor = ICE motor torque and with 3:1 Tmax this was close to the 1st gear ratio. Now if I used a 2 pole motor of 11kW it would have 36Nm of torque .... simply not enough.
I would need a 22kW 2 pole for the same torque as the 11kW 4 pole.
The 0-40kmph performance is better than original ICE but above that the voltage limitation cuts in.
Now it is apparent that to get the 80 or more kmph at full torque I need to change the emotor voltage by 1/2, 1/3 or even 1/4.
If I used a 2 pole I would have 1/2 the torque as mentioned and this would not be acceptable and I couldn't do anything to improve it. However I can rewire/rewind the 4 pole and get the required performance.
It appears from data sheets e.g. ASEA that the 4 pole (160M) 11kW 80kg (yes there are smaller) is equivalent to the torque of a 22kW 2 pole (72Nm) but in 180M frame and 150kg of the same vintage motor.
Yes there are better combinations available but still the 2 pole falls short of the 4 pole in power to weigh at the same kW. If you double the 2 pole kW to retain the Nm then the motor is somewhere between bigger and BIGGER. Please present any good combinations you find (that are available in Oz)
Well, from the sheet I have put together with specs of about 60 ACIMs (50 ABBs, 5 or 6 CMGs, a trojan and a qin wei):
The best T(max)/kg is the 92kg ABB 132-316 15kW 4 pole, with 97.8 * 4.0 / 92 = 4.25 Nm/kg (~AU$1000)
Next 2 are Johny's picks:
the unobtainium 61kg CMG 132MB-38 11kW HO with 72.7 * 3 / 61 = 3.58 Nm/kg
the 72kg qin wei 11kW 132 with 72.3 * 3.5 / 72 = 3.5 Nm/kg
The next 10 (2.98 - 3.51 Nm/kg) are 9 ABB 4 pole motors (162 034, 132 003, 132 315, 162 102, 182 103, 162 103, 132 006, 132 007, 182 033) ranging from 11 to 30 kW, 63 - 177kg, 132 - 180 frame, plus the CMG 160-42.
Then comes Weber & Coulomb's pick, the ABB 131-008 22kW @ 95kg 72.6*3.8/95 = 2.9 Nm/kg. (~AU$2000)
The "pair" of the SI units' favourite is possibly the 132-005 11kW @ 76kg 72.6*3.0/76 = 2.85 Nm/kg or about the same.
OK I'm talking direct drive here. You can use a gearbox to make up for an underpowered / undertorque motor up to a point only. But ... Once you haven't enough torque in first gear you are out of business. Once you can't climb a 1 degree slope at 100kmph you are out of business.
I still like the gearbox since the ACIM power curve has a fairly sharp peak (unless you are battery limited).
Star/Delta/Series/Parallel switching would also give you multiple peaks for a lot less weight/efficiency wasted.
I am still thinking direct drive with a large enough rewound motor and controller to suit is going to be right for me.
Remember though that the 4 pole at 4x frequency will give a peak of up to 12x power as I have demonstrated. A 2 pole at 2 times freq. (both 6000RPM) will only supply up to 6 x peak. On both accounts, original size / weight and potential peak power the 4 pole wins. No wonder the prius went even further to 8 pole !
From a quick scan of ABB cataloge:
99kg 8 pole is 72 * 2.8 / 99 = 2.0 Nm/kg
99kg 6 pole is 73 * 3 / 99 = 2.2 Nm/kg
So not much good for ACIM, probably permanent magnet is different
edit: Duh! forgot to paste !
Yes, my email version of your reply was a bit light on in content