# Rewinding compound to a series motor



## major (Apr 4, 2008)

Qmavam said:


> Hi all,
> I need to have my gokart motor rewound. It is a compound motor, it
> has overheated the field the coils on one end, nearest the brushes.
> Since I'm so much smarter now  I would
> ...


Hi MikeK,

First, yes, always N, S, N, S on a 4 pole motor.

And then, how much are you in love with this motor? Sounds like to me it would be better to get a series motor than rewind what you have. Finding and buying the proper magnet wire will likely exceed the cost of a used series motor.

But here's a suggestion. Just remove the shunt coils and run it with the 2 series coils in place and connected the way they are now. And go ahead and ventilate the motor. Try that first. {edit} You need to leave the steel poles in place after removing the shunt coils.

major


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## Qmavam (Aug 17, 2008)

major said:


> Hi MikeK,
> 
> First, yes, always N, S, N, S on a 4 pole motor.


 Ok good.



> And then, how much are you in love with this motor?


Love is a little strong, I like it cause it was free! and it has
worked fine for a year. I think it was slightly overheated 
dozens of times and finally it had enough and let out a some 
smoke.



> Sounds like to me it would be better to get a series motor than rewind what you have. Finding and buying the proper magnet wire will likely exceed the cost of a used series motor.


The motor is wound with 16 gauge wire ( several parallel wires)
so getting the wire isn't a problem. We have already put a spare
golfcart series motor on the gokart. It has more torque, but a little
less top end.



> But here's a suggestion. Just remove the shunt coils and run it with the 2 series coils in place and connected the way they are now. And go ahead and ventilate the motor. Try that first. {edit} You need to leave the steel poles in place after removing the shunt coils.


I do need to replace the original series fields as they have overheated.
(I know I didn't say exactly that before.)
I would take this on just for the education of my 16 yr old son.
The gokart project was to get him involved in something more 
than video games!
The armature looks good, no signs of heat. No wear ridge on the 
commutator.

If I double the number of series fields and go with four series fields,
Would you decrease the turns, increase the turns?
Put them is series or parallel? 

Just as background, 2 hp motor, 28V, 62 amps, 2600 rpm.
I'm running it on 48 volts with peak currents of 250 to 300 amps.
In fact we rarely start from a stop without the pedal to the floor
and peak current until the speed picks up a bit. 
Here's a picture of the stator;
http://i395.photobucket.com/albums/pp37/Qmavam/Stator.jpg
and the rotor;
http://i395.photobucket.com/albums/pp37/Qmavam/Rotor.jpg

Thanks, MikeK


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## major (Apr 4, 2008)

Qmavam said:


> The motor is wound with 16 gauge wire ( several parallel wires) so getting the wire isn't a problem.


Well, to do it right, you need HAPT 200°C magnet wire and then treated with high temperature polyester resin after winding and forming. But for a science project, WTH 



> I do need to replace the original series fields as they have overheated.
> (I know I didn't say exactly that before.)


O.K.



> If I double the number of series fields and go with four series fields, Would you decrease the turns, increase the turns?
> Put them is series or parallel?





> Here's a picture of the stator;
> http://i395.photobucket.com/albums/pp37/Qmavam/Stator.jpg
> and the rotor;
> http://i395.photobucket.com/albums/pp37/Qmavam/Rotor.jpg


O.K. So here's my suggestion. Not my usual analytical method, but SWAG. From the picture, the series coils are larger than the shunt coils. So it will be difficult to fit four of the same size series coils in the space between the poles. And you should have some space between the coil sides for ventilation. So reduce the number of turns on the original series coil using the same wire size and parallel strands. Say that is #16, 3 in parallel and originally 20 turns per coil. Wind the new series coil with 17 turns of 3 of #16. Make four of them.

Now assume the original 2 series coils were wired in series with each other. The wire the additional coils in series with each other and in series with the original two. If the original 2 series coils were in parallel with each other, then wire the 2 new series coils in parallel with each other and wire those two coils in series with the original pair.

Make sure when you wire these up they result in the N, S, N, S polarity.

Piece of cake 

major


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## Qmavam (Aug 17, 2008)

major said:


> Well, to do it right, you need HAPT 200°C magnet wire and then treated with high temperature polyester resin after winding and forming. But for a science project, WTH


 Ya, I'm familiar with that newfangled wire, well, NEW since I worked
in a motor shop 30 some years ago. 
The high temp polyester resin, I'll check with my local rewind shop and see
if I can get a quart. I'll bake it while the wife is shopping!



> O.K. So here's my suggestion. Not my usual analytical method, but SWAG. From the picture, the series coils are larger than the shunt coils.


I didn't notice that, Just looked at the picture, looks the same, but difficult to know for sure. I'll check when I get home.
hmm... did you mean poles pieces or coils?
Is there an online source to guide me through a more analytical method. 



> So it will be difficult to fit four of the same size series coils in the space between the poles. And you should have some space between the coil sides for ventilation. So reduce the number of turns on the original series coil using the same wire size and parallel strands. Say that is #16, 3 in parallel and originally 20 turns per coil. Wind the new series coil with 17 turns of 3 of #16. Make four of them.
> 
> Now assume the original 2 series coils were wired in series with each other. Then wire the additional coils in series with each other and in series with the original two. If the original 2 series coils were in parallel with each other, then wire the 2 new series coils in parallel with each other and wire those two coils in series with the original pair.
> 
> ...


 Piece of cake... To say!
Can I assume doubling the series poles will increase torque?
MikeK


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## major (Apr 4, 2008)

Qmavam said:


> Ya, I'm familiar with that newfangled wire, well, NEW since I worked in a motor shop 30 some years ago.


HAPT2000 has been around for 40 years. Maybe they have better now.



> I didn't notice that, Just looked at the picture, looks the same, but difficult to know for sure. I'll check when I get home.
> hmm... did you mean poles pieces or coils?


The coils. Notice how the series coil hangs out past the pilot on the end of the frame and the shunt coil doesn't. The series coil has a greater D²N, or total mass of copper than does the shunt coil.



> Is there an online source to guide me through a more analytical method.


Not that I know. But you can google as well as I can. Often I find professor's notes on line. Or scanned old books. Give it a try.



> Can I assume doubling the series poles will increase torque?


Not exactly. And not analyzing the existing design, can't be sure. But if it was a 50/50 compound motor at rated load, which is common, then the torque and speed will be about the same at rated load, minus a small deviation for less turns. At overload, the series version will yield more torque per amp and have a bit higher series resistance, so reduce the uncontrolled stall current. You never see that with the controller anyway. But the increase in series inductance could benefit your controller. And at lighter loads (than rated), it will draw more current and run faster. Beware of overspeed at no load, as with all series motors. Chain guard? RPM sensor and cutout circuit?

Regards,

major


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## Qmavam (Aug 17, 2008)

major said:


> HAPT2000 has been around for 40 years. Maybe they have better now.


 Maybe I don't know what I'm talking about! The guy at the motor shop told me they use a higher temp. wire in motors driven by VFDs.
Is that the HAPT200? 



> The coils. Notice how the series coil hangs out past the pilot on the end of the frame and the shunt coil doesn't. The series coil has a greater D²N, or total mass of copper than does the shunt coil.


This motor shows signs that it has been rewound. I would venture a guess that the coils are basically the same, just that it was harder to push the thicker wire into the tighter shape.

I removed the coils, got them out whole, which in my limited, long time ago experience, says the motor didn't get much of a varnish/polyester job.
I unwound the field coil and found it had 17 turns. Each turn has 8 parallel wires of #16 wire.
The two series field coils were in parallel with each other.
The shunt coils were in series.
Most of the heat damage seems to be at the connections where, the ends of the two coils connected to the high current cable. The coils have been hot, but only near where the connections were tied to the coils. If I had it to do over, I would have tried to disassemble just the connections
clean them up and install new cable. But now, as you say it is a science experiment.
Here's a picture of the stator with out wires.
http://i395.photobucket.com/albums/pp37/Qmavam/statornowires.jpg



Thanks, MikeK


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## major (Apr 4, 2008)

Qmavam said:


> Maybe I don't know what I'm talking about! The guy at the motor shop told me they use a higher temp. wire in motors driven by VFDs.
> Is that the HAPT200?


Computer problems here.

This is what I was talking about.



> Modified polyester is a two film insulation consisting of a base coatof polester-polyimide polymer and an overcoat of polyamide-imide resins. It offers excellent electrical properties, moisture and solvent resistance, superior dielectric strength, good film flexibility and abrasion resistance. Size range: 10-44 gauge.


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## Qmavam (Aug 17, 2008)

major said:


> But for a science project, WTH
> 
> O.K. So here's my suggestion. Not my usual analytical method, but SWAG. From the picture, the series coils are larger than the shunt coils. So it will be difficult to fit four of the same size series coils in the space between the poles. And you should have some space between the coil sides for ventilation. So reduce the number of turns on the original series coil using the same wire size and parallel strands. Say that is #16, 3 in parallel and originally 20 turns per coil. Wind the new series coil with 17 turns of 3 of #16. Make four of them.
> 
> ...


Hi major,
My background is electronics and I have some questions that may have no relevence, but I'm curious. In the above post you suggest I drop the turns count from 20 to 17 when I go from 2 poles to 4 poles. 

I'm thinking your shooting for approx, the same amount of inductance in the two original poles as in the four new poles. Is that correct? 
I'm thinking about putting original (happens to be 17) turns back on the stator and wire as original then measure the inductance, then put turns on the four poles and wire as you suggested and adjust turns to get approx. the same inductance?

Is this proper thinking?
Thanks, MikeK


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## major (Apr 4, 2008)

Qmavam said:


> Hi major,
> My background is electronics and I have some questions that may have no relevence, but I'm curious. In the above post you suggest I drop the turns count from 20 to 17 when I go from 2 poles to 4 poles.
> 
> I'm thinking your shooting for approx, the same amount of inductance in the two original poles as in the four new poles. Is that correct?
> ...


Hi MikeK,

No, it has little to do with inductance. It has a lot to do with excitation, or mmf, or ampere turns.

The motor is a 4 pole motor. It will always be a 4 pole motor. That is the way the armature is wound. And you surely don't want to get into armature winding. So it is a 4 pole motor. It has 4 steel pole pieces in the stator. The coils are different. You can have 2 coils (on opposite poles) with a 4 pole motor. The poles without coils become what are called consequent poles. You still end up with the N, S, N, S 4 pole configuration even though you just have the excitation on 2 poles.

My suggestion to reduce the number of turns was simply to enable you to physically fit the 4 new series coils into the allotted space inside the stator (frame).

The series motor has the armature current flowing thru the field coil circuit. So the objective here was to get the ampere turns (AT) near the original quantity. I was making the assumption that the shunt field was contributing approximately equal AT at rated load as was the series field. Then replacing the shunt coils with series coils would mean using 4 series coils of equal windings (AT).

The inductance was just a consequence of increasing the series turns in the field. And this would likely make your PWM controller happier 

Regards,

major


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## Qmavam (Aug 17, 2008)

major said:


> Hi MikeK,
> 
> No, it has little to do with inductance. It has a lot to do with excitation, or mmf, or ampere turns.
> 
> The motor is a 4 pole motor. It will always be a 4 pole motor. That is the way the armature is wound. And you surely don't want to get into armature winding. So it is a 4 pole motor. It has 4 steel pole pieces in the stator. The coils are different. You can have 2 coils (on opposite poles) with a 4 pole motor. The poles without coils become what are called consequent poles. You still end up with the N, S, N, S 4 pole configuration even though you just have the excitation on 2 poles.


Hmm... so what do I gain by putting turns on all four poles (as series fields)? Re: low end torque and upper end rpm.


> My suggestion to reduce the number of turns was simply to enable you to physically fit the 4 new series coils into the allotted space inside the stator (frame).


Ok, I don't think that physical area is a problem, the series coils seemed
not to fill the slot completely.



> The series motor has the armature current flowing thru the field coil circuit. So the objective here was to get the ampere turns (AT) near the original quantity. I was making the assumption that the shunt field was contributing approximately equal AT at rated load as was the series field. Then replacing the shunt coils with series coils would mean using 4 series coils of equal windings (AT).


Ok, is my thinking correct on this point, if I increase the turns on my poles, do I increase torque at the cost of higher cemf causing lower rpm?

Thanks for your help educating me, MikeK


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## major (Apr 4, 2008)

Qmavam said:


> Hmm... so what do I gain by putting turns on all four poles (as series fields)?


That's why I suggested earlier to just remove the shunt coils and run with only the two series coils. You had mentioned that it ran satisfactory without the shunt field energized before.

But to answer your question, it relates to the mmf and the losses in the field winding. Optimum is to have the space for the field copper filled with windings, allowing some space for ventilation. This typically is best accomplished with 4 coils one each on all 4 poles.



> Re: low end torque and upper end rpm.


To some degree. Field design only goes so far. Too little field and armature reaction causes problems. Too much field and it saturates and/or causes too much heat. The field needs to be in a somewhat narrow range for the particular armature design.



> Ok, is my thinking correct on this point, if I increase the turns on my poles, do I increase torque at the cost of higher cemf causing lower rpm?


You should say ampere turns. It depends on how the coils are connected as to how much mmf they produce. But generally speaking, on series motors, increasing the turns, increases the mmf (AT) and therefore the flux, up to the point of saturation. So below saturation, the increased flux for a given value of load current will increase torque and increase generated voltage (which will reduce RPM).

major


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## Qmavam (Aug 17, 2008)

major said:


> Optimum is to have the space for the field copper filled with windings, allowing some space for ventilation. This typically is best accomplished with 4 coils one each on all 4 poles.
> 
> To some degree. Field design only goes so far. Too little field and armature reaction causes problems. Too much field and it saturates and/or causes too much heat. The field needs to be in a somewhat narrow range for the particular armature design.
> 
> ...


 Let's see if I can wrap this up before I out question my welcome
 The plan at this point is to install 4 series field coils.
Regarding amp turns;
I have two 17 turn coils in parallel, that means the current through each is
1/2, so 1/2 amp x 17 turns = 8.5 amp-turns. Since I have two coils they
add and I get 17 amp-turns. Now assuming the shunts were wound to have 
the same amp-turns as the series fields, that would double the 
17 amp-turns to 34 amp-turns.
If that is so, I can make my 4 coils that match the original two
series coils and wire two in parallel, in series with the other two, in parallel.
This would give me the same amp-turns as the original compound motor.
I'm trying to learn here, so did I get this right?

Now, one complicating factor the load current is rated as 62 amps, 
when I put the pedal to the floor the current peaks over 250 amps, and that is
in the series fields only. My shunt field amp-turns doesn't change. 
So I think my torque will be higher at pedal to the floor, low RPMs. 
But what does it mean as far as max RPM?

Now if I'm right about the higher torque at pedal to the floor, low RPMs, 
I don't need any more torque at low rpms, 
I would like a little more top 
RPM, so I'm considering reducing turns on each series field coil.
Would you reduce the turns count based on the facts that I don't need more torque and want higher rpm?

You mentioned saturation, I seem to recall on inductors they go into saturation 
faster with less turns, although that may be an ac/dc thing.
As you would suspect I have no clue about where I will be putting the
poles on the saturation curve. 
Hmm.. do motors run intermmitently in the saturated mode on purpose?

There's my thought process, please tell me if/where I went wrong.

If you
Thanks, MikeK


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## major (Apr 4, 2008)

Qmavam said:


> The plan at this point is to install 4 series field coils.
> Regarding amp turns;
> I have two 17 turn coils in parallel, that means the current through each is
> 1/2, so 1/2 amp x 17 turns = 8.5 amp-turns.


Actually it will be effectively 8.5 * Ia ampere turns. Where Ia = armature current.



> Since I have two coils they add and I get 17 amp-turns.


Well yeah, kinda. It is almost universally stated in effective AT/p (ampere turns per pole averaged for the number of poles the machine is designed for). So if you have 2 coils of 17 turns each (T/c) and half the Ia thru each coil, then you have effectively 4.25 * Ia AT/p (for the 4 pole motor).



> Now assuming the shunts were wound to have
> the same amp-turns as the series fields, that would double the
> 17 amp-turns to 34 amp-turns.
> If that is so, I can make my 4 coils that match the original two
> ...


I think you get the basic idea.



> Now, one complicating factor the load current is rated as 62 amps, when I put the pedal to the floor the current peaks over 250 amps, and that is in the series fields only. My shunt field amp-turns doesn't change. So I think my torque will be higher at pedal to the floor, low RPMs.
> But what does it mean as far as max RPM?


Yes, when you replace the shunt coils with series coils as we have outlined, you will get more AT/p at the higher armature currents than you would have with old compound version. This will likely give you more torque for a said armature current, but not in direct proportion due to saturation. And there is another way to look at it. For a given load, meaning torque opposing rotation of the motor shaft, beyond the 62A rated torque, you will draw less current and therefore present a higher voltage to the armature which will tend to increase RPM. So it is not necessarily a situation where you will notice lower speed. In fact, it will likely increase your acceleration which will give you the feeling of higher speed.

If you are using this motor 100% of the time above that 62A rated load, then your max RPM may well decrease. In this case, I think you are better off with that situation as far as motor loading and if you need to get back the vehicle speed, just change the drive ratio.



> Now if I'm right about the higher torque at pedal to the floor, low RPMs, I don't need any more torque at low rpms,
> I would like a little more top RPM, so I'm considering reducing turns on each series field coil.
> Would you reduce the turns count based on the facts that I don't need more torque and want higher rpm?


Yeah, I think you can get by with a few less turns on each coil. That is why I suggested it before. It will not make a big overall difference in performance but make it easier to install the coils and give you space for ventilation. I suggest going from 17 T/c to 14 or 15. It is perfectly o.k. to use half turns if that makes it easier to connect the coils. Half turns count in the AT/p. And it is o.k. to have two 14.5 T/c coils and two 15 T/c coils, in series parallel (S/P) giving you effectively 7.375 * Ia AT/p. And when wiring the coils, it does not matter which coils go where in the S/P circuit, as long as each coil gets Ia/2 and has the polarity correct, N, S, N, S.




> Hmm.. do motors run intermmitently in the saturated mode on purpose?


Well, I guess it would be nice if steel never saturated. But it does, and motors, especially series motors, do often run into saturation. I guess "on purpose". I never thought of it that way. But opposed to building the motor with 3 or 4 times the amount of steel, yeah, I guess, on purpose.

Good luck with my little mmf lesson. Let us know how the science project turns out.

major


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## Qmavam (Aug 17, 2008)

major said:


> Actually it will be effectively 8.5 * Ia ampere turns. Where Ia = armature current.


Ya, understood as they are in series.



> Well yeah, kinda. It is almost universally stated in effective AT/p (ampere turns per pole averaged for the number of poles the machine is designed for). So if you have 2 coils of 17 turns each (T/c) and half the Ia thru each coil, then you have effectively 4.25 * Ia AT/p (for the 4 pole motor).


Ok the convention in motor speak is AT/p, amp-turns/poles.


> If you are using this motor 100% of the time above that 62A rated load, then your max RPM may well decrease. In this case, I think you are better off with that situation as far as motor loading and if you need to get back the vehicle speed, just change the drive ratio.


The current draw a full speed max RPM was down around 40 amps, so the motor was loafing once it got up to speed.



> Yeah, I think you can get by with a few less turns on each coil. That is why I suggested it before. It will not make a big overall difference in performance but make it easier to install the coils and give you space for ventilation. I suggest going from 17 T/c to 14 or 15. It is perfectly o.k. to use half turns if that makes it easier to connect the coils. Half turns count in the AT/p. And it is o.k. to have two 14.5 T/c coils and two 15 T/c coils, in series parallel (S/P) giving you effectively 7.375 * Ia AT/p. And when wiring the coils, it does not matter which coils go where in the S/P circuit, as long as each coil gets Ia/2 and has the polarity correct, N, S, N, S.


 Ok, on all that, except for the 1/2 turn, I want to make sure you have
done this and not had problems. Years ago while building inductors for a product we tried a 4-1/2 turn inductor and the 1/2 turn got HOT! Four turn were ok and five were ok, but not 4-1/2 turns. My physicist friend didn't understand it and sent the issue to an EE that he knew. This EE built similar inductors and proved the 1/2 turn heating, but never could explain the phenomena.
So can you confirm your use of 1/2 turns without trouble?

[quote/
Good luck with my little mmf lesson. Let us know how the science project turns out.
major[/quote]
Yes, thanks for the info.
I will, don't hold your breath though, since I have a working motor and 3 other projects plus work, it all slows me a bit.


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## major (Apr 4, 2008)

Qmavam said:


> So can you confirm your use of 1/2 turns without trouble?


Confirmed a hundred times or more. Thousands if you count all the individual motors using half turns on field coils. 

major


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## Qmavam (Aug 17, 2008)

major said:


> Confirmed a hundred times or more. Thousands if you count all the individual motors using half turns on field coils.
> 
> major


Yaa, yaa, I think that will make for a simpler wind, more room to lay 
connections.
Thanks, MiekK


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## major (Apr 4, 2008)

Qmavam said:


> So can you confirm your use of 1/2 turns without trouble?


Here's a photo of a series motor using half turns on the coils.









Photo from Jim Husted's web site. (thanks Jim)


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## Qmavam (Aug 17, 2008)

major said:


> Here's a photo of a series motor using half turns on the coils.


 Wow, that's pretty, and lots of room for air flow.
MikeK


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