# Kostov Different Sepex Field currents ranges



## DavidDymaxion (Dec 1, 2008)

I thought this to be of common enough interest I would ask publicly.

Kostov lists 3 sepex motors:

http://kostov-motors.com/files/productattachments/4fe8e6e6b3937617e6fd810eb916e2c1_N120E02.pdf

http://kostov-motors.com/files/productattachments/4a3d5cb93e787d31fd48632570735ce4_N80E01.pdf

http://kostov-motors.com/files/productattachments/34e66adbccf17f985b166dab89a94cd1_N120F01.pdf

The first 2 show field currents of roughly 10 to 30 Amps. The 3rd has 4 to 12 Amps.

So why the difference? Might it make sense to ask for the 3rd motor to be wound for 10 to 30 Amps rather than 4 to 12? That would have the advantage of changing field current faster (less inductance), and for me the minor advantage my controller wouldn't need reprogramming.

A little bit of background, I'm putting a new sepex in my car, and was debating twin 9, one 11, or one 13. Per advice from Plamenator and the Rebirth Auto guys I'm leaning towards the 11.

Thanks for any insights.


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## major (Apr 4, 2008)

DavidDymaxion said:


> The first 2 show field currents of roughly 10 to 30 Amps. The 3rd has 4 to 12 Amps.
> 
> So why the difference?


Hi David,

The links are not working and gottdi's have a repeat so I just see 2 different graphs. The motor using 4 -12 A field is plotted for 160V on the armature. The motor using 10 - 30 A field is at 80V on the armature. I suspect they want to keep the required field voltage well below the armature voltage so the higher current field is used for the lower voltage armature.

Regards,

major

edit: So looking at actual points from the graphs instead of the scales you get:

At 500 Amps on the armature,

Motor N120E02, 107V armature, 34A field.

Motor N80E01, 72V armature, 19A field.

Motor N120F01, 102V armature, 12A field.

Conclusion: 3 different motor designs.


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## DavidDymaxion (Dec 1, 2008)

Many thanks Major and Gottdi.

Thanks to an idea I got on the NEDRA list, maybe I have it figured out.

Volume of the 9 inch motor = pi * 9.3^2 * 14 = 3800 in^3
Volume of the 11 inch motor = pi * 11.5 * 11.5 * 18 = 7500 in^2

The 11 incher has close to twice the volume. That would mean about twice the length of field coil wire. That would mean about twice the field resistance. I'll hazard a guess that they use the same diameter wire, and twice the length goes into the larger motor. If they use the same voltage, then the smaller motors would draw twice the field current.

That's consistent, but not necessarily the truth. They might also have used different voltages, and also possibly different gauge wire.

Gottdi:

I now have a Kelly 1000A 144V controller. I'm putting in Headway batteries, it'll be something like 10P48S or thereabouts depending on fit. This is an interpoled motor (I believe all the Kostov DC motors are).

History:


V1.0: 48V lead direct connect to field and armature. Would go almost 40 mph. Great regen. Adequate as a city speeds car, and the "controller" was just a contactor.
V2.0: 48V lead with rheostat controller on field. Went 55 mph. Great regen. Overheated rheostat and had an arcing event that very slightly lifted a comm bar.
V3.0: 96V lead directly connected to field and armature. Just did that for < 60 seconds. Went 58 mph.
V4.0: 96V and 1000A Kelly sepex controller. Out accelerated my chase truck but the lifted comm bar flung out of the commutator and took out the brush gear on the way out. Did go 59 mph coasting through the lights.
V5.0: 144V nominal Headways and the Kelly controller. New Kostov sepex (has better commutator than my old one). Hopefully I'm commuting daily to work soon and go over 100 mph this summer!



major said:


> Hi David,
> 
> The links are not working and gottdi's have a repeat so I just see 2 different graphs. The motor using 4 -12 A field is plotted for 160V on the armature. The motor using 10 - 30 A field is at 80V on the armature. I suspect they want to keep the required field voltage well below the armature voltage so the higher current field is used for the lower voltage armature.
> 
> ...


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