Ammeter reading when engine is running?
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Joined: Sep 2003
Posts: 59
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From: McKinney TX
Ammeter
Acording to your profile you have a 74. The 74 uses an ammeter. An ammeter is a device that allows current to pass through it and depending on the direction of current flow it reads positive. The higher the current flow the higher the reading will be in the direction of flow. Ammeters actually are placed in parallell to a big buss or cable that carries the electrical current. In our case one end of the ammeter is connected to a point on the juction block on the left fender well and the other end is connected to the starter hot post. This path is parallel to the heavy gauge wire that runs from the junction block on left fender well to starter. So most current flows through the heavy gauge wire and a small amount of current will flow through the ammeter.
On other cars, sometimes a voltmeter is used. It senses the voltage by having one end wired to ground and the other end wired to the junction block where hot wires are connected together. A battery fully charged should read about 13 to 13.2 volts. The regulator of an altenator senses the voltage of the battery and the current flow demands (doesn' matter whether the meter is a ammeter or volt meter).
The output current of an altenator is under control of the regulator. If the battery is charged the alternator puts out about 13.2 volts. If the voltage of the battery is low this is sensed by the regulator and the output votage of the altenator is increased up to about 14 to 14.5 volts. The higher the difference in voltage between the altenator and the battery the more current there will be going to the battery. If the engine is running and an additional load is placed on the battery such as lights or AC, the Regulator senses this needs and increases the current output from the altenator. If the engine is running, the current needed by everthing comes from the altenator and not the battery and this will not pass through the altmeter. So the ammeter only reads how much current is going to the battery when car is running and when car is not running, it indicates how much current is being supplied from the battery to run devices.
A voltmeter simply indicates the status of the battery when engine is not running 12.45 to 13 volts is good and if it goes over 13 volts with engine running informs you the altenator is working.
On other cars, sometimes a voltmeter is used. It senses the voltage by having one end wired to ground and the other end wired to the junction block where hot wires are connected together. A battery fully charged should read about 13 to 13.2 volts. The regulator of an altenator senses the voltage of the battery and the current flow demands (doesn' matter whether the meter is a ammeter or volt meter).
The output current of an altenator is under control of the regulator. If the battery is charged the alternator puts out about 13.2 volts. If the voltage of the battery is low this is sensed by the regulator and the output votage of the altenator is increased up to about 14 to 14.5 volts. The higher the difference in voltage between the altenator and the battery the more current there will be going to the battery. If the engine is running and an additional load is placed on the battery such as lights or AC, the Regulator senses this needs and increases the current output from the altenator. If the engine is running, the current needed by everthing comes from the altenator and not the battery and this will not pass through the altmeter. So the ammeter only reads how much current is going to the battery when car is running and when car is not running, it indicates how much current is being supplied from the battery to run devices.
A voltmeter simply indicates the status of the battery when engine is not running 12.45 to 13 volts is good and if it goes over 13 volts with engine running informs you the altenator is working.
