# [EVDL] Sepex vs Shunt



## EVDL List (Jul 27, 2007)

Thanks Mark for chiming in on this interesting conversation.

I wonder which path would you choose: ie looking for the low hanging of fruit of regen. 
In a 120 volt system starting with a series motor. (Apparently only Kelly controllers have offerings in this voltage range)

Would you use a field weakening coil and a potentiometer? 
Would you rewind, for sepex, and add interpoles? 
Would you convert to a permanent magnet and electronically commutate and hence not need interpoles?

I have a series forklift motor out of a nissan forklift that had 'regenerative braking' using this idea of a field weaking resistor coil (to increase top speeds (ie like a shunt)is why I was told that the coil was there not necessarily that this is how regen is achieved). I have wondered if I could incorporate this into my proposed Jetta ev conversion. 

Or do you know if I have to rewind the field (change amp turns)to be sep ex, and make sure not to run high field currents for anything but very short periods of time.

Or perhaps I should convert it to a permanent magnet, get rid of the commutator and not need interpoles because the copper is wound around the stator like an ac induction motor. If I were commutate it electronically I could apparently then field weaken it.

It seems that there are many options, I am curious which path you would choose and why.

Any comments on the following conversation would also be of interes:
> To regen with a SepEx motor when it is above base speed, increase the
> field current (in the same direction as motoring). Once speed falls
> below base, keep the field strong in the same polarity and start
> boosting the armature voltage by means of the half bridge chopper in
> the armature controller.

>Jeff (Jeff Major) is correct for a sepex motor. But for the more common series motor,
>Davis has it right -- you *do* switch it into reverse for regenerative 
>braking! The motor is still rotating forward, but the current in it 
>reverses, which charges the battery.

>The common Curtis controllers have plug braking. In their 
>implementation, the armature is shorted by a diode, the field 
>connections are reversed (with the reversing contactor), and the 
>controller applies a high current at low voltage to the field alone. The 
>generated power does not charge the battery; it is just burned up as 
>heat in the motor and plug braking diode.

Cheers
Robin 

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## EVDL List (Jul 27, 2007)

> Robin wrote:
> > I wonder which path would you choose: ie looking for the low hanging
> > of fruit of regen. In a 120 volt system starting with a series motor.
> 
> ...


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## EVDL List (Jul 27, 2007)

Thank you Lee Hart for your response. 0

>"Regen on a series motor is hard. First, the motor itself needs to be 
>designed with regen in mind. This means it needs interpoles, or at the 
>very least, the brushes need to be timed to allow regen."

>Normal shunt and sepex motors (a.k.a. generators) use field control. I 
>guess some might call field weakening, but it is really something different.

That clarification will save me some grief!

I will take your word on adding interpoles or going commutatorless. 


> I have a series forklift motor out of a nissan forklift that had
> 'regenerative braking' using this idea of a field weaking resistor
> coil.
>Forklift controllers sometime use *plug* braking, which is simpler than 
>true regenerative braking. Plug braking does not use braking energy to 
>charge the batteries; it simply burns it up as heat in the motor and 
>controller. It is effective for limiting the speed of a vehicle, say, 
>when going downhill. But it is not strong enough for serious braking.

I will need to establish whether the 'regenerative braking' was true
braking or 'plug braking' as you describe. Again thanks for the clarification


Perhaps the most straightforward way to add regen to an EV with a series 
motor and controller is to add a separate generator or alternator. 
Connect it to the tailshaft of the motor, and enable it whenever you 
want regenerative braking.

I understand that this is what Roland does though the alternator could be only 12 or 24 volt.
Perhaps finding a 120 volt d.c. generator to charge the pack would be in order. Or settle with a separate
battery pack for heating or lights etc.

I have learned much from you Lee, thankyou for your generous contributions to the e.v.d.l.





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## EVDL List (Jul 27, 2007)

Lee,
When you had your contactor sepex controller, did you just open the 
armature contactor while current was still flowing? I think you said 
that you had a two-step contactor controller for the armature. So when 
either stopping or switching to another armature voltage, you had to 
open the contactor, right?

Bill Dennis


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## EVDL List (Jul 27, 2007)

> Bill Dennis wrote:
> > Lee,
> > When you had your contactor sepex controller, did you just open the
> > armature contactor while current was still flowing? I think you said
> ...


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