On Sun, 26 Feb 2017 14:08:57 -0600, Foxs Mercantile
wrote:

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.

That's kind of what I was thinking, but I had to ask to be sure.

I've never been good at math, but it makes sense that if I'm using 1/3
of the resistor, I am getting 1/3 of the wattage (about 8W).

I dont need to do this, because I have a pair of 8 ohm 100W fixed
resistors, but I was just curious.