It is just a theory I threw out there because of things I have heard in years past. I don’t think generators are magic, but, I thought it might be that newer cars pull power from the alternator and the alternator responds, but a generator creates energy whether or not it gets used. I thought it might be possible that automotive generators in older cars might have been designed to produce a constant amount of electricity at a constant engine speed.
If a generator in a 1956 Chevy was sophisticated enough to monitor power demand and adjust its output, I am ready to stand corrected. If, on the other hand, it produced a constant amount of power at a constant engine speed, that is probably where this idea came from.
It not that it monitors energy demand. It’s as simple as the generator/alternator can only produce as much current as is being consumed by the electrical system of the car. There is no where else for it to go. It’s kind of like having a pump and a water tank. The pump can’t pump more water into the tank than the tank will hold. If current isn’t consumed, it can’t be generated. It flows in a closed circuit.
That’s right, Tardis, the electricity has to do something - it’s not like the generator gets hot when it’s not under load. If the energy’s not being used for something, somewhere, it’s not a load on the engine.
The biggest difference between generators and alternators is that generators are reversable, they can be motors as well as generators. On some garden tractors, the generator did double duty as a starter. Generator regulators needed an extra relay in them to open the circuit to the armature when the voltage dropped too low so that battery voltage would not backflow through the generator when the engine is running too slow or is stopped. That backflow current would make the generator run as a motor and try to speed up the engine.
Even today, the DC current that powers high speed elevators in skyscrapers comes from a motor driven generator instead of being rectified from AC. The reason is that a generator can sink power as well as provide it. When the elevator car is overrunning the hoist motor, the hoist motor becomes a generator and holds the car back just like engine braking when you downshift. The generator sinks that power and becomes a motor which tries to overrun the 3-phase motor that drives it. When a 3-phase motor is overrun, it returns power to the power line and the electric meter turns backwards.
Okay, tardis. Let’s take your water pump analogy to the next level. While a water pump can’t pump more water than the tank can hold, it can keep pumping and increase pressure. The pump doesn’t have to stop pumping just because the tank is full.
Perfect analogy - let’s substitute air for water - ever put your hand over the hose to a vacuum cleaner? The electric motor suddenly speeds up because it isn’t doing any work. Hand off, the motor slows down because it’s now doing work. Same thing happens to an electrically driven water pump. Shut the valve, pressure may go up, but that’s not the same thing as doing work. The load is now largely eliminated.
No, it does have to quit pumping. Water doesn’t compress. Once the pump stops pumping, it stops doing work, so the load on the pump motor greatly decreases. The motor will speed up and draw less current. I think more people have trouble with this concept than they do with the power from an alternator.
I’m not going to bet with him again. He is VP of Engineering at my company and a former aircraft mechanic as well. If I debate him on drag with open windows he is likely to produce a spreadsheet full of drag coefficients and air tunnel research. Solar panels on his highly polished ultra-clean BMW would not go over well. I’m going to quit while I’m behind and get myself a key lime pie also when it’s time to pay up. Celebrate defeat!
Okay, so the pump isn’t doing any work any more, but it is maintaining pressure on the water so that when the tank drains, it will pump more water. In our theoretical alalogy, the water pump is still using energy to maintain water pressure. It can keep maintaining pressure even though water doesn’t compress.
Put a check-valve in, and it no longer has to maintain pressure. But anyway this is getting us nowhere towards the understanding of power generation and consumption. I have about 5 years of higher education in the subject, and about twenty years of experience, but communication has never been my strong point. I’m not sure where to point you from here, but again I wish to reassure you that it is impossible for a generator to be making extra energy that isn’t used somewhere somehow at the exact time it is made. Also every little bit of electrical energy out comes at the cost of mechanical energy in. Unless, of course, you believe in some of these quacks that claim to have made motors that produce more energy than they consume. Funny how after many many years they are yet to provide a working one for anyone in the mainstream to test. However, they have taken millions of investor dollars from people who also don’t understand the basic physics behind all of this.
Now that the headlights vs. gas issue is resolved (running headlights does cause a slight increase in gas use, which is probably more than offset by increased safety, except on the sunniest days), we can turn to AC vs. windows. According to Clank and Clunk themselves, for most cars, keep the AC off and windows down at “around town” speeds (up to 40 or so). The extra load on the compressor (and thus the engine) outweighs drag losses. At highway speeds, close all the windows and use the AC, as the savings in drag losses outweigh the extra compressor load. The cutoff point will of course vary by car design and how many windows are open by how much.
By the way, if your friend considers all lighting use in daytime “a waste”, he’s an idiot. There are many situations during daylight hours (rain; fog; heavily shadowed by trees, buildings, or topography; unlit tunnels; sun low and behind oncoming traffic; etc.) when having lights on is very helpful. It’s amazing how many people to too stupid to turn on lights in reduced visibility. Only in bright sunlight would lights be a waste.
The cost will come when you replace your headlamp bulbs a month or so earlier than you otherwise would have. Most folks drive FAR more during daylight hours. I agree with Rockford, the safety factor outweighs all. I always drive with lights a-blazin.
A centrifugal pump will hold that pressure without pumping, the power needed to drive the pump will go down.
A positive displacement pump will get harder to turn and the pressure will go extremely high. Stop all flow and the pump will lock up and stall the motor or shear the pump shaft in the case of a car engine’s oil pump. This type of pump needs a pressure relief bypass valve.
Alternators and generators are like centrifugal pumps. RPM= pressure. The flow is whatever the load allows and the higher the flow, the more torque is needed to spin the pump.
Electrostatic machines like Van deGraf generators and Wimhorst generators are like positive displacement pumps. They get harder to turn as the voltage (pressure) goes up and freewheel when the output is shorted.
Magnetic generators freewheel when the output is open and nearly lock up if the output is short circuited.