# armature and field winding votages (big starter-winch v cart motor)



## major (Apr 4, 2008)

tom_001 said:


> My question is (forgetting about insulation) what makes the voltage ratings on say a large 12v starer differ from a 48-72v cart or other series wound motor.


Hi Tom,

The voltage is proportional to the flux and to the armature equivalent turns. Flux is primarily determined by size. The motors you refer to likely have one-turn coils in the armature, so the number of turns is proportional to the # of comm segments and also inversely to the # of parallel circuits in the armature winding pattern.

Starters (technically called cranking motors) have smaller armature cores therefore less flux and low voltage, probably are lap wound meaning 4 circuits and have fewer comm bars for low voltage/high current.



> I find it hard to tell the armatures apart, both also are 4 pole, however the field winding do change, if you increase the number of windings on the field alone is the volt/rpm decreased with no change to the armature?


Field turns (or turns per coil, T/c) need be within reasonable proportion to the armature turns for reasonable motor performance. Increasing the field T/c increases the flux for a given armature current up to the region of saturation, so does increase the generated voltage in the armature.

Regards,

major


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## tom_001 (Mar 19, 2011)

Thanks you have helped me understand more,
I think some are lap wound and most close pattern wave suppose not much difference? 



> The voltage is proportional to the flux and to the armature equivalent turns. Flux is primarily determined by size. The motors you refer to likely have one-turn coils in the armature, so the number of turns is proportional to the # of comm segments and also inversely to the # of parallel circuits in the armature winding pattern.


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 windings to cart motors to decrease speed and increase power, 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.


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## major (Apr 4, 2008)

tom_001 said:


> ....I think some are lap wound and most close pattern wave suppose not much difference?.............This is what I'm finding it hard to understand, as starters get larger you have more comm segments and therefor more parallel circuits,


Armature coils are connected to the comm bars and are in series with each other in a circuit which closes on itself. The brushes come into play and make for parallel paths in the closed armature coil circuit. On 4 pole motors, a lap wound armature always has 4 parallel circuits and a wave wound armature always has 2 parallel circuits.

major

edit: True only for simplex armature windings  And we don't need to get into all that because I doubt anyone will ever see a duplex armature.


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## tom_001 (Mar 19, 2011)

oh yes now I understand, 
A wave wound dc motor is say a washing machine or mains drill (I know they not even meant to be a universal motor's these days but they have the same windings and some old ones really were for dc and ac) 

and a lap is your more normal dc motor winch, golf cart ect.

Now I actually understand how a lap series motor works (even watched a GIF to help me lol) 4-10kw low voltage dc motors are like rocking horse **** and if any appear they have a well funded home very fast in the south of the UK, thats why I'm trying to mod these truck-tractor starters (about 4-7kw) as they are only worth the copper in them. 

Field windings are easy on a starter as they are meant to be replaced (adding 1/3 to the field windings), the problem is limitation on voltage in the armature, the number of segments for the coils are fixed, but what about having say 3 coils of slightly thinner wire where there was only 1 thick loop on each segment? 

Thanks Tom.


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## tom_001 (Mar 19, 2011)

Hello again, looking at finding a motor on a budget thread I see you talking about bar voltage and multiple coils on each bar, sorry but the more I find out the more I'd like to know.

why is a higher voltage bar a bad thing? how about a bar with mutipul winds, or was that just relevent to the number of bars and the stated votage of that motor?

why do most dc motors use single coil bars with many of them and not less bars and more winds on each? is the efficacy greatly improved, is it to do with back emf, the comm and brushes or heat?

thanks again for any help
Tom.


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## major (Apr 4, 2008)

tom_001 said:


> Hello again, looking at finding a motor on a budget thread I see you talking about bar voltage and multiple coils on each bar, sorry but the more I find out the more I'd like to know.
> 
> why is a higher voltage bar a bad thing? how about a bar with mutipul winds, or was that just relevent to the number of bars and the stated votage of that motor?
> 
> ...


Too high a voltage between commutator segments can cause arcing.

Sure, armature coils often have multiple turns per coil. The relatively low voltage cranking and forklift motors typically have single turn armature coils. It all relates to the RPM and voltage.

I can't teach you motor design here. It is hard enough in a class room  There are some good basic resources on the web, or in the library. Do some reading up on the subject.

Regards,

major


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## tom_001 (Mar 19, 2011)

Ok, fair play you have spent time on me as it is, the web can be a harsh place, most infomation is verry basic then the rest is for people that alredy know, gaps in infomation and some times people just make it up lol! I'll do it the old fashened way, and try to find some books, so you teach? do you know any books that are a good starting point?

Thanks agane, Tom.


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## major (Apr 4, 2008)

tom_001 said:


> do you know any books that are a good starting point?


Hi tom,

Book recommendations are difficult without knowing your "level". Here is an informative article http://www.reliance.com/mtr/mtrthrmn.htm And below is a resource for motor windings in particular. I have obtained such books for very reasonable cost off eBay.

Regards,

major


View Larger Image

*9780030790904 *

*Electric Motor Repair: A Practical Book on the Winding, Repair, and Troubleshooting of A-C and D-C Motors and Controllers*

*Robert Rosenberg *


ISBN 10: *0030790905 / 0-03-079090-5 *
ISBN 13: *9780030790904*
Publisher: *Holt, Rinehart and Winston*
Publication Date: *1970*
Binding: *Spiral-bound*


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## tom_001 (Mar 19, 2011)

ledgend, thanks.


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