alternator test
07-01-2018, 07:06 PM
#16
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guys, if it was that simple, i would have missed it. does this make sense to anyone? can we expand on this theory?note
"To check to see if your alternator is working, unplug or remove the two field wires from the back of the alternator. Then ground one of the field terminals on the alternator and jumper the other field terminal to the positive battery post on the back of the alternator. It does not matter which terminal is grounded and which one get positive power. When you connect the ground and positive wires to the field terminals you will get a small spark, this is normal. This is by-passing the voltage control and will cause your alternator to run full blast, if it is working. Put a multi-meter on your battery and run your engine on high idle, do not allow your alternator to charge the battery much over 16 volts." -the alternator man-
"To check to see if your alternator is working, unplug or remove the two field wires from the back of the alternator. Then ground one of the field terminals on the alternator and jumper the other field terminal to the positive battery post on the back of the alternator. It does not matter which terminal is grounded and which one get positive power. When you connect the ground and positive wires to the field terminals you will get a small spark, this is normal. This is by-passing the voltage control and will cause your alternator to run full blast, if it is working. Put a multi-meter on your battery and run your engine on high idle, do not allow your alternator to charge the battery much over 16 volts." -the alternator man-
07-01-2018, 07:12 PM
#17
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Sure. the pcm regulates how much voltage the alternator puts out, thereby how much it charges ( you have to have higher voltage on the battery than the battery reads to charge it, or current won't flow into it.) The way the pcm regulates the output voltage is by how much voltage it puts across the rotor, (field terminals) which it rotating through an magnet called the stator. So if you put the full 12 volts on the field terminals, you get a big electric field on the rotor, and that field cutting across the field of the stator causes the max amount of output voltage. Ill skip how the voltage is rectified by the diodes.
Does that help? This is an old test. Delco alternators have a little place you push a tab on that does the same thing, full output test. I don't recommend you do it unless you understand it though.
Does that help? This is an old test. Delco alternators have a little place you push a tab on that does the same thing, full output test. I don't recommend you do it unless you understand it though.
Last edited by 97grand4.0; 07-01-2018 at 07:21 PM. Reason: electromagnet to magnet, still not right, its a 3 pole fixed coil
07-01-2018, 07:30 PM
#18
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Sure. the pcm regulates how much voltage the alternator puts out, thereby how much it charges ( you have to have higher voltage on the battery than the battery reads to charge it, or current won't flow into it.) The way the pcm regulates the output voltage is by how much voltage it puts across the rotor, (field terminals) which it rotating through an magnet called the stator. So if you put the full 12 volts on the field terminals, you get a big electric field on the rotor, and that field cutting across the field of the stator causes the max amount of output voltage. Ill skip how the voltage is rectified by the diodes.
Does that help? This is an old test. Delco alternators have a little place you push a tab on that does the same thing, full output test. I don't recommend you do it unless you understand it though.
Does that help? This is an old test. Delco alternators have a little place you push a tab on that does the same thing, full output test. I don't recommend you do it unless you understand it though.
07-01-2018, 07:52 PM
#19
CF Veteran
And without regulation they will put out almost 40 volts. I have built quite a few wind generators using car alternators. Just rig up an external adjustable regulator (like the old regulators that mounted on the fender well) and you can put out the right voltage for both 24v systems and 36 volt systems.
Open circuit voltage.. I never really saw what that is...Interesting.
Last edited by 97grand4.0; 07-01-2018 at 08:11 PM.
07-01-2018, 08:31 PM
#20
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07-01-2018, 10:16 PM
#21
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I hate to throw another cat into the fray, but one of the ways the PCM does a better job of controlling the alternator is by monitoring the battery TEMPERATURE. If the battery gets too hot, the PCM cuts back the charge rate so the battery doesn't cook. This sensor is in the battery tray underneath the battery. If it's not working correctly it could effect the charge rate. Most people don't even know it's there. It's a resistor that changes value as temp changes, decreasing when temp increases, increasing when temp decreases. SO when is voltage signal coming back to the PCM is high because the resistance is low, the alternator doesn't charge as much.
07-01-2018, 10:29 PM
#22
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I hate to throw another cat into the fray, but one of the ways the PCM does a better job of controlling the alternator is by monitoring the battery TEMPERATURE. If the battery gets too hot, the PCM cuts back the charge rate so the battery doesn't cook. This sensor is in the battery tray underneath the battery. If it's not working correctly it could effect the charge rate. Most people don't even know it's there. It's a resistor that changes value as temp changes, decreasing when temp increases, increasing when temp decreases. SO when is voltage signal coming back to the PCM is high because the resistance is low, the alternator doesn't charge as much.
07-02-2018, 06:04 AM
#23
CF Veteran
Oh... A bad regulator will cook a battery up in no time because of this capability. Had it happen lots of times. Ever watch the points close on an old style regulator? There are three resistance coils all rated different. The alternator puts out enough voltage that the first highest resistance coil points are closed constantly to reduce it. Only the third lowest resistance coil points open and close to "fine tune" it to the proper voltage. With an adjustable regulator you can mix and match these individual coil adjustments to get a desired voltage.
07-02-2018, 08:14 AM
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lol
07-02-2018, 08:43 AM
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I hate to throw another cat into the fray, but one of the ways the PCM does a better job of controlling the alternator is by monitoring the battery TEMPERATURE. If the battery gets too hot, the PCM cuts back the charge rate so the battery doesn't cook. This sensor is in the battery tray underneath the battery. If it's not working correctly it could effect the charge rate. Most people don't even know it's there. It's a resistor that changes value as temp changes, decreasing when temp increases, increasing when temp decreases. SO when is voltage signal coming back to the PCM is high because the resistance is low, the alternator doesn't charge as much.
