John Deere 6120 charging issue. I have a John Deere 6120 that does not load until the tractor reaches 1700 RPM. The alternator wire does not energize until 1700 RPM, not that the alternator is not charging. To check this, I connected a wire to the lug of the alternator and started the tractor. The charging light started flashing so I touched the cable from the alternator to the battery for a second. The light went out and continued charging from then on, furthermore, once it starts charging, it doesn’t stop. Also, once it starts charging, it doesn’t stop. So if I bring it to 1700 RPM, and the light goes out, then I can bring it back to normal RPM.
The reasons may be the following:
JOHN DEERE Special Equipment is a very reliable technique and rarely fails. But even she breaks sometimes. There is a very unpleasant situation when the JOHN DEERE engine stalls and does not want to start. In this case, a message describing the error code of the fault lights up on the instrument panel display. But there are also exceptions where the errors do not stand out. Our company’s diagnostic specialists have accumulated solid experience in repairing the above-mentioned faults.
- In cases where the diesel generator is not supplying voltage at all, you should pay attention to the circuit breaker or fuses, which may fail due to a current overload or a short circuit in the circuit.
- The reason for the drop from 380 to 330 V in a three-phase unit may be associated with insufficient voltage supply to the excitation circuit, in addition, phase imbalance can play a role with uneven load.If the diesel generator generates overvoltage, the problem should be looked for in the AVR (voltage regulator) device.
The alternator energizing circuit is controlled by the BCU (Basic Control Unit). It is supposed to prevent the alternator from energizing until the engine speed is 800 rpm. At 800 rpm, the BCU sends voltage to the K02 relay / the relay then sends voltage to the alternator. I would test the operation of the relay first. The BCU relies on an engine speed signal from the ECU (engine control unit). Also check the wiring between the BCU and the ECU – pin 59 on the BCU receives this signal. If there is no signal from the ECU, the alternator will not charge. Also something to keep in mind, the alternator on these tractors has a clutch built into the pulley. It is a one-way clutch that must slide in one direction. Failure of this clutch causes loading problems as well.