# Armature adventure



## major (Apr 4, 2008)

jackbauer said:


> Just pulled the armature out of my latest motor. Its an 80V 15kw pump motor from a Still lift truck. I've never seen an armature wound this way and was just wondering why its done in this manner and what are the advantages / disadvantages. Motor is compound wound. Two series and two shunt field poles.


Hi jackb,

It is not uncommon to wind armatures like this. Can't really count from here, but say like 21 slots in the core (lamination stack) and 63 comm bars. So the armature coil form consists of 3 formed coils and inserted as a group, ending with 6 coil sides per slot. The coil form is a bit more complex than single coils. The laminations are a bit easier to punch. You have only a single slot liner (Nomex) per 3 coils and therefore maybe a higher fill factor. Commutation may be uneven resulting in patterns on the comm repeating every 3 bars. 

Maybe this type of winding is seen more in older and larger motors. It doesn't lend itself readily to automation. Nothing wrong with it for the intended application. If you intend to run in excess of nameplate voltage, it may not be as good as the 1 for 1 slot/bar combo.

Regards,

major


----------



## DJBecker (Nov 3, 2010)

Are you talking about the cant / helix to the windings?

That's to reduce the force pulsing and thus one source of vibration.


----------



## major (Apr 4, 2008)

DJBecker said:


> Are you talking about the cant / helix to the windings?
> 
> That's to reduce the force pulsing and thus one source of vibration.


Usually called a skew. And done primarily to reduce low speed cogging. It does subtract from performance.


----------



## DJBecker (Nov 3, 2010)

major said:


> Usually called a skew. And done primarily to reduce low speed cogging. It does subtract from performance.


I've seen it on lightweight wind generators, where the problem is at high speed. The cogging can trigger resonances in the blades.

No doubt it also helps start-up at low wind speeds, but barely any power is extractable so that's not the reason.


----------



## jackbauer (Jan 12, 2008)

Thanks Major.


----------



## major (Apr 4, 2008)

gottdi said:


> I had a series motor from GE that used two bars in the armature and double the com bars from my other GE that only used single bars in the armature. I figured it was to help prevent arcing or to give better contact overall while running. Sort of like the helwig split brushes. Just better contact overall. But mine was a series and not compound. The motor ran smoothly and quietly too. Much quieter than my current GE motor.
> 
> 
> It is possible that the angle is for better low speed torque and to prevent low speed cogging. My GE did not have the angled layout on the armature but did have double the bars on the com and used twin bars over singe. See below.





> I figured it was to help prevent arcing or to give better contact overall while running. Sort of like the helwig split brushes. Just better contact overall.


No, it is done to double the torque constant, that is to double the effective armature turns, without making a closed loop multi-turn coil, which would be difficult to insert into the core slot.



> ...but did have double the bars on the com and used twin bars over singe.


Actually 2N -1. So if it has 33 core slots, it would have 65 comm bars. Wave wound armatures need an odd number of comm segments. Therefore your armature has a dummy coil which is left unconnected and just along for the ride and to keep it mechanically balanced.

In motor manufacture the armature lamination tooling is a big ticket item. This method allows them to use a common lamination for several winding configurations. Like a 25 slot core with a 25 bar comm, or 49, or 75.

But like I said before, when they get into higher volume or automated manufacture, the single coil per slot wins outs. I think the single coil has a slight performance advantage and better commutation.

Probably more than you wanted to know 

major


----------



## Kptn_Chaos (Apr 4, 2011)

Hi JackB,

I can get the same motor for my conversion, but am not sure, if it fits my needs.

So I have a few questions.
- Can you tell me the size of the motor and weight
- you wrote that it is a compound wound shunt motor. Can I use it with my Curtis 1231C Controller (for series shunt)
- it has a duty cycle of 15%. Is this sufficient for a car?
- I need 3000rpm and have 96V. Any chance the motor will reach it?

In Germany it more than difficult to find a motor out of a forklift, that will work in my conversion.

By the way, I´m converting a VW Polo with lead acid and the original gearbox.

A Advanced, Kostov or similar would work. But the cost to get it over and the tax are busting my limits. 

Have a nice day,

Martin


----------



## major (Apr 4, 2008)

jackbauer said:


> Thanks Major.


You're welcome. I just happened to notice that your armature does not have banding. Opposed to the GE armature pictured from gottdi. Yours does have top sticks (sometimes called wedges) in the slots. But even still, most times there will be a band around the knuckle end of the coils. Perhaps it isn't needed in the OE application due to contained RPM from the shunt field, but when using it at higher RPM as with higher voltage or field weakening, beware


----------



## jackbauer (Jan 12, 2008)

Major , I noticed that on reassembly. Could I add banding? What material should i use? 

Kptn_Chaos , the motor is about 250mm diameter and weight approx 50kg. I think it would run fine at 96v with some brush advance which is easy on this motor as the brush holder is slotted. It could run on a curtis controller if you have a seperate supply for the shunt windings. The duty cycle shouldn't be an issue with sufficient forced air cooling. That's my plan anyway.


----------



## Woodsmith (Jun 5, 2008)

Hmmm, I guess the armature from my 11" is similar.


----------



## major (Apr 4, 2008)

jackbauer said:


> Major , I noticed that on reassembly. Could I add banding? What material should i use?


A glass fiber tape impregnated with a high temp insulating polyester resin or varnish. I'd see if there is a motor rebuilder in the neighborhood whose brain you could pick. Maybe check McMaster Carr. Carbon fiber would be cool but you'd have to insulate under it. But notice gottdi's GE armature has steel banding with insulation under. That really holds well, but the steel screws with the magnetics a bit. And then you should balance the armature, which I guess would be proper if you intend to run faster anyway.


----------

