# Successfully powering a Sep-Ex with two controllers



## mechman600 (Oct 16, 2010)

I thought this worthy of a new thread, because in all my searching for a solution I never found anything. This is basically a continuation of this thread:
http://www.diyelectriccar.com/forums/showthread.php/sepex-field-current-voltage-questions-79936.html
Thanks to those on this forum who steered me in the right direction, especially major.

Long story short, Paul from "EPC Corporation" (whom I later found out from this site to stay far away from) sold me a used Prestolite series wound motor. When it arrived, I quickly realized it was a sepex motor instead. I was going to send it back but he somehow convinced me to use my already purchased Alltrax series/PM controller to power the armature and give the field 12V and it would be the same. Right. Not quite. He even send me a "field control module" which I quickly dissected to discover a relay and a big blue motor run capacitor which basically transferred the massive inductive spark from the key switch (or likewise) to inside this relay.

Lots of tinkering later, I found the best solution, performance wise, was to give the field 24V and toggle it with a switch to 48V for starting off and climbing hills. Since the field windings are 1 ohm, 24V = 24A, 48V = 48A.

I then starting throwing around the idea of using a small PWM controller. Major suggested that I get an amp transducer to measure armature current and feed the 0-5V signal to the PWM field controller, which is what I have done.

I purchased a Kelly 72100 - 72V/100A controller. I know, I know...it's a Kelly, but I am only using it to half capacity, so it should be good, right?

The LEM amp transducer has a resting signal of 2.5V. Current going one way causes the signal to go higher and current going the other way causes the signal to go lower. At 450A in the direction I am measuring, the signal is 3.9V.

You can see in the attached Kelly screenshot how I dealt with these odd voltages by moving the throttle effective starting position and throttle effective ending position.








I fine tuned it so that at key on ("idle"), the field is getting 9A. When the armature is at full current, the field is getting 50A.

I was going to employ my idle microswitch to turn the field off altogether, but what I am finding is that when I am coasting down a hill at high motor RPM, if the field is zero and you turn it on, it confuses the Alltrax controller by suddenly generating voltage and it goes dead for a few seconds. So I am leaving the field on at idle for now. 81W of power isn't much anyway.

So there you have it. I have only gone for one test drive (with my remote inductive ammeter installed on the field wire) and it worked brilliantly. Tomorrow's commute to work should a better test.


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## tylerwatts (Feb 9, 2012)

Fascinating! Thanks mechman600 for posting this! I liken it to the RC guys taking alternators and driving hte armature with a small DC controller and the field with an AC controller! They get some scary outputs from little alternators! It seems with som etuning you could get very effective outputs from this set-up!

I['m thinking, without evidence or justification, that this could behave simething like slip in an AC motor, where you increase armature current similar to increasing slip, giving higher starting torque, and the torque can then be carried to higher rpm.

I look forward to hearing what the effects are.

PS, do you have a build thread of the application you have this motor in please?


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## major (Apr 4, 2008)

mechman600 said:


> I thought this worthy of a new thread,


Great news  I did have some concern about stability. Do you sense any hunting or does it seem stable?


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## Salty9 (Jul 13, 2009)

http://www.rcgroups.com/forums/showthread.php?t=1123956&highlight=reem

Discusses varying field current of an alternator.


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## mechman600 (Oct 16, 2010)

tylerwatts said:


> Fascinating!PS, do you have a build thread of the application you have this motor in please?


My build thread is here:
http://ecomodder.com/forum/showthre...oger-budget-ev-conversion-92-mazda-22478.html
It is more or less the same as my blog in my signature.


major said:


> Great news  I did have some concern about stability. Do you sense any hunting or does it seem stable?


On my one test drive so far I didn't notice any hunting whatsoever. But I update after today's commute.


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## mechman600 (Oct 16, 2010)

I just drove to work. It's nice not having to flick a toggle switch back and forth on the gear shift to control field current!

But...at high rpm part throttle the motor surges like crazy. I imagine it is field current reacting to armature current too quickly...field goes up, back EMF goes down slowing down armature current so field goes back down and up and down...etc. All multiple times per second.

I will see what slowing down throttle response in the field controller does to help this.


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## major (Apr 4, 2008)

mechman600 said:


> But...at high rpm part throttle the motor surges like crazy. I imagine it is field current reacting to armature current too quickly...field goes up, back EMF goes down slowing down armature current so field goes back down and up and down...etc. All multiple times per second.


Kind of what I was worried about. Not sure what to do to dampen it


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## mechman600 (Oct 16, 2010)

I decreased the throttle sensitivity parameter. It was at 1 (out of 10). I tried 3, then 6. It slows the oscillations down dramatically. At 1 it was like a high speed vibration. At 6 it's much better, although I can still feel it. I have turned it up to 9 for the drive home. We'll see what happens.


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## mechman600 (Oct 16, 2010)

I have been driving the car every day to work. I have the field controller throttle sensitivity set to 10 which is the slowest, and it works very well this way. I do notice a bit of a surge with small throttle position changes at light load but it's no big deal. I have learned how to modulate the throttle to almost eliminate it altogether.

So there you go - I dub this endeavor a smashing success!


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## Electric Forklift Guy (Dec 13, 2012)

You've basically re-invented the field circuit in a sep-ex controller


What you can do with this

What you'll quickly discover is that the more current you feed the field the more torque the motor will have , but it will limit maximum RPM of the motor.

Because your field control circuit is separate from the main controller it isn't integrated and automatically adjusting the field current for you.

Normally you want high current when accelerating from a stop and low current once you get moving.

You can actually limit your top speed by raising the field current.
You can limit your acceleration by lowering the field current.

You can also use your "home made field controller" to put the vehicle in reverse , all you do is reverse polarity to the field terminals and the motor will reverse. 

Have fun.


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## major (Apr 4, 2008)

Electric Forklift Guy said:


> You've basically re-invented the field circuit in a sep-ex controller.


That was the whole idea 



Electric Forklift Guy said:


> Because your field control circuit is separate from the main controller it isn't integrated and automatically adjusting the field current for you.


He uses the current transducer to couple the field controller to the armature current. It does automatically adjust the field current for him.



Electric Forklift Guy said:


> Normally you want high current when accelerating from a stop and low current once you get moving.


That's the function the current transducer provides. It gives him high field current when the armature current is high during acceleration and then reduces field current when the load is reduced at normal travel.

Read over the original thread which is linked in post #1.


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## mechman600 (Oct 16, 2010)

Thanks major. Well said. Now I don't need to reply!


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## Electric Forklift Guy (Dec 13, 2012)

major said:


> That was the whole idea
> 
> 
> 
> ...




I was under the impression that an integrated field controller looked at armature current versus armature voltage to determine motor RPM and then if motor RPM was over a certain level ( 50-75% depending on application) it would increase motor RPM by decreasing the field current to reduce CEMF and allow the motor to turn faster ( I could have sworn that was often called "Field weakening")

Which is a lot more involved , and more efficient , than his set up.

Is it OK if i show your post to the other techs at work ?...they'll get a kick out of it.


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## mechman600 (Oct 16, 2010)

Electric Forklift Guy said:


> ...it would increase motor RPM by decreasing the field current to reduce CEMF and allow the motor to turn faster...
> Which is a lot more involved , and more efficient , than his set up.


How is this more efficient? Higher field current than you might like, and the resulting higher CEMF doesn't waste energy because less energy is used in the armature as a result (because of the increased CEMF and resulting lower current in the armature). No matter what current you give the field vs armature (within reason), mechanical energy is produced at roughly the same efficiency.

Example 1. Low field current (10A) at low speed (1500 rpm) will produce very little torque with 450A in the armature. However, this 450A only takes a few volts (5V) because of the lack of CEMF. (10A*10V)+(450A*5V)=2260W. Not much power consumed but not much power given.

Example 2. High field current (50A) at low speed (1500 rpm) wlll produce much more torque with 450A in the armature. It will require a much higher armature voltage (25V) to achieve 450A because of increased CEMF. (50A*50V)+450A*25V)=13750W. Much higher power consumed and much more power given.

All numbers are theoretical but I think they make a point.


> Is it OK if i show your post to the other techs at work ?...they'll get a kick out of it.


Yes! By all means. I am always willing to learn from those much smarter than me!


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## major (Apr 4, 2008)

Electric Forklift Guy said:


> I was under the impression that an integrated field controller looked at armature current versus armature voltage to determine motor RPM and then if motor RPM was over a certain level ( 50-75% depending on application) it would increase motor RPM by decreasing the field current to reduce CEMF and allow the motor to turn faster ( I could have sworn that was often called "Field weakening")
> 
> Which is a lot more involved , and more efficient , than his set up.


mechman didn't choose his method to be better than the developed SepEx systems. We devised a method which utilized the equipment he had on hand and a few parts he could afford. What we accomplished was just the basic function which pretty much mimics the series wound system and gives him good accelerating torque and field weakening at lower loads. It doesn't come close to all the bells and whistles like contactorless reversing and regeneration, but then doesn't need a dedicated microcomputer either. It is a simple solution


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## gunnarhs (Apr 24, 2012)

Congrats to get this working. I have been thinking about such solution for the Peugeot 106 replacing the original damaged SAGEM-control Box but did end up mixing it with one Sep-Ex Kelly and a seperate PWM (in one car, the other used a hand-shifted field solution).

During the process I found this thread, mabe you are interested in this
http://home.earthlink.net/~evtkw/controller/TechPage.html

ed: Sorry did previously post the wrong link


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## teverth (May 18, 2009)

Hi Mechman! Sounds like a great idea. How are things by now? Still running happily with this? I have a D&D Sepex motor and in four years burned through 4 sepex controllers. I was thinking along your lines of using a series controller as I have been fed up with the low number of suitable sepex controllers out there. I was thinking of using a Kelly HSE Sepex controller but unsure if they are good for the job.


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## mechman600 (Oct 16, 2010)

My setup still runs like a charm. The only issue I have is the surging that happens under light loads as the two controllers oscillate, but I quickly learned what to do with my right foot to stop it when it happens. In the end it's not an issue.


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## electro wrks (Mar 5, 2012)

mechman600 said:


> My setup still runs like a charm. The only issue I have is the surging that happens under light loads as the two controllers oscillate, but I quickly learned what to do with my right foot to stop it when it happens. In the end it's not an issue.



OK, what do you do with your right foot that remedies this oscillation problem? You keep leaving us in suspense! So we keep having to ask you dumb questions!

Can somebody explain (again?) what causes the oscillation? And possible electronic remedies? I'm not that good of a dancer to do a right foot two-step.


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## teverth (May 18, 2009)

You could experiment with a low pass filter to slow down the field response to armature current changes perhaps:










Uin = 0-5V from your armature shunt signal amplifier
Uout = control voltage to your field controller throttle input

With R= 10kOhm and C=50uF you would get a 1/2 Second time constant. Should perhaps flatten out your oscillations with pennies worth of components?

But I don't know the kelly throttle input internal resistance so R and C might need to be modified to suit, perhaps 1kOhm and 500uF is better.


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## mechman600 (Oct 16, 2010)

What happens is that when the field current increases, back EMF increases, causing armature current to decrease. The amp transducer picks this up and decreases field current, decreasing back EMF, causing armature current to increase. And on and on.

I adjusted the throttle delay time in the field controller to help this, which changed it to a fast driveline vibration to a slower oscillation - maybe 1 HZ or so.

As soon as it does it, I simply increase or decrease throttle input a bunch and it stops. The trick was to learn when it happens and either accelerate or decelerate before it does. With my lower power 72V system it is easy to do, but I imagine in a more powerful system it might be more of an issue.

It really is hard to explain unless you drive it yourself. If you are near Surrey, BC, come on down!


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## teverth (May 18, 2009)

I am in New Zealand I am afraid, a bit to far for a visit. On another thought, could you not have simply installed a second throttle pot in parallel to the main throttle to drive the field controller, or even use the same signal? Then the output of the field controller would depend only on throttle position and not on the arm current and hence there would be no feedback? This is my car: http://www.evalbum.com/1772


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## major (Apr 4, 2008)

teverth said:


> I am in New Zealand I am afraid, a bit to far for a visit. On another thought, could you not have simply installed a second throttle pot in parallel to the main throttle to drive the field controller, or even use the same signal? Then the output of the field controller would depend only on throttle position and not on the arm current and hence there would be no feedback? This is my car: http://www.evalbum.com/1772


But the point was to make the field current dependent on the armature current. That is how a proper SepEx maps it and it mimics the behavior of a series motor giving high torque for acceleration and overloads.

Putting the field on the pedal would cause difficulty as reducing pedal position would weaken the field and cause motor to increase in speed even as the decrease in armature voltage would tend to decrease speed. This would be tricky to say the least.


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## mechman600 (Oct 16, 2010)

That would not work.
The field windings have a fixed resistance of one ohm.
The armature windings effective resistance changes because of back EMF. At zero RPM, it takes 2V to get 450A. At 4000 RPM, it takes 72V to get 450A.
Proper sepex control has the field current adjusting proportionally to (or a calculation based on) armature current. Half throttle with my contoller means half _voltage_ to the armature which will equate to an armature current based on how fast the motor is turning (because of the back EMF vs speed variable).


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## mechman600 (Oct 16, 2010)

Ha! Major, you snipered me on that one!


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## teverth (May 18, 2009)

Yes of cause, you are both correct. I guess mechmans's solution is quite good. You could perhaps, if you wanted to put an RC filter in the line, use a pot as the resistor to adjust the time constant of that to smooth out your oscillations further it it ever was an issue.


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## ken will (Dec 19, 2009)

I have been doing a little research on Sep-Ex motors and am approaching a solution by thinking of a Sep-Ex motor as a Variable/Permanent Magnet Motor.

A very strong Magnet gives high torque, but at higher RPM induces more back EMF. 
A weaker Magnet induces less torque, but also less back EMF.

Changing the current in the field windings acts the same as changing the strength of a Permanent Magnet. 

I am also researching micro-controllers (Arduino) with the hopes of building a controller that can increase the field when it senses I want more torque and decreases the field when I want more efficiency.

I may be way off base, but I think it will work.


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## major (Apr 4, 2008)

ken will said:


> I have been doing a little research on Sep-Ex motors and am approaching a solution by thinking of a Sep-Ex motor as a Variable/Permanent Magnet Motor.
> 
> A very strong Magnet gives high torque, but at higher RPM induces more back EMF.
> A weaker Magnet induces less torque, but also less back EMF.
> ...


It sounds like you're thinking along correct lines. Good luck.


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## mechman600 (Oct 16, 2010)

I played around with my field current this past week. Till now I was running 50A max and decided to lower it to 30A to see if I could get more speed up the hill on the way home from work. My reasoning is that with a 50A field, max HP is at 49 km/h (2nd gear) and I top out on the hill at 58 km/h (2nd gear) at an RPM well above peak horsepower. Lowering the field would raise the RPM at peak HP, albeit with a lower torque output.

The result was a top speed of 61 km/h on the same hill, but with less torque across the usable RPM range. With only 72V and 450A, it's not like I have a lot of torque to spare, so I have settled at 40A max field for the time being.

I also played with field idle current. Till now it has been 8A. As soon as the key switch is on, the field gets 8A. For fun I adjusted it down to zero, syncing it with armature current - as soon as the armature got current, the field started as well. The results were very weird.

First off, this motor makes an awful lot of noise on coast (with 8A going through the field) but as soon as field current is gone, it becomes silent. (Is this normal??). So for the first time ever I could coast (with motor spinning) silently.

Second off once things warmed up, it developed a WICKED oscillation. Like...a violent, scary amount, along the lines of what I experienced earlier in this thread times 1000. So I increased idle field current back up to 3.5A and it seems to work okay again. But no silent coasting anymore.....


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## major (Apr 4, 2008)

mechman600 said:


> I played around with my field current this past week. Till now I was running 50A max and decided to lower it to 30A to see if I could get more speed up the hill on the way home from work. My reasoning is that with a 50A field, max HP is at 49 km/h (2nd gear) and I top out on the hill at 58 km/h (2nd gear) at an RPM well above peak horsepower. Lowering the field would raise the RPM at peak HP, albeit with a lower torque output.
> 
> The result was a top speed of 61 km/h on the same hill, but with less torque across the usable RPM range. With only 72V and 450A, it's not like I have a lot of torque to spare, so I have settled at 40A max field for the time being.
> 
> ...


With zero armature current and zero field current the motor is off and should basically rotate silently being back driven by the drive train. I wouldn't have expected much noise when back driven with 8A field and zero armature current.

And the oscillation I suspect is from a difference in time constants for the armature and field. The armature reacts much faster than the field. So when you attempt to *synch* the two, things get weird. And as the field heats up the time constant gets slower likely to a greater degree than the armature change. If you're going to shut the field down during coast I suggest you figure a way to start the field up a fraction of a second before energizing the armature.

Sounds like you're having fun 

major


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## mechman600 (Oct 16, 2010)

major said:


> I wouldn't have expected much noise when back driven with 8A field and zero armature current.


It is brush/comm noise. What I suspect is that when the armature controller goes to zero current, the voltage generated in the armature (because of the always on field current) has nowhere to go (open circuit) and becomes extremely high, making the brushes yelp with agony. I should measure this voltage.

I tried to remedy this by running the throttle signal to the field controller through the idle microswitch, but this created a throttle fault in the Kelly and it wouldn't turn back on until the key switch was cycled.

I could figure out what resistor is required to pull the throttle signal down from 2.5V (the output of the current transducer at zero measured current) to a voltage that just turns the field off without creating a throttle fault in the Kelly, turning it on at idle with the idle microswitch.....

.....BUUUUUUUUUUUUT.....

.....I have a new motor coming. It's a series wound 8" Otis that weighs 110 lbs. It's a forklift hydraulic pump motor. It was given to me by Darin, one of the creators of the infamous Forkenswift - a twin motor to the one he used in that car. I just have to pay for shipping. That should take care of my "tiny motor getting really hot" issue as well.


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