Radio Preppers

General Category => Technical Corner => Topic started by: gil on May 22, 2017, 09:37:44 AM

Title: Easy Dummy Load Project.
Post by: gil on May 22, 2017, 09:37:44 AM
Hello,

Here is an easy project involving a BNC connector, small plastic box and eighteen 100-Ohm 2W resistors. Total resistance is of course 50-Ohms. What is the total power handling?  ;D

(http://radiopreppers.com/images/dummyload.jpg)

Gil.
Title: Re: Easy Dummy Load Project.
Post by: cockpitbob on August 22, 2017, 12:45:33 PM
What is the total power handling?  ;D
I'll comment because I've seen quite a few engineers miss this one.  You've got 18 resistors rated for 2W so 36W...for a short time.  Actually, the the pulse handling ability of the resistors is much more than 2W.  I wouldn't hesitate to put a few 100W dits or dahs into it.  But then I would wait quite a while for it to cool down.

The real limitation is because the resistors aren't in open air but a plastic box.  The continuous power rating will be whatever heat can pass through that box into the air without melting the box ;) .   Guessing the size of the box and using a little rule of thumb,  I estimate you can't leave it cooking key down with more than 5W before the box starts to get soft :o
Title: Re: Easy Dummy Load Project.
Post by: gil on August 22, 2017, 12:59:28 PM
I estimate you can't leave it cooking key down with more than 5W before the box starts to get soft.

A few holes might be in order  ;D

Gil.