# Interpoles in a Nut shell



## Georgia Tech (Dec 5, 2008)

I have been doing some research on interpoles. From my understanding Interpoles allow for higher currents or is it higher voltages? I always thought it allowed for Higher voltages..... 

In the case of a Sep Ex do the interpoles allow for the feild NOT to be varied with the Armature? in other words could I just tack the voltage at a particulare level on the feild and just use a normal series controller for the armature? Would this cause bad commutation even with interpoles?

Hate to ask this but I REALLY thought I already knew the answers to these questions, but maybe I am going nuts from reading too many different answers.


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## Tesseract (Sep 27, 2008)

"In a nutshell", interpoles are windings that are placed in between the main field poles (hence the name, "interpole"). They are permanently wired in series with the armature (regardless of the field connections) to produce a magnetic field proportional to armature current. The sole purpose of this is to correct the distortion in the magnetic field caused by "armature reaction". 

More specifically, the goal is to ensure that the intersection of the magnetic fields of the stator (field) and rotor (armature) stays aligned with where the brushes contact the commutator, minimizing arcing as power (speed & torque) demanded from the motor goes up.

With properly designed interpoles you no longer need (nor want!) to advance the brush timing to let the motor tolerate a higher voltage.

And with neutral brush timing, electronic reversing (and regen braking) of a series motor can be done with less chance of zorching it.


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## Georgia Tech (Dec 5, 2008)

OK thanks alot ..Yeah, this was stuff I already knew, so I'm NOT crazy...So really it helps improve both Max voltage and current....
And also with a sepex..it really DOSE NOT amtter what the field is...the flux will be always aligned..


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## GerhardRP (Nov 17, 2009)

Georgia Tech said:


> OK thanks alot ..Yeah, this was stuff I already knew, so I'm NOT crazy...So really it helps improve both Max voltage and current....
> And also with a sepex..it really DOSE NOT amtter what the field is...the flux will be always aligned..


I have always wondered why the users havn't demanded the inclusion of interpoles on all traction motors, no matter how small. I'm also partial to sepex, but maybe that is another thread.
Gerhard


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## major (Apr 4, 2008)

GerhardRP said:


> I have always wondered why the users havn't demanded the inclusion of interpoles on all traction motors, no matter how small.


Hi Gerhard,

It is simply economics. Interpoles are an expensive feature to design into a motor. If the application doesn't require it, what is the sense? Interpoles and comm coils do not contribute to the torque production so actually reduce the torque density of the motor. They use material and consume space inside the motor which typically means a smaller armature for a particular frame size and/or reduced pole arc and field copper.

And what can users demand? Unless you buy a million dollars of motor from a manufacturer, you think he'll listen to you? Why don't we demand a decent performance curve from Warfield? 

major


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## MJ Monterey (Aug 20, 2009)

major said:


> And what can users demand? Unless you buy a million dollars of motor from a manufacturer, you think he'll listen to you? Why don't we demand a decent performance curve from Warfield?
> major


Major,

Just to clarify:

Are you asking for different data on existing motors or a change in the motor for a different curve?

MJ


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## major (Apr 4, 2008)

MJ Monterey said:


> Major,
> 
> Just to clarify:
> 
> ...


Hi MJ,

The curves for the Warp9 in particular suck. See thread http://www.diyelectriccar.com/forums/showthread.php/dc-motor-theory-and-model-39931p4.html post 37 attachment.

I have run into "discrepancies" with this curve many times. And now it appears that it may be way off. I don't know for sure, but I find it odd that two different engineers (Tesseract and Mike) at different times come up with data which match each other and are a far cry from the "published" curve.

You get a lot of guys that study that curve to make money decisions about their projects. Then most never know they don't get what they paid for 

Regards,

major


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## GerhardRP (Nov 17, 2009)

major said:


> Hi MJ,
> 
> The curves for the Warp9 in particular suck. See thread http://www.diyelectriccar.com/forums/showthread.php/dc-motor-theory-and-model-39931p4.html post 37 attachment.
> 
> ...


Anyone running a warp 9 can help unravel this mystery... Run your vehicle at at least one constant speed, measure RPM, motor voltage and current and report the values on the thread major quoted. I will put your data on a plot of field value vs. current.
Gerhard


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## MJ Monterey (Aug 20, 2009)

O.K. guys, I have PMed James (EVcomponent) and asked him to take a peek at this thread.

I asked if he would be willing to get Netgain to come over and talk with us.

Let's see if we can run it up the chain and get a response/change.

To better focus on this subject, do you guys want to start a new thread called, allong the lines of, "Validated motor data"?

MJ


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## major (Apr 4, 2008)

MJ Monterey said:


> O.K. guys, I have PMed James (EVcomponent) and asked him to take a peek at this thread.
> 
> I asked if he would be willing to get Netgain to come over and talk with us.
> 
> ...


O.K. MJ,

Good for you. Seems like this thread is a bad place for it. I suggest you use http://www.diyelectriccar.com/forums/showthread.php/dc-motor-theory-and-model-39931p4.html or start a new one and refer back to these two threads.

I just like to see valid data presented well.

Thanks,

major


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## MJ Monterey (Aug 20, 2009)

Agreed Major, Will start a new thread in the near future, with back references.

MJ


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## GerhardRP (Nov 17, 2009)

MJ Monterey said:


> Agreed Major, Will start a new thread in the near future, with back references.
> 
> MJ


I have put out requests for data on three or four threads with only the excellent response from Tesseract. i would like to have the data file from Electrabishi, but am stuck with only his graphs. And random or extensive data from others would be kewl. I *really* do have a model which will tie the data together.
It is premature for a new thread... when a FEW others answer, I will start a warp 9 [or warp 11 hv] thread with updated graphs maintained in post #1 of each of those threads.
Post on the "motor theory" thread proposals for special graphical presentations.
Gerhard
PS How do I create a back reference to other posts? GRP


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## MJ Monterey (Aug 20, 2009)

Received a pm back from James. He has sent a link via e-mail to his contact at Netgain.

Back reference: The links in thread as Major and I have used in this thread. Just let folks know where the back story is.

New thread: I agree. Your call on when to start. Should your final graphs be a WIKI thread?


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## Bowser330 (Jun 15, 2008)

GerhardRP said:


> ...warp 11 hv] thread with updated graphs maintained in post


+1000000

I couldn't agree more! We need power/torque graphs at rpms (for different voltages) we will be using.

Trying to create an apples to apples comparison with the power/torque graphs of ICEs can help people better understand what the expect and from their motor and how to best size it for their conversion....

I want to see a 13" Kostov @ 300V with a 1000A controller


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## Tesseract (Sep 27, 2008)

Bowser330 said:


> ...
> I couldn't agree more! We need power/torque graphs at rpms (for different voltages) we will be using.


Yes, I thought GerhardRP's pursuit was admirable and worthwhile, too, but then a couple of people here went ballistic over the data I provided - one has even personally attacked me in another post - so now I'm not so sure.


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## GerhardRP (Nov 17, 2009)

Tesseract said:


> Yes, I thought GerhardRP's pursuit was admirable and worthwhile, too, but then a couple of people here went ballistic over the data I provided - one has even personally attacked me in another post - so now I'm not so sure.


I am baffled by the response too... I'm trying to stay with science and engineering... the only flames should be from burning rubber at the drag strip.
PS. Thanks


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## Plamenator (Mar 6, 2009)

Bowser330 said:


> +1000000
> 
> 
> I want to see a 13" Kostov @ 300V with a 1000A controller


 
Have you seen the upgraded 13"?
http://kostov-motors.com/files/productattachments/368d71ead58e43d575e4cd3581254a93_G01A1220.pdf

I will upload curves for it by the end of the month.
Only up to 500A+220V though. We actually blew the generator motor with the prototype - the dyno motor was simply not up to the task I guess  and it will take some time to rebuild it with the new high rpm collector.

Reliability of provided motor data is quite important for us though.
To say the least, it makes for a nasty marketing dilemma...


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## GerhardRP (Nov 17, 2009)

Plamenator said:


> Have you seen the upgraded 13"?
> http://kostov-motors.com/files/productattachments/368d71ead58e43d575e4cd3581254a93_G01A1220.pdf
> 
> I will upload curves for it by the end of the month.
> ...


Do you have the performance curves in tabular form.. 9- inch first.. I get cross-eyed picking points from a graph.
BTW what does the expression "U=144-5.3/In**I" mean on the 11" 144V Kostov curve?
http://kostov-motors.com/files/productattachments/4777daf364d61560a2b7091ec822ae63_S144F05.pdf
Gerhard
PS some of the PDFs are behind the wrong links on the index page.


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## Plamenator (Mar 6, 2009)

"144-5.3/ln I" is the formula for calculating voltage sag at the different amp draws. I.e. when you draw 280 assumed votage is 139V, but when you draw 500A voltage will be less than 139V and for the purpose of the curve is calculated using the above expression.


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## Bowser330 (Jun 15, 2008)

Plamenator said:


> Have you seen the upgraded 13"?
> http://kostov-motors.com/files/productattachments/368d71ead58e43d575e4cd3581254a93_G01A1220.pdf
> 
> I will upload curves for it by the end of the month.
> ...


Indeed I have seen the motor schematics and am patiently waiting for the torque curve...


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## major (Apr 4, 2008)

Plamenator said:


> "144-5.3/ln I" is the formula for calculating voltage sag at the different amp draws. I.e. when you draw 280 assumed votage is 139V, but when you draw 500A voltage will be less than 139V and for the purpose of the curve is calculated using the above expression.


Hi Plamenator,

We are (or at least I am) used to seeing the motor terminal voltage expressed as a battery voltage represented by an open circuit voltage (Voc) minus a term representing the sag expressed as a resistance times the current (R * I). Hence, Vm = Voc - R * I. 

The term "5.3/ln I" is confusing. Is this 5.3 divided by the natural log of the current?

This seems redundant because your graph shows the voltage trace. Using that voltage trace (U), I calculate a battery resistance of about 18 milliohms. In terminology we are accustomed to seeing, that would be Vm = 144 - 0.018 * I.

Regards,

major


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## Georgia Tech (Dec 5, 2008)

Plamenator,

could you tell me How interpoles have been a major feature in your motors and how an important role they have played? For high power applications would you take a Series motor timing advanced or would you take a sep-ex motor with neutral timing with interpoles?


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## Plamenator (Mar 6, 2009)

major said:


> Hi Plamenator,
> 
> We are (or at least I am) used to seeing the motor terminal voltage expressed as a battery voltage represented by an open circuit voltage (Voc) minus a term representing the sag expressed as a resistance times the current (R * I). Hence, Vm = Voc - R * I.
> 
> ...


 
I consulted with our engineers and you are right. 
It is not ln as in natural log but ln is nominal current (I nominal or In).
Hence the expression is 144-5.3/In*I, where I is the current you are interested in. For example at the nominal 280A, the expression will be 144-5.3/280*280=139V. Overloading to 350A will result in 144-5.3/280*350 or 132V.
Of course this is an approximation as it is battery capacity specific.
Hope I got it right this time...


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## Plamenator (Mar 6, 2009)

Georgia Tech said:


> Plamenator,
> 
> could you tell me How interpoles have been a major feature in your motors and how an important role they have played? For high power applications would you take a Series motor timing advanced or would you take a sep-ex motor with neutral timing with interpoles?


 
These are quite a few questions 

Some 6 months ago we decided to produce a non-interpoled motor to supplement our portfolio. We wanted to make it similar to our competitors' and achieve better amp abuse capabilities (interpoles take valuable space in the stator and hence it can handle less amp abuse compared to a non-interpoled model).
We tried with several EV-worthy constructions but the results were dissappointing. We only managed to reach 75V - beyond that arcing was horrible and the collector overheated rapidly so we gave up.
Advancing the brushes made a small positive difference (10%) in collector temperature.
We know of no useable construction that will allow you continuous work above 80V. The only way is to double collector bars to 120-130 but then conductor cross-section drops so much that nominal amps fall to 100-150A which is not good.
You may ask how our competitors do it - no idea. Maybe we are missing something. Note that in an EV the vast majority of time one uses 30-50% of max voltage so this maybe the answer.

For high power usage, if you stay below 100V most of time, go for a non-interpoled motor; otherwise use an interpoled one.
The only difference between sepex and series is that sepex has regen but no good controllers and lower peak torque, while series has no regen, great controllers and better peak torque.

I am really hoping for EVnetics to make a good sepex controller but they are scarce on news there


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## Georgia Tech (Dec 5, 2008)

Plamenator said:


> These are quite a few questions
> 
> Some 6 months ago we decided to produce a non-interpoled motor to supplement our portfolio. We wanted to make it similar to our competitors' and achieve better amp abuse capabilities (interpoles take valuable space in the stator and hence it can handle less amp abuse compared to a non-interpoled model).
> We tried with several EV-worthy constructions but the results were dissappointing. We only managed to reach 75V - beyond that arcing was horrible and the collector overheated rapidly so we gave up.
> ...


WOW!!! what an EXCELNT response!!
Buddy now this takes my breath away!! Like you said it your comptitors claim that they can go up to these high voltages but i don't know how they do it!!! 
*Maybe there IS a real reason why warp ONLY gives their curves in 72 volts!!!* *It's PROBEBLY BECASUE THEY ONLY RUN AT 72 VOLTS!!!!*

Man I know I asked alot of questions but this I think was SOOO important to this community and industry.. thank you again


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## major (Apr 4, 2008)

Plamenator said:


> ........For example at the nominal 280A, the expression will be 144-5.3/280*280=139V. Overloading to 350A will result in 144-5.3/280*350 or 132V........Hope I got it right this time...


Still doesn't look right to me. That's the trouble with dual dimensioning. You have the U curve and also the equation, which don't match. The U curve shows 137.5 (near as I can read it) at 350A and you say the equation yields 132 volts.

Ooops, looks like a math error on your part. My calculator shows 144 - [(5.3/280) * 350] = 137.4. 

major


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## Plamenator (Mar 6, 2009)

Do not be quick to jump to conclusions.
We are all small companies.
We do not know everything about DC motors and despite producing DC motors for 60 years now we heavilly rely on testing rather than calculations. Just because Kostov does not know a non-interpoled construction that can work above 150-200A+80V does not mean there is no such construction (we have many forklift motors without interpoles that work at 80V but with 100-150A+1000 to 2000rpm). And I DO work at Kostov so my opinion is not to be trusted lightly  
They probably test at 72V because their dyno can only produce 72V. Dynos are expensive...we use 3 generator motors (all interpoled) to get to 250V.


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## Plamenator (Mar 6, 2009)

major said:


> Still doesn't look right to me. That's the trouble with dual dimensioning. You have the U curve and also the equation, which don't match. The U curve shows 137.5 (near as I can read it) at 350A and you say the equation yields 132 volts.
> 
> Ooops, looks like a math error on your part. My calculator shows 144 - [(5.3/280) * 350] = 137.4.
> 
> major


 
Indeed....


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## major (Apr 4, 2008)

MJ Monterey said:


> Received a pm back from James. He has sent a link via e-mail to his contact at Netgain.


Hey MJ,

Any word back from these guys?

major


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## MJ Monterey (Aug 20, 2009)

major said:


> Hey MJ,
> 
> Any word back from these guys?
> 
> major



Not yet. I am letting the response time and quality flavor my opinion of their customer service. The longer a wait the more likely I'll by Kostov.

It may be harsh but that is the way it is.

MJ


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## Dennis (Feb 25, 2008)

> thanks alot ..Yeah, this was stuff I already knew, so I'm NOT crazy...So really it helps improve both Max voltage and current....
> *And also with a sepex..it really DOSE NOT amtter what the field is...the flux will be always aligned.. *



This is not true. What you were not told is that interpole coils are wired such that their magnetic field polarity is always opposing the armature field. This is how it is able to shift the field to the neutral position. This also weakens the torque output of the motor, but nearly all motors in the industry and rail traction applications use interpoles. There is really no way around them once you go up in high current, high voltage if reliability is of concern. 

Side note: In drag racing it is not super important to have interpoles as the motor is only being asked to survive down the 1/4 mile without turning into a pile of molten copper and steel, much like top fuel dragster engines are literally on the edge of blowing themselves to pieces.


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## Georgia Tech (Dec 5, 2008)

Dennis said:


> This is not true. What you were not told is that interpole coils are wired such that their magnetic field polarity is always opposing the armature field. This is how it is able to shift the field to the neutral position. This also weakens the torque output of the motor, but nearly all motors in the industry and rail traction applications use interpoles. There is really no way around them once you go up in high current, high voltage if reliability is of concern.
> 
> Side note: In drag racing it is not super important to have interpoles as the motor is only being asked to survive down the 1/4 mile without turning into a pile of molten copper and steel, much like top fuel dragster engines are literally on the edge of blowing themselves to pieces.


Oops I use the WRONG terms here...What I ment was that the Feild current did not have to track the Armature current. Sorry about my miss wording here.

As far as performance yeah...I think alot of time it is no different than our V8 hotrod buddies. they are running their motor Way beyond the margins of their spec. Their motor are on the verge of blowing up. I sort of don't want to be like this with DC motors. I do want alot of performance But I sort of like the idea that DC Motors are more durable than Gas Motors, dunno I'm just sort of wierd like that I guess.


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## dcb (Dec 5, 2009)

sorry for the zombie thread awakening here (what happens when you search I guess).

So I'm trying to understand something, armature reaction is a function of rpm and current, no? i.e. flux concentration and speed.

interpoles only seem to compensate for current, or is there something inherent in the design that compensates for speed as well?

or is it just the fact that the armature is a strong magnet itself pulling on the field, and current really is the dominant variable?

and I've seen mention of on-the-fly adjustable brushes, if they were reliable, accurate and responsive, and could compensate for speed AND current, would they be better? (there are a few online neutral detection possibilities).

or if it is just current and not speed, what would be the tradeoffs between an auto brush advance and interpoles? Interpoles would *probably* consume more power and take up critical space, but that's all I got.

or is it just silly, just advance them for worst case and wang open the throttle? (280v pack??)

Thanks.


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## dcb (Dec 5, 2009)

fwiw, I did find this 1912 thesis from U of I, it indicates shifting commutation moves off the meat of the field poles basically, weakening the field strength @ commutation.

(slow loading)
https://www.ideals.illinois.edu/bitstream/handle/2142/54006/studyoffluxdistr00fedd.pdf?sequence=2

"The usual method employed to produce this result is to shift
the brushes until the main field flux reverses the armature reac-
tion and so generates an e # m#f. in the armature coil, which rever-
scs the current and thus acts as commutating flux. The magnetic
flux of the field pole however, docreases with increasing load at
the pole corners towards which the brushes are shifted, by the
demagnetizing action of the armature reaction, and the shift of
the brushes therefore has to be increased with the load. At over-
load the pole corners toward which the brushes are shifted may
become so far weakened that even under the pole, not sufficient
reversing e.in.f . is generated and satisfactory commutatin ceases."


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## dcb (Dec 5, 2009)

oh and kostov faq says don't advance, so theres that too..
http://kostov-motors.com/faq/
"SHOULD THE BRUSHES OF AN INTERPOLED MOTOR BE ADVANCED?
The interpoles create a magnetically neutral point whose position is independent of rotation direction, rpm, amps or voltage. The brushes are positioned exactly in this point. Advancing them will result in moving away from the neutral zone and will worsen commutation/arcing drastically. This, in turn, can have very bad consequences for the motor."


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## major (Apr 4, 2008)

dcb said:


> So I'm trying to understand something, armature reaction is a function of rpm and current, no?


No. Armature reaction is not speed dependent. Armature reaction is defined as a distortion to flux in the air gap. I don't see how speed is going to affect that. Now there is reactance voltage in the armature coils undergoing commutation which is speed dependent. Basically commutation forces current reversal in a certain angular distance so the higher RPM makes the time interval less therefore higher dI/dt.


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## dcb (Dec 5, 2009)

Thanks for the confirmation, lots of misinformation on that stuff.

i.e. here is lugnut straightening folks out on elmoto
http://elmoto.net/showthread.php?t=938&p=8418&viewfull=1#post8418


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