# What does Separately Excited mean?



## gregski (Sep 6, 2011)

Looking at the Kelly controllers some say they are Separately Excited, I searched this Forum for an answer but didn't get any hits, I Googled it and got lost in the explanations all I learned is that it is opposite of Self Excited, wow that helps... Not!

Could someone explain it to me in John Madden terms, lol please?


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## DavidDymaxion (Dec 1, 2008)

I just bought a Sepex Kelly and like it so far.

A series motor runs the same current through both the field and the armature -- a single switch can control both. Double the current, and both see double the current. This is very simple, reliable, and gives good torque. Regen is very difficult, as the motor is inherently unstable under regen. More current --> more regen --> more current --> more regen --> something suddenly blows up.

Sepex = "Separately Excited." The field and the armature are controlled independently. Regen is easy and stable. Since you don't have a fixed relationship between the field and armature currents, you can regen and get a bit more power. Sepex requires switching for the armature, and switching for the armature, so the controller is more complicated. You also need more knowledge about a particular motor to tune the sepex controller to that motor.

Although you can theoretically do sepex on a series wound motor, this would involve hundreds or even thousands of Amps on just a few turns of wire for the field -- that's expensive. Typically sepex motors wind the field with fine wires, and do many more turns of wire with lower Amps (but the "amp turns" are similar). Since the field doesn't need to change quickly this works fine, greatly lowers the field current needed, and makes the switches cheaper and simpler.

Most hobbyists prefer series DC -- it is more common. Chrysler and Peugeot did sepex systems in their production cars. Modern production cars favor AC now.


gregski said:


> Looking at the Kelly controllers some say they are Separately Excited, I searched this Forum for an answer but didn't get any hits, I Googled it and got lost in the explanations all I learned is that it is opposite of Self Excited, wow that helps... Not!
> 
> Could someone explain it to me in John Madden terms, lol please?


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