DC Series Motor, armature designs

[tom0001]

Hello, I hope some one can explane this to me as I'd likr to learn,

The question is, take a large 12v starter motor and the armature is singel thick gauge, take a say 48v golf cart motor it's armature is also singel thick gauge, infact I find it hard to tell them apart, also both are four pole and have 4 brushes.

Is the diffrence in the field winding? Can just the field windings be changed to increase votage and reduce current draw. I think simple rule is more turns thiner wire lower rpm/volt and less current draw, but is this only done on the field winding? how is the current shared between them and both have equal field strengths?

Sorry for the silly question but i'm a bit lost and thanks for any help.
Regards Tom.

 

[tom0001]

apologies for the atrocious spelling makes for even harded reading!

 

[waross]

Did you check the insulatioon characteristics on both armatures, how about the length, the depth of the rotor slots, the width of the slots, the spacing?
The fields are probably different.
A starter is connected straight across a 12 Volt battery. A golf cart motor is generally controlled by some type of controller.
There are probably a lot more differences than "singel thick gauge,"

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[tom0001]

Good point a starter draws as much curent as the bat can supply, and a say golf cart has 200A ish cuttent limiter.
Do you know what the relation ship between the armature and the field windings are? I was under the inpresion that they are blanced or had the same resistence and cuttent draw, If they dont, when connected in searies what is the effect, is it balanced between them even though thay differ?

Thanks agane.

 

[waross]

When the fields are in series the current must be equal. Not just a good idea, it's the law. grin (Kirkoff's). When a starter is energized, most of the applied voltage is dropped across the field. As soon as the starter starts to turn, back EMF across the armature starts to build. As the speed and the back EMF increase, the current and the torque drop. Also, as the back EMF increases, the voltage across the field drops. When the torque out equals the torque demanded by the load, there is no further change in speed unless the applied voltage or the torque demands change. (neglecting thermal effects)
Some golf cart motors have a compound field. (separate series and shunt windings) which, combined with a control scheme that may be treating the field and armature differently, makes comparisons with starter motors less than dependable.
But I haven't seen a lot of golf cart motors. Stand by for posts on the construction of golf cart motors.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[tom0001]

Thanks you have helped me understand more,

This is what I'm finding it hard to understand, as starters get larger you have more comm segments and therefor more parallel circuits, this is to handle more current not voltage, but will increase flux and voltage handling surely, if so why don't these large starters have a reduced speed when on 12v perhaps made up in the field windings?

May be I just answered my own question, as starters get larger and have bigger cores and more parallel armature circuits perhaps the field windings have to be reduced to keep the speed and current handling high?

I have found many people that add/remove windings to cart motor fields, not sure how high I can take the votage in a big starter armature, Building is easy testing will be harder.

Thanks again sorry if it makes for hard reading.

Regards Tom.