How do I check whether my tractor alternator is working

tommyboy1 · Jan 20, 2014

I have a Ford 4600 diesel tractor that doesn't seem to be able to charge the battery.

I took the alternator off last year and took it to the local implement dealer who sent it out to be tested. upon return, the dealership informed me that the alternator was good so I reassembled the unit and bought a new battery thinking that the battery wouldn't hold a charge.

Since then I have had to recharge the battery nearly every time I use the tractor while using some type of electrical devise. I'm sure it's the alternator, but I'm not sure how to test the alternator to validate whether i's good or not.

Is there any simple test that i can do to determine if the alternator is good?

diesel lover · Jan 20, 2014

Your alt may have tested good but the electrical on your machine may have something to do with your starting/ charging issues.

Do you have a voltmeter? Check battery voltage with engine off, then check battery voltage with engine running at idle, then 1500 rpm +/-.

You may have a paracitic draw on your battery!! My dads cockshutt did. All he did was added a battery disconnect since to him its an old tractor and the charging system does not work. He charges the battery on a trickle charge st the end of the night.

Industrial Toys · Jan 20, 2014

The leakage in the diodes in some (or all) alternators is said to slowly discharge your battery.

If the machine is running and you turn on lights, does the motor change it's tone? If it does, it means the alternator is making power.

If you have access to a clamp on meter that does DC (rather expensive) it can be a great trouble shooting tool.

Does this machine have an integral voltage regulator in the alternator or seperate? If you say the alternator tested good, maybe it's the vr.

EDIT: I guess another simple (tool less) check would be to start the thing, turn on the lights and disconnect the battery. See if the lights stay on. Watch that the battery leads don't short on something.

tommyboy1 · Jan 20, 2014

diesel lover, I do have a voltmeter and I will check the voltage as you described. What type of battery voltage difference do you think I should see between an idle and 1,500 rpms if the alternator is working properly?

tommyboy1 · Jan 20, 2014

I can't remember if the tone of the motor changes when I turn the lights on. I will check it tonight when I get home from work. I'm not sure about the internal voltage regulator. I don't have the original owner's manual. Is there a way to visually check to see if I do? Perhaps I can try to find out on the web.

diesel lover · Jan 20, 2014

No real voltage difference or not much difference is usually measured in alternators. A difference is noted in generators.

The difference in Rpm can decide if the rpm is charging at one rpm and not the other. If charging at idle and not at a higher rpm your brushes may be an issue as they are worn out and cannot make contact at a higher rpm.

The other major thing to check is connections. All connections need to be shiney!! I cannot stress it enough. Without shiney connections voltage has trouble traveling through any connection due to rust, paint, or corrosion. Connections can be cleaned with a stiff brush on a drill or can be cleaned with a die grinder/ electric angle grinder. Once they are back together you can clean them with brake clean, dry them and paint over them to protect them from any rust etc.

If this is the tractor you need for snow plowing than I suggest don't take the large wire off the battery if it looks like its going to break. This happened on my dads cockshut and almost had to buy a new starter. The lug off the starter was threaded copper I believe.

deerseeker001 · Jan 20, 2014

I had the same problem charge battery would be good for 3-4 weeks then you tell she was not turn over as fast.took alternator into a shop that works on alternators had it tested said it was charging.i knew this guy that works on tractors for a living he said he had a new alternator put it on and try it out and that took care of the problem.

diesel lover · Jan 20, 2014

You can find bad connections by preforming voltage drop test with your voltmeter. Place positive lead of dvom on pos battery post and negative on positive of alternator or starter.

Place neg lead of dvom on neg battery terminal and positive on ground of starter or alternator. If no ground place positive on Case.

Voltage should be read close to 0.0 volts. If half a volt cables will have to be checked for internal corrosion and connections need to be cleaned.

Oldtractorfixer · Jan 20, 2014

Does the tractor have an ammeter. If so when you start the engine it should move toward plus. If it shows nothing it could be the problem. The current from the alternator flows through the ammeter. Another way to check is with a voltmeter. Check the voltage at the battery before you start the tractor. It will be in the 11 to 12 volt range. Once you start the tractor it should start to climb until it reaches about 14 volts. If it does not climb nothing is getting from the alternator to the battery. The big post on the alternator should be battery voltage at all times and should go to 14 volts as it charges the battery.