Jinma 254 not charging

well the voltage reg. would be the easiest to replace and the cheapest place to start, I can not remember what lead to short to ground to bypass the reg. and make the alt. charge , hopefully someone will know and chime in or do a goggle search to find out, I assume your reg. in mounted on the fuse panel?

You have done a very good job investigating and troubleshooting so far. The details of the voltages is the key.

In normal operation the voltage regulator  controls the voltage going to the field connection at the alternator. If battery voltage is low (usually less than about 14.5v), the regulator sends battery voltage to the field winding of the alternator (rotor), which causes a voltage output in the stator coil. This is tapped at various locations and rectified through the diodes to put a steady DC voltage out on the Battery connection at the alternator. If this voltage is greater than the battery voltage, it will charge the battery.

One way to test an alternator is to “full field” it by temporarily applying battery voltage to the field terminal. This will cause the alternator to go to maximum output (if it is working properly).

Since your alternator is getting battery voltage from the regulator, that indicates the regulator is doing its job and that the wiring is sound.

Conclusion is that your alternator has failed.

I would remove it and take it to an automotive parts store (NAPA, Pep Boys, etc.) and see if they can bench test if for you.

If your alternator is bad, you will have a decision or two to make. I am not sure if internal parts are available or not. If not, you will be looking at a replacement of some kind.

For me personally when my regulator failed, I replaced the alternator with a re-manufactured Delco 10si model for about $65. I had to do a little re-wiring and make an extension for the adjuster bracket. The Jinma regulator was $30 and some of the wiring was bad anyway.

There are pros and cons of doing so, but the results are a better charging system than came from the factory.

The Sense wire on my alternator was labeled “I”. It was used to activate the light on the dash which was redundant because my 284 had an ammeter too. The 10si I bought did not have the sense wire output so the light on the dash is non-functioning. If I felt the need a voltmeter could be added easily enough.

Let us know if you have any more questions.

Stuart

As an addendum to Piper, your OEM alternator only has a nominal 14 amp output. Barely enough to keep up with the lights. BUT it is a TEFC alternator, which is a very good thing on a tractor. The Delco’s are not TEFC so consequently all the dust and chaff that goes through your radiator also goes into the alternator. The Delco’s have a 35+ amp output (depending on the model) so you will have to upgrade your output wiring. In my case the Delco 12sI was a direct fit, no modification of any sort was needed, but I did install a smaller pulley in order to get the alternator revs up to be somewhat comparable to a high speed automotive engine. It’s also my understanding that Tommy now has a higher output OEM alternator available. Check with him for pricing.