I have a John Deere 4240, the alternator stopped charging, I relaced the alternator, started up the tractor, alternator was charging normal, then it got hot and began smoking. Took the alternator back and got a replacement, by the way it is a Delco alternator, the replacement alternator would not charge, took it back and had it tested, it tested fine. I found that the resistance wire was not hot with the key in the on position, repaired the wire, started the tractor, was charging, than the alternator got hot and began smoking. Does anyone know what may cause this. Any suggestions would be greatly appreciated...
Alternator
- Thread starter tlezak11
- Start date
Roadworthy
Elite Member
What is the output voltage when it's charging? It sounds like a defective voltage regulator perhaps? Some alternators have an internal voltage regulator while with others it's external.
Yeah I agree, it's a internal regulator. But to have two in a row. It was putting out around 13.8 volts.
Roadworthy
Elite Member
Have your battery load tested. You may have a shorted cell and the alternator is trying to compensate. Other than that there may be an excess drain on the battery. If it tends to go flat while sitting either can be the case.
Just out of curiosity, what terminal does the exciter wire go on ? 1 or 2 ? The exciter wire is hot with the key on, the other wire is hot at all times, just like the wire that attaches to the terminal on the back of the alternator..
Batteries have been holding up, no problems with battery drain ?
Keoke
Gold Member
Number 1 terminal is from the ignition sw to the chg indicator bulb in series and then on to the alternator fld coil. This is to excite the alt fld to start charging. After starting #1 terminal will go pos from the internal diode trio and this will put out chg light which is now pos on both ends.
Number 2 terminal is the sensor terminal that tells the voltage regulator what the battery voltage is so it can adjust the chg rate accordingly. In a perfect world, it should go right to the positive battery post. The closer to the battery pos this wire is the more accurately it can read battery voltage. The easy, cheap hook-up for #2 is to run a short stub lead to the alternator output post. A common occurrence. However, the reading at the alt post will always be the higher alt voltage rather than the real and lower battery voltage. Consequently, the vr after seeing the higher alt voltage rather than the real and lower battery voltage will direct a chg a rate that is less than the battery needs.
lots of luck zak
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Thank you sir !!
Zac, thanks for replying, you seen like you are very knowledgeable about this problem with my 4240, well I have all the wires attached correctly, when I start the tractor the volt meter is showing the correct charge like it always does, but I'm having a issue with the alternator getting hot and smoking. I'm really confused, any help would be greatly appreciated.. Thank You.
Keoke
Gold Member
Hi Zac, assuming the alternator has no internal defects the running hot problem can be caused by the following.
1. Normal voltage at the output terminal should be around 13.8 to 14.6 if all is normal. If yours is higher, a good chance if your running hot, then the first move is to be sure the current from the alternator is getting to the battery with as little resistance as possible. If electron flow is restricted it will generate heat at its source and connecting circuitry on its way to load.
2. Check the voltage drop between the alt out terminal and bat pos post with digital meter as follows. Put red lead on alt output terminal and blk on bat pos terminal. The max number you want here is about .1 volt drop for every 10 amps flowing in the circuit. Or .3 of a volt drop if your chg rate is about 30 amps. If you don't have an amp meter then put every load on (lights) and see what the voltage drop is. In no case should it be over .5 of a volt. It is not likely that alt output lead goes directly to bat so if your drop is higher than .5 volt then while leaving red meter lead on alt output terminal, poke blk lead down the circuit wiring to the bat to find the hi resistance spot. When checking circuit quality it is best to run upper normal current through it.
3. On the negative side of the circuit, again load circuit as much as possible (lights) and put blk voltmeter lead on alt case and red lead on bat negative post, max here is .2 of a volt.
4. If after checking out the above you find no problems but voltage is still high then look to be sure your vr sensor wire (#2 terminal) is going directly to the battery since the vr must-see battery voltage in order to modulate chg rate. This is a problem on the Delco 10 SI.
5. Last, but not least possibility is that the voltage regulator is simply not doing its job of modulating current flow.
lots of luck,
1. Normal voltage at the output terminal should be around 13.8 to 14.6 if all is normal. If yours is higher, a good chance if your running hot, then the first move is to be sure the current from the alternator is getting to the battery with as little resistance as possible. If electron flow is restricted it will generate heat at its source and connecting circuitry on its way to load.
2. Check the voltage drop between the alt out terminal and bat pos post with digital meter as follows. Put red lead on alt output terminal and blk on bat pos terminal. The max number you want here is about .1 volt drop for every 10 amps flowing in the circuit. Or .3 of a volt drop if your chg rate is about 30 amps. If you don't have an amp meter then put every load on (lights) and see what the voltage drop is. In no case should it be over .5 of a volt. It is not likely that alt output lead goes directly to bat so if your drop is higher than .5 volt then while leaving red meter lead on alt output terminal, poke blk lead down the circuit wiring to the bat to find the hi resistance spot. When checking circuit quality it is best to run upper normal current through it.
3. On the negative side of the circuit, again load circuit as much as possible (lights) and put blk voltmeter lead on alt case and red lead on bat negative post, max here is .2 of a volt.
4. If after checking out the above you find no problems but voltage is still high then look to be sure your vr sensor wire (#2 terminal) is going directly to the battery since the vr must-see battery voltage in order to modulate chg rate. This is a problem on the Delco 10 SI.
5. Last, but not least possibility is that the voltage regulator is simply not doing its job of modulating current flow.
lots of luck,