Power Wastage.

After looking at linear regulators, and the resistors you need....

Who in this day and age is going to design a circuit with a 100watt + resistor? when will these go the same way as incandescent bulb? I don't think I like the idea that 50+ watt resistors are hiding away in power supplies and god knows what else.. people are always focusing on greener idea's yet a 100watt resistor!

rant over, can't PWM power supplies be scaled up on an industrial level so huge wattage resistors can go bye bye? and if this is already the case, why and where would a 100watt resistor come in handy?

cjdelphi: why and where would a 100watt resistor come in handy?

I've seen them used to heat up the base plates of 3D printers.

if this is already the case, why and where would a 100watt resistor come in handy?

Anywhere you wish to have a 100% efficient electric to heat transducer. Think of it as a heating element utilized in a temperature control application.

Lefty

cjdelphi: I don't think I like the idea that 50+ watt resistors are hiding away in power supplies

Why are you assuming the only use for these resistors is power supplies?

Since the wirewound type you picture can be cost in the 1s to 10s of dollars (through authorized channels), I doubt many are "hiding away" in applications. If they're being used, it is because it is the most cost effective option.

cjdelphi: why and where would a 100watt resistor come in handy?

Current sense for motors in industrial applications. High Power RF Transmitters Industrial power systems Bleed resistors Balancing resistor networks

Power dump resistors for electric vehicle braking (to avoid over-charging battery)...

EDM (Electric Discharge Machining) circuits, or in laymans terms, creating sparks between a workpiece and electrode with the intent of burning away parts of the workpiece. If you rectify 110V or 220V AC and use a power resistor like the one linked to limit current it makes the circuit pretty straightforward. Doing current limiting of high voltage without a resistor ... not so straightforward.

They are rare… I’ve worked in electronics for about 30 years, and I don’t remember ever seeing a 100W resistor in “real life”. Where I work now, we may have a few boards that use 1W resistors, but most are 1/4 or 1/8W.

If you are going to test a power supply, batteries, or amplifiers, you need a “dummy load”. Once (probably while I was in college), I built an 8-Ohm, 200W, dummy-load for testing audio amplifiers. I don’t remember exactly what resistors I used, but I used several lower-power resistors (probably 10W). I also don’t remember if I did that because I couldn’t find an 8-Ohm 200 resistor, or if it was cheaper to use several smaller resistors.

P.S
Now I remember something… When I was in college, I took a “Motors & Generators” class. We had dummy loads that were BIG, maybe kilowatts! They didn’t look like power resistors, they looked more like electric heaters.

Why am I feeling like this is the silliest rant in long while? There are of course reasons for these to exist, you just have not been exposed to the likely environment. Working with small voltages and small current... you are unlikely to ever see the need for a 100W resistor.

In the Radio Broadcast industry, at least when I was involved, seeing large watt resistors (and large voltages) was rather common around high power transmitters.

cjdelphi: After looking at linear regulators, and the resistors you need....

Which regulators are those? The typical ones discussed here usually only need some capacitors, and maybe a couple small resistors for setting a feedback voltage, not power resistors.

Who in this day and age is going to design a circuit with a 100watt + resistor? when will these go the same way as incandescent bulb?

They already have. Back in the day of tube (valve) circuits, 10W and 5W resistors were commonplace. Several could be found in any TV, they were also in radios, stereo gear, guitar amplifiers, etc. That stuff threw off tons of heat. A 10W resistor running at full power or even half power is fairly impressive.

If I use a 1/4W resistor now (which is hardly ever), it's gross overkill, and probably has a safety factor of several hundred percent as far as power dissipation.

As others have noted, niches remain for power resistors, so they continue to be produced. Don't panic ;)

As a matter of fact really old tube type receivers had really big resistors both inside and outside too… The Inside ones were called ballast resistors and the ones outside were resistance wire wound around an asbestos/fiberglass composite and were used to drop the line voltage for the tube filaments (both served the same purpose). Every high power transmitter (< 1kW) had a really big resistor… JUST like that… Or I wouldn’t work on it… Issues of Certain Lethality…

Doc

[quote author=Jack Christensen link=topic=163265.msg1223309#msg1223309 date=1367365290]

cjdelphi: After looking at linear regulators, and the resistors you need....

Which regulators are those? The typical ones discussed here usually only need some capacitors, and maybe a couple small resistors for setting a feedback voltage, not power resistors.

I know all that....

pwillard: Why am I feeling like this is the silliest rant in long while? There are of course reasons for these to exist, you just have not been exposed to the likely environment. Working with small voltages and small current... you are unlikely to ever see the need for a 100W resistor.

Maybe you never read my sentence properly?...

In the Radio Broadcast industry, at least when I was involved, seeing large watt resistors (and large voltages) was rather common around high power transmitters.

"at least when i was involved"

So maybe you'd like to explain WHY such high load resistors are needed? and WHY something more efficient can't replace them... (EG, PWM) with exception to these things being used as heater elements (which there's no way to avoid really) why can't something more "EFFICIENT" be used... this is about being more responsible with energy, so how you consider it to be a "silly rant" is beyond me.

Perhaps someone would like to explain how you replace a resistor with a PWM? In an industry where you have towers blasting out a 50KW signal a 100W resistor is a tiny percentage. When working with high powers you will have higher losses. I'd suggest you study the industries and technologies before you assume there are better solutions. These parts are manufactured because they have a purpose and people buy them. To assume you know their needs better than they do is naive at best.