Aluminium power inductors

[dr pepper]

Being interested in smps's I found this interesting.
I just pulled out an industrial power factor correction system, as I'm replacing it the caps have failed.
After dragging the old stuff out I had a look at the chokes, thinking they'd be copper wound, and maybe salvage a length of copper tape for fuure projects.
But these are air cored aluminium, I've never seen ally ones before, these are 550uH, 250 amps at 660 volts, the system has 27 of them in stacks of 3.
Some naff pics:

 

[dknguyen]

Are those non-conductive spacers between the coils? For cooling airflow? They have a fan or something?

 

[dr pepper]

Yes they look like cooling fins.
No fan, just slots in the base of the housing & a gap in the lid.
This gizmo is sposed to reduce the leccy bill, so I wouldnt have thought chucking out heat would be acceptable.

 

[unclejed613]

i would have thought Al is an awful material to make an inductor with. with an AC magnetic field, there can be enough motion in the inductor to eventually cause failure by metal fatigue. maybe with those spacers there's not as much motion...

 

[BobW]

Al is commonly used for large inductors because of the cost savings over copper. Under normal operation there wouldn't be enough force to cause any significant movement. Under fault conditions where there could be current transients in the thousands of amps, then the forces between adjacent conductors can be extremely high, and some form of physical bracing is required to prevent physical deformation.

 

[dr pepper]

There was some force involved as the thing used to hum, but you get that with pfc machines anyway.
And I wouldnt have said the machine was particularly cheap.