# Kostov k11 catastrophic failure!



## azdeltawye (Dec 30, 2008)

My Kostov 11” motor failed again! This time it appears that I was not directly to blame – ref brush failure thread: http://www.diyelectriccar.com/forums/showthread.php?t=88672

Symptoms were: Left the house, first drive of the day (cold motor), drove through the neighborhood. Got onto the main road and started accelerating, got up to speed (approx 4000 rpm) and noticed severe lurching. Let off throttle, turned down radio and gently applied throttle again, no more lurching but significant loss of power. Limped along for a few more blocks and found safe place to pull off the road. I opened the hood and smelled smoke which appeared to be coming out of the front DE end of the motor. 

After towing the car home I pulled the brush inspection cover – brushes and commutator looked fine. I then peered into one of the front vent holes with a flashlight and saw evidence of burnt windings and flash marks. I disconnected the motor leads from controller and applied 12VDC with bench power supply. The motor started slowly spinning but was drawing over 100 Amps! Normally it draws about 25A @ 12V, unloaded. I let it run for about 10 seconds and started to smell something getting hot so I shut it down.

I removed the motor from the vehicle and removed the DE bell from the motor. It appears one of the interpole windings made contact with the armature. One section of the armature windings has burn marks and signs of overheating. There is also evidence of molten copper spray from the armature on the field and interpole windings. It looks like the armature windings are toast!

I’ll take it to the local motor shop tomorrow and see what they say.


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## RIPPERTON (Jan 26, 2010)

Time to go AC


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## Tesseract (Sep 27, 2008)

What do you have motor current set at?


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## PZigouras (Jun 5, 2010)

We saw the same thing happen with a customer's K9 motor. 


In his case, it turned out that a screw had embedded itself into one of the interpoles, and shorted the field and rotor in a few places (by damaging the insulation). We located [what was left of] the screw, and it turned out to be a shroud screw -- from what we could tell.


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## azdeltawye (Dec 30, 2008)

Tesseract said:


> What do you have motor current set at?


 After the recent brush failure incident I experienced a few months ago I reduced the motor current limit from 1000 A to 800 A. While repairing the motor and getting a closer look at the inside I was amazed that the brush wiring and rigging hardware could handle the 1000 A of current the Soliton would occasionally throw at it. I still think 800 Amps is pushing it for this motor. 

Definitely not built like a NetGain…


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## azdeltawye (Dec 30, 2008)

I took the dead Kostov to the motor shop and confirmed my supposition. The guy there said the armature would need to be rewound. Additionally the field and interpole coils would need a new coat of insulation. He said it looked like the root cause of the failure was a foreign object in the motor. During disassembly of the motor they found pieces of balancing putty. That was the most likely culprit…
He said that they could repair the motor but it would be expensive. He went on to say that it would probably be more cost effective to just get a new motor…


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## PZigouras (Jun 5, 2010)

How hard is the balancing putty? Can you break it apart by hand?

It's hard to believe that putty can cause all that damage...


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## kennybobby (Aug 10, 2012)

*Using the screw holes of the field poles?*

i have to wonder if those side motor-mounts screwed in to the field poles may have loosened or vibrated the pole windings to allow contact? i would think it better to drill and tap separate blind holes for bracket mounts and not disturb the pole pieces.


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## Batterypoweredtoad (Feb 5, 2008)

What rpm range did you typically operate in? The lower voltage pack and high amp controller may have had you operating at high amps and too low of an rpm range for the motor fan to be effective .


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## azdeltawye (Dec 30, 2008)

PZigouras said:


> How hard is the balancing putty? Can you break it apart by hand?...


 The chunks of balancing putty that were found inside the motor are pretty hard – similar to the consistency of car body filler. 

I believe the kiss of death for this motor was the close proximity of the one interpole winding to the armature – shown in pic. Once the insulation was compromised then a flash was imminent… To give an idea of the distance; without the DE end bell in place, if you push the armature in the direction of the offending coil, the copper of the armature will actually make contact with the coil instead of the steel of the armature and steel of the stator. Pushing in the other direction yields about 1/16” of clearance between the same spot. So assuming the armature is properly centered, you would have about 1/32” of nominal clearance between the interpole and armature…

I think the workmanship of this motor was notably sub-standard as I also stated in my initial findings when the motor was purchased back in 2009 – ref thread: 
http://www.diyelectriccar.com/forums/showthread.php?t=34775


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## azdeltawye (Dec 30, 2008)

Batterypoweredtoad said:


> What rpm range did you typically operate in? ...



 Typical rpm range I kept was around 2500 – 3500. I would usually start out in 2nd gear and shift to 3rd above 30 mph or so. 

3rd gear starts were very rare...


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## azdeltawye (Dec 30, 2008)

*Re: Using the screw holes of the field poles?*



kennybobby said:


> i have to wonder if those side motor-mounts screwed in to the field poles may have loosened or vibrated the pole windings to allow contact? i would think it better to drill and tap separate blind holes for bracket mounts and not disturb the pole pieces.



All field pole bolts were tight and had not loosened. They were installed with blue locktite. 

I agree; using the field pole bolts for mounting is a bad practice. Unfortunately my options were limited with the single shaft model. In my design The clamp band supported the bulk of the load and the field bolts were mainly for locating…


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## azdeltawye (Dec 30, 2008)

EJETTA is back on the road again with a brand new shiny RED motor. 

Performance/acceleration comparison between the Warp 9 and K11 seems about the same with the exception of the warP which keeps pulling well past 3000 rpm. The Kostov would suffer torque reduction when it ran out of steam at around 3000 rpm. This makes sense since the Kostov was wound for higher voltages than the W9 and I am only working with 144 V. 

I will keep the motor current limit set at 800 A until the brushes are fully seated. After that I’m looking forward to cranking it up to 1000A…

I guess the one positive aspect of this whole Kostov premature failure debacle is that I am now the proud owner of a 174 lb Bulgarian paper weight! However, as great as that may sound, I think the novelty of owning this special paper weight will rapidly fade and I will want to dispose of it. So if anyone out there wants a spare parts motor or extra set of new brushes; send me a PM.

Cheers,


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## bwjunkie (Jul 31, 2013)

> I will keep the motor current limit set at 800 A until the brushes are fully seated. After that I’m looking forward to cranking it up to 1000A


I ran mine 50 miles without going above 150amps for final seating. Did you use the 12v seating process at least for a few hours?

-josh


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## marc02228 (Jan 15, 2011)

These Kostovs, at least mine, are/is just rubbish. 
My Kostov 11 Alpha had such a extreme imbalance, the whole car was shaking at above 4k RPM. (No, it wasn't the flywheel)

Luckily I work for a company that builds huge generators for power plants or drive systems for big ships, so I have been able to make a FFT analysis of the vibrations and reduce the imbalance with balance gum. I think I still have the balance results on my notebook at work.


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## azdeltawye (Dec 30, 2008)

bwjunkie said:


> …Did you use the 12v seating process at least for a few hours?


 
Yes, I ran the motor unloaded at 15V for approx. 10 hrs before I took it out on the road.
 




marc02228 said:


> These Kostovs, at least mine, are/is just rubbish.
> My Kostov 11 Alpha had such a extreme imbalance, the whole car was shaking at above 4k RPM. ….


 
Interesting. Yes the balancing putty or ‘gum’ as you put it was the apparent cause of my motor failure. However the root cause was due to not enough clearance between the interpole winding and the armature – in other words poor workmanship/quality…


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## DavidDymaxion (Dec 1, 2008)

Thanks for posting the experiences. I just ran my new Kostov 11 inch sepex for the first time, on 24V up and down a hill. 11 A to idle, about 100A up the hill and about 50 A regen going down. The motor is very smooth at lower rpms, hopefully that holds for higher rpm.

Azdeltawye, when you removed field bolts to attach the mount, did you do anything special to make sure the field poles stayed flat to the case? Why didn't you use the lifting eye hole to stabilize the mount? My 11 has flats in the case, they make for very nice mounting points. In any case, bummer on the problems but thanks again for posting.

BTW this is my 2nd Kostov 11 inch, but the first one was harmed by racing abuse.


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## onegreenev (May 18, 2012)

> about 50 A regen going down.


Regen? Do tell the setup for this.


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## Old.DSMer (May 18, 2012)

marc02228 said:


> My Kostov 11 Alpha had such a extreme imbalance, the whole car was shaking at above 4k RPM. (No, it wasn't the flywheel)


I have the K11-250. I notice a slight vibration right around 3000 RPM. Transmits through the whole car. Low frequency...maybe 50 Hz. I've dismissed it as caused by solid urethane motor mounts and maybe some system harmonics. But perhaps I also have an imbalance. Curious to hear if anyone else has had these experiences?


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## kennybobby (Aug 10, 2012)

3000 rpm is equal to 50 Hz synchronous speed. Mass imbalance vibration is at 1x synch, out of round vibration is at 2x synch.


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## Old.DSMer (May 18, 2012)

kennybobby said:


> 3000 rpm is equal to 50 Hz synchronous speed. Mass imbalance vibration is at 1x synch, out of round vibration is at 2x synch.


Interesting. That would indicate a rotor mass imbalance. But wouldn't it also be noticeable through the entire RPM range? It seems perfectly smooth up to approximately 2500 and over 4000?


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## DavidDymaxion (Dec 1, 2008)

It was just the natural capability of a sepex. We just jumper cabled up a couple of 12V batteries direct to the motor. As the hill wanted to spin the motor faster than key speed it did natural regen.

My sepex Kelly controller is out right now to ease the motor mount and battery box installation, I'll report on how it regens when I get everything together.


onegreenev said:


> Regen? Do tell the setup for this.


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## kennybobby (Aug 10, 2012)

Old.DSMer said:


> Interesting. That would indicate a rotor mass imbalance. But wouldn't it also be noticeable through the entire RPM range? It seems perfectly smooth up to approximately 2500 and over 4000?


There is a resonant natural frequency that is being excited which amplifies the vibration at that speed--so don't dwell there for very long as it will do mechanical damage (e.g. Tacoma Narrows Bridge is classic example). Above and below the resonant frequency, the amplitude is much lower but it is still there.


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## Old.DSMer (May 18, 2012)

kennybobby said:


> --so don't dwell there for very long as it will do mechanical damage--


That sucks. 3000 RPM is the perfect cruising speed with my gear ratios. Both on the freeway and on city streets. Lower RPM pulls more amps and increases motor temp. Higher RPM gets to close to redline. Frequency increases,obviously,above 3000 RPM, but I would guess the amplitude is about the same.

To clarify...it's not rattling the whole car like a high powered stereo. It's a slight vibration and hum. However,it's still there and I would like if everything was perfectly smooth. Not sure if that's even possible. For all I know, it could be something in the tranny.

Does Kostov dynamically balance the rotors, or just statically balance them?


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## azdeltawye (Dec 30, 2008)

DavidDymaxion said:


> …
> Azdeltawye, when you removed field bolts to attach the mount, did you do anything special to make sure the field poles stayed flat to the case? Why didn't you use the lifting eye hole to stabilize the mount? ...


 
The motor has two bolts per shoe. I only messed with one side on four different shoes. Yes, bad design, should have used lift eye or other blind hole for mounting…

Hope you have better luck on motor #2!


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