# DC-Kostov @ 300V vs 192V ?



## Bowser330 (Jun 15, 2008)

DC-Kostov 11" @ 300V vs 192V.....

- Will the extra voltage lengthen the powerband enough to efficiently handle direct-drive?

http://kostov-motors.com/files/productattachments/da0012f5e806b95241ea09d19be9abe3_11-192V.pdf

It was mentioned in other threads that a 10% increase in voltage would result in a 10% increase of power and 10% increase in rpm at a given torque...

So referencing the above linked power-graph....
- 180V with 50% increase is 270V
- 72kw of power (at 3800rpm) with 50% increase is 108kw (145hp)
- 3800rpm with 50% increase is 5700rpm (with power of 145hp available)

Do I have something wrong?


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## major (Apr 4, 2008)

Bowser330 said:


> Do I have something wrong?


Hi Bowser,

Maybe just the physical limitations of the motor.  You think she'll hold together at 5700 RPM? And, do you think she'll commutate successfully at 270v and 500A?

Other than that, your logic and math seem good.

As for direct drive, if the motor can possibly survive at those RPM, then you can gear the motor down and probably do a direct drive.

Regards,

major


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## Bowser330 (Jun 15, 2008)

major said:


> Hi Bowser,
> 
> Maybe just the physical limitations of the motor.  You think she'll hold together at 5700 RPM? And, do you think she'll commutate successfully at 270v and 500A?
> 
> ...


I didnt want to state it, but i was hoping for your input, you seem to have a lot of knowledge in this area...

5700rpm is alot and I would probably gear that to be the upper end of the direct drive speed....

example...if 1000rpm = 71mph then 4.5:1 ratio would be...

4500 (motor) rpm = 71mph... which would be a good speed to cruise the freeway at since the efficiency is closer to 90% and would still leave some room up top...

at lower speeds 35mph (2250rpm at 4.5:1 ratio) the motor would be very inefficient but it wouldnt be demanding many amps to only move at 35mph....

can you help me understand what " commutate successfully at 270v and 500A" means?

Thanks Major!


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## major (Apr 4, 2008)

Bowser330 said:


> can you help me understand what " commutate successfully at 270v and 500A" means?


Well Bowser,

When it does not commutate successfully, the electric drag race boys use the term "zorched". And it is the end of the race day for them.

You know these motors have commutators and brushes. This is how all the current is transmitted to the armature, where it produces torque. Commutation is the process of conducting and reversing the armature current. Each armature coil has inductance, and therefore a resistance to change in current. Yet, by commutation, the current is being forced to change. This, along with the magnetic distortion of the main field due to armature reaction, causes the voltage between the brush edge and the commutator segment (or bar) to spike very high. High line voltage, high currents and high speeds (RPM) all exasperate the situation. 

Successful commutation is when the voltage between the brush edge and comm bar is reasonable. Usually some small sparking is visible. On over loads, maybe some steakers (long sparks) which subside quickly. Nothing which causes excessive heat (like glowing red spots) or damage to surrounding components.

Zorching (unsuccessful commutation) occurs when the voltage exceeds the dielectric limits of the insulation in the commutator and brush rigging. A flash over will carbonize the atmosphere in the area making it conductive. And then you have what is described as a plasma event. In other words, a ring of fire around the whole commutator. Pretty neat to see, unless you own the motor. It is essentially a circular arc welder or plasma cutter. I've seen it actually cut pieces of cast brush boxes off. It usually only takes a couple of seconds to find a critical circuit component to sever. Then everything comes to a stop and you get that awful smell of abused electrical machinery.

These are the good and the bad (and ugly). But there is a whole range in between. Where there is too much sparking, but not enough to zorch. This can result in rapid brush wear. I recently saw a report of "bad" commutation due to excessive field weakening where the brushes wore completely out in about a week. So, I'd define successful commutation as about 5000 hours of brush life, maybe a bit less for EV motors. For industrial motors, 10,000 hours is expected.

I know Kostov will use interpoles in their motors. This helps greatly with commutation. But even still, there will be a limit. Maybe this motor will work, maybe not.

Regards,

major


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## major (Apr 4, 2008)

Bowser330 said:


> then 4.5:1 ratio would be...


 
WRT direct drive, you need to look at the torque. If you have a 500 amp limit controller, then max motor torque is 180 Nm. That is 4.5 * 180 = 810 Nm at the wheel. Is that enough for you?


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## Bowser330 (Jun 15, 2008)

major said:


> WRT direct drive, you need to look at the torque. If you have a 500 amp limit controller, then max motor torque is 180 Nm. That is 4.5 * 180 = 810 Nm at the wheel. Is that enough for you?


WRT?

Max torque is 180 Nm? 

Im not sure I follow...

The graph shows 180 Nm being available at 3800rpm (motor)

4.5:1 ratio means that 180 Nm is available at 60mph (if 1000rpm=71mph) right? where does the multiplication come in?


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## Tesseract (Sep 27, 2008)

Bowser330 said:


> WRT?
> ...


WRT = "with respect to"

Also abbreviated as w/r/t


My understanding - somewhat verified from testing my prototype controller with a Warp 9 at 192V* - is that as long as your controller can limit it's maximum duty cycle so that the motor voltage doesn't exceed the manufacturer's maximum, you can use a much higher pack voltage. Even though the peak voltage seen by the motor exceeds its rating, the chopping action of the controller helps to enforce commutation, so to speak.


* - According to NetGain, 170V is the maximum recommended voltage to apply to the Warp motors and 192V is the absolutely maximum. During our testing we loaded the motor down just enough for it to draw 500A at 192V but with the duty cycle at 60%. There was not much sparking at the commutator, so we are tentatively encouraged that as long as we ensure that duty cycle * pack voltage < 170V the motor will commutate fine.


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## Bowser330 (Jun 15, 2008)

Tesseract said:


> WRT = "with respect to"
> 
> Also abbreviated as w/r/t
> 
> ...


Thank you Tesseract..


So the interface between battery and controller is always the same, 192V and whatever amps you draw as you press the potentiometer...example 500A = 96kw

The controller to motor interface is where things can change based on dutycycle manipulation which really is transparent to the battery pack...
example 60% DC of 192V = 115.2V and to equal 96kw the controller would make the 500A into 833.33A to acheive that...

If this is correct, then a lower duty cycle % will retard the expected higher voltage = higher rpm advantage...

At what point does the controller determine what % duty cycle to apply to the motor?

Let me ask this...the reason I have been so focused on higher voltage is that I was thinking I would need less amps out of my pack to create the same amount of power and be able to use that power in a larger rpm range..meaning more miles and a direct drive setup... was this wrong thinking?


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## Tesseract (Sep 27, 2008)

Bowser330 said:


> Let me ask this...the reason I have been so focused on higher voltage is that I was thinking I would need less amps out of my pack to create the same amount of power and be able to use that power in a larger rpm range..meaning more miles and a direct drive setup... was this wrong thinking?


First, a reminder: except for the 1-5% lost in heat, power into a PWM controller equals power out to the motor. And controllers ALWAYS care about motor amps - battery amps are irrelevant (to the controller).

So, in my previous post the pack voltage was 192V, the duty cycle was 60% and the motor current was 500a. This is all you need to figure out motor OR battery power:

Power (W) = Pack V * Duty Cycle * Motor I
or, 192 * 0.6 * 500 = 57.6kW

To determine battery current, multiply motor current and duty cycle. In this example, the current demanded from the pack was 300A.

Thus, using a higher battery pack voltage will allow you to draw less amps from the pack for a given amount of motor power BUT because each cell has some non-zero amount of internal resistance, the more cells you have in series the higher the internal resistance any current flow must overcome (read: more voltage drop). Don't get me wrong - there is a definite improvement from increasing the pack voltage, but there is also a point where the returns go from diminishing to destructive and/or impractical.

Finally, if your motor is rated for 192V maximum but your pack consists of thirty batteries in series (360V), then your controller needs to be able to limit its duty cycle to ~53% (192/360 = 0.533) so the motor does not see more than 192V. Duty cycle will be varied, then, from 0 - 53.3% by the controller to deliver whatever current is being demanded by the position of the throttle.


Just remember: Power In = Power Out


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## Bowser330 (Jun 15, 2008)

Tesseract said:


> First, a reminder: except for the 1-5% lost in heat, power into a PWM controller equals power out to the motor. And controllers ALWAYS care about motor amps - battery amps are irrelevant (to the controller).
> 
> So, in my previous post the pack voltage was 192V, the duty cycle was 60% and the motor current was 500a. This is all you need to figure out motor OR battery power:
> 
> ...


What determines the controller's Duty Cycle? Does motor speed determine the Duty Cycle?

300V * 50%DC * 1000A = 150kw (1000 Motor Amps)

1000A * 50%DC = 500 Battery Pack Amps

So you can keep the batteries in pretty good shape while still producing lots of power...

I have heard the Internal resistence of lithiums is lower than other battery chemistries is this true?

Tesseract, When is your controller coming out!?!?! I need some high voltage controlling!!!


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## DavidDymaxion (Dec 1, 2008)

John Wayland ran a Kostov at 336 Volts, direct drive in his drag race car: http://www.plasmaboyracing.com/reviews.php (search on "Kostov")

Caveats:


His car was very light
He had extensively modified the motor
He ran it hard for only 15 seconds at a time
He wound up frying his Kostov


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## Bowser330 (Jun 15, 2008)

DavidDymaxion said:


> John Wayland ran a Kostov at 336 Volts, direct drive in his drag race car: http://www.plasmaboyracing.com/reviews.php (search on "Kostov")
> 
> Caveats:
> 
> ...


Be wound up frying it BECAUSE he ran it hard for 15 seconds at a time! 

And to be even more accurate the actual point in time of total motor meltdown was when he was revving it up for fun or something like that...not while driving it down the track for example...


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## DavidDymaxion (Dec 1, 2008)

Actually it fried because it was not revved up. He was skidding the locked front wheels at very low rpm.


Bowser330 said:


> Be wound up frying it BECAUSE he ran it hard for 15 seconds at a time!
> 
> And to be even more accurate the actual point in time of total motor meltdown was when he was revving it up for fun or something like that...not while driving it down the track for example...


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## Bowser330 (Jun 15, 2008)

DavidDymaxion said:


> Actually it fried because it was not revved up. He was skidding the locked front wheels at very low rpm.


right, the motor went through hell and back over and over...good motor in my mind...


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## major (Apr 4, 2008)

Bowser330 said:


> WRT?


WRT = with regards to.....Thanks again Tess.



> Max torque is 180 Nm?
> 
> Im not sure I follow...


On the graph, 180 Nm requires 500 amps of motor current. If you have a motor controller with a 500 amps current limit, then 180 Nm is the most motor torque you will get.



> The graph shows 180 Nm being available at 3800rpm (motor)


RPM doesn't matter WRT motor torque, current does.



> 4.5:1 ratio means that 180 Nm is available at 60mph (if 1000rpm=71mph) right? where does the multiplication come in


If you have 180 Nm of motor torque and a 4.5 to 1 ratio (motor shaft to wheel), then wheel torque is 810 Nm, regardless of RPM or mph. That is the torque multiplication. That wheel torque (810 Nm) divided by the wheel radius is the force to propel the vehicle. So, is that enough force to get you up an incline? And that force plays into the acceleration, F=ma, remember? So, the more force, the more acceleration. Things to consider before you throw out the tranny.

Regards,

major


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## Tesseract (Sep 27, 2008)

Bowser330 said:


> What determines the controller's Duty Cycle? Does motor speed determine the Duty Cycle?


If the torque demanded from the motor remains constant, then, yes, duty cycle is proportional to motor rpm. 



Bowser330 said:


> 300V * 50%DC * 1000A = 150kw (1000 Motor Amps)
> 
> 1000A * 50%DC = 500 Battery Pack Amps
> 
> So you can keep the batteries in pretty good shape while still producing lots of power.


This is true to an extent, though I am skeptical that any of the currently available motors will accept 1000A and 150V at the same time. Also keep in mind that the power loss inside a controller is split between the switch and the freewheeling diode and that split is only equal near 50% duty cycle. If you use a really high pack voltage relative to rated motor voltage, the controller will spend most of its time between 0 and 50% duty cycle (the FWD will bear most of the losses); conversely, if you use too low a battery voltage the duty cycle spends a lot of time between 50% and 100% and the switch will bear most of the losses.



Bowser330 said:


> I have heard the Internal resistence of lithiums is lower than other battery chemistries is this true?


Ni-Cd still has the lowest internal resistance, I believe, but Li chemistry is generally much lower than Pb.




Bowser330 said:


> Tesseract, When is your controller coming out!?!?! I need some high voltage controlling!!!


We are probably down to a matter of weeks at this point. Dimitri has been testing the first beta unit for awhile now without incident and yesterday we installed the second beta unit into a custom-built "hot-rod" replica with a TransWarP 11 direct drive setup. Took it for a test drive and while performance off the line with current limited to 500A wasn't thrilling (it weighs 3500lbs and is geared for high speed, not acceleration) we did get it up to about 70mph on the interstate.


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## 7circle (May 29, 2010)

Sorry I just found this topic on the Kostov 11"

I posted this in "*DC motor theory and model*"
'Have you/anyone found the Piece wise resistances for each field and the Rotor?

I'd like to work out the modelling of a DC motor like the Kostov 11" with interpole/commutating-poles.

I've been try to come up with the details using the Kostov Spec too.
I'm not sure if it's the saturation or the armature reaction or the size of the interpoles that makes it so difficult to analyse.

I just want to know what voltage to apply to the field and armature to make a direct drive setup go in reverse at a low 200RPM."

The Flux Gain factors would be good to.
T= pHi x I x Ka
pHi = Kf x If 

Also there isn't much info on Stall Torque, the graphs in the PDF don't show them.

Any suggestions?


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## major (Apr 4, 2008)

7circle said:


> Sorry I just found this topic on the Kostov 11"
> 
> I posted this in "*DC motor theory and model*"
> 'Have you/anyone found the Piece wise resistances for each field and the Rotor?
> ...


Hi 7,

Join the club. That is the club of uninformed consumers. The motor companies do not want us to know the information you seek. The only way of which I am aware to get such is to buy the product and test it for yourself.

I have to say that Kostov is the best that I've seen for publishing performance characteristic curves. 

Regards,

major


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## 7circle (May 29, 2010)

You sound defeated Major, 

Get your synapsii marching and pull you brain cells together.

It's a competive world, just 'cause we might think opensource software is a good thing, winding wires is another ball game.

Just try and find out about solar cells, battery technology or superconductors.

Being saturated in Directly Competitive motor theory is what it's all about.

The world is going to be rejuvenated by the technology of the 19th century.
............
Sorry reading all those argumentative posts in too many topics on what motor is best has sent me of into an unloaded series motor spin.

......

Come'on Field resistance and Armature resistance cant be that hard to measure at 20% 40% full load current with a sprung braked stationary armature.


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## major (Apr 4, 2008)

7circle said:


> You sound defeated Major,


Hey 7,

Defeated  Not by a long shot. Been at this for a long time and know what information is available and what you must get on your own 



> Get your synapsii marching and pull you brain cells together.
> 
> It's a competive world, just 'cause we might think opensource software is a good thing, winding wires is another ball game.
> 
> ...


This is a bit difficult to understand 



> Come'on Field resistance and Armature resistance cant be that hard to measure at 20% 40% full load current with a sprung braked stationary armature.


I agree. Not particularly difficult to measure, but nearly impossible to obtain from the manufacturer who should have it at his fingertips. So buy a motor, test it and post up the numbers 

Regards,

major


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