[TowerTalk] Balun Overheating?

Jim Lux jimlux at earthlink.net
Mon Apr 21 08:32:04 EDT 2014

On 4/20/14, 10:16 PM, Jim Brown wrote:
> On 4/20/2014 9:24 PM, Roger (K8RI) on TT wrote:
>> As they "Prevent" current flow" I'd not expect a lot of heat.
> When guys started building W2DU Baluns, they wanted to make money, so
> they built Walt's smallest design with only 50 beads. That choke does
> not provide much noise suppression, and it allows four times more
> current than the choke with 200 beads, so the choke dissipates 4X the
> power of the choke with 200 beads. If you're running 100W, you may get
> away with that, but running power will likely fry something.

Just to elaborate on the math..
50 beads is 1/4 R of 200 beads..

So I is  4 times greater, for the same voltage.

I^2*R is then 16* (1/4) .. the total dissipation is 4x greater.

I think the other factor in overheating is that W2DU had the beads 
hanging (literally) in the wind. A commercial product is often something 
that looks neater: inside a nice tube, or covered in shrink tubing, etc. 
but which also has poorer thermal properties.

The real sticky issue when trying to calculate stuff is "what is the 
voltage".  And that's something that is hard to determine in a simple 
way.  One can do a numerical model (using NEC, for instance), but in 
practice it's highly installation dependent.

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