Electrolytics have flat sides?

[eeka chu]

I've just finished stripping my CNC lathe for it's retrofit and was giving the power supply a clean.

I noticed the massive 100V 10,000uF smoothing capacitors looked as though they've been hit on the side as some point. I remembered seeing this in a few pictures of big electrolytics.

Once I had the capacitors free of their clamps and was cleaning them off, I realised that the sides have purposely been flattend to form three flat surfaces on the capacitor.

Why might this be?

The only things I can think of are to make their production simpler in some way or to stop them rolling around if mounted horiztonally.

If it was done after the capacitor was rolled, it'd almost certainly damage the layers. Which means the cans must have these surfaces formed before the capacitor is installed. This must significantly reduce the available volume of can by comparison with modern day electronics, not only because the can is being squashed smaller, but the capacitor that it will later house is also cylinderical, so it can only have a diameter the same as the distance between two of the flats.

There's some strange in my neighbourhood! I'm arming the ectogun...

[AndrewT]

Hi,
I have seen upto six flats fromed in the sides of electrolytics extending almost the full length of the can.
My guess is it may squeeze the coil and impart a non unifrom arrangement of stress & strain and so avoid vibration??? or shift its frequency into another spectrum??.
After the coil is inserted into the can there must be a gap. Maybe this is just a method of securing the coil to reduce/eliminate movement in the internal connecting wires to improve reliability??
regards Andrew T.

[lowlevel]

I've seena number of bigger electros with various types of "forming" on the sides. My guess its to increase the strength of the can.
Because it times the capacitor can my become a preasure vessel.