# Advantages/Disadvantages to Bar Wound Stators



## major (Apr 4, 2008)

wilcorp70 said:


> Does anyone know the disadvantages of using solid bars over wire coils in a motor?


Hi wil,

It is difficult to get multiple turns per coil with bar wound armatures.

Regards,

major


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## wilcorp70 (Jul 9, 2008)

I read a few motor design books, but it seemed like they glossed over why having more turns was important. From what I read, more turns leads to higher flux which means greater power density for the motor. Larger wire means fewer turns but the ability to take more current increases the flux but possibly not as much as with smaller wire because of the decreased copper fill percentage. It was a couple of years ago I read these, so I could easily be remembering them wrong. But if flux is the key reason to have multiple turns it seems like the increased copper fill and decreased resistance of a solid bar could adequately compensate. Is there another reason why having multiple turns is important?


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## major (Apr 4, 2008)

wilcorp70 said:


> I read a few motor design books, but it seemed like they glossed over why having more turns was important. From what I read, more turns leads to higher flux which means greater power density for the motor. Larger wire means fewer turns but the ability to take more current increases the flux but possibly not as much as with smaller wire because of the decreased copper fill percentage. It was a couple of years ago I read these, so I could easily be remembering them wrong. But if flux is the key reason to have multiple turns it seems like the increased copper fill and decreased resistance of a solid bar could adequately compensate. Is there another reason why having multiple turns is important?


Hi wil,

I doubt those motor design books glossed over the armature turns. The number of series connected turns in the armature is directly related to the generated voltage versus rotational velocity. Yeah, you have flux in there, but that can only go so far due to saturation for a given size machine.

You'll notice that machines in the size applicable to EVs having bar wound armatures, especially like that Ecycle which has only a half turn per slot, are low voltage for reasonable RPM range, relatively speaking.

Bar wound armatures are great, whether be it the rotor or the stator. I like 'em  And there are ways to get 2 turns per coil with rectangular ribbon. And I have seen at least one example of 3 or more turns. But the multiple turn construction takes a higher level of process engineering (read expensive equipment and tooling for manufacture). Single turn bar wound machines are fairly simple using preformed hairpins, either top or end inserted into the slots. Been done for decades on automotive style cranking motors and then expanded into larger sizes for forklifts. Your really large machines are often bar wound, ones like in the multi magawatt range.

Recently Remy has developed two turn bar wound stators for PMSM. Take a look at those. Very impressive. But those designs take a multimillion dollar outlay to design and manufacture. Using higher pole count, large diameter air gaps and lots of slots and coils, the Remy motors do function at what we consider high voltage (300 or even 600). But the typical 230VAC 25hp 1800RPM induction motor might have 20 to 30 turns per coil. I don't think you'll see bar wound construction there anytime soon.

Regards,

major


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## steven4601 (Nov 11, 2010)

What about AC resistance (skin-effect)? 

Using multiple finer strands seems preferable to an AC motor.


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## wilcorp70 (Jul 9, 2008)

Thanks for the reply Major, that makes sense now. I figured it might be most applicable to lower voltage motors from looking at the motors that used it (low voltage high current), but wasn't certain. That being said, the motor GM tested had 24 turns (just like the traditionally wound one) according to their SAE power point presentation and they said their new plant (announced last January) would be producing bar wound motors. So maybe we'll start seeing these types of motors in the not-so-distant future. Thanks again.


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## major (Apr 4, 2008)

steven4601 said:


> What about AC resistance (skin-effect)?
> 
> Using multiple finer strands seems preferable to an AC motor.


Hi stev,

Might be a concern. It would be similar to the frequency seen in the bar wound DC armatures at speed, maybe higher due to increased pole count. But the rectangular conductors aren't that large, so I don't know how many skin depths you can go  Been a while since I had to do such a calc. I guess it is not too big of a concern, maybe outweighed by the increased copper cross section (reduced DC resistance) and improved thermal properties of the end turns (better cooling).

Regards,

major


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