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Ferrite core securing bolt metal or nylon.

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dr pepper

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I have some circular ferrite bobbins with a hole down the centre.
I'v seen these commercially installed with a steel bolt down the centre, is this going to significantly affect the bh curve or saturation point?, this example has a 10mm winding diameter and a 4mm bolt, so the bolt diameter is significant.
In professional speaker cabs crossover chokes always had nylon bolts holding them down.
 
Agree nylon.
JimB
 
If you or someone else happens to use metal, be sure the ends of the bolt are not electrically connected to each other. It will act like a one-turn, shorted secondary. Not good.

John
 
Nylon would normally be used, particularly in transformer applications, although I have also seen Brass bolts and fibre washers being used to hold large chokes, but never steel on ferrite formers :)
 
Depends on whether the centre leg is gapped or not. If not gapped I wouldn't worry. Brass is often use too, with gapped cores.
My feeling is that the initial permeabilty of ferroxcube is greater than that of steel and the bolt wouldn't carry much flux anyway. The other thing is that the bolt isn't really a part of the magnetic circuit so it couldn't carry much flux.
 
I have some circular ferrite bobbins with a hole down the centre.
When I first read this, I assumed that a toroid was being described, in which case - nylon.

However, in the cold light of day, maybe a "pot core" is being described.
In which case steel will be OK, but be carefull to use washers to spread the clamping force, otherwise you may shatter the core.

JimB
 
No not a pot core, it looks just like a cotton bobbin with flanges top & bottom.
Actually when I said I've seen steel screws holding these down that might not be true, I've recently used some brass screws that are nickel plated and they look just like steel being a silver finish, thats probably what they were.
But I'll take heed and use nylon, these are fairly small choke cores.

Yes an unplanned shorted turn isnt good, unless I wanted to seriously reduce inductance.
 
Hello,

Back sometime in the 1980's we used pot cores for the main control circuit power supply for solar panel converters. We switched from using stainless steel to nylon when we found the screws were heating up and thus using power. If the screw goes through the center it is in a parallel magnetic path and so will be subject to eddy currents and heating. How much it heats up depends on a number of factors like how much power the device has to handle to begin with, so the effect will vary from application to application.
If you are unsure then nylon is the best bet. You can always do a few tests too, one with nylon one without, as long as the operating parameters are the same for both.
 
With a torriod surely the bolt is well away from the magnetic path which is within the torus itself.
 
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