Home > TECHNICAL > CHARGING STARTING SYSTEM CIRCUIT VOLTAGE-DROP TESTING

The Battery, the Alternator, and the Starter are the major components of the Automotive Starting and Charging System. When your engine cranks slowly or not at all and/or your battery wont stay charged, but these components check out fine, where do you check next?

You need to check for Voltage-Drop in these high amperage circuits. It may be obvious when you see bad corroded connections where wires or cables attach. When corrosion forms inside a cable or wire or at a connection that looks okay on the outside, a voltage-drop test will quickly find it.

If you have added accessories that require more amperage, undersized wiring may be creating high resistance. This keeps the circuit from carrying required amperage. Additional accessories require upgraded (or supplemented) wiring. Maybe you need additional power with an Alternator Upgrade ( High Output Alternator ).

Voltage-Drop Testing is easy but use caution and safety around hot and moving engine parts. With your voltmeter use test leads with alligator clips to hold leads in place at the test points keeping your hands out of the engine compartment while testing. And Testing will not produce accurate results unless you "Load The Circuit". Current flowing through the circuit needs to be near maximum for that circuit.

Printable PDF Version - Safety, Testing & Voltage Drop Check




IF YOUR ALTERNATOR IS EXTERNALLY REGULATED THEN ANYTIME THE ACTION REQUIRES TO REPLACE ALTERNATOR YOU MAY ALSO NEED TO REPLACE THE REGULATOR. THIS SIMPLE DIAGRAM SHOWS ONLY MAJOR COMPONENTS OF THE CIRCUITS. MANY VEHICLES HAVE OTHER COMPONENTS IN THE CIRCUITS LIKE CONTROL MODULES, RELAYS, SWITCHES OR SENSORS. THEY WILL NOT EFFECT THE ACCURACY OF THE TESTING, BUT THE COULD IMPACT THE FUNCTION OF THE STARTER OR ALTERNATOR.




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