How to Test the Amperage Output on Alternators
- 1). Remove loose jewelry and ensure you have no loose clothing that may get caught in the engine. Put on protective gloves and goggles. You need to run your car engine to test the amperage output on your alternator. Open and secure your car hood.
- 2). Set an ammeter in the range of output expected from your alternator. This is marked on the side of the alternator or in your car's service manual. Car alternators generally produce 70 to 100 amperes, depending on the electrical equipment in use.
- 3). Connect the ammeter's red positive wire to the positive terminal of your battery. Connect the black negative wire to the negative terminal of your battery. Secure the alternator so that it can't move, and ensure that the wires are away from any parts that move once the engine is started.
- 4). Turn on the engine and let it idle. Ensure that all electrical equipment is turned off. Read the amperage display on your ammeter. It should indicate about 50 amperes or less, depending on the charge on your battery.
- 5). Turn on as many electrical items as you can in your car. Get a friend or adult family member to sit in your car.
- 6). Check the ammeter display. Your engine idle speed is reduced as more energy is required to run the electrical equipment. The ammeter should show increased amperes in the range of 60.
- 7). Ask your friend or family member to increase the engine revolutions to about 2,000 RPM. Check your ammeter display. It should read in the range of 70 to 100 amperes. If the amperes don't increase significantly you need ask a professional to examine your alternator.
- 8). Turn off your engine and disconnect the ammeter wires. Close your car's hood.
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