# [EVDL] Shunt motor regen braking with alltrax 7245.



## EVDL List (Jul 27, 2007)

Hi ampaynz1,

Looks to me like you do not need any additional diodes
or switches. And the controller will have a diode in
parallel (reversed biased) with the main transistor. 
All you need to do is get the armature speed high
enough while maintaining field current to regenerate. 
No extra parts required.

Hopefully some others will confirm this.

Jeff M





> --- ampaynz1 <[email protected]> wrote:
> 
> >
> > My question, will I get regen braking with my
> ...


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## EVDL List (Jul 27, 2007)

I'll try to answer, but you might want to wait for some
corroboration and/or better responses. 



> --- ampaynz1 <[email protected]> wrote:
> >
> > My question, will I get regen braking with my circuit as a I drew
> > it?
> ...


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## EVDL List (Jul 27, 2007)

I think that if you downshift and hook up the motor's EMF to the battery
through your diodes, you will get very rapid, uncontrolled braking. If you
have 120V of back emf and a 72V battery, you'll get a huge burst of current
and deceleration. The huge current could hurt the parasitic diodes in your
controller's mosfets. Regen would work better if you had it more gradual.
Downshifting just the right amount would work, but it could be a pain.

Also, I think that your setup with the diodes and switches might not be
necessary. All you're doing is controlling which way the current is allowed
to flow. A simpler circuit would be the controller+ directly connected to B+
and a left-facing diode in parallel with a switch between the controller and
M+. That way, in normal operation, the switch is pressed and the motor is
directly connected to the controller. In regen operation, the switch is open
and current can only flow from M+ to the battery.

I also advise you to find someone more experienced.
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## EVDL List (Jul 27, 2007)

I was looking over all the comments, thanks. However, I forgot to include the
precharge resistor over the contactor labeled SW1. So when the regen is
taking place, the controller will get a little of the 120 volt current
through the precharger resistor. 

My question: Would this ruin the controller as the voltage climbs through
this little 200 ohm 10W resistor?
One solution would be to run it all at a lower voltage of say 60V or 72V.
The controller I am using can run as high as 84V constantly, and has
tolerance for 100V for a while. Actually, don't have it yet, but it has been
ordered. 

I suspect it wouldn't ruin the controller since it isn't on technically. It
does have over voltage protection, so it might just shut it off. Or maybe
the batteries will sink all this current and voltage instantly and
controller would never see it. The regen will only happen if I downshift, so
with newly charged batteries I'd just not downshift. andrew payne


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## EVDL List (Jul 27, 2007)

Andrew,

I'd leave SW1 closed. Take it off a foot switch and
use the key switch. I don't think it should matter if
the controller is on during regen. If you run a 72
volt battery, you should never see 120 V. That would
probably put your face into the windshield. Your max
regen voltage should be about the same as your highest
charge voltage.

Now, I am not familiar with the Alltrax. You should
check with them. Or perhaps someone here can verify. 
During regen, current will be reversed thru the
controller current sensor. I don't think that is a
problem, but I don't know for sure how the control
electronics work in there.

As far as your basic regen scheme, down shifting to
raise motor speed is pretty primitive type of control.
There would be no voltage or current control if you
leave the full voltage on the field. Therefore, it
would be advisable to have a means to reduce field
current to control the regen torque and therefore
voltage and current.

I think you said you were driving it now, just 48
volts, no controller. Does it regen now if you go
downhill?

Anyway, sounds like you're having fun. Keep at it.

Jeff M. 




> --- ampaynz1 <[email protected]> wrote:
> 
> >
> > I was looking over all the comments, thanks.
> ...


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