What causes an alternator diode to fail?

Because of the substantial load handled by the alternator, the rectifier diodes fail because of overheating, overloading or because of poor connection between the alternator output and the battery positive terminal. Leaky or shorted alternator diodes can cause rapid changes in the output voltage of the charging system.

How do you know if your alternator diode is bad?

Usually, a bad alternator diode will cause your headlights or instrument panel lights to flicker or dim and, sometimes, drain battery power overnight, or in minutes. * To check for a possible bad alternator diode, switch your voltmeter to a low setting on the AC (alternating current) voltage scale.

Can you replace a bad diode in an alternator?

It is possible to replace all the parts of the alternator, including the diodes in the rectifier plate. The only sure dead of an alternator is a breakage of the case. Even a defect in one of the windings is curable, although it requires expensive rewinding.

What does alternator diode do?

Diodes are responsible for converting alternating current (AC—what the alternator produces), into direct current (DC— which is what the vehicles battery and other electrical components run on).

Can an alternator go bad from sitting?

Premium Member. Battery warning light SHOULD come on if it’s an electrical issue, and NO – sitting generally WON’T kill an alternator, short of a year in a corrosive environment…

What happens when a diode goes bad?

A bad (opened) diode does not allow current to flow in either direction. A multimeter will display OL in both directions when the diode is opened. A shorted diode has the same voltage drop reading (approximately 0.4 V) in both directions.

What happens if one of the diodes on an alternator fails?

If the diode shorts you will drain your battery when the engine is off. If the diode goes open you will only lose some output and it won’t be necessary to do anything. If only one diode shorts, you can cut it and it’s pair out and still get 2/3’s output. If two different winding diodes fail, it’s a lost cause. You alternator has three windings.

What causes an alternator to fail while the engine is running?

Diodes can be damaged when there is an attempt to swap out a battery while the engine is running. As soon as the battery cables are disconnected, the current will seek out another route to flow, causing the diodes to overheat and fail.

What causes an alternator fuse to blow out?

These fuses blow out after a while or when there is a power surge. In these cases, your alternator would fail and your battery would not charge. If you have a bad alternator, look in the owner’s manual to see where the alternator fuse is in your car and check to see if it is blown.

Where does the current go when the alternator is running?

Diodes As the alternator is running, it produces current that passes through the diodes to the battery connection on the alternator. The current then travels to the battery through the positive battery cable.

What happens if I have a bad diode in my alternator?

Can a bad fuse cause an alternator to go bad?

Bad Fuse – Some vehicles use fuses to keep the alternator functional. These fuses blow out after a while or when there is a power surge. In these cases, your alternator would fail and your battery would not charge. If you have a bad alternator, look in the owner’s manual to see if there is a fuse in your car.

What causes an alternator solder joint to blow out?

Using the radio, headlights, air-conditioning and other accessories can cause more heat to pass through the diode, putting it at risk of burning out over time. Dry diode solder joints – in use the soldering around the alternator diodes expands and contracts with the heating and cooling of the vehicle engine and alternator.