building my power resistor

hi

i am trying to wind or build a power resistor that is:

what is the formula and what is a good wire to use i have may sizes of enamel copper wire.

thanks

Jif

copper

If you want this for a dummy load or something, you might consider as a general strategy using series and parallel connections of other values. Two equal-value resistors connected in series or parallel will have a power rating that is the sum of the individual ratings. You can often find oddball size resistors on sale in large lots, then play around with the math to get the right series/parallel combination.

Of course, if you elect to combine 90 one-watt resistors to get a 90-watt total, you will need to do a lot of soldering. But having a lot of resistors spread out over a large area will certainly help with heat dissipation.

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

copper

Copper wire is for inductors. Nichrome is for resistors.

Easiest way: a 225W resistor with a slider. You can reuse it for other similar values.

Way most of us do it: junk-box parts series-paralleled like Masta said.

Cheapest way: Keep busted appliances around? Strip the nichrome out of a junked toaster, toaster oven, iron, or heater. Making the copper connection to the nickel-chromium metal is the hard part.

copper

I think noone else has mentioned this yet but it might be important in your application. If you end up making it from wire, and if you wind it, it could end up having significant inductance depending on how close the turns are to each other. Winding a layer in the reverse direction of the layer underneath it can help decrease inductance.

copper

Another alternative is to use a short length of nicrome from an old hotplate and submerge it in water or oil to keep it cool. Particularly useful if the load is only used for short periods. Even an undersized wire can be used.

Gary

On 2 Mar 2004 18:56:26 -0800, snipped-for-privacy@att.net (Bill Bowden) Gave us:

copper

Copper wire is rated by ampacity. #26 can only handle one amp before it heats excessively, and that is for open air. Cramped up on a tube, and shellacked over, it would probably heat up a lot!

At a one amp max, the resistor would only be able to pass a couple watts before heating up big time.

First off, the better wire for this is resistance wire, specifically made for the purpose.

Short of that, buying two 10% tolerance 3.3 Ohm high power resistors and putting them in parallel would likely be cheaper both time and money wise. Especially time wise. My time is worth a lot, especially my free time.

On Wed, 03 Mar 2004 13:41:02 GMT, snipped-for-privacy@daqarta.com (Bob Masta) Gave us:

This is not true. If their power ratings are unequal, the bank will be limited to that power which makes the smaller rated resistor max out in dissipation. That power level is NOT the sum of the two power levels of the resistors. It is two times the smallest power value.

Also, one should not dissipate into a power resistor at the rated power. If one want to dissipate 90 watts, one should get a 200 watt resistor. At the very least 1.5 times the desired dissipation rate.

On Wed, 03 Mar 2004 21:42:45 GMT, Michael Gave us:

copper

It's for DC from what I saw. If that is the case, it won't matter. Particularly since there is no magnetic core involved.

On 4 Mar 2004 06:50:30 -0800, snipped-for-privacy@hotmail.com (Gary Lecomte) Gave us:

copper

A series of oven heating coils. They usually dissipate 1200 plus watts each.