alternator?
- Thread starter vader6
- Start date
if you just want to know the answer, the correct answer to your question is simple ---- the stock 120 amp alternator is more than adequate for a system several times the size of yours the explanation as to why is rather technical but if you really need to know why let me know and i can explain it in detail
you have mentioned this before, please explain so that we can understand.
its thanksgiving and i am busy so i will have to divide this into several posts to cover it all since there are several things that determine the final answer to this often asked question. There is a lot of misinformation and confusion in this area because the answers cover several areas of expertise. They are in no particular order 1- the baseline electrical needs of the car before the stereo is added 2- the crest factor and duty cycle of music 3- the size of the system and the level the listener wants to listen to their music 4- the class of amplifiers used in the system 5- how the car is used/driven. As I get a chance i will cover these subjects and their interactions in detail............RC
sorry guys but its been a very busy season here at the garage. Finally got a spell to start some comments on this subject. For starters this should be enough data for most normal systems.......
Calculating if you need an upgrade to your alternator and if so just how much of an upgrade can involve several factors. The first thing to consider is how adequate is the alternator that came with the car to begin with.
The subject of adequate can vary based on the car model but one thing you can be certain is that a lot of testing and engineering went into the choice of capacity to begin with. Car companies balance several factors when they make this decision. First is the cost. They are not going to give you an alternator the is so overkill that it amounts to throwing a lot of money away. On the other hand they want to make sure that what comes on the car has enough reserve so that you are not going to have problems that could make for warranty problems. Different accessories, driving habits, weather conditions and numerous other factors can affect this decision. Modern cars tend to have a little more reserve than most older cars due to the numerous electronic gadgets that typically end up in our cars.
Really at this point all we care about is the VIN7 package so we will limit this discussion to that. For a car of its time the turbo Regal actually came with a rather robust alternator for how it was equipped. The 120 amp (1700 watt) alternator was larger than most all passenger cars of the era. A few years ago I was preparing data for a seminar on this very subject and I did a very interesting experiment to get some actual measurements.
For the test I put a fully optioned nearly stock GNX on a dyno. Only mods were it had a Walbro 340 fuel pump and a F.A.S.T. engine management controller. I had two people helping me and with the car warmed up and running 60MPH on the dyno we started to turn on every accessory on the car. Things like high beams, windshield wipers, turn signals, both windows up and down continuously, AC on high, light foot on the brake to turn on tail lights, radio up loud, cigarette lighter on, rear defogger, horn, and everything else we could think that could use power. The most current draw we could measure from the alternator was a comfortable 105 amps. Needless to say it's not very likely that anyone would ever duplicate these conditions in actual driving since it took 3 people to do it on a stationary car.
Worse case conditions we could duplicate in actual driving took place immediately after starting the car while the alternator was initially recharging the battery from the starter drain and the AC was running i.e. meaning fan on. This case resulted in a short term 75 amp (1050 watts) drain that tapered off after about a minute to about 45 amps (630watts).
Just for the record the largest user of electrical power in a GN is the radiator fan at a whopping 16 amps. When it first starts up for a fraction of a second it actually draws over 60 amps! A 340 walbro uses about 16 amps at 70 psi.
Now the question was what would be the impact of a 500 watt amplifier on a similar car. To really understand this question we need to look at amplifier designs and the nature of music. Let's start with amplifier design. For many years amplifiers made for use in cars were of the Class A-B type. These amplifiers generally had efficiencies that varied with actual power output. By efficiency we mean how much power did they consume (from the car) for the amount of power that they actually put out to the speakers. All car amps are essentially divided into two sections. First is the power supply and second is the audio section. Older designs and lower cost newer designs have power supplies that were of the PWM type (pulse width modulation) these supplies actually increased in efficiency the closer they got to full output. At full output many could actually achieve 85% to 90% efficiency. Efficiencies got lower at lower power levels but it did not matter since at lower power levels it was not as important. The audio sections of these same amplifiers typically ranged from 15% to 70% percent. When the power supply and audio sections were combined the overall efficiency of these designs resulted in efficiencies at full power of about 60%.
Newer amplifier designs, especially higher powered units are what is classified as "switching" or "digital" types. There are numerous variations on these designs but the common thread among them is overall high efficiency that that can sometimes result in numbers in the 90% range. Needless to say this type of amp can take a big load off the alternator.
At this point let's see how far we have come in our calculations. We are considering adding a 500 watt amp to our GN. Assuming that it is really a 500 watt amp (not unusual for specs to be exaggerated) but for the sake of this we will assume it's really 500 actual watts. I will also make another assumption that since 500 watts these days is not really very large I will also assume that it is a PWM class AB design. such an amp would draw about 800 watts from the car at full power. If these assumptions are correct the amp would require a 50 amp fuse in order to output 500 watts. If it is a switching design it will draw less than 600 watts at full power and need a 35 amp fuse.
Either way on the surface it would look like our 120 amp alternator which is a 1700 watt unit would be ok in either case since real world driving demand would be 100 to 300 watts under the alternators limit.
But that's just how it looks on the surface and like the ocean there's a lot more underneath than appears on the surface. Many folks really have an elementary understanding of electricity and a kindergarten understanding of music. When we rate an appliance at 500 watts that means that when it is connected to an electrical circuit it will consume 500 watts of power. If it is a device intended to operate on 120 volts this means that slightly over 4 amps will flow through it and if it is designed for 12 volts 40 amps will flow through it at the same 500 watt power level.
Unlike constant power sources like we have in our homes of 120 volts AC and our cars at 12 volts DC (usually more like 14 if the engine is running) music is not continuous at all. By its very nature it is constantly changing both in frequency and amplitude. There is really no such thing as continuous music. It is true that amplifier measurements are usually made with continuous sine waves and the term "RMS power" (root mean squared) is used as a specification but it has little to no relation to actual music signals. The little understood fact is that if you have an amplifier that has a RMS power rating of 500 watts the most UNDISTORTED wattage you can get out of it when playing music is about 50 watts of average power. This is because music and speech have what is known as "crest factor". Crest factor is the term that is used to define the average power level of a signal to the peak level of the same signal. The crest factor of average music and speech is about 10 db. The measurement of DB is a log unit that is used to measure audio and electrical analogous signals that represent audio. 10 db represents a power ratio of 10:1. If you were to monitor with an oscilloscope the amplifier signal actually going to your speaker at an average power level of 50 watts you would see that the highest momentary peaks would be about 500 watts and at about the same amount of time the power level would be as low as 5 watts. That's just how music is.
Now that we know the difference between driving a light bulb, fan or fuel pump verses a speaker what does this really mean as far as our alternators ability to power an audio amp? It means that when driving an audio amp that is going to be playing music that things are totally different. The 120 amp alternator in your car can easily supply power to 2000 watts of modern amplifiers and 1500 watts worth of "older style" amps.
Don't believe it. At one time I competed in professional car audio championships with a GN that had 3500 watts worth of "old style" class AB amplifiers. That was 5 amplifiers with a continuous RMS power rating of 700 watts each. The car had a 160 amp alternator. I was world champion in the IASCA unlimited professional class and was never defeated a single time in 4 years of competition. I also won the Masters invitational tournament 3 times. First prize in the Masters was $25K. I never had a single charging problem at all. If a bigger alternator would have made any difference you can bet I would have had it.
Calculating if you need an upgrade to your alternator and if so just how much of an upgrade can involve several factors. The first thing to consider is how adequate is the alternator that came with the car to begin with.
The subject of adequate can vary based on the car model but one thing you can be certain is that a lot of testing and engineering went into the choice of capacity to begin with. Car companies balance several factors when they make this decision. First is the cost. They are not going to give you an alternator the is so overkill that it amounts to throwing a lot of money away. On the other hand they want to make sure that what comes on the car has enough reserve so that you are not going to have problems that could make for warranty problems. Different accessories, driving habits, weather conditions and numerous other factors can affect this decision. Modern cars tend to have a little more reserve than most older cars due to the numerous electronic gadgets that typically end up in our cars.
Really at this point all we care about is the VIN7 package so we will limit this discussion to that. For a car of its time the turbo Regal actually came with a rather robust alternator for how it was equipped. The 120 amp (1700 watt) alternator was larger than most all passenger cars of the era. A few years ago I was preparing data for a seminar on this very subject and I did a very interesting experiment to get some actual measurements.
For the test I put a fully optioned nearly stock GNX on a dyno. Only mods were it had a Walbro 340 fuel pump and a F.A.S.T. engine management controller. I had two people helping me and with the car warmed up and running 60MPH on the dyno we started to turn on every accessory on the car. Things like high beams, windshield wipers, turn signals, both windows up and down continuously, AC on high, light foot on the brake to turn on tail lights, radio up loud, cigarette lighter on, rear defogger, horn, and everything else we could think that could use power. The most current draw we could measure from the alternator was a comfortable 105 amps. Needless to say it's not very likely that anyone would ever duplicate these conditions in actual driving since it took 3 people to do it on a stationary car.
Worse case conditions we could duplicate in actual driving took place immediately after starting the car while the alternator was initially recharging the battery from the starter drain and the AC was running i.e. meaning fan on. This case resulted in a short term 75 amp (1050 watts) drain that tapered off after about a minute to about 45 amps (630watts).
Just for the record the largest user of electrical power in a GN is the radiator fan at a whopping 16 amps. When it first starts up for a fraction of a second it actually draws over 60 amps! A 340 walbro uses about 16 amps at 70 psi.
Now the question was what would be the impact of a 500 watt amplifier on a similar car. To really understand this question we need to look at amplifier designs and the nature of music. Let's start with amplifier design. For many years amplifiers made for use in cars were of the Class A-B type. These amplifiers generally had efficiencies that varied with actual power output. By efficiency we mean how much power did they consume (from the car) for the amount of power that they actually put out to the speakers. All car amps are essentially divided into two sections. First is the power supply and second is the audio section. Older designs and lower cost newer designs have power supplies that were of the PWM type (pulse width modulation) these supplies actually increased in efficiency the closer they got to full output. At full output many could actually achieve 85% to 90% efficiency. Efficiencies got lower at lower power levels but it did not matter since at lower power levels it was not as important. The audio sections of these same amplifiers typically ranged from 15% to 70% percent. When the power supply and audio sections were combined the overall efficiency of these designs resulted in efficiencies at full power of about 60%.
Newer amplifier designs, especially higher powered units are what is classified as "switching" or "digital" types. There are numerous variations on these designs but the common thread among them is overall high efficiency that that can sometimes result in numbers in the 90% range. Needless to say this type of amp can take a big load off the alternator.
At this point let's see how far we have come in our calculations. We are considering adding a 500 watt amp to our GN. Assuming that it is really a 500 watt amp (not unusual for specs to be exaggerated) but for the sake of this we will assume it's really 500 actual watts. I will also make another assumption that since 500 watts these days is not really very large I will also assume that it is a PWM class AB design. such an amp would draw about 800 watts from the car at full power. If these assumptions are correct the amp would require a 50 amp fuse in order to output 500 watts. If it is a switching design it will draw less than 600 watts at full power and need a 35 amp fuse.
Either way on the surface it would look like our 120 amp alternator which is a 1700 watt unit would be ok in either case since real world driving demand would be 100 to 300 watts under the alternators limit.
But that's just how it looks on the surface and like the ocean there's a lot more underneath than appears on the surface. Many folks really have an elementary understanding of electricity and a kindergarten understanding of music. When we rate an appliance at 500 watts that means that when it is connected to an electrical circuit it will consume 500 watts of power. If it is a device intended to operate on 120 volts this means that slightly over 4 amps will flow through it and if it is designed for 12 volts 40 amps will flow through it at the same 500 watt power level.
Unlike constant power sources like we have in our homes of 120 volts AC and our cars at 12 volts DC (usually more like 14 if the engine is running) music is not continuous at all. By its very nature it is constantly changing both in frequency and amplitude. There is really no such thing as continuous music. It is true that amplifier measurements are usually made with continuous sine waves and the term "RMS power" (root mean squared) is used as a specification but it has little to no relation to actual music signals. The little understood fact is that if you have an amplifier that has a RMS power rating of 500 watts the most UNDISTORTED wattage you can get out of it when playing music is about 50 watts of average power. This is because music and speech have what is known as "crest factor". Crest factor is the term that is used to define the average power level of a signal to the peak level of the same signal. The crest factor of average music and speech is about 10 db. The measurement of DB is a log unit that is used to measure audio and electrical analogous signals that represent audio. 10 db represents a power ratio of 10:1. If you were to monitor with an oscilloscope the amplifier signal actually going to your speaker at an average power level of 50 watts you would see that the highest momentary peaks would be about 500 watts and at about the same amount of time the power level would be as low as 5 watts. That's just how music is.
Now that we know the difference between driving a light bulb, fan or fuel pump verses a speaker what does this really mean as far as our alternators ability to power an audio amp? It means that when driving an audio amp that is going to be playing music that things are totally different. The 120 amp alternator in your car can easily supply power to 2000 watts of modern amplifiers and 1500 watts worth of "older style" amps.
Don't believe it. At one time I competed in professional car audio championships with a GN that had 3500 watts worth of "old style" class AB amplifiers. That was 5 amplifiers with a continuous RMS power rating of 700 watts each. The car had a 160 amp alternator. I was world champion in the IASCA unlimited professional class and was never defeated a single time in 4 years of competition. I also won the Masters invitational tournament 3 times. First prize in the Masters was $25K. I never had a single charging problem at all. If a bigger alternator would have made any difference you can bet I would have had it.
Royal-T-Ltd
Well-Known Member
- Joined
- Jul 12, 2003
Always amazed.... thank you Mr. Clark!
Sent from my iPhone using Tapatalk Pro
Sent from my iPhone using Tapatalk Pro
And that was the 099 version...lol
. Thank you for taking the time to post.Thread resurrection: my car killed the stock alternator after upgrading to intrepid fans and at least one other in our group had a similar story. How much do they affect your opinion of the stock charging system? Were we just bitten by a combination of bad luck and old parts or should we consider an upgraded alternator? My car has a custom harness that retains hi/low operation like the stock fan so inrush current doesn't hit the alternator like the caspers harnesses that I've seen. One friend's car, when sitting there idling, will have a noticeable rpm drop when the intrepid fans turn on (hi speed only) and since they flow so much air on high, it cycles the fan on/off frequently and sometimes even has a slight belt chirp when they kick on. Is this operation bad for a stock alternator at idle?
