Just in case most of you aren't old enough to remember generator systems on cars, you need to polorize the regulator and or generator after reinstalling a new one. Sometimes you had to do it if the unit was disabled for a period of time. The generator will only produce about half the output if you don't.
Generator charge circuit troubleshooting
- Thread starter BobReeves
- Start date
Well shoot, new regulator didn't fix it..
Checked all the wiring for continuity. Am 99.9% sure generator is good, passed the ford test and will output plenty if I apply an external voltage to the field. Even briefly put 12 volts on the field and the voltage across the battery went to 15 volts.
Does anything need to be done to a new regulator?
What are the odds of getting a new regulator that is bad? I know the generator needs to be polorized if it is replaced but nothing I could find on-line says anything about the regulator. In fact most say to disconect the field wire from the regulator to polarize the generator.
Help! any ideas???
Checked all the wiring for continuity. Am 99.9% sure generator is good, passed the ford test and will output plenty if I apply an external voltage to the field. Even briefly put 12 volts on the field and the voltage across the battery went to 15 volts.
Does anything need to be done to a new regulator?
What are the odds of getting a new regulator that is bad? I know the generator needs to be polorized if it is replaced but nothing I could find on-line says anything about the regulator. In fact most say to disconect the field wire from the regulator to polarize the generator.
Help! any ideas???
JustGary
Silver Member
Yes, jump the field to 12V. The regulator works by interrupting the field voltage when it decides that the battery has a full charge. You can test the alternator without the regulator.
1) Disconnect both the "field" and "bat" terminals from the alternator.
2) Jumper 12V to the "field" terminal.
3) Jumper a lamp from "bat" to ground (I use the high beam of an old headlamp; you do save them when you change them, don't you?).
4) Start the engine.
5) Measure the DC voltage from "bat" to ground.
Output voltage should vary with engine RPM, and should be over 12V, but might be close at low idle. Even better is to use an oscilloscope so you can see the waveform. You could have a blown diode and still get > 12V out with a light load.
I would seriously consider rebuilding the alternator or taking it to the local alternator shop. We can help you take it apart and get it back together (especially with photos) if you want to do it. That way you can test all four diodes and be sure. It might need new brushes anyway, so think about it.
My local alternator shop only charges me about $12 for a GM diode plate, and I'm sure they have loose ones for odd alternator models too. Actually, I'd check with them for your regulator also. You might be surprised.
Regards,
- Just Gary
1) Disconnect both the "field" and "bat" terminals from the alternator.
2) Jumper 12V to the "field" terminal.
3) Jumper a lamp from "bat" to ground (I use the high beam of an old headlamp; you do save them when you change them, don't you?).
4) Start the engine.
5) Measure the DC voltage from "bat" to ground.
Output voltage should vary with engine RPM, and should be over 12V, but might be close at low idle. Even better is to use an oscilloscope so you can see the waveform. You could have a blown diode and still get > 12V out with a light load.
I would seriously consider rebuilding the alternator or taking it to the local alternator shop. We can help you take it apart and get it back together (especially with photos) if you want to do it. That way you can test all four diodes and be sure. It might need new brushes anyway, so think about it.
My local alternator shop only charges me about $12 for a GM diode plate, and I'm sure they have loose ones for odd alternator models too. Actually, I'd check with them for your regulator also. You might be surprised.
Regards,
- Just Gary
Great info Gary cept it's a generator and doesn't have diodes /forums/images/graemlins/smile.gif
Called NH and they will exchange the regulator which is a suprize. Most auto supply stores I have been in have a big sign behind the counter that says no returns or exchanges on electrical parts.
Called NH and they will exchange the regulator which is a suprize. Most auto supply stores I have been in have a big sign behind the counter that says no returns or exchanges on electrical parts.
JustGary
Silver Member
Gad. Sorry, I've been working a lot lately. Still, I don't know how I missed that.
The part about taking it to your local shop is probably still good, though. Ooh, and come to think of it, taking things apart is always good, too!
- Just Gary
The part about taking it to your local shop is probably still good, though. Ooh, and come to think of it, taking things apart is always good, too!
- Just Gary
JustGary
Silver Member
Bob -
Out of embarassment, I decided to try to actually help. Here goes.
This web page tells a bit more about testing generators than I knew 20 minutes ago.
Jumping the field to ground should cause plenty of voltage with the tractor running at high RPM. Note that it may not put out much voltage at all unless the RPMs are high enough. A few seconds won't hurt the battery.
Also, trying the polarizing trick should also tell you if your generator works. I would expect plenty of torque with 12V applied, but any motion at all is a really good sign.
If all else fails, change the diodes anyway... /forums/images/graemlins/grin.gif
- Just Gary
Out of embarassment, I decided to try to actually help. Here goes.
This web page tells a bit more about testing generators than I knew 20 minutes ago.
Jumping the field to ground should cause plenty of voltage with the tractor running at high RPM. Note that it may not put out much voltage at all unless the RPMs are high enough. A few seconds won't hurt the battery.
Also, trying the polarizing trick should also tell you if your generator works. I would expect plenty of torque with 12V applied, but any motion at all is a really good sign.
If all else fails, change the diodes anyway... /forums/images/graemlins/grin.gif
- Just Gary
It's fixed /forums/images/graemlins/smile.gif
Pulled the new regulator off and removed the cover. Started probing around with an ohm meter and discovered two normally closed contacts weren't conducting. Burnished the contacts with a relay burnishing tool, put everything back together and success it worked...
Guessing the regulator had sat on the shelf for a while and the contacts developed a thin film of corrosion that kept them from making good contact. Hurray....
Pulled the new regulator off and removed the cover. Started probing around with an ohm meter and discovered two normally closed contacts weren't conducting. Burnished the contacts with a relay burnishing tool, put everything back together and success it worked...
Guessing the regulator had sat on the shelf for a while and the contacts developed a thin film of corrosion that kept them from making good contact. Hurray....
uhmgawa
Gold Member
</font><font color="blue" class="small">( I know the generator needs to be polorized if it is replaced but nothing I could find on-line says anything about the regulator.)</font>
"polarizing" as it is being used here is only necessary in the case
an external source of current is not available. If the regulator
is able to energize the field using battery current for example,
technically there is no need to magnetize the field laminations
to create the residual field. If this external current source is
not available, the residual magnetism in the field needs to be
sufficient to induce current in the rotor which is then fed
to the field winding thereby bootstrapping the generator.
AC generators/alternators used in vehicles or for mains power
generation operate similarly.
"polarizing" as it is being used here is only necessary in the case
an external source of current is not available. If the regulator
is able to energize the field using battery current for example,
technically there is no need to magnetize the field laminations
to create the residual field. If this external current source is
not available, the residual magnetism in the field needs to be
sufficient to induce current in the rotor which is then fed
to the field winding thereby bootstrapping the generator.
AC generators/alternators used in vehicles or for mains power
generation operate similarly.
Syncro
Platinum Member
<font color="blue">Started probing around with an ohm meter and discovered two normally closed contacts weren't conducting. </font>
Goes to show even brand new parts can be defective. I had that happen to me on an old Ford one time, got a brand new set of ignition points that had an intermittant short, talk about driving me crazy! At first I rulled out the points because 'they were brand new' and wound up changing everything else, before, as a last resort, replacing the new points.
Good lesson here though, just cause a part is new doesn't mean it necessarily works.
Goes to show even brand new parts can be defective. I had that happen to me on an old Ford one time, got a brand new set of ignition points that had an intermittant short, talk about driving me crazy! At first I rulled out the points because 'they were brand new' and wound up changing everything else, before, as a last resort, replacing the new points.
Good lesson here though, just cause a part is new doesn't mean it necessarily works.
Soundguy
Old Timer
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The NAA and up will have a b-circuit setup.. they need field power to charge.. you full field them by applying bat power to the field.
The oldies... like the 8n used a-circuit setups, and full fielded by grounding them.
If you have any genny questions, le me know. i've done lots of work with ford gennies in particular. Real easy to onvert 3rd brush to 2 brush.. and diagnose vr and gennies, as well as swap 'will fit' older regulators in to replace the chincy Lucas (prince of darkness) jobs many of the later fords came with. Also real easy to make a high/low/iso charge 'switch' in the extreme cases where you had a 2 brush genny and could not find a regulator.. just need a couple power resistors, and a dpdt center off switch, and some wire...
soundguy
The oldies... like the 8n used a-circuit setups, and full fielded by grounding them.
If you have any genny questions, le me know. i've done lots of work with ford gennies in particular. Real easy to onvert 3rd brush to 2 brush.. and diagnose vr and gennies, as well as swap 'will fit' older regulators in to replace the chincy Lucas (prince of darkness) jobs many of the later fords came with. Also real easy to make a high/low/iso charge 'switch' in the extreme cases where you had a 2 brush genny and could not find a regulator.. just need a couple power resistors, and a dpdt center off switch, and some wire...
soundguy