Speaking Of Harbor Freight...
This load tester costs fifty dollars. I own one. It will CORRECTLY load test a tiny garden tractor battery all the way up to a 160 lb 8-D battery. CORRECTLY The cheese grater type testers ...
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Use a variable carbon pile load tester
In conjunction with a DC inductive ammeter
Place inductive loop around battery wire coming from the alternator.
Increase engine speed to 2,000 RPM
Slowly crank up the load. Observe inductive ammeter amperage it will climb.
At a certain point near 12 volts the inductive ammeter will start showing less and less amps as the carbon pile load keeps increasing
This is because the carbon pile load has reduced alternator voltage so low the rotor (field) current is insufficient to develop maximum excitation of the rotor field strength.
In conjunction with a DC inductive ammeter
Place inductive loop around battery wire coming from the alternator.
Increase engine speed to 2,000 RPM
Slowly crank up the load. Observe inductive ammeter amperage it will climb.
At a certain point near 12 volts the inductive ammeter will start showing less and less amps as the carbon pile load keeps increasing
This is because the carbon pile load has reduced alternator voltage so low the rotor (field) current is insufficient to develop maximum excitation of the rotor field strength.
