# Time to get rid of the resistor.

Discussion in 'Electronic Basics' started by [email protected], Mar 12, 2005.

1. ### Guest

As I understand it the resistor wastes energy by converting it into
heat. Consider this simple circuit a battery connected to a light bulb.
The light bulb shines onto a photocell the photocell charges the
battery. Thus the light bulb functions as a resistor but some of the
energy has been recovered. Now that the problem has been defined
someone who understands the physics better can work on making a
resistor that does not waste power.

2. ### Larry BrasfieldGuest

Why don't you get yourself an education and
pursue this breakthru idea yourself? While you
are at it, maybe you can invent a noiseless
resistor for use in amplifier circuits.

3. ### Robert MonsenGuest

Back in physics class, many years ago, I heard about schemes to use
flywheels to store braking energy. This is the same deal. The idea is
that instead of just dissipating the energy into heat, one somehow
couples the brakes into a flywheel, saving some of the energy.

I believe the Toyota Prius uses a scheme where braking force is used to
charge the battery, but this may be more sales pitch than reality.

Switch mode power supplies are devices that attempt to cleverly
circumvent resistive losses by transferring energy using a magnetic field.

Just because they say you can't do it doesn't mean it can't be done. You
are never going to win the game (zero energy dissipation), but you may
be able to hedge against loss somewhat. 50 years ago, nobody could have
imagined the complexity of integrated circuits today. Who knows what the
next 50 years will bring?

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

4. ### Anthony FremontGuest

The entire NY MTA fleet of "new technology" subway cars uses this
technique to feed electricity back to the "third" rail instead of
generating pure heat while braking. This and an adjustment in
acceleration of the trains results in 240,000,000 killowatt-hours per
year. That's allota juice.

http://www.mta.nyc.ny.us/nyct/facts/ffenvironment.htm

I believe that there are also large city buses that compress air to help
slow down. They then release the air to help get the bus moving again.
Seems smarter than just making heat to get stopped. I would also think
that you could wind up a spring and use the stored energy to get going.
But it would be heavy and large not to mention quite dangerous.

* I think they actually pump hydraulic fluid from one holding tank to
another while compressing air is a side effect to store the energy.
field.

I'd say that by acheiving >90% efficiency, it's more than a "clever
attempt". ;-)

5. ### Tom BiasiGuest

Hi,
The resistor doesn't waste energy it just transforms it.
If you have no need for the heat then to you it is wasted.
What you are saying is that a portion of the energy that supplies the light
bulb does not make light.
You wish to recover the energy that does not make light.
It can and is done now.
Take a look at some of the efficienticencies of transforming energy and see
what is feasible.
Could we power a generator with a motor and power the motor with the
generator and have a continuous supply of motion?
Regards,
Tom

6. ### Silver SurferGuest

"Could we power a generator with a motor and power the motor with the
generator and have a continuous supply of motion?"

Even if the generator and motor did not each have inherent losses then what
would this accomplish?

7. ### Larry BrasfieldGuest

Their technical descriptions indicate this clearly
enough that it would be fraudulent if not true.
Of course, one could assert the the energy
losses make it a gimic, and some performance
numbers would be needed to gainsay that.
Can you imagine a non-dissipative resistor that
could accept thermal noise from another resistor
and convert any fraction of it into work? (This
question is either trick, rhetorical, or a starting
point for an interesting discussion.)

8. ### Tom BiasiGuest

That was for the OP to ponder

9. ### PeteSGuest

Of course, there are other good reasons we use resistors (and yes, they
'waste' power).

As noted, switch mode power supplies (and class D amplifiers) make
slick use of integrating energy so they are far more efficient, but the
complexity of these is such you could not (at present; I've been in
this game long enough to know what we do not do now can change rapidly)
use such techniques everywhere.

Consider the lowly ordinary linear amplifier. It will, by definition,
waste power if one simply does the mathematics of Po/Pi where Pi is the
input from the power supply and the energy from the input source. There
you have the efficiency of the amplifier and it will always be fairly
low (for a linear amp - let's say Class A). Non-linear amplifiers have
been used for many years where efficiency was a concern and circuit
techniques could be used (Class C amplifiers for RF power sections are
an example).

This reminds me of the laws of thermodynamics:
1. You can't win.
2. You can't break even
3. You can't get out of the game.

So will there eventually be a replacement? Perhaps; but the utility of
the humble resistor in many areas (pullups/downs, termination devices
and thousands more) will have it living in new systems for some time to
come

Cheers
PeteS

10. ### Rodney KelpGuest

I think the idea is to have surplus power to have the motor do work and yet
maintain the motor with the generator. But I think you would need to inject
an antimatter stream somewhere to make it work.

11. ### Guest

OK here is another one have the light bulb shine on the photocell and
connect the solarcell in series with the bulb biased the other way.
With a solarcell of .5 volts you can have a reverse voltage of just
about anything you want. I can see some one making this as a single
device, a tungstan filiment enclosed with the solarcell sealed with
epoxy for 69 cents. Yes I know this is inefficent I just want to
stimulate discussion.

12. ### Larry BrasfieldGuest

Ok, I'll bite. Voltage is not power, and few
people want voltage for its sake alone.
To see that requires some lack of
aquaintance with simple economics.
(I assume this is still related to the
You are bordering on a troll. Perhaps you
the history of perpetual motion machines.
They have long appealled to some people,
and you may be one of them. If not, that
study will be educational in ways that go
beyond the science involved.

13. ### phaetonGuest

Or on a similar note (to the point about transformed energy is only
wasted if you don't want it)...

Some of those very large electrical junctionboxes (look like a huge
heat sink) that you'll find in a lot of industrial parks or on the
edges of shopping centers. You know, the big green ones that buzz
loudly. iirc, they've got a huge step-down transformer in there that
is converting line voltage into something useable by industrial
equpment.

Does the gigantic transformer throw off enough electromagnetic
oscillation to energize the coils of a smaller transformer (about the
size of your fist) if it is placed nearby? Could you used this "waste"
to power anything? I've always wanted to take a small transformer and
meter up to one and see what i'd get, but with the Patriot Act and
all....

....or maybe i'm just insane. I have pondered a "lossless resistor"
like the OP speaks of, as well. I'm unfortunately not educated enough
to do anything about it :-(

16. ### John LarkinGuest

I think I could design such a device, depending on what you mean by
"non-dissipative." It might deliver something close to 1e-24 watts if
you allow me to run it in liquid helium.

You can actually, fairly easily, build a black-box device that runs at
room temp but appears as a very cold 50 ohm resistor.

John

17. ### John LarkinGuest

It's not waste power; you'd be stealing real energy from whoever owns
the shopping center, but not a lot.

John

18. ### Larry BrasfieldGuest

That was a little vague, alright. I was just trying to
indicate that not all its input power was converted
to heat, which is redundant in this context.
If it can recover some thermal noise from passive
devices that exist same ambient temperature, and
if it delivers any fraction of that power as work
without consuming more power from an outside
source, then you can run it in any medium you
like, and I would like to be an early investor!

Even if it is not that miraculous, I would like to
know how you would do that, in general terms.
I don't know if it would work in the black box
you have in mind, but a high gain antenna would
do that if aimed right, at least for some range of
frequencies. (We do get to limit that, right?)

19. ### Guest

Yes this a serious post. At some point in basic electronics you are
asked to compute the power used by a resistor. For some reason
engineers don't care if the devices they design use energy efficently.
Pick up some batteries off the street that some one has thrown away
they average 1.2 volts. At 1.2 volts an alkaline battery still has
about 40 percent of its energy left. Design a radio to use 4.5 volts
but takes 4 batteries. Have a circuit that uses 3 batteries at a time
while rotating the unused battery at a regular interval. Then when the
voltage of the batteries drops to 1.2 volts each the circuit switches
to using all 4 batteries in series. All the batteries can be run down
to .9 volts each where they have about 10 percent of their energy left.
This idiot circuit could have been made 100 years ago. A modern radio
would test each battery, you could then mix types of batteries in a
radio. A resistor that throws away heat is only one part of an energy
wasting device. Perhaps what I am thinking of is instead of a resistor
you need a current limiting device.

20. ### Robert MonsenGuest

Sadly, a current limiting device wastes the same amount of energy as a
resistor (perhaps more, since it will require some control, which could
take power as well.) The problem is that many times, engineers use the
fact that resistors 'waste' power in their circuits. Dropping a given
amount of current from voltage a to voltage b means that a certain
amount of power must be taken out somehow. Your light idea was a way to
regain some of that power (a very small amount).

However, if you are worried about battery pollution, you should rest
easy knowing that there are circuits that can draw batteries down to
quite low levels. They are proliferating in the form of white light LED
driver circuits. They generally use the magnetic field in inductors to
drive the thing. This is similar to two paddle wheels which are coupled
by a mechanical connection of some kind. If the driving paddle wheel
takes energy from a stream that is dropping 5 meters, it can raise 1/3
of the amount of water up to 15 meters (minus some loss for friction,
energy collection efficiency, etc).

However, considering energy efficiency of resistors when people drive
SUVs to the supermarket and leave their computers on all night is like
rearranging the deck chairs on the titanic as it sinks.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.