# 10x Power from Curtis Sepex?



## DavidDymaxion (Dec 1, 2008)

(Cross posted to EVtech)
I'm looking for ideas on how to fool a Sepex Curtis controller into controlling the field as usual, but having the armature directly switched to a high voltage battery pack.

I know I could do something like this with a regular series controller and some added circuitry. I'm thinking it would be neat to exploit some of the extra features of the sepex controller. It would also be neat to control 200 kW of power with $1k of controller.

Here is a possible concept of operations: Have a 48 V pack and a high voltage pack. Run the Sepex controller on 48 V, as a regular sepex controller in 1st gear. Upon enough speed and a shift to 2nd gear, the controller switches the armature directly to the high voltage pack. An external circuit provides a signal to the controller to fool it into thinking it is controlling a lower Voltage, lower Amperage armature current. The high voltage current is proportional to the signal to the controller, so it does things like current limiting and controlled regen still.

I have read the Curtis 1268 and 1244 manuals. I'm still not clear on this point: Once revved up a bit, does the Curtis control the armature current by adjusting the field current? Or does it just blindly follow the field maps you program into it? The inputs to the Curtis sepex include the pedal potentiometer, and a speed input. An implied input is the armature current.

So I have a couple of thoughts on control.

1) Fake the signal to the speed sensor input. If the Curtis blindly follows its field maps this might work.

2) Find out how the Curtis measures the armature current (I assume it would be voltage drop across the transistors?). Feed this voltage sense with a voltage proportional to the actual armature current -- then the Curtis would be fooled into controlling the high power current as if it were its usual armature current control.

I realize I have glossed over the detail of switching the armature to the high voltage pack for now, but figured this post is long enough for this first question.

Your thoughts are appreciated! I have a Curtis 1268 controller I got for $50, and a sepex motor to experiment with.


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## piotrsko (Dec 9, 2007)

there is a person with the handle of major that is on board which seems to have an huge expertise regarding motors. I'm not sure if this topic will attract him. i wanted to go the other direction by exciting the field and controllong the armature, sort of like a perm mag motor, but that may not be efficient. this could be another possibility, but I'm no expert.


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## major (Apr 4, 2008)

DavidDymaxion said:


> (Cross posted to EVtech)
> I'm looking for ideas on how to fool a Sepex Curtis controller into controlling the field as usual, but having the armature directly switched to a high voltage battery pack.


Hi David,

I doubt you'll have success with this concept. The main reason is that field control (to control RPM and/or armature current) is only effective for the low load range. Once you get into moderate to high power, the field can no longer limit armature current due to saturation. You can lower the field excitation to cause increase in RPM and Ia, but increasing the field will not lower RPM below base speed and therefore not reduce Ia.

Also, the jump from 48 volt base speed (and Ia) to a "high voltage pack" would likely cause enormous current surge wiping out your brushes and toasting the motor. You might be able to jump from a 48V field weakened condition to like a 72V full field condition, but I suspect you're looking for much more.

Regards,

major


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## DavidDymaxion (Dec 1, 2008)

Thanks for inputs. There are definitely some landmines in there, and sepex is definitely a bit more complicated. Obviously I still think I have some chance for success. 

John Wayland ran a 336 Volt pack and 1200 Amps through his series Kostov. It seems a sepex wound should be capable of the same thing, is there any fundamental reason why not?

I have measured my base speed to be about 500 rpm for Va = Vf = 12 Volts. Note the speed would be close to 500 rpm for Va = Vf = 48 Volts also. Suppose you go to Va = 5*Vf = 240 Volts. Now base speed is 2500 rpm. Yes, higher than ideal, but for a race car with a clutch that should work. I realize one would not want to crank up If to hundreds of Amps to force the idle speed down.

I think my bigger worry will be weakening the field too far. Obviously I can weaken it to the series field point, but going beyond that might induce excessive arcing. I'll have to creep up on that, raising the voltage, videoing the brushes, and measuring the acceleration (good Rudman idea). If the acceleration lessens more than the current change would imply, or the video shows bad arcing, you've passed your safe limit.

I agree I can't just suddenly slap 240 Volts across the armature. There are two tricks to lessen the shock: Spin up the motor first on low voltage (or with current limiting resistors) before switching on the big voltage.

Also, I don't expect miracles, but in theory the sepex should be a bit more efficient, and hence a bit more powerful. At low rpm, the series motors multiplies current, so I^2*R losses increase. The sepex increases the field current instead, avoiding the extra I^2*R loss. If I can get away with a bit more field weakening than the series case, I'll have a bit fatter of a torque curve.

Hopefully I won't be making an offering to the smoke gods!



major said:


> Hi David,
> 
> I doubt you'll have success with this concept. The main reason is that field control (to control RPM and/or armature current) is only effective for the low load range. Once you get into moderate to high power, the field can no longer limit armature current due to saturation. You can lower the field excitation to cause increase in RPM and Ia, but increasing the field will not lower RPM below base speed and therefore not reduce Ia.
> 
> ...


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## major (Apr 4, 2008)

DavidDymaxion said:


> but in theory the sepex should be a bit more efficient, and hence a bit more powerful.


Hi David,

What theory is that? Same size, same copper and steel content, same load, series and sepex will be the same efficiency. SepEx will give you more control latitude, meaning you may be able to gain some advantage at lighter loads in regards to efficiency, but I doubt more that a percent or two. I don't think peak power would be higher for the sepex. And the sepex will likely have lower peak torque.




> At low rpm, the series motors multiplies current,


What does this mean?



> so I^2*R losses increase. The sepex increases the field current instead, avoiding the extra I^2*R loss.


I think you're mistaken. For equal copper, steel and load, the I^2*R loss for the two will be the same.

But hey, go for it. What's a little smoke in the big scheme of things

Regards,

major


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## major (Apr 4, 2008)

DavidDymaxion said:


> I have measured my base speed to be about 500 rpm for Va = Vf = 12 Volts.


I doubt that is base RPM. You say that you also get 500 RPM at Va = Vf = 48V. This implies that Vf = 12V is not full field. Base speed at a particular Va is determined with full field.

Put 12V on the armature and increase the field voltage until your see a marked decrease in the decreasing RPM. Meaning the point where further increase in Vf no longer reduces RPM significantly. That will tell you what the base RPM is for that Va and full field.

major


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## major (Apr 4, 2008)

DavidDymaxion said:


> I realize one would not want to crank up If to hundreds of Amps to force the idle speed down.


I guess you're talking field current. Which would not work anyway. You'll saturate. You cannot force the RPM below base speed with the field.

major


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## DavidDymaxion (Dec 1, 2008)

We agree! If you try to force the base speed RPM down by going higher and higher on the field, you'll melt the field. That's why I would just let it idle fast and use the clutch. This is not an original idea to me, some old timer EVs used to do it this way.
Quote:
Originally Posted by *DavidDymaxion*  
_I realize one would not want to crank up If to hundreds of Amps to force the idle speed down._

I guess you're talking field current. Which would not work anyway. You'll saturate. You cannot force the RPM below base speed with the field.

major


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## DavidDymaxion (Dec 1, 2008)

I see that I was not using terms accurately. I probably should have said "idle speed." I see now you are defining "base speed" as a saturation point for the field. That is a good test you mention -- I'll try that. Thanks! I'll report my results, too.


major said:


> I doubt that is base RPM. You say that you also get 500 RPM at Va = Vf = 48V. This implies that Vf = 12V is not full field. Base speed at a particular Va is determined with full field.
> 
> Put 12V on the armature and increase the field voltage until your see a marked decrease in the decreasing RPM. Meaning the point where further increase in Vf no longer reduces RPM significantly. That will tell you what the base RPM is for that Va and full field.
> 
> major


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## major (Apr 4, 2008)

DavidDymaxion said:


> That's why I would just let it idle fast and use the clutch. This is not an original idea to me, some old timer EVs used to do it this way.


You have an example of an old timer doing this with 2500 RPM, 240V and no armature current control?

major


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## DavidDymaxion (Dec 1, 2008)

Current multiplication: At low rpm with a PWM controller, the controller increases the current and decreases the voltage. It's like a kid on a swing. If you pushed him every swing he might go too high (like a motor with full pack voltage thrown onto it). So you push him every 3rd swing, and all is well. Likewise, in your series motor, you might be drawing 200 battery Amps, but 600 Amps are spinning through the motor loop. When the PWM goes on, the motor gets a big spank of voltage, and the batteries conduct current. When the PWM goes off, the motor continues to conduct the current, so you get current multiplication.

The sepex motor, once above idle speed, has battery current = motor current.

Suppose you have 0.040 Ohms of armature resistance. Suppose you are current multiplying so you have 400 Amps in the series motor, but only 200 Amps in the sepex motor. The sepex motor gets equal torque with more field current.

Series motor armature resistance loss = (400 Amps)^2*(0.040 Ohm) = 6.4 kW

Sepex motor armature resistance loss = (200 Amps)^2*(0.040 Ohm) = 1.6 kW

You aren't in current multiplication very often (like just when first taking off or climbing a steep hill), so usually the efficiencies are close. However, don't forget it is much easier to do regen with a sepex, which gets you 5 or 10% more range. The sepex system should generally be more efficient overall.

I appreciate the concerns, I realize I'm definitely stepping off the beaten path! I'll plan to creep up in voltage, current, and field weakening and hopefully stop well short of total motor destruction.



major said:


> Hi David,
> 
> What theory is that? Same size, same copper and steel content, same load, series and sepex will be the same efficiency. SepEx will give you more control latitude, meaning you may be able to gain some advantage at lighter loads in regards to efficiency, but I doubt more that a percent or two. I don't think peak power would be higher for the sepex. And the sepex will likely have lower peak torque.
> 
> ...


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## DavidDymaxion (Dec 1, 2008)

2/3 yes. Someone I traded emails with many years ago idled his sepex motor at about 2000 rpm. The armature switched on first with a resistor and then right to the pack. Field weakening was via a rheostat, which was the only speed/torque/current control the car had. There was no armature control beyond the driver's foot. I forget what his system voltage was, but it was well below 240 V. http://www.mrsharkey.com/rabbit.htm is another sepex guy, it idles about 1650 rpm at full field. Not that it is a strong recommendation, but the Wilderness EV guys also sell sepex systems that idle the motor and vary speed via a field rheostat.

I'll have 4 controls on armature current. First, the driver. Second, a circuit that will measure armature current and vary the field to control it (the accelerator will control armature current). Third, a contactor that will drop out on too high a current. Fourth, a fuse that will blow on high current.

Don't forget, I plan to creep up in voltage and watch things. My first drive won't be on 240 V, but that (and hopefully even more) is a goal. Also, don't forget Wayland has run a series version of this motor at 250 Volts (336 Volt pack) and 1200 Amps.


major said:


> You have an example of an old timer doing this with 2500 RPM, 240V and no armature current control?
> 
> major


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## major (Apr 4, 2008)

DavidDymaxion said:


> Suppose you are current multiplying so you have 400 Amps in the series motor, but only 200 Amps in the sepex motor. The sepex motor gets equal torque with more field current.


David,

I know what current multiplication with PWM is.

However, your logic here is incorrect. You cannot get equal torque at equal speed from a sepex motor at 200 amps as you get from a series motor at 400 amps when the motors have the same armature. The sepex armature would need twice the turns and therefore 4 times the resistance, so the losses would be the same. All this assuming the same size motors. Once you get up to these power levels, both types are into saturation.

The only way for your scenario to work is if the sepex motor had twice the flux as the series motor, which would make it twice as massive.

Regards,

major


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## major (Apr 4, 2008)

DavidDymaxion said:


> http://www.mrsharkey.com/rabbit.htm is another sepex guy, it idles about 1650 rpm at full field.


David,

This guy had an armature controller. "model EHV-1. Obviously, this was a proprietary controller, specifically designed and built for this car. It includes armature current limiting, motor over temperature protection and motor over current protection. Motor start up is provided with series resistors and contactors." And he ran at 108 volts.

I am not saying that sepex control cannot be done without a PWM armature controller, just that it is complex. You talk of efficiency, what do those series resistors for armature control do to that?



> I'll have 4 controls on armature current. First, the driver. Second, a circuit that will measure armature current and vary the field to control it (the accelerator will control armature current). Third, a contactor that will drop out on too high a current. Fourth, a fuse that will blow on high current.


First: How does the driver control armature current?

Second: Will only work in a limited range.

Third: At 240V inductive, that might work 2 or 3 times before it welds shut.

Forth: Good idea.

Like I said, go for it. But you'll not end up with a more efficient drive or more powerful drive than an equivalent size series motor/PWM system.

Regards,

major


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## DavidDymaxion (Dec 1, 2008)

Comments interspersed.


major said:


> David,
> 
> I know what current multiplication with PWM is.


My apologies -- when I wrote "multiplies current" you wrote "What does this mean?" -- it sounded like you didn't know. Not to worry, though, it is still valuable knowledge to post for the newbies.


major said:


> ... You cannot get equal torque at equal speed from a sepex motor at 200 amps as you get from a series motor at 400 amps when the motors have the same armature. The sepex armature would need twice the turns and therefore 4 times the resistance, so the losses would be the same. All this assuming the same size motors. Once you get up to these power levels, both types are into saturation.
> 
> The only way for your scenario to work is if the sepex motor had twice the flux as the series motor, which would make it twice as massive.


Those numbers were referring to motor amps, not battery Amps, and a PWM controller was assumed for the series motor. Black box it, and say you are putting 200 Amps and 100 Volts into a box, and some torque at some rpm comes out (minus losses, of course). The box might happen to buck the voltage up and current down (like a Prius), or keep the same voltage and current (like a sepex in some operating regions), or knock down the voltage and bump up the current (like a series motor). Like you say, another way to change things is to change the windings to alter the current vs. volts relationship.


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## major (Apr 4, 2008)

DavidDymaxion said:


> Those numbers were referring to motor amps, not battery Amps, and a PWM controller was assumed for the series motor.


 
Of course.


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## DavidDymaxion (Dec 1, 2008)

Comments interspersed.


major said:


> David, This guy had an armature controller. "model EHV-1. Obviously, this was a proprietary controller, specifically designed and built for this car. It includes armature current limiting, motor over temperature protection and motor over current protection. Motor start up is provided with series resistors and contactors." And he ran at 108 volts.
> 
> I am not saying that sepex control cannot be done without a PWM armature controller, just that it is complex. You talk of efficiency, what do those series resistors for armature control do to that?


Yes, it does have "armature control." It also says it idles at 1650 rpm, and "startup is provide with series resistors and contactors."
I don't know how long the EHV-1 uses a startup resistor. You are right, resistors waste energy! I would use startup resistors just long enough to get the motor spinning, just a fraction of a second. The energy loss would be quite small.



major said:


> First: How does the driver control armature current?


Current gauge and right foot! Just like the tachometer in your car -- avoid redline!



major said:


> Second: Will only work in a limited range.


Agreed. It should work at anything above idle speed. For a straight line car, control of about 3000 to 5000 rpm would be fine (you are abusing the clutch in racing, anyway). For racing with corners, around 2500 rpm to 5000 rpm should work fine. If parking lot speeds are really important, one could switch the pack in parallel for 1/2 or 1/4 voltage, and get the idle speed down to about 700 to 1400 rpm. Another alternative would be to run both the field and armature in parallel off the weak 48 Volt 50 Amp field controller, to be able to creep around 0 to 500 rpm. If you have a clutch, though, this doesn't sound worth the bother.



major said:


> Third: At 240V inductive, that might work 2 or 3 times before it welds shut.


Yep, true for a series motor, too. Obviously it is an emergency disconnect if your controller misbehaves.



major said:


> Forth: Good idea.
> 
> Like I said, go for it. But you'll not end up with a more efficient drive or more powerful drive than an equivalent size series motor/PWM system.
> 
> ...


How could you be less efficient with regen? Regen is also going to make you more powerful for the same distance, the batteries won't be as tired near the end. I also think sepex is a bit (alot for some operating points, but just a little overall) more efficient on average than series, but I realize there are contrary opinions on that.

In any case, I'm putting my money where my mouth is!

Major has given some good warnings, I think it is worth a list:


You can't just suddenly switch high voltage to the motor
You can't just keep cranking up field current to slow the idle speed
You will have limitations on low rpm operation without more sophisticated sepex control
You get diminishing effect with increasing field current, as the field saturates eventually


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## major (Apr 4, 2008)

DavidDymaxion said:


> _First: How does the driver control armature current?_
> 
> Current gauge and right foot!


 
O.K. David. What does his right foot do? And how does that in turn control armature current? 

Regards,

major


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## major (Apr 4, 2008)

DavidDymaxion said:


> This is not an original idea to me, some old timer EVs used to do it this way.


Hi David,

Some old timers used to do it this way. Wonder why? Or why hardly anyone since has? Well, I guess I'd have to put myself in that old timer class. And here is my theory. Back in the old days, pre 1980, micro controlled transistorized PWM motor controllers weren't invented yet. So these old timers had few options. Maybe go with SCR controllers. Expensive and troublesome. Or devise their own method. A shunt motor with field weakening was an option. They likely ended up using oversized motors and controls fashioned by themselves. These used elaborate schemes of battery switching and resistor current limiting, as well as gear changing. The result for those successful was a jerky ride requiring driver skill and an inefficient system requiring lots of maintenance.

Once the transistorized PWM controllers became available, even the old timers saw the benefits and put aside those shunt drives for the new technology. The size, efficiency, controllability and reliability were well worth it.

Now for some reason you want to go back. Go ahead.

I have used both series and sepex systems. I like the sepex. It depends on the application particulars as to which I prefer. The sepex systems use standard sepex controllers from Curtis or Sevcon. I have had to test the sat curve on some motors to actually tune the control. I have experience here.

You can listen to the voice of experience and reason, or go your own way.

Regards,

major


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## DavidDymaxion (Dec 1, 2008)

Thank you for your concerns Major. I share similarities with you. For instance, I built my own adapter from scratch, and would do it again. However, I also warn people away from that, and urge most folks to just buy one. It is not for everyone to buy a Smithy and a welder, teach themselves machining and welding, and then to do it. So I hear you loud and clear, "there be dragons" down some paths, but there can be great rewards, too.

While sepex has definitely been the minority of hobbyist systems, I find it interesting that GM, Citroen, Peugeot, Renault, and Chrysler built sepex vehicles that the public could buy in the circa 1990s era. BTW the GM and Chrysler sepex systems ran at 200 and 180 Volts. Why didn't they do a simpler, "more efficient," and "more powerful" series setup? I have my own ideas, but would like to hear your take on that. Obvious to everyone is that AC is the most deluxe solution, which is the direction the car companies are taking today.



major said:


> ... Now for some reason you want to go back. Go ahead. ...


Subtle and good double entendre! There are many reasons folks might do this (not all of these reasons apply to me):


Lead acid and series is going back -- compared to AC and lithium -- yet this is a great, practical choice for many
Going with the flow (lead acid and series DC) is definitely easiest -- but there are folks that like to try something different
I am willing to fail. Sepex and series motors are more fundamentally similar than different, and in theory sepex is more efficient with regen and is more tunable than series DC (kind of 1/2 way between series DC and AC in capability).
While I am not actively trying to break anything, I realize things break in racing. I sacrifice tires, brake pads, brake disks, brake fluid, and bearings in the name of speed, and realize there is a chance I'll sacrifice a motor or bodywork someday. I realize I'll be pushing things beyond the commuter driver's needs. I'll work my way up to and hopefully not pass the destruction point.
I want to be able to descend steep hills safely (my wife has warped brake discs three times on 2 different cars) -- Major would you still recommend series DC in this situation?
I "own" the adapter I built, it's better for my case than one I could buy (due to needed to satisfy racing rules), and it's a great feeling to build something like that
I think retro is neat in a way -- it would be neat to be able to say "This could have been built 20 (or 40 or 100!) years ago.
I realize it is not "best" -- I would fork out $60k for two AC propulsion systems if I wanted "best"
I'm willing to do some compromises, like idling the motor and having to slip the clutch. It won't be a car I would throw the keys to anyone to drive
While not my primary goal, saving money is a fun talking point. If I can get V8 performance for 1/3 the cost of a new V8 car, that would be awesome.
I'm very glad to hear you have real-life sepex experience. Please share the knowledge wealth!

What voltages and currents did your sepex systems run?

Did you measure the efficiency? Why did you think it was less than series? (BTW on the evalbum someone with the 7000 lb. GVan claimed 500 Whr/mile, and the 5000 lb TEVan said 380 Whr/mile -- not bad for vehicles that heavy).

You said something about sepex systems having poor torque -- what are your real life experiences there?

I realize its not likely, but have you ever compared the same car, same battery pack, same everything else, but sepex vs. series? (Hopefully I won't be doing that!)



major said:


> Hi David,
> Some old timers used to do it this way. Wonder why? Or why hardly anyone since has? Well, I guess I'd have to put myself in that old timer class. And here is my theory. Back in the old days, pre 1980, micro controlled transistorized PWM motor controllers weren't invented yet. So these old timers had few options. Maybe go with SCR controllers. Expensive and troublesome. Or devise their own method. A shunt motor with field weakening was an option. They likely ended up using oversized motors and controls fashioned by themselves. These used elaborate schemes of battery switching and resistor current limiting, as well as gear changing. The result for those successful was a jerky ride requiring driver skill and an inefficient system requiring lots of maintenance.
> 
> Once the transistorized PWM controllers became available, even the old timers saw the benefits and put aside those shunt drives for the new technology. The size, efficiency, controllability and reliability were well worth it.
> ...


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## major (Apr 4, 2008)

DavidDymaxion said:


> While sepex has definitely been the minority of hobbyist systems, I find it interesting that GM, Citroen, Peugeot, Renault, and Chrysler built sepex vehicles that the public could buy in the circa 1990s era. BTW the GM and Chrysler sepex systems ran at 200 and 180 Volts. Why didn't they do a simpler, "more efficient," and "more powerful" series setup? I have my own ideas, but would like to hear your take on that.


Hi David,

I am not familiar with these systems, but I venture to say they included an armature controller, probably solid state. This is similar to the modern day sepex systems and those compete favorably to series motor systems. What I am objecting to is your apparent approach of using no armature control except a starting resistor for a fraction of a second.

The comparison of the more powerful and efficient series systems I made was in regard to a sepex or shunt motor system using battery switching and/or series resistors for armature control and multispeed transmission needing constant shifting. 





> I want to be able to descend steep hills safely (my wife has warped brake discs three times on 2 different cars) -- Major would you still recommend series DC in this situation?


Obviously regeneration is a problem with series motors. Sepex systems do regenerate nicely. However if she is warping disc brakes on those inclines, I think you'll be disappointed with regen. Better look into a resistor bank back up to the batteries, and then monitor motor temperature. I have a lot of experience with regen. I use it on those sepex systems. Works great. Those are IUVs. 10 to 15 mph speeds, maybe a ton or so. Also on high speed cars and commercial hybrid vehicles up to 20 tons. Those are AC drives. Regen is great. But on the race track or normal driving cycle, don't count on it for much in the way of extended range, what I think you refer to as efficiency. Regen does however do quite a bit for those commercial heavy hybrids where you have 7 to 10 stop per mile.



> I'm willing to do some compromises, like idling the motor and having to slip the clutch.


And that isn't going to adversely affect efficiency? And have you figured out how much clutch slip you'll be doing? And the current spike when it grabs? Using 240 volts and 2500 RPM idle even with the field maxed out, I think you're in for a rude awakening. Let me know how that works out for you.



> I'm very glad to hear you have real-life sepex experience. Please share the knowledge wealth!


That's what I've been trying to do.




> What voltages and currents did your sepex systems run?


48V, 500A. IUVs. Industrial Utility Vehicles.



> Did you measure the efficiency?


Not on these particular systems.



> Why did you think it was less than series?


You misunderstand me. I was talking about the system you describe, not well done sepex systems. When properly done, the efficiency, under the classical definition (power out/power in) is equal for a series and a sepex at rated load for the same amount of steel and copper. I said about 10 or 12 posts ago that sepex gives you some control advantage which can increase efficiency at certain load condition by a few percent, typically at lighter loads. And you if broaden the efficiency term to include things such as regen, then the sepex will gain further over the series system.

But looking at a sepex or shunt motor system which has battery switching, series resistor armature control and multiple gears with slipping clutch, then the pwm series motor system is likely way ahead in efficiency and power, even including non regen capabilities.



> You said something about sepex systems having poor torque -- what are your real life experiences there?


I think you have taken this out of context. Yes, a sepex can have lower torque than a series motor. If you over excite the sepex field, you can come close to series motor torque within the usable range, under the normal armature current limit, for example in the 48 volt systems I use. There is no noticeable difference between the draw bar pull between the series and sepex versions. But the context of my comment, I believe, related to maximum torque such as you can expect with controllers like the Zilla. Try 2000 amps with a sepex.



> I realize its not likely, but have you ever compared the same car, same battery pack, same everything else, but sepex vs. series? (Hopefully I won't be doing that!


Actually, kind of. Not a car, but that IUV. Had a series wound motor and 400 amp controller for years on the prototype. Got a sepex motor which fit that axel and tried it. Different motor manufacture but same size, 6.6 inch. Got a sepex controller. It was 500 amp limit. But vehicle, battery and everything else was the same. Did not do very extensive test, like efficiency or range, but overall performance was very comparable. Like I said, about the same draw bar pull, same speed, etc. Sepex gave us regen and programmability, so we went over to that system. It also saved contactor set for reverse and some large cables for the field connects. So, sepex was a winner there. 

You going to tell me how that right foot controls armature current or not?

Regards,

major


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## DavidDymaxion (Dec 1, 2008)

Sure, slipping the clutch is a moment of lessened efficiency. Adversely affect efficiency? Probably not too bad. On my gas car the motor gets really hot, the radiator and exhaust literally throwing away the majority of the energy as heat. The brakes get quite hot, literally throwing away the energy of motion as heat. My tires get hot during racing, hot enough to steam when driving through puddles, and too hot to touch. Even the wheel bearings get hot.

Notice the clutch has no provisions for cooling, yet survives just fine under racing abuse. The only time I hear of a clutch overheating is if it is slipping. A clutch is not a big energy waster.

But it would be fun to estimate how much energy is wasted by idling and by the clutch. Let's say I engage the clutch 23 times during my 20 mile commute to work. Let's say my future conversion takes about 1/2 second to spin up to idle speed, and about 1 second to slip the clutch to get going. Mr. Major, would you be kind enough to estimate how much energy is lost, compared to the total energy of the trip?

It would also be great if you'd estimate how much of a current pulse you'd think I would get if the "clutch grabs" for the extreme conditions you listed.

With a race car, (or many regular cars, for that matter) there are some risks. Put sticky race tires on an all wheel drive car, dump the clutch at high rpm, and you are likely to break something. Likewise, on my conversion if I put it in a high gear, hold on the brakes, and dump the clutch, something is likely to break. If the controller/fuse doesn't catch the current quickly enough, it might cook the motor or batteries or controller, too. For a more "normal" mistake (foot off the brakes, and in 1st or 2nd gear), popping the clutch too quickly will more likely spin the rear tires for a moment. Indeed, I want to be able to spin my tires! 

I'll comment on more in upcoming posts, as I think we are getting too many topics going at once.



major said:


> ... And that isn't going to adversely affect efficiency? And have you figured out how much clutch slip you'll be doing? And the current spike when it grabs? Using 240 volts and 2500 RPM idle even with the field maxed out, I think you're in for a rude awakening. Let me know how that works out for you. ...


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## major (Apr 4, 2008)

DavidDymaxion said:


> about 1 second to slip the clutch to get going. Mr. Major, would you be kind enough to estimate how much energy is lost, compared to the total energy of the trip?
> 
> It would also be great if you'd estimate how much of a current pulse you'd think I would get if the "clutch grabs" for the extreme conditions you listed.


Hi David,

Looks like 2 questions with an either/or answer. If you have 240 V and 2500 RPM at the motor and engage the clutch in a second, I'd venture to say you'll see a 3000 amp spike. All depends on the battery resistance. Could be 1000 amps higher. Now if you slip the clutch to avoid the current spike (keeping the motor RPM, say above 2200 RPM) (and it will take longer than one second), then you will dissipate one half of the energy needed to accelerate the vehicle in the clutch.

How's that sound?

major


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## major (Apr 4, 2008)

DavidDymaxion said:


> I'll comment on more in upcoming posts,


 
Hey David,

Cat got your tongue (or keyboard)? 

major


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