Unappreciated sarcasm at that, not only unappreciated but unintelligent. If you don’t know what you are talking about you should keep your comments to yourself.
I will use an example of something I am very familiar with, the custom chopper that I built. The alternator puts out three phase AC voltage, this three phase AC ( just over 50 VAC ) is sent to the rectifier in which the 6 diodes clip the AC voltage. The rectifier rectifies the AC into DC and regulates this DC to 14.5V to ensure proper battery charging. To keep the battery from over charging the regulator sends all excess voltage to ground where it is dissipated as heat. This is why they get hot, if the ground is weak the unit will melt. I am pretty sure my motorcycles all have rubber tires.
Maybe I am wrong with the new cars but I know how this works without question and have always assumed that the cars were the same way.
To clarify, i asked about a car alternator but i did not mention a Batterie, now i know that you need a Batterie to create the magnetic field you need in order for the alternator to produce electricity, but after it runs and produces power you can disconnect the Batterie and it will keep on producing power, i also know that you are not supposed to do that. i guess the answer is that the power not cosumed is simply not generated, i am right?
Are you sure there is an excess sent to ground? Voltage regulators and rectifiers produce a lot of heat anyway. But shunt regulators will end up dumping excess current, but generally only produce heat from excess voltage (IIRC). Does the regulator use the heat sink as ground? Also, some regulators just switch off in the case of over-current.
Car electrical systems rely on the battery to do a lot of the voltage regulation and bulk filtering. If you remove the battery you’ll get wild voltage swings that can easily damage the car’s electrical components.
In the old days when cars ran off of DC generators and car electrical systems were much simpler anyway, you could disconnect the battery and use the power from the alternator to power the car’s electrical system.
Correct. If you have a 500 watt alternator then it can produce up to 500 watts, but it will only produce as much power as is needed. If your car’s electrical system only needs 100 watts then the alternator will only produce 100 watts.
You can’t completely take the battery out of the picture. The alternator produces alternating current, which is not constant. At times when the current isn’t there from the alternator, it’s the battery that is supplying the current to the car’s electrical system. On average, the alternator produces enough current to supply all of the current needed by your car, plus some leftover to charge the battery, but that’s only on average.
Nothing “sends…excess voltage to ground,” and indeed, that statement doesn’t make any physical sense. Voltage is the potential energy difference between one element of a circuit and another, and the voltage between two points depends exclusively upon the resistance of that element to conducting a difference of electrical charge (conventional current) not upon the power that can be supplied to it (at least for linear circuits).
Voltage doesn’t go anywhere, any more than the distance between Boston and Atlanta becomes less when you fly, drive, or bike there. The alternator provides current, which supplies power (energy per unit time) as an impedance element like a resistor, capacitor, inductor, or motor applies a load on the circuit. Now, it is true that a real world alternator will always be providing a trickle of current (due to the base resistance in the circuit) and that the voltage regulator will apply a small load to keep the voltage across the battery in balance, both of which create small amounts of heat, but there is no mass dumping of generated energy from the alternator to “ground”, which as Rick and others have pointed out, is the chassis body and therefore does not actually contact the earth unless you have grounding straps on your chassis (which in any case serve only to dissipate the small amount of static charge that can build up).
I don’t know about choppers, but this is at odds with how most if not all car alternators work.
They work by regulating the field voltage which crudely put means that the alternator output is regulated by increasing and decreasing the magnetic field.
When the demand on the alternator is low and/or engine revs high, the voltage will rise very high, to compensate the regulator reduces the current flow to the field windings to reduce the magnetic field strength, which drops the voltage output.
When there is high current demand on the alternator, the voltage droops, and the regulator will allow more current to flow to increase the magnetic field and hence output.
Perhaps choppers do use a current limiting shunt but it seems a very inefficient and difficult way about it!
Yes my bad I meant current, both times I replied I was in a hurry and trying to get it wrote down as quickly as I could. First my wife was rushing me to go out to buy a new bed and the second time I was rushing out the door to go play hockey. I looked around and can see where you are getting that the regulator sends voltage to the field windings, but my bikes work differently. There are three wires, these are the three phase AC, that go into the regulator and one positive that comes out, this is the red wire that supplies power to the electrical system. There are no control wires to regulate winding voltage. So I guess we are both right. My bad. I still don’t like the sarcasm.
The battery has a couple of jobs in a car/motorcycle/truck
[ol]
[li]Provide the energy to start the engine via the starter motor[/li][li]Act as an instantaneous reservoir when a large increase in current is need RIGHT NOW. (such as the ABS modulator coming on) the alternator takes a small amount of time to ramp up the current[/li][li]Act as a “shock absorber” in the system to help regulate the voltage output fluctuations.[/li][li]Act as a reserve power supply in the event of an alternator failure.[/li][/ol]
Do not under any conditions disconnect a battery on an alternator equipped car with the engine running. Voltage can swing wildly and you could destroy anything that has microprocessors. This would not be good and it can be very expensive.
For more on how an alternator works, see below.
your understanding of how an alternator works on a motorcycle or anything else is 100% incorrect.
OK Starting and Charging system class is now in session.
if you run current though a wire, you will get a magnetic field around that wire.
Conversely if you move a wire though a magnetic field, you will generate a voltage. The same thing will happen if you hold the wire stationary and move the magnetic field though the wire. The more wire that is exposed to the magnetic field the more current that can be generated.
Parts of the Alternator Refer to this picture (scroll down just a bit) Stator also sometimes called the armature. A set of three winding that are stationary inside the center of the case of the alternator. These three winding are what generate the electricity. Here is a picture of just the stator Rotor sometimes called a claw pole rotor. This is the thing inside that spins. The rotor consists of a large winding of wire, and two claw shaped pieces of metal one on each side of the large winding of wire. Also there is a pair of slip rings. which are attached on the ends of the winding of wire. Here is an excellent picture of a rotor. You can see the winding, the slip rings (red) and the two claw shaped magnets. When voltage is applied to the rotor the winding becomes an electromagnet. The claw on one side becomes the North pole of the magnet, the other claw becomes the south pole Slip rings What the brushes ride on to provide voltage to create the magnetic field around the rotor.
So how does it all work?
The stator consists of 3 sets of windings. Each set of winding has six small winding arranged around the circumference of the alternator. Let’s call them A, B and C. The arrangement is ABCABCABCABCABCABC Here is a better picture of a statorand rotor.
Now if you put the whole thing together and spin it nothing will happen as there is no magnetic field in the rotor, and therefore no current being generated.
However if you apply a small voltage to the slip rings, the rotor winding becomes an electromagnetic. As the magnetic field from the rotor cuts though
the wires in the stator voltage and current is generated. The North claw pole will align with all the A winding, then all the B winding and then the C windings. same with the South pole. The greater the voltage applied to the rotor the stronger the magnetic field and the more current that is generated.
The voltage that is generated is AC. Batteries use DC, so it has to be converted.
The regulator uses six diodes arranged into a diode bridge to change AC to DC. On this page is a very good description of how the alternator works and a good picture of the voltages and how AC changes to DC.
So if my alternator can put out 140 amps, but my car needs only 15 to run what happens to the other 125 amps?
Nothing, it was never generated. As I mentioned before, if there is no voltage to the slip rings, there is no magnetic field and no current being generated. The voltage regulator reads the system voltage and regulates the voltage to rotor to keep the system voltage right. Let’s say the system is set to 14.0 volts. The car is running, with no accessories or light turned on. System voltage is 14.0 volts and the regulator is supplying just enough voltage to the rotor to hold 14.0 volts. Now you hit the high beams, brakes, and heater fan all at once. System voltage will drop. the regulator senses this and increases the voltage to the rotor. the magnetic field gets stronger, more current (and voltage) is generated, until 14.0 is reached and then the system again supplies just enough voltage to the rotor to maintain 14.0 volts.
Kinda neat actually.
You guys now know more about the theory of alternators than a good portion of the guys out there that get paid to work on them.
It’s late, I’m tired and I probably missed a few details, but this is close enough for your general fund of knowledge.
Look, I explained how the charging system works. I admitted I may be wrong on the cars. WTF. Explain where the DC voltage comes from to excite, with three AC inputs and one DC output. Actually, never mind.
Nothing, repeat, nothing “sends voltage”. Voltage is not a commodity or a quantity of change; it is just a measure of potential difference between one point and another in a circuit that predicates how much current it will take to overcome a given impedance. I don’t know what you mean about “control wires”; most if not all alternators (certainly any modern ones) have a built-in bridge rectifier consisting of six solid state diodes like this which serve to flatten out the ripples by rectifying (making positive) all off the phases. This is what regulates the voltage to be within a specified range.
In any case, excess electrical power, save for that drawn by the inherent impedance of the wires, is not wasted as heat, any more than electricity leaks out of an empty light socket if the switch is on. It is simply not generated by the alternator unless a load is placed upon the circuit.
That’s not the regulator. That’s the output rectifier. It basically converts the sine wave output from the three stator coils into a very ripply DC-ish kind of thing. It’s up to the battery to filter off the ripple and turn it into a smooth DC.
Alternator designs vary, and I don’t know what they’ve put in motorcycles over the years, but it is possible that your field coil doesn’t actually have a regulator on it. The alternator will be cheaper and simpler without it, but it won’t be as efficient. Since there isn’t anything to scale back the voltage at higher revs, the alternator will tend to try to overcharge the battery, which is a little harsh on the battery. It generates more heat in the battery and electrolyzes more of the water into hydrogen and oxygen, which then can escape from the battery forcing you to add more water periodically. The higher voltage and resulting higher current also means that your engine will have to supply a bit more mechanical energy to the alternator.
It’s also possible that the regulator for the field coil is buried somewhere inside the alternator where you can’t see it.
Excitation current comes usually from the ignition light bulb.
all it takes to regulate the field strength is a transistor, 3 small diodes, and a resistor or two. It can quite easily could be built into the brush assembly.
PS an alternator is an alternator it doesn’t matter if it is on a Chevy or a Harley the theory is the same.
