JD 850k no ECU alternator field output

[clearprop]

Troubleshooting an alternator charge problem here.

Alternator works great when field is powered by temporary batter power.

The continuity has been traced back to the x3 connector of the ECU from the alternator and is good along with the inline resistor.

Before I call it an ECU problem, can anyone tell me if there are other parameters that must be met before the ECU will excite the field wire?

Thanks

 

[Vetech63]

Post your machine serial #. I'll post an *MG ALERT!!!**

 

[mg2361]

Definitely need a serial number. Also are there any codes, active or stored?

 

[Birken Vogt]

I'm sorry if this is a hijack but this is exactly the sort of problem that makes people hate modern equipment and hate JD. Why does an alternator need to have any input from the ECM, it is just stupid. Makes a half day problem turn into a goose hunt.

 

[clearprop]

Post your machine serial #. I'll post an *MG ALERT!!!**

The serial is E233320

Yes the only code is low switched voltage.

 

[mg2361]

What was the resistance of the resistor?

What is the static voltage of the battery?

With the D+ wire removed and engine idling is there voltage at the excitation wire?

If you raise the engine speed to 1800 rpm what is the voltage at B+ and D+ terminals of the alternator?

 

[clearprop]

What was the resistance of the resistor?
499 ohm
What is the static voltage of the battery? 24.1

With the D+ wire removed and engine idling is there voltage at the excitation wire? No it reads 0 volts

If you raise the engine speed to 1800 rpm what is the voltage at B+ and D+ terminals of the alternator?

at around 1800 or so B+ came up to around 24.6 or so. Did not measure D+

 

[mg2361]

When you start the engine you do see engine rpm in the monitor, correct?

The D+ wire should have a connector within 6 inches of the alternator. Unplug it and measure voltage on the wire from the ECU. I know the resistance you measured is within spec, I just want to see if any change in voltage with the resistor out of the equation. If still 0 volts then yes you are down to wiring issue or ECU. You could pull the wire out of the ECU and start the engine to see if there is voltage (should be 14 volts) on the ECU pin you removed the wire from. That would confirm a wiring issue or an ECU issue.

at around 1800 or so B+ came up to around 24.6 or so. Did not measure D+

At 1800 the alternator should self excite. Try full throttle. Again measure B+ and D+ on the alt.

 

[clearprop]

When you start the engine you do see engine rpm in the monitor, correct?

The D+ wire should have a connector within 6 inches of the alternator. Unplug it and measure voltage on the wire from the ECU. I know the resistance you measured is within spec, I just want to see if any change in voltage with the resistor out of the equation. If still 0 volts then yes you are down to wiring issue or ECU. You could pull the wire out of the ECU and start the engine to see if there is voltage (should be 14 volts) on the ECU pin you removed the wire from. That would confirm a wiring issue or an ECU issue.



At 1800 the alternator should self excite. Try full throttle. Again measure B+ and D+ on the alt.

Thank you sir very much.

I did measure voltage at the plug you mentioned (before the resistor) and with the engine running it showed 0 volts when disconnected.

Additionally a burned diode has been found in the alternator rectifier. The only explanation I can think of is, the reason the alternator showed an output when manually supplied voltage to the field could possibly be a coincidence of the arcing and connection at the burned diode.

A replacement alternator is on the way, however, I am guessing I still have a problem with output from the ECU and could possibly be a burned ECU circuit as a result of the rectifier diode loading and unloading the AC current.

Will follow up in a few days.

 

[clearprop]

New alternator works great. Output from ECU is ~14v when idling with field wire disconnected and battery buss voltage around 24.5v. with field connected the alternator output is 28.1v.

All good. Thanks for the suggestion and support!