altenator or charger
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05-21-2005, 12:25 PM
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altenator or charger
#2
05-21-2005, 12:37 PM
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I believe you are thinking a generator? Altenator produces ac current which is rectified(changed) to dc current and can be most any output dc voltage depending how it is configured. A generator generates dc current and can also be most any practical dc volage. The disadvantage with a generator is mostly size. More volts usually means a larger unit. Also a generator is typically larger and heavier than an altenantor.
#4
05-21-2005, 02:54 PM
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A generator has a big drawback: in order to get electricity to flow to the rotating part of the system, a commutator is used. This is the segmented part that the brushes ride on. This feature causes several problems, but the chief advantage of using a commutator is that is allows DC current to flow from the windings. When the current output of the windings is small or reversed, the commutator switches the output of the generator to different armature windings.
But since the 60s, when practical, reliable, and inexpensive semiconductor rectifiers became available, one was able to overcome the generator's advantage: production of DC current. The Alternator's disadvantage was that it produced AC current, which couldn't be stored in a battery. With the small rectifiers, this enabled the alternator to be superior to the generator, because the generator:
Is less reliable. The running of brushes over a segmented commutator makes them wear out faster. The Alternator uses slip rings to transfer electrical current to the rotating assembly, and since slip rings are smooth, the brushes last longer.
The slip rings do, too: segmented commutators need to be turned down and then undercut between the commutator segments. This makes them expensive to be rebuilt, besides making rebuilds necessary more often.
Then, the commutator "switches off" most of the windings of the armature most of the time. The windings that are switched on are those that are producing the maximum amount of current because of the angularity of the windings to the field of magnatism, and when the current is only flowing one way.
But the alternator is ALWAYS connected. The rectifiers make the issue of whether the current is alternating immaterial. So, instead of being able to produce current at only one spot in the rotation of the armature, the power generating windings produce current all the time except at two very brief spots in the armature rotation. This means that much more power is derived from each winding in an alternator, because they are on all of the time.
Because each winding loop that produces electricity is being used all the time, you don't need nearly as many of them to produce the same amount of power from an alternator as you would in a generator, where the power producing windings only work a small portion of the time.
Another advantage this confers to the alternator is that it produces more power at slow rpms. So, if you are driving around town a lot, an alternator does a better job of keeping the battery charged.
And, another advantage of alternators is for high performance. Switching on and off the windings in a generator, as the commutator does, causes lots of sparks. And, since a commutator is not very smooth (because of the undercutting of the segments), at high rpm it is harder for the brushes to stay in contact with the commutator. In effect, the commutator is like a cam and the brushes are like lifters: When the rpm is high enough the intertia of the brushes is greater than the power of the springs to make them ride the commutator.
This effect of the brushes having poor contact with the commutator and the commutator being switched on and off from winding to winding makes lots of electrical arcing, which then burns the commutator, making it pitted, and causing more arcing, brush wear, and unevenness of the commutator -- a viscious cycle.
I have driven a car around with a generator with the hood off and run it at high rpm. (This was preparing a 1960 Buick for a demolition derby and taking it for "test drives" in an abandoned railroad switching yard.) The arcing from the generator at high speed was like a small arc welder. I knew of friends who had older cars, that when they would go out racing on Friday nights, would come home needing a new generator. They'd get a rebuild and install it, and the rebuild would last precisely one Friday nite.
Unless you are one of those folks doing a restoration, where you will be penalized for swapping out a generator for an alternator, generators are an inferior choice for any kind of driving.
However, the size of a given generator or alternator has little to do with its voltage: the size is determined by the power output, which is current times voltage.
Generators and alternators will put out quite a bit more volts than they are rated for. It is the voltage regulator, whether that regulator is made up of relays or semiconductors (or, transistorized) that controls the voltage to prevent too much voltage from being applied to the car's electrical system.
You can get devices that will tap the unrectified AC voltage from your alternator that will power hand drills and the like. This voltage, which is unregulated, will approach 100 volts and is 3 phase current. The AC frequency, of course, is dependent on the speed that the alternator is being run at, but may be around 400 Hz. Many electrical devices cannot use this higher frequency 3 phase current, but universal electric motors (like a drill or vacuum cleaner) or heating elements don't care -- they work fine with it.
This brings me to one more advantage of alternators over generators, and that is the electrical device that regulates their outputs.
Generators are the poorest choice, because their regulator is seldom transistorized (they were made before transistors were practical for this use in cars) and so their relays require adjustment and also have their contacts get pitted and burned, requiring more frequent replacement.
The first alternators also used relay-regulated regulators, but they were better. Generators will also work as a motor when electrical power is applied to them (which you can test out for yourself). The problem is that, when the car is shut off or when the engines is idling so low that the generator isn't making any power, current will flow from the battery back into the generator! Inside the regulator, there is a cut out relay that prevents this from happening. Because an alternator has rectifiers in it that only allow current to pass OUT of the unit rather than both ways, there is not need for a cut out relay in an alternator system.
In my Harley, I use a magneto and don't have a battery, so this is no problem -- I don't need a cut out regulator. The electrical system is wired so that when the generator makes electricity, the lights come on (if they are switched on). Because Harley parts are expensive, I use an old 6v Volkswagen regulator with the cut out relay removed.
Some, and most American cars (unlike the Volkwagen I mentioned) have a 2nd relay for limiting the current of the generator. This keeps the generator from burning out because of too much current draw. Most alternators don't have this need, since by their design, they are somewhat self regulating as far as current is concerned.
Finally, both alternators and generators use a relay to regulate the voltage. You know that when a wire loop is passed thru a magnetic field, electricity is produced. This magnetic field comes initially from the battery, but once the alternator or generator is producing power, it produces its own power for the electromagnets that produce this magnetic field. Both systems regulate the current that is passed to these electromagnets to maintain the voltage at a constant 14.7 or so volts for a 12 volt system, or about 7.3 volts for a 6 volt system.
However, in the latest alternators (those made for the past 25 years or so) the voltage relay is replaced by another transistorized unit, so this point of wear and adjustment is also missing in the more modern alternator systems.
There are alternators that you can buy, the fully transistorized ones, that have been modified to produce 6 volts if that's what you want.
Now, there are those who will tell you that generators work fine and that 6 volts systems work fine, blah blah blah. I have presented you with the facts here, so you can make up your own mind without needing to listen to "grandpa stories". (You know, those where we had to walk 10 miles to school in a blizzard, uphill both ways. BTW, I'm a grandpa, too, x7)
There is one technical advantage to using a generator over an alternator:
When the battery is dead, I mean REALLY dead, remember that both the generator and the alternator need some initial electricity to produce magnatism so that they can begin to produce power. However, the generator has large iron pole pieces in it, whichi will usually retain a slight amount of residual magnatism, where an alternator does not. For this reason, on a car with a generator and a dead battery, you may be able to get it started by rolling it down a long hill or push starting it. The generator may then get enough power going to power the ignition.
But since the 60s, when practical, reliable, and inexpensive semiconductor rectifiers became available, one was able to overcome the generator's advantage: production of DC current. The Alternator's disadvantage was that it produced AC current, which couldn't be stored in a battery. With the small rectifiers, this enabled the alternator to be superior to the generator, because the generator:
Is less reliable. The running of brushes over a segmented commutator makes them wear out faster. The Alternator uses slip rings to transfer electrical current to the rotating assembly, and since slip rings are smooth, the brushes last longer.
The slip rings do, too: segmented commutators need to be turned down and then undercut between the commutator segments. This makes them expensive to be rebuilt, besides making rebuilds necessary more often.
Then, the commutator "switches off" most of the windings of the armature most of the time. The windings that are switched on are those that are producing the maximum amount of current because of the angularity of the windings to the field of magnatism, and when the current is only flowing one way.
But the alternator is ALWAYS connected. The rectifiers make the issue of whether the current is alternating immaterial. So, instead of being able to produce current at only one spot in the rotation of the armature, the power generating windings produce current all the time except at two very brief spots in the armature rotation. This means that much more power is derived from each winding in an alternator, because they are on all of the time.
Because each winding loop that produces electricity is being used all the time, you don't need nearly as many of them to produce the same amount of power from an alternator as you would in a generator, where the power producing windings only work a small portion of the time.
Another advantage this confers to the alternator is that it produces more power at slow rpms. So, if you are driving around town a lot, an alternator does a better job of keeping the battery charged.
And, another advantage of alternators is for high performance. Switching on and off the windings in a generator, as the commutator does, causes lots of sparks. And, since a commutator is not very smooth (because of the undercutting of the segments), at high rpm it is harder for the brushes to stay in contact with the commutator. In effect, the commutator is like a cam and the brushes are like lifters: When the rpm is high enough the intertia of the brushes is greater than the power of the springs to make them ride the commutator.
This effect of the brushes having poor contact with the commutator and the commutator being switched on and off from winding to winding makes lots of electrical arcing, which then burns the commutator, making it pitted, and causing more arcing, brush wear, and unevenness of the commutator -- a viscious cycle.
I have driven a car around with a generator with the hood off and run it at high rpm. (This was preparing a 1960 Buick for a demolition derby and taking it for "test drives" in an abandoned railroad switching yard.) The arcing from the generator at high speed was like a small arc welder. I knew of friends who had older cars, that when they would go out racing on Friday nights, would come home needing a new generator. They'd get a rebuild and install it, and the rebuild would last precisely one Friday nite.
Unless you are one of those folks doing a restoration, where you will be penalized for swapping out a generator for an alternator, generators are an inferior choice for any kind of driving.
However, the size of a given generator or alternator has little to do with its voltage: the size is determined by the power output, which is current times voltage.
Generators and alternators will put out quite a bit more volts than they are rated for. It is the voltage regulator, whether that regulator is made up of relays or semiconductors (or, transistorized) that controls the voltage to prevent too much voltage from being applied to the car's electrical system.
You can get devices that will tap the unrectified AC voltage from your alternator that will power hand drills and the like. This voltage, which is unregulated, will approach 100 volts and is 3 phase current. The AC frequency, of course, is dependent on the speed that the alternator is being run at, but may be around 400 Hz. Many electrical devices cannot use this higher frequency 3 phase current, but universal electric motors (like a drill or vacuum cleaner) or heating elements don't care -- they work fine with it.
This brings me to one more advantage of alternators over generators, and that is the electrical device that regulates their outputs.
Generators are the poorest choice, because their regulator is seldom transistorized (they were made before transistors were practical for this use in cars) and so their relays require adjustment and also have their contacts get pitted and burned, requiring more frequent replacement.
The first alternators also used relay-regulated regulators, but they were better. Generators will also work as a motor when electrical power is applied to them (which you can test out for yourself). The problem is that, when the car is shut off or when the engines is idling so low that the generator isn't making any power, current will flow from the battery back into the generator! Inside the regulator, there is a cut out relay that prevents this from happening. Because an alternator has rectifiers in it that only allow current to pass OUT of the unit rather than both ways, there is not need for a cut out relay in an alternator system.
In my Harley, I use a magneto and don't have a battery, so this is no problem -- I don't need a cut out regulator. The electrical system is wired so that when the generator makes electricity, the lights come on (if they are switched on). Because Harley parts are expensive, I use an old 6v Volkswagen regulator with the cut out relay removed.
Some, and most American cars (unlike the Volkwagen I mentioned) have a 2nd relay for limiting the current of the generator. This keeps the generator from burning out because of too much current draw. Most alternators don't have this need, since by their design, they are somewhat self regulating as far as current is concerned.
Finally, both alternators and generators use a relay to regulate the voltage. You know that when a wire loop is passed thru a magnetic field, electricity is produced. This magnetic field comes initially from the battery, but once the alternator or generator is producing power, it produces its own power for the electromagnets that produce this magnetic field. Both systems regulate the current that is passed to these electromagnets to maintain the voltage at a constant 14.7 or so volts for a 12 volt system, or about 7.3 volts for a 6 volt system.
However, in the latest alternators (those made for the past 25 years or so) the voltage relay is replaced by another transistorized unit, so this point of wear and adjustment is also missing in the more modern alternator systems.
There are alternators that you can buy, the fully transistorized ones, that have been modified to produce 6 volts if that's what you want.
Now, there are those who will tell you that generators work fine and that 6 volts systems work fine, blah blah blah. I have presented you with the facts here, so you can make up your own mind without needing to listen to "grandpa stories". (You know, those where we had to walk 10 miles to school in a blizzard, uphill both ways. BTW, I'm a grandpa, too, x7)
There is one technical advantage to using a generator over an alternator:
When the battery is dead, I mean REALLY dead, remember that both the generator and the alternator need some initial electricity to produce magnatism so that they can begin to produce power. However, the generator has large iron pole pieces in it, whichi will usually retain a slight amount of residual magnatism, where an alternator does not. For this reason, on a car with a generator and a dead battery, you may be able to get it started by rolling it down a long hill or push starting it. The generator may then get enough power going to power the ignition.
Last edited by wild.bunch; 05-21-2005 at 03:02 PM.
#7
05-22-2005, 05:37 PM
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#9
05-23-2005, 11:33 AM
Logistics Pro
Excellent discription of the differences and advantages!
I'll add that you can get alternators that are called "Single wire" (in fact I think most of them are single-wire now)....Meaning that you do not need an external regulator connected. All you need to do is ensure that it's well grounded and connect the output directly to the electrical system. YOu can still connect it through an ammeter if you want to know how much current (in AMPS) it's delivering or you can just connect it directly to the battery and connect a voltmeter to the system. Any time the Voltage is above about 12.5 volts or so (usually 13.8-14.2V) the ALT is charging.
You can get a pretty cheap junk yard alternator (or an EBAY yard one!) and all you gotta do is make/adapt a bracket, connect 1 wire (to the battery/electrical system) and you're "Good to go".
Regards,
Rick
I'll add that you can get alternators that are called "Single wire" (in fact I think most of them are single-wire now)....Meaning that you do not need an external regulator connected. All you need to do is ensure that it's well grounded and connect the output directly to the electrical system. YOu can still connect it through an ammeter if you want to know how much current (in AMPS) it's delivering or you can just connect it directly to the battery and connect a voltmeter to the system. Any time the Voltage is above about 12.5 volts or so (usually 13.8-14.2V) the ALT is charging.
You can get a pretty cheap junk yard alternator (or an EBAY yard one!) and all you gotta do is make/adapt a bracket, connect 1 wire (to the battery/electrical system) and you're "Good to go".
Regards,
Rick
Originally Posted by chipmunck
Whats the diffrence when ya look at them? I know an altenator is for a 12 volts system, and a charger is for a 6 volt system.
Pat
Pat
#10
05-24-2005, 12:13 PM
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#11
05-26-2005, 08:24 PM
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I made one of those with a 194something (1944, if I’m not mistaken) Briggs & Stratton engine… I used to carry it around to charge batteries of tractors that were out on the field and far away from a 110v plug.
Usually it would take more time to get the little Briggs started than to charge the battery.
Best regards,
Lucas (Lobo)
Usually it would take more time to get the little Briggs started than to charge the battery.
Best regards,
Lucas (Lobo)