In this article, Chica Mecánica makes a simple circuit that can measure the charge of a car battery. Very simple to do and economical.
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Necessary materials:R1: Resistance of 50 ohms 1/4 W
Two alligators, red and black.
Cables, tin and as always a lot of enthusiasm.
As always, you can see the enlarged image by clicking secondary to the image and selecting to see image in the contextual menu.
As you can see in the previous figure, connecting the alligators to the battery will produce a stable voltage drop that does not depend on the voltage of the battery limited in current by the resistor R1. Then we have these reference voltages in each of the stages marked with arrows. As you can see it is possible to add or remove stages in our circuit. Resistor R1 is calculated in such a way that the Zener diode is protected by overcurrent and in turn ensures that the base current absorbed by the transistors does not influence the regulation voltage of the system. That is why I put a 50 ohm, which is possible to lower even more if we assume that we will not exceed 14.5V of battery charging voltage.
The second part is the voltage comparators that I built using the transistor-resistance-diode kit, as you can see in the following figure:
In this case, as can be seen in the diagram to the right, the base-collector current only circulates when the input voltage to the base exceeds the voltage passing through the PN semiconductor of the transistor, which in this case is a bipolar transistor. 0.7V. Then for the red LED diode stage for the diode to turn on it needs to exceed the voltage of [10.1 + 0.7 +0.7] V (Zener voltage, Rectifier diode voltage, base-collector junction voltage). Finally, the resistances of this zone are placed for the protection of the transistor and the led.
It is quite simple to take it to 24V, you just have to change the Zener for a 22.1V and add the stages with rectifier diodes to the voltage they want to sample.
I encourage you then to make this small circuit, very economical and simple to put together.
Well it's all for the moment, if you have any questions or comments, because below is the question box where you can do it.
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