# Kostov 11 inch DC motor construction and pics



## azdeltawye (Dec 30, 2008)

I got my new Kostov 11” motor the other day. Curious about the workmanship and quality of this motor I took a look inside to check it out. Overall construction of the armature seems pretty robust. The commutator was large and brush holder design seemed rugged. The field windings however I thought could use some attention. The spot weld splice of the Interpole winding conductors seemed a bit shoddy as they were not insulated or strain relieved. I could see the possibility of these splices fatiguing or making contact with the case in a prolonged heavy vibration environment. I don’t think it would pass a shaker table test… Aside from that the motor looks to be built pretty well. Here are some of the internal dimensions:

Field iron length = 4.75”
Armature diameter = 6.87”
Magnetic volume of armature = 176.1 in^3 
Commutator diameter = 5.85”
Commutator segment = 0.25” X 2.10”
Brush contact area = 0.49” X 1.56”


----------



## Georgia Tech (Dec 5, 2008)

Wow I was always told that the magnetics for a Kostov motor was rather on the small side due to the inter poles but the magnetics look as big as a GE 11.


----------



## Bowser330 (Jun 15, 2008)

Good Stuff! Congratulations, what controller do you plan to use with it?

Are you considering cranking up the voltage to see what this K-11 can handle?


----------



## CroDriver (Jan 8, 2009)

Great info!! Thank you for sharing!

How long did you wait for your motor? Where do you got this dimensions from?



azdeltawye said:


> Field iron length = 4.75”
> Armature diameter = 6.87”
> Magnetic volume of armature = 176.1 in^3
> Commutator diameter = 5.85”
> ...


And just one more thing I forgot to ask the guys at Kostov... Can this motor run in reverse?


----------



## azdeltawye (Dec 30, 2008)

Bowser330 said:


> Good Stuff! Congratulations, what controller do you plan to use with it?
> 
> Are you considering cranking up the voltage to see what this K-11 can handle?


I'm hoping to get my hands on one of the first production Soliton-1 controllers from evnetics.com. I'm still a few months out from needing the controller. Maybe they'll be ready by then...

Initially my pack voltage will only be 128V. But I plan on adding more cells at some point in the future.


----------



## azdeltawye (Dec 30, 2008)

CroDriver said:


> Great info!! Thank you for sharing!
> 
> How long did you wait for your motor? Where do you got this dimensions from?
> 
> ...


 
It took about two weeks from Bohlinger Inc. in PA, USA.

A mitutoyo caliper and depth gauge.

Yes. Neutral brush timing allows for operation at full voltage in forward and reverse.


----------



## Plamenator (Mar 6, 2009)

Well, I am not claiming that our motors have no defects whatsoever but I cannot quite agree about the shaker table test.
First of all, there is an insulation strip going round the inside of the case so the winding connections cannot short to the case (you can see the insulation strip's edge on the last photo - as it is all painted black, it is difficult to see it clearly if you do not know what to look for).
Second, the two conductors with the weldings are actually carrying the same current in paralel so even if they touch, this will not be detrimental to the motor.
Third, if I am not mistaken, during varnishing of the windings the welds also get covered with varnish. As the varnish is transparent you can only see it by very close inspection or if you scratch the weld with a knife (there should be some fine dust).

Regarding the reversing, indeed the brushes are neutral timed and the motor can safely run at high voltage in both directions. Contrary to non interpoled motor, it is not advisable to advance the brushes of our motors as this will significantly worsen commutation.

P.S. ...maybe I should have started with the fact that I work for Kostov in Bulgaria (www.kostov-motors.com).


----------



## Bowser330 (Jun 15, 2008)

Plamenator said:


> Well, I am not claiming that our motors have no defects whatsoever but I cannot quite agree about the shaker table test.
> First of all, there is an insulation strip going round the inside of the case so the winding connections cannot short to the case (you can see the insulation strip's edge on the last photo - as it is all painted black, it is difficult to see it clearly if you do not know what to look for).
> Second, the two conductors with the weldings are actually carrying the same current in paralel so even if they touch, this will not be detrimental to the motor.
> Third, if I am not mistaken, during varnishing of the windings the welds also get covered with varnish. As the varnish is transparent you can only see it by very close inspection or if you scratch the weld with a knife (there should be some fine dust).
> ...


On your website you have listed Kostov 11" *400V*...is this the maximum voltage allowed for this motor? Can the Kostov 13" be used at 400V as well?
Are there custom modifications that are required to use 400V? What is the estimated price of those modifications?


----------



## Plamenator (Mar 6, 2009)

It is actually a dual motor consisting of 2 x 11" 192V motors.
I have put a drawing on the site to avoid misunderstandings (not a final one though - still needs to be changed here and there).
When used in serial, the combined motor can take 400V (200V on each of the two 11"s). Alternatively you can switch in paralel and get 500A at 192V to achieve again 80kW+.
Hence no, you cannot use the 13" at 400V .
Even 168V is too much for it. Problem is that the collector is so massive (copper for it weights 15kg alone) that centrifugal force will tear it appart at high rpm.

Anyway, I would love to hear your opinions and suggestions on the dual 11" motor and especially its length. We also have plans for dual 9" model so feel free to comment that too.


----------



## azdeltawye (Dec 30, 2008)

Plamenator said:


> ... if I am not mistaken, during varnishing of the windings the welds also get covered with varnish. As the varnish is transparent you can only see it by very close inspection or if you scratch the weld with a knife (there should be some fine dust).


Well I guess my motor must have missed the final QA/QC inspection then. It definitely did not have any varnish on the weld splices of the interpole field winding conductors. I verified this with an ohm meter. Just touching the meter probes to the weld zone yielded continuity – did not have to scratch at the surface with the probes…

Not to worry as this was easily remedied by applying a couple thin coats of class F red insulating enamel to the exposed areas. This type of insulating enamel has a dielectric strength of 2100 V/mil and can be purchased from Grainger or motor rewinding shops.


----------



## Bowser330 (Jun 15, 2008)

Plamenator said:


> It is actually a dual motor consisting of 2 x 11" 192V motors.
> I have put a drawing on the site to avoid misunderstandings (not a final one though - still needs to be changed here and there).
> When used in serial, the combined motor can take 400V (200V on each of the two 11"s). Alternatively you can switch in paralel and get 500A at 192V to achieve again 80kW+.
> Hence no, you cannot use the 13" at 400V .
> ...


What types of modifications will allow a collector to stay together at higher rpms? Kevlar banding?


----------



## Plamenator (Mar 6, 2009)

azdeltawye said:


> Well I guess my motor must have missed the final QA/QC inspection then. It definitely did not have any varnish on the weld splices of the interpole field winding conductors. I verified this with an ohm meter. Just touching the meter probes to the weld zone yielded continuity – did not have to scratch at the surface with the probes…
> 
> Not to worry as this was easily remedied by applying a couple thin coats of class F red insulating enamel to the exposed areas. This type of insulating enamel has a dielectric strength of 2100 V/mil and can be purchased from Grainger or motor rewinding shops.


This is why I added "If I am not mistaken" to this argument 
Otherwise the first 2 arguments are still valid.

Regarding the collector, I believe that for the size used in the 9" and 11" motors, 6000-6500 is the maximum safe rpm and there is no easy/economical way to increase it.
Most important is the form of the lamella, the quality of the plastic material and the quality of production. We also put metal rings inside but this is not decisive. Kevlar banding will also help a bit but do not expect miracles (if you use it, be very carefull not to short the lamellas during machining and use 2 bands - at the top and the bottom; the one at the top is problematic as there is very little sticking above the brushes)


----------

