MF 575 alternator at fault or not?

[oakleaf]

My 575 only does about 150 hours per year.
Now the alternator light has come on (fast flashing as opposed to permanently on). When I put the multimeter across the battery it reads 14.8 to 15 volts. I swapped the battery from another tractor and the same thing happens.
Why would the light come on when it is charging?

 

[Flatlander]

Voltage regulator possibly. Seems a little high at 15 volts

 

[Wisconsonian]

Agree, even 14.5 is high. I don't know MF wiring, and it wouldn't matter anyway as they'll use different alternators, but I'd suspect it's wired for a voltage sense that has been disconnected, and/or grounded somehow. Find a wiring diagram for the alternator model on there, and see how it needs to be connected to run correctly. The "remote voltage sense" terminal should be connected to some central point in the wiring harness, NOT grounded. It will work fine hooked directly to the B+ big terminal, for testing purposes at least and usually permenantly.

If you connect the voltage sense to B+ and it still overcharges to 15, then the voltage regulator is not working. Probably internal to the alternator, but often easy to replace.

 

[C.J]

Rectifier fault.

 

[oakleaf]

Agree, even 14.5 is high. I don't know MF wiring, and it wouldn't matter anyway as they'll use different alternators, but I'd suspect it's wired for a voltage sense that has been disconnected, and/or grounded somehow. Find a wiring diagram for the alternator model on there, and see how it needs to be connected to run correctly. The "remote voltage sense" terminal should be connected to some central point in the wiring harness, NOT grounded. It will work fine hooked directly to the B+ big terminal, for testing purposes at least and usually permenantly.

If you connect the voltage sense to B+ and it still overcharges to 15, then the voltage regulator is not working. Probably internal to the alternator, but often easy to replace.

Sorry I don’t understand what you mean by voltage sense

 

[MF-ANDY]

Disconnect both wires. Test heavy wire. It should have 12v permanently. Test small wire. It should have 12v with the key turned on and nothing with the key turned off. Turn on the key, the charge light shouldn't come on,earth the small wire and the charge light should come on.
If all the above works, repair or replace the alternator.

 

[Wisconsonian]

A voltage sense is an optional way of compensating for the voltage drop from the alternator to a more central point of the wiring harness. You'd think it wouldn't be needed on most cars or tractors, but it's a common option on alternators, whether Delco style, or Lucas style or others. If that terminal is disconnected, it should work fine, and regulate from the internal voltage of the alternator pretty close to 14V. If the alternator has a voltage sense terminal, and it becomes grounded or even hooked to a part of the harness that doesn't see the full voltage, then alternator will increase current to try to raise the voltage it senses on that wire. You'd have to find a wiring diagram for the make of alternator you have, their wiring terminals will be SIMILAR across different models if you can't find the exact model.

Unless you have an AC line for a tachometer feed, or an "R" terminal on some Delco's, then you can connect the B+, and the excite terminal, and any voltage sense terminal all together and it should charge at 14v. If not, then the alternator is faulty, assuming it is an internal regulator.

The simpler test is with the engine running, check the voltages on the wires on back of the alternator. They should all be very close. Again, unless there's an AC "W", or "R" terminal.

 

[Flatlander]

A voltage sense is an optional way of compensating for the voltage drop from the alternator to a more central point of the wiring harness. You'd think it wouldn't be needed on most cars or tractors, but it's a common option on alternators, whether Delco style, or Lucas style or others. If that terminal is disconnected, it should work fine, and regulate from the internal voltage of the alternator pretty close to 14V. If the alternator has a voltage sense terminal, and it becomes grounded or even hooked to a part of the harness that doesn't see the full voltage, then alternator will increase current to try to raise the voltage it senses on that wire. You'd have to find a wiring diagram for the make of alternator you have, their wiring terminals will be SIMILAR across different models if you can't find the exact model.

Unless you have an AC line for a tachometer feed, or an "R" terminal on some Delco's, then you can connect the B+, and the excite terminal, and any voltage sense terminal all together and it should charge at 14v. If not, then the alternator is faulty, assuming it is an internal regulator.

The simpler test is with the engine running, check the voltages on the wires on back of the alternator. They should all be very close. Again, unless there's an AC "W", or "R" terminal.

ohhh. You know it well. Very well explained too.

 

[oakleaf]

A voltage sense is an optional way of compensating for the voltage drop from the alternator to a more central point of the wiring harness. You'd think it wouldn't be needed on most cars or tractors, but it's a common option on alternators, whether Delco style, or Lucas style or others. If that terminal is disconnected, it should work fine, and regulate from the internal voltage of the alternator pretty close to 14V. If the alternator has a voltage sense terminal, and it becomes grounded or even hooked to a part of the harness that doesn't see the full voltage, then alternator will increase current to try to raise the voltage it senses on that wire. You'd have to find a wiring diagram for the make of alternator you have, their wiring terminals will be SIMILAR across different models if you can't find the exact model.

Unless you have an AC line for a tachometer feed, or an "R" terminal on some Delco's, then you can connect the B+, and the excite terminal, and any voltage sense terminal all together and it should charge at 14v. If not, then the alternator is faulty, assuming it is an internal regulator.

The simpler test is with the engine running, check the voltages on the wires on back of the alternator. They should all be very close. Again, unless there's an AC "W", or "R" terminal.

Very informative thank you

 

[C G Parts]

My 575 only does about 150 hours per year.
Now the alternator light has come on (fast flashing as opposed to permanently on). When I put the multimeter across the battery it reads 14.8 to 15 volts. I swapped the battery from another tractor and the same thing happens.
Why would the light come on when it is charging?

You can check the voltage at the battery with the engine stopped and the engine running, if its more when running then the battery is charging, it could be the alternator electrical bits starting to fail. Carpenter Goodwin do a Vapormatic Alternator for the MF 575 part no. VPF4005 if it needs replacing

My 575 only does about 150 hours per year.
Now the alternator light has come on (fast flashing as opposed to permanently on). When I put the multimeter across the battery it reads 14.8 to 15 volts. I swapped the battery from another tractor and the same thing happens.
Why would the light come on when it is charging?

 

[oakleaf]

Disconnect both wires. Test heavy wire. It should have 12v permanently. Test small wire. It should have 12v with the key turned on and nothing with the key turned off. Turn on the key, the charge light shouldn't come on,earth the small wire and the charge light should come on.
If all the above works, repair or replace the alternator.

Thanks for above tips.
I have done this and all works as you described.
I have removed alternator and handed it in to a local repair man so will find out next week if it’s goosed or fixable.

 

[oakleaf]

This story has a happy ending.
The alternator was repairable and I fitted it back on today. All working as it should. Thanks to all who replied to the OP.