New alternator no change in voltage
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Rock Crawling
Joined: Jul 2012
Posts: 464
Likes: 5
From: Warren PA
New alternator no change in voltage
Okay, brand new alternator, and belt. Was getting 12.6 - 13.3 volts with the old one that sounded like it had a few marbles bouncing around in it. Although the new one sounds nice & smooth, the voltage is exactly the same 12.6 - 13.3. The RAVE manual says 13.6 to 14.4 I believe, so what am I missing?? The battery is a few years old & the posts & terminals were cleaned with the alternator change.
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Joined: Jan 2011
Posts: 16,322
Likes: 88
From: Savannah Georgia
Let us agree that all voltmeters don't read exactly the same.
For the battery to be charged you need 13.2 at the bottom end. 14.4 would be top of the pile going the other way. Norm is 13.8-14.2 ish.
Here is a shade tree way to confirm things be working as desired. After cleaning up the ground connection down below battery to frame next to radiator, and the jumper that goes from threaded stud on rear of engine head driver side to firewall stud.
Reading "X" = Truck off, hood up, meter across battery.
Reading "Y" = condition X, and turn on head lights on bright, AC fan on, key in position 2. Truck not started. Reading "Y" will be less than "X". If it drops like a stone by a couple of volts, you have dirty connections on battery cables and those two large connection in front part of the underhood fuse box.
Crank truck, wait a minute, and measure again across battery. We'll call this reading "RL" for running under load.
"RL" should be greater than "X". Normally it is 13.2 or higher. Running with load.
Turn off lights, AC, etc., but leave truck running. Volts should come up a little, we'll call this "RNL", or running with no load. The volts increase because the the internal loss of the alternator (voltage drop) is less with a smaller amp drain. This will be the highest value the system will produce, because there is a minum number of amps the computer, fuel pump, sensors, etc. take to keep motor running.
Y is less than X which is less than RL which is less than RNL.
Battery does not get many amps to float charge across this. That is why people with lots of short 1/2 mile trips are harder on the battery.
So you can have an alternator putting out 13.2 and the truck will charge back up if driven long enough. And a few dirty connections can cut 0.5 volts in a hurry.
The alternators are three-phase devices, and have diodes to convert that AC into DC (direct current). If a diode is blown, you drop 1/3 of the amp output of the alternator. So you have a 66 amp output instead of 100. My D1 with every stock thing switched on draws 85 amps. I had a vehicle with a bad diode that would run normal as long as it wasn't raining. When AC and defrost and wipers and lights were going, the alternator could not keep up and in about 3 hours the battery was dead (reserve capacity depleted).
BTW the light vaseline or silicon bulb grease or dielectric grease is good for these contacts. Under a microscope, the two pieces of metal look like sand paper touching sand paper. The space between the points don't carry any electrical current. But those spaces can build up carbon (arcs) and corrosion and reduce the contact surface for the rest of the connector. Throw in heat cycles and the crud moves into spaces that used to carry power. This added resistance to current flow causes a voltage drop across it, based on the amps. The starter needs about 300 amps. So 1/100 ohm of resistance at 300 amps will produce a drop of 3 volts.
You can take a volt meter, put one proble on the center of the battery terminal stud, and the other on the outer edge of the terminal, and see a voltage drop if enough current is passing through th connetor. It is possible with a volt meter to hunt down dirty connectors. You can also jump around connectors for testing, like taking a battery jumper cable from (-) negative battery lug to engine block.
For the battery to be charged you need 13.2 at the bottom end. 14.4 would be top of the pile going the other way. Norm is 13.8-14.2 ish.
Here is a shade tree way to confirm things be working as desired. After cleaning up the ground connection down below battery to frame next to radiator, and the jumper that goes from threaded stud on rear of engine head driver side to firewall stud.
Reading "X" = Truck off, hood up, meter across battery.
Reading "Y" = condition X, and turn on head lights on bright, AC fan on, key in position 2. Truck not started. Reading "Y" will be less than "X". If it drops like a stone by a couple of volts, you have dirty connections on battery cables and those two large connection in front part of the underhood fuse box.
Crank truck, wait a minute, and measure again across battery. We'll call this reading "RL" for running under load.
"RL" should be greater than "X". Normally it is 13.2 or higher. Running with load.
Turn off lights, AC, etc., but leave truck running. Volts should come up a little, we'll call this "RNL", or running with no load. The volts increase because the the internal loss of the alternator (voltage drop) is less with a smaller amp drain. This will be the highest value the system will produce, because there is a minum number of amps the computer, fuel pump, sensors, etc. take to keep motor running.
Y is less than X which is less than RL which is less than RNL.
Battery does not get many amps to float charge across this. That is why people with lots of short 1/2 mile trips are harder on the battery.
So you can have an alternator putting out 13.2 and the truck will charge back up if driven long enough. And a few dirty connections can cut 0.5 volts in a hurry.
The alternators are three-phase devices, and have diodes to convert that AC into DC (direct current). If a diode is blown, you drop 1/3 of the amp output of the alternator. So you have a 66 amp output instead of 100. My D1 with every stock thing switched on draws 85 amps. I had a vehicle with a bad diode that would run normal as long as it wasn't raining. When AC and defrost and wipers and lights were going, the alternator could not keep up and in about 3 hours the battery was dead (reserve capacity depleted).
BTW the light vaseline or silicon bulb grease or dielectric grease is good for these contacts. Under a microscope, the two pieces of metal look like sand paper touching sand paper. The space between the points don't carry any electrical current. But those spaces can build up carbon (arcs) and corrosion and reduce the contact surface for the rest of the connector. Throw in heat cycles and the crud moves into spaces that used to carry power. This added resistance to current flow causes a voltage drop across it, based on the amps. The starter needs about 300 amps. So 1/100 ohm of resistance at 300 amps will produce a drop of 3 volts.
You can take a volt meter, put one proble on the center of the battery terminal stud, and the other on the outer edge of the terminal, and see a voltage drop if enough current is passing through th connetor. It is possible with a volt meter to hunt down dirty connectors. You can also jump around connectors for testing, like taking a battery jumper cable from (-) negative battery lug to engine block.
Super Moderator
Joined: Jan 2011
Posts: 16,322
Likes: 88
From: Savannah Georgia
Here's the stud, and there is another on the fire wall in that area. I'm going to add the braided strap that others have mentioned after I get my heads finished. Mine has run fine since I owned it, but that strap would be a little insurance if the other one got loose.
Thread Starter
|
Rock Crawling
Joined: Jul 2012
Posts: 464
Likes: 5
From: Warren PA
Let us agree that all voltmeters don't read exactly the same.
For the battery to be charged you need 13.2 at the bottom end. 14.4 would be top of the pile going the other way. Norm is 13.8-14.2 ish.
Here is a shade tree way to confirm things be working as desired. After cleaning up the ground connection down below battery to frame next to radiator, and the jumper that goes from threaded stud on rear of engine head driver side to firewall stud.
Reading "X" = Truck off, hood up, meter across battery.
Reading "Y" = condition X, and turn on head lights on bright, AC fan on, key in position 2. Truck not started. Reading "Y" will be less than "X". If it drops like a stone by a couple of volts, you have dirty connections on battery cables and those two large connection in front part of the underhood fuse box.
Crank truck, wait a minute, and measure again across battery. We'll call this reading "RL" for running under load.
"RL" should be greater than "X". Normally it is 13.2 or higher. Running with load.
Turn off lights, AC, etc., but leave truck running. Volts should come up a little, we'll call this "RNL", or running with no load. The volts increase because the the internal loss of the alternator (voltage drop) is less with a smaller amp drain. This will be the highest value the system will produce, because there is a minum number of amps the computer, fuel pump, sensors, etc. take to keep motor running.
Y is less than X which is less than RL which is less than RNL.
Battery does not get many amps to float charge across this. That is why people with lots of short 1/2 mile trips are harder on the battery.
So you can have an alternator putting out 13.2 and the truck will charge back up if driven long enough. And a few dirty connections can cut 0.5 volts in a hurry.
The alternators are three-phase devices, and have diodes to convert that AC into DC (direct current). If a diode is blown, you drop 1/3 of the amp output of the alternator. So you have a 66 amp output instead of 100. My D1 with every stock thing switched on draws 85 amps. I had a vehicle with a bad diode that would run normal as long as it wasn't raining. When AC and defrost and wipers and lights were going, the alternator could not keep up and in about 3 hours the battery was dead (reserve capacity depleted).
BTW the light vaseline or silicon bulb grease or dielectric grease is good for these contacts. Under a microscope, the two pieces of metal look like sand paper touching sand paper. The space between the points don't carry any electrical current. But those spaces can build up carbon (arcs) and corrosion and reduce the contact surface for the rest of the connector. Throw in heat cycles and the crud moves into spaces that used to carry power. This added resistance to current flow causes a voltage drop across it, based on the amps. The starter needs about 300 amps. So 1/100 ohm of resistance at 300 amps will produce a drop of 3 volts.
You can take a volt meter, put one proble on the center of the battery terminal stud, and the other on the outer edge of the terminal, and see a voltage drop if enough current is passing through th connetor. It is possible with a volt meter to hunt down dirty connectors. You can also jump around connectors for testing, like taking a battery jumper cable from (-) negative battery lug to engine block.
For the battery to be charged you need 13.2 at the bottom end. 14.4 would be top of the pile going the other way. Norm is 13.8-14.2 ish.
Here is a shade tree way to confirm things be working as desired. After cleaning up the ground connection down below battery to frame next to radiator, and the jumper that goes from threaded stud on rear of engine head driver side to firewall stud.
Reading "X" = Truck off, hood up, meter across battery.
Reading "Y" = condition X, and turn on head lights on bright, AC fan on, key in position 2. Truck not started. Reading "Y" will be less than "X". If it drops like a stone by a couple of volts, you have dirty connections on battery cables and those two large connection in front part of the underhood fuse box.
Crank truck, wait a minute, and measure again across battery. We'll call this reading "RL" for running under load.
"RL" should be greater than "X". Normally it is 13.2 or higher. Running with load.
Turn off lights, AC, etc., but leave truck running. Volts should come up a little, we'll call this "RNL", or running with no load. The volts increase because the the internal loss of the alternator (voltage drop) is less with a smaller amp drain. This will be the highest value the system will produce, because there is a minum number of amps the computer, fuel pump, sensors, etc. take to keep motor running.
Y is less than X which is less than RL which is less than RNL.
Battery does not get many amps to float charge across this. That is why people with lots of short 1/2 mile trips are harder on the battery.
So you can have an alternator putting out 13.2 and the truck will charge back up if driven long enough. And a few dirty connections can cut 0.5 volts in a hurry.
The alternators are three-phase devices, and have diodes to convert that AC into DC (direct current). If a diode is blown, you drop 1/3 of the amp output of the alternator. So you have a 66 amp output instead of 100. My D1 with every stock thing switched on draws 85 amps. I had a vehicle with a bad diode that would run normal as long as it wasn't raining. When AC and defrost and wipers and lights were going, the alternator could not keep up and in about 3 hours the battery was dead (reserve capacity depleted).
BTW the light vaseline or silicon bulb grease or dielectric grease is good for these contacts. Under a microscope, the two pieces of metal look like sand paper touching sand paper. The space between the points don't carry any electrical current. But those spaces can build up carbon (arcs) and corrosion and reduce the contact surface for the rest of the connector. Throw in heat cycles and the crud moves into spaces that used to carry power. This added resistance to current flow causes a voltage drop across it, based on the amps. The starter needs about 300 amps. So 1/100 ohm of resistance at 300 amps will produce a drop of 3 volts.
You can take a volt meter, put one proble on the center of the battery terminal stud, and the other on the outer edge of the terminal, and see a voltage drop if enough current is passing through th connetor. It is possible with a volt meter to hunt down dirty connectors. You can also jump around connectors for testing, like taking a battery jumper cable from (-) negative battery lug to engine block.
