voltmeter question
08-09-2018, 10:27 AM
#21
Being an ex-automotive electrician I can tell you some of these posts are worthless.
First, you should not be changing pulleys to get more voltage on a Corvette. That's nonsense.
Secondly, when you check the output of a charging system on ANY car, you don't worry about amperage. If the voltage is correct, the amperage will be there. You put a voltmeter across the battery terminals and forget about the amperage.
Checking a system is simple. Either go by the dash gauge (if it is accurate) or put an additional voltmeter across the battery. Rev the engine up to operating speed, pull on the AC and the headlights. The voltage should be between 13.8 and 14.2 volts. Or close to that. The system should carry the load. If it does, you're ok. If the voltage drops way back down under that when you turn these on, then you have a problem.
Good luck.
First, you should not be changing pulleys to get more voltage on a Corvette. That's nonsense.
Secondly, when you check the output of a charging system on ANY car, you don't worry about amperage. If the voltage is correct, the amperage will be there. You put a voltmeter across the battery terminals and forget about the amperage.
Checking a system is simple. Either go by the dash gauge (if it is accurate) or put an additional voltmeter across the battery. Rev the engine up to operating speed, pull on the AC and the headlights. The voltage should be between 13.8 and 14.2 volts. Or close to that. The system should carry the load. If it does, you're ok. If the voltage drops way back down under that when you turn these on, then you have a problem.
Good luck.
Last edited by Jimmy W1; 08-09-2018 at 10:29 AM.
08-09-2018, 06:20 PM
#22
We can play the voltage or amperage game, but lets break it way down to wattage isntead.
Hence 1 volt, times 1 amp, equals 1 watt.
Simply voltage is the working current, and amperage is the power behind the current of how much is can supply. When the power behind the voltage drops down below the need threshold of the demand, they you get a drop in voltage plan and simple.
So the alternator is working at 14.7 volts, it ends up being 14.5 volts by the time that the power makes it to the battery, and at idle, the OEM alternator is good for 203 watts at the battery (14.5v X14 amps that the oem alternator puts out at idle).
Now the glitch, with the AC on which turns the raditor fan running (it has a 14 amp load itself), and just motor running, the charge to the battery from the alternator needs to be 240 watts to keep up with the running demand (12 volts at the 20 amps the car is pulling with just the A/C on). If the lights are on, the windshield wipers and even the radio, then even higher wattage demands isntead. The billet 6 pole/phase alternator puts out 45 amps, 14.7 volts at idle, hence puts out 652.5 watts at idle, and well above what the car will be demanding at idle with everything tuned on instead.
So again, the problem is not the max amperage that either the billet or oem alternator will put out at full spin, but what they put out at idle when you are sitting at a stop light instead. Using the wattage really breaks the problem down to the basics, and is and has always been the problem with the OEM alternator not keeping up with the demand of the car with the A/c and you at a stop light. Also to point out, the needed min voltage to the modules in the car needs to be 12 volts or greater. If at any point the modules in the car dip below 12 volts, the modules glitch to hell instead.
So across the board.
Alternator runs at 14.7 volts, byy the time the power gets to the battery, it down to 14.5 volts. The DIC and gauge voltage is telling you the voltage to the ECM (not the dash cluster), so by the time 14.5 volts at the fuse box gets to the BCM, then sent to the ECM, it down to 14.3~14.1 volts (due the lenght of wire and there gauge sizes). When you don't have enough amperage to keep up with demand, then you get voltage drops, and really on the C6, if the voltage to the modules drops below the 12.8 volt threshold on the dash (voltage at the ECM), your get charging system codes.
So fully charged and good battery, everything on, it not out of the question to be at 13.5 volts at the ECM when you first stop at the stop light, and if you have to sit there long enough, could end up down to 13.1 volts as the battery drains down. Battery less then perfect from all the drain and recharge cycles every stop light with the A/C on in a fews years, and this is where you end up with the ECM voltage down in the 12.5 range and the car starting to throw codes.
FYI, but fully charged good car battery is about 13.7 volts.
Does everyone need a billet alternator, not really and I'm a good example since I really never have the A/C on to begin with, so my battery pretty much stays charged after is charged back up from starting the car (voltage holds at 14.3 volts on the DIC even at idle since I don't use the A/C).
On the other hand, if someone is living in the desert or other high heat areas where the A/C is going to be used every time the car is run, then something like the billet for an upgraded alternator is a must isntead.
Bluntly put, do the math on how many batteries that you will go through using the OEM alternator, verse the billet in say a 8 year period, and the billet alternator has pretty much paid for itself since a single battery will last the 8 years without problems using the billet alternator on the C6 isntead.
Hence 1 volt, times 1 amp, equals 1 watt.
Simply voltage is the working current, and amperage is the power behind the current of how much is can supply. When the power behind the voltage drops down below the need threshold of the demand, they you get a drop in voltage plan and simple.
So the alternator is working at 14.7 volts, it ends up being 14.5 volts by the time that the power makes it to the battery, and at idle, the OEM alternator is good for 203 watts at the battery (14.5v X14 amps that the oem alternator puts out at idle).
Now the glitch, with the AC on which turns the raditor fan running (it has a 14 amp load itself), and just motor running, the charge to the battery from the alternator needs to be 240 watts to keep up with the running demand (12 volts at the 20 amps the car is pulling with just the A/C on). If the lights are on, the windshield wipers and even the radio, then even higher wattage demands isntead. The billet 6 pole/phase alternator puts out 45 amps, 14.7 volts at idle, hence puts out 652.5 watts at idle, and well above what the car will be demanding at idle with everything tuned on instead.
So again, the problem is not the max amperage that either the billet or oem alternator will put out at full spin, but what they put out at idle when you are sitting at a stop light instead. Using the wattage really breaks the problem down to the basics, and is and has always been the problem with the OEM alternator not keeping up with the demand of the car with the A/c and you at a stop light. Also to point out, the needed min voltage to the modules in the car needs to be 12 volts or greater. If at any point the modules in the car dip below 12 volts, the modules glitch to hell instead.
So across the board.
Alternator runs at 14.7 volts, byy the time the power gets to the battery, it down to 14.5 volts. The DIC and gauge voltage is telling you the voltage to the ECM (not the dash cluster), so by the time 14.5 volts at the fuse box gets to the BCM, then sent to the ECM, it down to 14.3~14.1 volts (due the lenght of wire and there gauge sizes). When you don't have enough amperage to keep up with demand, then you get voltage drops, and really on the C6, if the voltage to the modules drops below the 12.8 volt threshold on the dash (voltage at the ECM), your get charging system codes.
So fully charged and good battery, everything on, it not out of the question to be at 13.5 volts at the ECM when you first stop at the stop light, and if you have to sit there long enough, could end up down to 13.1 volts as the battery drains down. Battery less then perfect from all the drain and recharge cycles every stop light with the A/C on in a fews years, and this is where you end up with the ECM voltage down in the 12.5 range and the car starting to throw codes.
FYI, but fully charged good car battery is about 13.7 volts.
Does everyone need a billet alternator, not really and I'm a good example since I really never have the A/C on to begin with, so my battery pretty much stays charged after is charged back up from starting the car (voltage holds at 14.3 volts on the DIC even at idle since I don't use the A/C).
On the other hand, if someone is living in the desert or other high heat areas where the A/C is going to be used every time the car is run, then something like the billet for an upgraded alternator is a must isntead.
Bluntly put, do the math on how many batteries that you will go through using the OEM alternator, verse the billet in say a 8 year period, and the billet alternator has pretty much paid for itself since a single battery will last the 8 years without problems using the billet alternator on the C6 isntead.
Last edited by Dano523; 08-09-2018 at 06:22 PM.
The following users liked this post:
dpigguy (08-09-2018)
08-10-2018, 06:21 AM
#23
We can play the voltage or amperage game, but lets break it way down to wattage isntead.
Hence 1 volt, times 1 amp, equals 1 watt.
Simply voltage is the working current, and amperage is the power behind the current of how much is can supply. When the power behind the voltage drops down below the need threshold of the demand, they you get a drop in voltage plan and simple.
So the alternator is working at 14.7 volts, it ends up being 14.5 volts by the time that the power makes it to the battery, and at idle, the OEM alternator is good for 203 watts at the battery (14.5v X14 amps that the oem alternator puts out at idle).
Now the glitch, with the AC on which turns the raditor fan running (it has a 14 amp load itself), and just motor running, the charge to the battery from the alternator needs to be 240 watts to keep up with the running demand (12 volts at the 20 amps the car is pulling with just the A/C on). If the lights are on, the windshield wipers and even the radio, then even higher wattage demands isntead. The billet 6 pole/phase alternator puts out 45 amps, 14.7 volts at idle, hence puts out 652.5 watts at idle, and well above what the car will be demanding at idle with everything tuned on instead.
So again, the problem is not the max amperage that either the billet or oem alternator will put out at full spin, but what they put out at idle when you are sitting at a stop light instead. Using the wattage really breaks the problem down to the basics, and is and has always been the problem with the OEM alternator not keeping up with the demand of the car with the A/c and you at a stop light. Also to point out, the needed min voltage to the modules in the car needs to be 12 volts or greater. If at any point the modules in the car dip below 12 volts, the modules glitch to hell instead.
So across the board.
Alternator runs at 14.7 volts, byy the time the power gets to the battery, it down to 14.5 volts. The DIC and gauge voltage is telling you the voltage to the ECM (not the dash cluster), so by the time 14.5 volts at the fuse box gets to the BCM, then sent to the ECM, it down to 14.3~14.1 volts (due the lenght of wire and there gauge sizes). When you don't have enough amperage to keep up with demand, then you get voltage drops, and really on the C6, if the voltage to the modules drops below the 12.8 volt threshold on the dash (voltage at the ECM), your get charging system codes.
So fully charged and good battery, everything on, it not out of the question to be at 13.5 volts at the ECM when you first stop at the stop light, and if you have to sit there long enough, could end up down to 13.1 volts as the battery drains down. Battery less then perfect from all the drain and recharge cycles every stop light with the A/C on in a fews years, and this is where you end up with the ECM voltage down in the 12.5 range and the car starting to throw codes.
FYI, but fully charged good car battery is about 13.7 volts.
Does everyone need a billet alternator, not really and I'm a good example since I really never have the A/C on to begin with, so my battery pretty much stays charged after is charged back up from starting the car (voltage holds at 14.3 volts on the DIC even at idle since I don't use the A/C).
On the other hand, if someone is living in the desert or other high heat areas where the A/C is going to be used every time the car is run, then something like the billet for an upgraded alternator is a must isntead.
Bluntly put, do the math on how many batteries that you will go through using the OEM alternator, verse the billet in say a 8 year period, and the billet alternator has pretty much paid for itself since a single battery will last the 8 years without problems using the billet alternator on the C6 isntead.
Hence 1 volt, times 1 amp, equals 1 watt.
Simply voltage is the working current, and amperage is the power behind the current of how much is can supply. When the power behind the voltage drops down below the need threshold of the demand, they you get a drop in voltage plan and simple.
So the alternator is working at 14.7 volts, it ends up being 14.5 volts by the time that the power makes it to the battery, and at idle, the OEM alternator is good for 203 watts at the battery (14.5v X14 amps that the oem alternator puts out at idle).
Now the glitch, with the AC on which turns the raditor fan running (it has a 14 amp load itself), and just motor running, the charge to the battery from the alternator needs to be 240 watts to keep up with the running demand (12 volts at the 20 amps the car is pulling with just the A/C on). If the lights are on, the windshield wipers and even the radio, then even higher wattage demands isntead. The billet 6 pole/phase alternator puts out 45 amps, 14.7 volts at idle, hence puts out 652.5 watts at idle, and well above what the car will be demanding at idle with everything tuned on instead.
So again, the problem is not the max amperage that either the billet or oem alternator will put out at full spin, but what they put out at idle when you are sitting at a stop light instead. Using the wattage really breaks the problem down to the basics, and is and has always been the problem with the OEM alternator not keeping up with the demand of the car with the A/c and you at a stop light. Also to point out, the needed min voltage to the modules in the car needs to be 12 volts or greater. If at any point the modules in the car dip below 12 volts, the modules glitch to hell instead.
So across the board.
Alternator runs at 14.7 volts, byy the time the power gets to the battery, it down to 14.5 volts. The DIC and gauge voltage is telling you the voltage to the ECM (not the dash cluster), so by the time 14.5 volts at the fuse box gets to the BCM, then sent to the ECM, it down to 14.3~14.1 volts (due the lenght of wire and there gauge sizes). When you don't have enough amperage to keep up with demand, then you get voltage drops, and really on the C6, if the voltage to the modules drops below the 12.8 volt threshold on the dash (voltage at the ECM), your get charging system codes.
So fully charged and good battery, everything on, it not out of the question to be at 13.5 volts at the ECM when you first stop at the stop light, and if you have to sit there long enough, could end up down to 13.1 volts as the battery drains down. Battery less then perfect from all the drain and recharge cycles every stop light with the A/C on in a fews years, and this is where you end up with the ECM voltage down in the 12.5 range and the car starting to throw codes.
FYI, but fully charged good car battery is about 13.7 volts.
Does everyone need a billet alternator, not really and I'm a good example since I really never have the A/C on to begin with, so my battery pretty much stays charged after is charged back up from starting the car (voltage holds at 14.3 volts on the DIC even at idle since I don't use the A/C).
On the other hand, if someone is living in the desert or other high heat areas where the A/C is going to be used every time the car is run, then something like the billet for an upgraded alternator is a must isntead.
Bluntly put, do the math on how many batteries that you will go through using the OEM alternator, verse the billet in say a 8 year period, and the billet alternator has pretty much paid for itself since a single battery will last the 8 years without problems using the billet alternator on the C6 isntead.
Just simply check your car the way I said. Forget about the WATTAGE and the amperage. Obviously GM did. That's why they only put a voltmeter in their cars. And I can assure you, if you put a voltmeter across the battery on a C6 Corvette, the voltage on the dash will more than likely be the same.
So please, don't confuse these guys with talk about wattage dropping. Wattage doesn't even belong in a conversation about a charging system on a car.
Last edited by Jimmy W1; 08-10-2018 at 07:24 AM.
08-10-2018, 06:32 PM
#24
Output of the alternator is 14.7 volts.
Down line at the battery with the car idling, and A/C off, you will have 14.5 volts.
Power goes to the engine fuse box from the battery, to the BCM, and then to the modules down line like the ECM from the BCM.
The dash voltage gauge and DIC set to voltage, will be showing you the voltage at the ECM. Hence dash is all digital and its readout readings are coming from the GM land bus to display that information only. So the best voltage your going to see is 14.3~14.1 volts to start with on either of the gauges, and again with the raditor fan and other accessorizes off. With the A/C on to cause the raditor fan to run, normal voltage at the dash will be 13.8volts, and as the battery discharges with you sitting at a stop light long enough since the OEM alternator can not keep up with the demand, and/or you have other items on, can end up with a dash voltage (ecm) of less than 13 volts by the time the light turns green on a longer light.
08-10-2018, 09:27 PM
#25
Safety Car
That's the problem and it will not be the same the same.
Output of the alternator is 14.7 volts.
Down line at the battery with the car idling, and A/C off, you will have 14.5 volts.
Power goes to the engine fuse box from the battery, to the BCM, and then to the modules down line like the ECM from the BCM.
The dash voltage gauge and DIC set to voltage, will be showing you the voltage at the ECM. Hence dash is all digital and its readout readings are coming from the GM land bus to display that information only. So the best voltage your going to see is 14.3~14.1 volts to start with on either of the gauges, and again with the raditor fan and other accessorizes off. With the A/C on to cause the raditor fan to run, normal voltage at the dash will be 13.8volts, and as the battery discharges with you sitting at a stop light long enough since the OEM alternator can not keep up with the demand, and/or you have other items on, can end up with a dash voltage (ecm) of less than 13 volts by the time the light turns green on a longer light.
Output of the alternator is 14.7 volts.
Down line at the battery with the car idling, and A/C off, you will have 14.5 volts.
Power goes to the engine fuse box from the battery, to the BCM, and then to the modules down line like the ECM from the BCM.
The dash voltage gauge and DIC set to voltage, will be showing you the voltage at the ECM. Hence dash is all digital and its readout readings are coming from the GM land bus to display that information only. So the best voltage your going to see is 14.3~14.1 volts to start with on either of the gauges, and again with the raditor fan and other accessorizes off. With the A/C on to cause the raditor fan to run, normal voltage at the dash will be 13.8volts, and as the battery discharges with you sitting at a stop light long enough since the OEM alternator can not keep up with the demand, and/or you have other items on, can end up with a dash voltage (ecm) of less than 13 volts by the time the light turns green on a longer light.
08-10-2018, 11:14 PM
#26
Melting Slicks
Member Since: Jul 2010
Location: Tacoma, Wa/Surprise, Az
Posts: 2,841
Received 178 Likes
on
160 Posts
Dano, good comments all along the thread, tha wattage comparison may help deepen the understandings of those who want to know more. There are so many threads on the forum from folks concerned about their charging systems, this should go a long way to helping them too.
I was riding in my wife's Ford SUV, it's one of the little ones, talk about voltage drop, the engine shuts down at trffic lights with AC, lights, whatever running. All I can think of is shortened battery life at the expense of a few drops of gasoline.
I was riding in my wife's Ford SUV, it's one of the little ones, talk about voltage drop, the engine shuts down at trffic lights with AC, lights, whatever running. All I can think of is shortened battery life at the expense of a few drops of gasoline.
08-11-2018, 06:17 AM
#27
That's the problem and it will not be the same the same.
Output of the alternator is 14.7 volts.
Down line at the battery with the car idling, and A/C off, you will have 14.5 volts.
Power goes to the engine fuse box from the battery, to the BCM, and then to the modules down line like the ECM from the BCM.
The dash voltage gauge and DIC set to voltage, will be showing you the voltage at the ECM. Hence dash is all digital and its readout readings are coming from the GM land bus to display that information only. So the best voltage your going to see is 14.3~14.1 volts to start with on either of the gauges, and again with the raditor fan and other accessorizes off. With the A/C on to cause the raditor fan to run, normal voltage at the dash will be 13.8volts, and as the battery discharges with you sitting at a stop light long enough since the OEM alternator can not keep up with the demand, and/or you have other items on, can end up with a dash voltage (ecm) of less than 13 volts by the time the light turns green on a longer light.
Output of the alternator is 14.7 volts.
Down line at the battery with the car idling, and A/C off, you will have 14.5 volts.
Power goes to the engine fuse box from the battery, to the BCM, and then to the modules down line like the ECM from the BCM.
The dash voltage gauge and DIC set to voltage, will be showing you the voltage at the ECM. Hence dash is all digital and its readout readings are coming from the GM land bus to display that information only. So the best voltage your going to see is 14.3~14.1 volts to start with on either of the gauges, and again with the raditor fan and other accessorizes off. With the A/C on to cause the raditor fan to run, normal voltage at the dash will be 13.8volts, and as the battery discharges with you sitting at a stop light long enough since the OEM alternator can not keep up with the demand, and/or you have other items on, can end up with a dash voltage (ecm) of less than 13 volts by the time the light turns green on a longer light.
And if you want to check the system properly, you check it the way I said.
And there's no sense worrying about what the voltage is at idle speed. You don't drive the car at idle speed. You drive the car at the operating rpm. So when you want to see if your system is charging properly, you rev the engine up to the operating rpm- pull on the lights and turn on the AC and the system should be holding the load and remaining the same. And the voltage should read somewhere in the neighborhood of 13.8- 14.2 volts.
And there's no sense worrying about what your car reads at idle- just because it may drop a little bit. As long as your car has gasoline, it will run for hours, probably days, at idle speed and the battery won't go dead if your system is charging properly.
So forget about the amps and the wattage and check the system the way I said. It's not rocket science. Just check the VOLTAGE at the battery and forget about all this other nonsense.
Good luck.