DIYbanter - View Single Post - Is the wattage linear on a wirewound adjustible resistor?

Foxs Mercantile

On 2/26/2017 1:51 PM, wrote:
While looking at resistors on ebay, to use as an 8 ohm speaker load, I
developed a question.

There is a 25 ohm 25 watt wirewound resistor with adjustible slider. In
other words, the two ends of the resistor are 25 ohms, but there slider
can be adjusted to get any resitance between 1 and 25.

So, if I had one of these, and put the slider at 8 ohms, to use for a
speaker load, would it still be rated at 25 watts? -OR- does the allowed
wattage drop when only part of the resistor is being used?

I'm not sure how this works????? (In this case, I'd be using about 1/3
of the entire resistor).

Wire wound resistors, are rated at total watts across the entire
resistor.

For less than the total amount you are limited to what would be the
current through the entire resistor.

SQRT(25/25) = 1 amp.
Dialing it back to 8 ohms, 1^2 * 8 = 8 watts.

--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com