How to know if the alternator is not charging the battery

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Explanation of why the alternator is not charging the battery. And put together a small tester that does not use a tester to know if the battery is charging.

How to know if the alternator is not charging the battery?

This is the question that many people ask themselves when they start the problems with loose starting of the vehicle, dim or blinking lights. And when we do not have a voltmeter on hand, it is possible to rely on the load light of the board. If it turns off when the engine is started, is the battery really charging?

The answer to this question is a resounding yes. In fact, the little light on the board shuts off when the alternator is generating voltage, so the battery is receiving charge, but the problem is, if the battery receives the necessary amount of charge.

Understanding the alternator's power generation system.

As you can see in the following image, the alternator is an electric machine that produces alternating energy.

esquema del alternador

An important rule of thumb in electric power generation systems is that the generator must always comply with the power equation. He is an obedient slave, since he can not escape the premise that the power he delivers is proportional to the voltage and current he supplies.

Written mathematically is: P = V x I

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What is this translated into?

Well, as we demand more current from the alternator, the charge voltage (generated voltage) is reduced to meet the equation. It is for this reason that when turning on all the equipment in our car the voltage drops from the nominal values of just over 13.5V.

So by way of example:

A standard alternator can deliver 50A to 13V. Then our vehicle generator has a generating power of 50Ax13V equal to 650VA.

If now we turn on the lights, the car air conditioner, and the defroster, etc. which increases the total energy consumption of the car to about 60A. To know the charge voltage that our generator can deliver, we find out by clearing the voltage of our power equation. And we would stay like this:

V = P / I => 650VA / 60 = 10,83V o unos 11 Voltios.

As you can see, although the alternator is generating energy, it is not enough to supply the entire load and then in these cases the battery begins to supply the deficiency and starts the discharge process.

If this continues for a long time, the battery voltage will go down until it reaches 11Volts, which is the voltage supplied by the alternator. And that's when people notice the lights low or blinking.

That is why it is important to choose a good alternator when we incorporate high consumption equipment in our car as they are, high power sound equipment, additional lights, refrigerators, among others.

How to know if the battery is charging

Returning to the question of how to know if the alternator is charging the battery, it is simple. If the supply voltage exceeds 12.7V our battery is charging.

And to find out we just need a voltmeter and we made the following measurements:

Or, failing that, put together a small battery charge tester like the following:

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circuito electronico para saber si carga bateria

How to put it together? Visit this article where I explain this battery charge tester.

It's all for the moment. If you have questions, below in the comments.

Questions or suggestions

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Written by

Dennis García

Chica Mecánica

10/12/2018

Grade 
12/11/2018

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    How to know if the alternator is not charging the battery

    How to know if the alternator is not charging the battery

    Explanation of why the alternator is not charging the battery. And put together a small tester that does not use a tester to know if the battery is charging.

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