Connect a voltmeter across the battery and resistor to measure the battery voltage during discharge. Stop the discharge disconnect the resistor when the battery is down to the desired voltage. Begin typing your search term above and press enter to search.
Press ESC to cancel. Skip to content Home Essay What causes an alternator to put out High voltage? Ben Davis April 8, What causes an alternator to put out High voltage? What stops the alternator from overcharging the battery? How can I tell if my alternator is overcharging? Traditional, sealed car batteries contain a sulphuric acid and distilled water electrolyte that facilitates repeated charging and discharging of the battery.
Continuous overcharging when the engine is running causes this liquid inside the battery to heat up to the point where a chemical reaction occurs that releases hydrogen and oxygen. However, loss of the electrolyte reduces the ability of the battery to discharge and recharge properly. Newer vehicles often use AGM battery technology where the acid electrolyte is bound to a fleece textured mat that helps to protect the electrolyte from damage caused by overcharging.
This also allows for more frequent charging and discharging. A basic alternator test can be performed using a multimeter. Using a diagnostic tool such as an OBD II reader will give you access to stored error codes and some can allow you to record the voltage output of the alternator in real-time under varying conditions. This is usually somewhere between 13 and 15 volts when the engine is running, but it can be higher or lower on some vehicles. When checking the voltage output of the alternator you should try to get a reading at the alternator terminals instead of at the battery terminals.
This will give you a more accurate reading without wiring or auxiliary device voltage loss. Testing the alternator is as simple as starting the engine and measuring the voltage by placing the tip of the multimeter leads on the corresponding output terminal on the alternator. If the basic multimeter reading is way above the expected voltage range, then there is a good chance that the alternator is overcharging. This should increase the voltage output. You can further test it by turning on some auxiliary systems such as the headlights and air conditioning or heating.
This is not the most accurate way to test the alternator but it will give you an idea of how well it responds to increased engine speed and increased load. No, as a general rule, you should not drive your car if the alternator is continuously overcharging the battery.
An overcharging alternator will cause damage to the battery and wiring of the charging system. Most newer vehicles have a battery management sensor that monitors the current state of the battery and the electric charge that is coming from the alternator. If the voltage is too high, the alternator may be disengaged so it no longer produces a charge, or the battery circuit may be isolated to protect the battery from damage.
In general, a voltage regulator stops the alternator from overcharging the battery. The voltage regulator can be part of the alternator or on some older vehicles it is fitted near the battery as a separate component. The voltage regulator can be a mechanical device that physically breaks the circuit when the voltage exceeds a preset value. In modern vehicles the voltage regulator is electronic and is controlled by the ECU. Batteries on newer vehicles are much more sensitive to over and under charging.
This surge disrupts the wiring in the alternator, causing an overcharging condition. Additionally, an incorrect replacement battery in the vehicle can cause an overcharging condition.
This happens in newer vehicles with alternators that need signals from the vehicle's electronic control unit. Most replacement alternators have design and voltage output specifications meant for a specific vehicle and its requirements.
Some replacement and re-manufactured alternators have much higher output ratings and designs. When the wrong alternator has been installed in a stock vehicle or if the pulley has undersized dimensions causing extra alternator rotation , the charging supply will be higher than the demand and cause an overcharged state. High performance or racing alternators should not be installed on stock passenger vehicles. The external regulator, usually mounted on the engine firewall or fender well, supplies current to the internal rotor field coil inside the alternator.
It regulates the amount of electricity that the alternator needs to perform at different speeds. The external regulator usually has three electromagnetic contact switches inside its housing that open and close. A stuck contact switch that refuses to disengage will cause an overcharging problem.
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