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Discussion Starter · #1 ·
I have a couple of similar sized older motors, one series and one sepex. I'm trying to determine which is best suited for the application as well as trying to determine if the sepex can be set up to have similar torque and performance. to the series motor. Power specs are really close
The series motor is an 11" Hitachi ( same as in in Duncan's car in the banner picture). Rated at 10kw but if ran at 90v should be 20kw. Data specs are 55 lb-ft. at 280 amps and 2600 rpm's if at 90 volts. 120v should be about 3500rpm maybe? Duncan has proved the motor can take at least 10x rated
Sepex motor is a Kostov 11" rated at 20kw at 90 volts. Rated speed is 4000 rpm but only 35lb-ft of torque. 55 lb-ft would require 360 amps and 3500 rpm according to the motor graph. So, while both motors make about the same amount of power, the sepex appears to need more current for the same torque. My Sepex controller only goes to 500 amps peak current which limits motor torque to about 85 lb-ft, according to the motor graph I have. (The motor performance graph is done with If as a percentage of Ia to mimic a series motor)
In a series motor, I understand the current/torque relationship is linear. If 500amps is peak and gives 110 lb-ft torque, for example, That will be my starting and acceleration torque at full throttle till I hit the voltage/rpm limit.
Is this the same linear relationship for the SepEx motor? Is it possible to increase the lower rpm torque to compare with the series motor by increasing the field current?
I like the rpm range of the sepex motor, but the low torque limit will be a problem.
 

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Discussion Starter · #3 ·
Thank you, you are probably right. I think it's capable of more than the controller can put out but it looks much less robust. It would probably take higher voltage and rpm's better, but at less torque. It has some impressive features though. A higher power controller would help, but I don't have the skills to do it and it's pretty much obsolete tech now.

I still hope someone can answer my question about whether or not the current/torque relationship can be modified with sepex though.
 

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Discussion Starter · #5 · (Edited)
Thank you zubmio, that's helpful. I really wasn't asking for a recommendation as to which motor was best even though it may have come across that way. I'm just weighing out pros and cons to make the best choice, and trying to understand the sepex motor characteristics better as well. To do that I wanted to determine if the lower torque of the sepex motor ( con) could be improved by manipulating the field current a bit. You are right that sepex controllers are rare and building one would be very complicated. (a really big con) This motor is definitely limited by the controller it has now. At least it has a controller and does regen (pros). I don't have one for the series motor.
 

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Discussion Starter · #6 ·
What I meant by the linear relationship (maybe not the best choice of words) of amps/torque in a series motor, according to a post I read by major in another thread, is that a given amperage (e.g. 500 amps) will yield the same amount of torque, regardless of rpm. So, if a graph shows 100 lb-ft. of torque at 500 amps, then it won't change whether it's at 5 rpm or 5000 rpm. I assume the same would be the case for a sepex motor if the relationship between the field and armature currents remain constant. E.g. the Kostov motor graph shows 28.5 field amps 500 armature amps and produces 85 lb-ft of torque. The controller I have limits armature current to 500 amps but has 50 amps available for the field. I'm wondering if higher field amps would increase the torque.
I know it would reduce the rpm and probably wouldn't be a good idea to overload the field continuously as I suspect they would overheat, but having a little extra would improve acceleration.
 

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Discussion Starter · #8 ·
increasing the field coil current will increase the torque PROVIDED that
The field coil magnet is not already saturated
Thanks Duncan. Yes, this is why I'm wondering if it would improve torque much at the upper end of the current limit.
As I understand it, field weakening reduces the magnetic flux and BEMF in the field allowing higher speed and reduced torque for a given armature current. Increasing the field current has the opposite affect and should increase torque and lower speed. But, saturation is probably close to nominal field current ( 14-15 amps on this motor), so if the field is already well beyond saturation I don't know if increasing current will still increase torque, or just increase heat in the field windings and shorten the life of the motor.
The sepex motor is a much more refined unit with some cool features compared to the Hitachi motor, but I don't know how to make a controller that can unlock it's full potential. I think it would still work well with the current controller, if it was going into a smaller lighter car. I like the idea of having regen braking.
The Hitachi has a proven track record though (your car), and even though I don't have a controller for it, there are a few inexpensive options out there still. I'm leaning toward using it instead, for this car, if I can ever complete it. I wish I could find the plans for the controller you have. I got the coding files from someone, but not the plans and parts list for the boards.
 
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