# just curious, split field series wound



## dcb (Dec 5, 2009)

More motor newbiness, So I have a motor for my scooter that I got for cheap:
BOSCH 0 136 501 003 24V 1800W 2000 RPM MOTOR

It is a split phase series wound. About 6" dia, 3 terminals, 4 brushes, 4 coils (only 2 in use at a time). The brushes alternate polarity every 90 degrees. The coils seem to be wound so the same pole faces the rotor, instead of one being north and one south. Brushes align with field bolts. 49 commutator bars and slots.

I'm sure it will be plenty at 45v on a scooter, though advancing the brushes will be a bit of a pita if needed. Easy regen is nice too (though counter to brush advancement).

But I am curious if anyone has experimented with a split field, i.e. to bring the other fields into play for better forward performance or somesuch.

It seems like two basic possibilities, correct the polarity(if that even interacts well with the rotor) and put the fields all in series, or put them in parallel. If I'm limited by the brush current, it seems I would want them in series right? Otherwise I have the same field strength as each field gets 1/2 as much current.

And when I need field weakening, I just bypass one set of coils? This is where I'm confused, how does doubling the magnetic field strength affect the series motors performance? More startup torque and less torque at speed, or something like that?

Is there a way I can put current to the commutator and figure out if energizing the additional poles will change the operating parameters? (it is at the machine shop currently getting fitted for a 5/8 sprocket).

Just curious, thanks.


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## major (Apr 4, 2008)

dcb said:


> More motor newbiness, So I have a motor for my scooter that I got for cheap:
> BOSCH 0 136 501 003 24V 1800W 2000 RPM MOTOR
> 
> It is a split phase series wound. About 6" dia, 3 terminals, 4 brushes, 4 coils (only 2 in use at a time). The brushes alternate polarity every 90 degrees. The coils seem to be wound so the same pole faces the rotor, instead of one being north and one south. Brushes align with field bolts. 49 commutator bars and slots.
> ...


Probably don't need advance at 45V. If you do, just go about 5º. And forgetabout regen with a series motor.



dcb said:


> But I am curious if anyone has experimented with a split field, i.e. to bring the other fields into play for better forward performance or somesuch.


Yep, I know split series motors. They are nice in applications like forklift where you go F & R like 50/50 regularly. It requires less reversing contactors/contacts and the field coils see a 50% duty cycle apiece so heating isn't typically a problem. There is a slightly higher voltage drop in the series field but it isn't that much of a concern.

You're correct that all 4 coils would be wound in the same direction. However only 2 coils opposite each other (180º mech) are energized so the other 2 poles are consequent poles and assume the opposite polarity (N/S). Then when the the opposite direction of rotation is desired, the other other 2 coils are energized and the total N-S-N-S becomes S-N-S-N sequence.



dcb said:


> It seems like two basic possibilities, correct the polarity(if that even interacts well with the rotor) and put the fields all in series, or put them in parallel. If I'm limited by the brush current, it seems I would want them in series right? Otherwise I have the same field strength as each field gets 1/2 as much current.


It is probably more trouble than it's worth (unless you find you have field overheating) because the voltage drop in the field is so low to begin with. But should you alter it to use all 4 coils, put them in series/parallel, not all in series. That will give you equal performance to what you have now with a slight added boost from less field voltage drop.

Say you have 10 turns per coil. With 2 coils only energized at 100A, you have 500 AT/pole effectively. With 4 coils in series/parallel, you half the current thru each coil and then the same 500 AT/pole.

If you wire all 4 in series, then at 100A you'd have 1000 AT/pole. That would significantly alter the performance characteristics and probably not for the better, especially as to the field heating. I can't imagine you being better off doing that.



dcb said:


> And when I need field weakening, I just bypass one set of coil?


No, because you should use S/P and then bypassing one set won't make any difference, essentially. It is rare, IMO, that field weakening series motors is worth the trouble given modern PWM controllers. Just design your system to give top speed at full field and use the controller for reduced speed.



dcb said:


> This is where I'm confused, how does doubling the magnetic field strength affect the series motors performance? More startup torque and less torque at speed, or something like that?


Remember you're talking about field strength and not necessarily flux. Start up torque is typically well into saturation, so those extra Ampere-turns are buying you precious little if any more flux. At speed, as you call it, it will simply alter the V and I ratio needed at the motor terminals to yield the same torque and RPM. Assuming the motor was properly designed by the Bosch engineers (a good bet), you would likely make the motor less efficient and increase the field heating.



dcb said:


> Is there a way I can put current to the commutator and figure out if energizing the additional poles will change the operating parameters?


I suppose, if you had a dynamometer to load the motor. I mean you can play with the field strength with an unloaded motor and get drastic speed change. But that fades quickly as the motor is loaded.


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## dcb (Dec 5, 2009)

cool, well less heat (more efficiency) is definitely something, so 2S2P it is. Might make up for lack of regen somewhat. Thanks for all the tips.

Edit: answered own question :/


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## dcb (Dec 5, 2009)

Mostly for my own notes, but let me know if something looks wrong pls. Is there any reason to stack the fields on one side of the rotor (on the ground side or the pwm side or?)


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## major (Apr 4, 2008)

Looks o.k. to me.


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## dcb (Dec 5, 2009)

Sweet, then I can just unbolt the fields where they join at the one internal brush terminal and jump one field lead (the trick is the right one) to the other brush terminal and leave everything else alone, (except for hooking up power to the outer terminals instead of the middle and an outer). 

Gracias! Wish the machine shop would hurry up with my rotor now 

oops, nope, sounds like that would make it series, my bad. But at least the polarity was right 

Gonna need two jumpers.

This looks more doable/ with existing fixtures:


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