Kostov performance curves

Bellistner said:

G'day. I'm trying to find performance curves for Kostov's motors, with torque at several points along the curve. I'd like to put them into Franky.EV's spreadsheet. I've found the 'compare' PDF on the Kostov website, but that only lists continous ratings? Other PDFs are available on the web such as this one, but they do my head in and I can't read them.

I'm specifically looking at the 17R (9") and R20 (10") motors, at between 144 and 192VDC. At least three RPM/torque points would be nice. Or at least hammer into my thick head how to read the graphs.

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Hi Belli,

Beats me why people have difficulty with electric motor speed torque graphs. They make perfect sense to me. But then I've been using them for many years. The big problem I see is getting good graphs from the motor suppliers. And Kostov seems to be one of the better companies about supplying quality motor specs. They also appear to respond to inquiries. So you can put your questions directly to them.

I have discussed "how to read motor curves" a number of times on this board. It is difficult even for me to get back to some of those posts. But spend a while with the search feature and you can find some. Here are a couple of starters for you:

http://www.diyelectriccar.com/forums/showthread.php?p=149088&highlight=characteristic#post149088

http://www.diyelectriccar.com/forums/showthread.php/electric-motor-output-wrt-voltage-32492.html

Please read up on it and come back with specific examples and questions and I'll try to explain it for ya

major

Tesseract said:

Hey Major - Qer and I have been hypothesizing about the series/parallel fields in the Kostov motors - particularly whether there is enough benefit in switching between the two configurations with a single rotor - but I am very curious as to what your take is. Worthwhile, or barely worth the effort?

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I'd say if you have a good controller, there is no need to use field weakening, either by diverter or by field switching.

Back in the old days, S/P field switch was done to compensate for marginal current and voltage control. Putting the field coils in series would increase the equivalent series resistance and provide increased inductance which was beneficial to slow switching PWM and even more so to stepped resistor starting schemes. However the series coil arrangement in the motor made for a lot of coil heat and therefore reduced rating when in S mode. The switch to SP mode was essentially field weakening, but the motor could be rated normally with 1/4th field coil heat.

You get twice the AT/p in the S mode as the SP mode. So the old time motors would have the SP mode "normal" with regard to Field to Armature mmf ratio. When the motor was in the S mode, twice the field mmf, the motor was over-fielded*, and not efficient.

To do the field S/P switch requires contactors and some logic. I just don't see the value with these modern controllers.

Regards,

major

*new word alert

Tesserac/Major,
I cannot quite agree with you (which seems to be my default position in the situation ).
The way I see it there are several major benfits from shifting the field:
1) S/P mode allows good rpm to be achieved with lower voltages.
Take both K9" 220V and K11" 250V - going to S/P allows 4000-5500rpm to be achieved with only 120V/168V respectively. I.E. one can buy the motor with shifting and use it initially with a lower voltage battery maintaining the car's top speed potential while battery can be upgraded at a later stage.
2) In S/P mode K9" 220V and K11" 250V are equivalent performance-wise to K9" 144V and K11" 192V so it is a kind of an upgrade option.
3) K11" 250V gets 72Nm with 250A in S/P mode and 77Nm with 210A in S mode. My probably naive reasoning is that in S mode the car will have more range as power is conserved at 40-45kW while torque is marginally higher but with almost 20% less amps.
4) S/P mode really shines in race conditions. Imagine K11" 250V overloaded with 1500-2000A (do not take this as an offical endorsement to do it ) - its rpm will fall to 2500-3000 which is not good. In S/P rpm will be 4000-4500 and as an added benefit the coils will handle abuse much better. Indeed range will suffer but power/acceleration is what is utmost important here.

Plamenator said:

Tesserac/Major,
I cannot quite agree with you (which seems to be my default position in the situation ).
The way I see it there are several major benfits from shifting the field:
1) S/P mode allows good rpm to be achieved with lower voltages.
Take both K9" 220V and K11" 250V - going to S/P allows 4000-5500rpm to be achieved with only 120V/168V respectively. I.E. one can buy the motor with shifting and use it initially with a lower voltage battery maintaining the car's top speed potential while battery can be upgraded at a later stage.
2) In S/P mode K9" 220V and K11" 250V are equivalent performance-wise to K9" 144V and K11" 192V so it is a kind of an upgrade option.
3) K11" 250V gets 72Nm with 250A in S/P mode and 77Nm with 210A in S mode. My probably naive reasoning is that in S mode the car will have more range as power is conserved at 40-45kW while torque is marginally higher but with almost 20% less amps.
4) S/P mode really shines in race conditions. Imagine K11" 250V overloaded with 1500-2000A (do not take this as an offical endorsement to do it ) - its rpm will fall to 2500-3000 which is not good. In S/P rpm will be 4000-4500 and as an added benefit the coils will handle abuse much better. Indeed range will suffer but power/acceleration is what is utmost important here.

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Hi Plamen,

In the design of the series motor there is a fairly small range of field strength (mmf) ratio to armature strength (mmf) which will result in near optimum performance for the motor. Two to one, as in the series to series parallel field switching arrangement is outside this range. So motor performance suffers in either S or P field connection or both depending on how the design was compromised to start with.

You are much better off in regards to motor rating (power density) and motor efficiency by designing the motor with the proper field and then letting an efficient PWM controller assume the job of speed and torque control.

And in your point #3, come on, get real? The only way you'd see a 20% reduction in current at equivalent power for switch from P to S in the field was if the P connection was terribly inefficient. So why design such a motor which would allow that P connection in the first place?

I see nothing to be gained by field switch (S/P) in series motors and operational modes which can be troublesome. Why take that chance, add the complexity and cost of the additional motor terminals, external wiring and contactors, and control logic, when a good controller will do all that for you?

Use the proper motor design for the application, gear it correctly and use a good controller. Let the motor designer choose the proper field for the armature, not the customer.

And besides that, someone might get the field wiring diagram wrong

Good to see you still watch this board. I even said a few nice things about your company recently

major

major said:

Hi Plamen,

In the design of the series motor there is a fairly small range of field strength (mmf) ratio to armature strength (mmf) which will result in near optimum performance for the motor. Two to one, as in the series to series parallel field switching arrangement is outside this range. So motor performance suffers in either S or P field connection or both depending on how the design was compromised to start with.

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Theoretically you are right. Field strength should match armature strength.
In practice we have discovered the range is not fairly small. For example efficiency of our 11" series is more or less constant with 5-15 loops. If optimal is 7 loops, going to 10 reduces efficiency by 0.2-0.3% which is not significant. Further going to 15 loops has almost no effect as the coil's field becomes saturated (not sure about proper term) and each additional loop adds almost nothing to the field's strength.
So designing the motor with optimal 7-8 loops (S-P) and doubling those to 15 (S) leads to no detrimental effect.
Reducing loops too much to 5 and less has a very pronounced effect on commutation making it much worse which is why S-P loops should not be too low.

You are much better off in regards to motor rating (power density) and motor efficiency by designing the motor with the proper field and then letting an efficient PWM controller assume the job of speed and torque control.

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Crodriver is the perfect illustration where a controller cannot cope.
Initially he used Zilla2K with our dual 11" motor applying 260V+2000A in parallel motor mode. RPM were 3000 and there was nothing the Zilla could do to increase those as battery could not provide more voltage.
And if you design the motor to have 5000rpm at 1500-2000A, the motor will not be fully useable in normal driving where rpm will shoot to 8000. If you think about it, W11HV is exactly that - 8000rpm at its nominal 250A point. Great for racing but city driving needs about 3000rpm where motor will spend most of its time at 100V. Field switching gives you best of both worlds.

And in your point #3, come on, get real? The only way you'd see a 20% reduction in current at equivalent power for switch from P to S in the field was if the P connection was terribly inefficient. So why design such a motor which would allow that P connection in the first place?

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The S-P and S modes here are 250A/192V/72Nm/40kW and 210A/250V/77Nm/44kW respectively. Power is actually increased due to the hike in voltage. As S mode overheats the coils quicker, amps here are reduced from 250A to 210A with the latter only being able to last 60min.

I see nothing to be gained by field switch (S/P) in series motors and operational modes which can be troublesome. Why take that chance, add the complexity and cost of the additional motor terminals, external wiring and contactors, and control logic, when a good controller will do all that for you?

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One actually needs only one additonal contactor (assuming one main contactor is already in place) to implement it.
If Tesseract adds the logic to Soliton1 (which already has the hardware), the implementation will not be that difficult.

Use the proper motor design for the application, gear it correctly and use a good controller. Let the motor designer choose the proper field for the armature, not the customer.

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Indeed it is not a revolutionary feature though usefull in my opinion.
I still have no real life data on the range benefits and it is up to the customer to decide.

And besides that, someone might get the field wiring diagram wrong

Good to see you still watch this board. I even said a few nice things about your company recently

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There are no bad feelings on my behalf about your opinion of field switching - no worries here . It is a great marketing oppportunity if I manage to convince you though
major[/quote]

Plamenator said:

Theoretically you are right. Field strength should match armature strength.

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That's life Full of compromises.

Take this example:

The S-P and S modes here are 250A/192V/72Nm/40kW and 210A/250V/77Nm/44kW respectively. Power is actually increased due to the hike in voltage. As S mode overheats the coils quicker, amps here are reduced from 250A to 210A with the latter only being able to last 60min.

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Here is a case where the guy using the S mode is forced to use a 250A armature at only 210A (and for less allowable time). So he has been compromised to use more armature than he needs so the motor company can sell a product into more applications.

Hey, not that there is anything wrong with that Motor companies cannot be expected to design, tool and make an unique product for each one-off application. This may be the best choice for that guy. But it is far from optimal.

The simple fact that there is a 4 to 1 difference in field coil loss (heat) between S and P, tells you that a single field structure isn't "right" for both cases.

The 2 to 1 range of field mmf is tolerable for the armature. Certainly SepEx motors operate with wider margins. However what do they do? Carefully field map the system and emulate the proper "series" field mmf condition for overloads. I suspect the use of interpoles contribute to the success of your motors to commutate well in the weak field condition, however that will not compensate for armature reaction.

It is fine with me if people want to use field switching or field weakening. And if controller makers want to add some code to accommodate it, fine. I am glad to see motor and controller companies taking this much interest

major