Alternator has Low output Volts

So I'm equally lost when I measure the output voltage of my F140 alternator and it only outputs 5 volts. I don't think that will be enough to charge a 12 volt battery!!!

I inherited the problem with the tractor so I have no idea what the history is really. Anyone got any ideas what's wrong?

Alternator has 2 wires. There was an old, old regulator bolted to the outside of the tractor grill. Might have been upgraded from original equip with 10A or 15A alternator. Original may have had low Amp output with seperate lighting wires - that setup didn't use a regulator.

If there is no ground to the block, the output is solely the two leads.

If that voltage is the 5 volts you mentioned initially, even if measured on "AC" scale of meter, the magnet ring is to blame as there may not be enough magnetism left to induce the voltage and current required to even fully overcome the internal resistance of the wire in the coils.

Previous owner told me that it didn't charge so I was quite prepared to replace/rewind the stator. However I am not sure that's the problem.

I am testing AC voltage right off what remains of the output leads - not connected to anything. I bought a new regulator but there's not much sense hooking that up till I have some voltage to rectify/regulate.

When I got the tractor the magnets and stator were removed. (removable magnet ring - first time I've ever seen that!) So I checked them to make sure there is clearance just in case they are not the right parts. It's tight! But probably .002" all round (hard to actually measure). I checked for play in the crankshaft (because it's such a close fit) none is evident and I think I would notice a .003" slop. When I installed the flywheel I spun it and listened for contact - none heard - seems okay.

The only other thing that I noticed is that the magnets are not as strong as I expected. Things stick to them alright and I had a devil of a job removing the little bits of metal filings that they had managed to pick up, but not as much as I have experienced before. Though I don't mess with motors that much any more so it's hard to really tell - just a feeling.

Where are you taking the measurement? Have you tried switching to the voltage range in "AC"?

If external- Is it truly an alternator, or is it really a generator? (alternator has continuous slip rings in contact with the brushes and often internal diodes. Generator has segmented commutator in contact with the brushes.)

One thing to keep in mind is that most AG and most all automotive programs have poor track records in teaching electrical theory and practical basic electronics as used in the auto and AG industry, so don't worry if it did not make sense- They did not know what they teaching themselves more than likely.

As for the voltage of 5 volts. Does the tractor seem to operate okay and keep the battery charged? If the battery charges fine, the answer could be that your meter is somewhat at fault. Set your voltmeter to read "AC" volts. Pulsed DC voltage, such as you find with some alternator windings that are under the flywheel, or externals with a high "cut in" speed, are too slow to be read correctly by most multimeters set on "DC".

If you disconnect any external connections (in the case of a B&S or Tecumseh alternator where the windings are under the flywheel) you should be able to see 12 to 16 volts across the 2 wires that come out in the pigtail from under the flywheel.

If the wrong flywheel was installed, you do not get enough "magnetic flux" (strength) through the alternator windings to produce adequate voltage or current to do much of anything. Some flywheels have several magnets, which are just for the alternator windings on the underside, and some flywheels have just the magnets for the ignition magneto.

If the alternator is an external unit, check to make sure it is connected correctly, and swap out the regulator for another one and see if that corrects the situation. If not, bypass regulator, and see what voltage the alternator is capable of putting out. It is a slight possiblity that you have one for 6 volt batteries, in which case you would be hard pressed to get more than 8 volts out of the alternator.