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Old 25-01-2015, 05:25   #1
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Testing an alternator

I have been having trouble charging my engine batteries. How do I test the alternator to see if that is the problem? Thanks


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Old 25-01-2015, 05:55   #2
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Re: Testing an alternator

BASIC Alternator Testing

GENERAL INSPECTION:

A loose drive belt can cause slipping and undercharging, noise and vibration, and premature belt wear. An over-tight belt may cause bearing wear.

Look at and feel the drive-belt, examining for cracking, fraying, glazing, and/or separation. Replace damaged belt(s).

Test the belt tension by firmly depressing midway between the sheaves. The belt should deflect between 1/4" (for sheaves with 7" - 10" centerline separations) and ˝" for 12" - 16"separations). Adjust tension as necessary.

Inspect all wiring and terminations. Wire should be adequately sized for the application (see “Ohm’s Law & Boats”), secured at least every 18", and run as high and dry as possible. Termination s must be clean (no visible corrosion), and tight. Examine the wire for thermal (melting or charred insulation) or mechanical damage (frayed, cracked, or missing insulation).
Replace damaged or undersized wire, and replace or repair inadequate terminations.

ALTERNATOR VOLTAGE TESTS:

1. Set Voltmeter to DC Volts (20V scale), and connect the DC Voltmeter test leads to the battery post (Red lead to Positive Post, and Black(or Yellow) to Negative). With engine “off”, read and note battery voltage (see “Battery Testing”).

2. Start the engine, and at “Idle” RPM, check the voltmeter reading. At very low speeds the alternator output may be lower than the regulator setting; hence you will expect to read the battery voltage.

3. Increase engine RPM, and note increasing voltage reading to a maximum of about 14.2 volts (12V Nominal System - expect ± 29.5V in 24V system).

If no voltage increase noted, you likely have a bad voltage regulator, or poor wiring
(Alt’ to Batt.). Go on to test 3B.

If Voltage increases go on to test 4.

3B. With engine “off”, connect Positive test lead to Alternator Output (“B+”, or “A”), and Negative Lead to the Negative Ground Post (“Neg”, or “E”) of Alternator. Start engine. If Voltage increases with increased RPM, your regulator is OK, and the problem is in the wiring. Go on to test 3C.

3C. Discharge the Battery to less than 12.5 Volts. Check for Voltage drop between the Alternator and Battery, as follows..
Connect the Positive Test Lead to the Alternator Positive Output Terminal (B+) and the Negative Lead to the Positive Battery Post. Crank the engine, and increase RPM to a fast idle. Observe Voltage. If the voltage climbs to as much as 0.02 Volts (or more), the positive cable has a high resistance. Repair or replace cable.

Check for voltage drop in the negative cable, as above - but: connect the Positive Lead to the Alternator’s Negative Output Terminal, and the Negative Lead to the Negative Battery Post. Analyze as above.
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Old 25-01-2015, 08:19   #3
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Re: Testing an alternator

Thanks, I will test this afternoon


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