Basic Principles of 12Vdc Circuits

I began re-learning my high-school physics by reading some of BillaVista's pages .

If nothing else, remember:

Voltage is pressure;

Current is flow;

Resistance is...uhh...resistance; and

Voltage = current multiplied by resistance (V = I * R).

Electricity is the movement, or "flow", of electrons. It is a form of energy.

Electrons have a negative (-) electric charge.

A common analogy for the flow of electrical current is that of water flowing through a pipe.

I find an equally useful analogy for automotive 12V DC is that of compressed air in a workshop environment. In this way:

The vehicle's alternator is like the compressor (converting energy from one form to another).

The battery is like the compressor's tank - storing the energy for use.

The wiring is like the shop plumbing, conducting the energy to where it is needed to do useful work.

We use electrical pressure to make the electrons flow (electrical pressure is known as voltage

In order to maintain the continuous flow of electrical current through a circuit, the circuit must connect the source (battery (-) terminal) to the destination (electrical device - e.g. light bulb) and back to the source again (battery (+) terminal) in a continuous, unbroken loop of conductor (wire).

If a circuit is unbroken it is said to have continuity.

Potential energy is expressed as voltage, which you may think of as "electrical pressure"

It is the battery's negative terminal that has a surplus of electrons.

Electrons move through even the best conductors with some degree of "friction", or opposition to motion. In electricity this opposition to motion is called resistance

Ohm's law states that voltage = current multiplied by resistance, or in equation form: V = I * R

So, as an example, suppose we create a circuit consisting of a 12V battery connected to a lamp with a resistance of 3 ohms. The current would be 4 amps. Knowing this we could now decide what size wire we would need to use, which would subsequently tell us what size fuse we would need to use. This would be a practical example of the use of Ohm's Law.

A multimeter can be a terribly complicated-looking thing, but in fact, for the simple measurements we are interestedin, it is quite simple. The dial is rotated to the correct position for the measurement we wish to take. There are different positions for AC and DC power, so make sure to select the proper DC position.

For measuring current greater than 10 amps … you can measure the values that are easily measured with your multimeter (namely, voltage and resistance), and simply (and safely) calculate the current!!

Power is the measure of how much work can be done in a given amount of time. Electrical power is almost always measured in watts.

P = I * V (power equals current multiplied by voltage) In other words - want more power? You need more current and/or higher voltage.

1 horsepower equals 745.7 watts

One thing most of us already know is that automotive electrical systems are 12 Volt DC. BUT - it is important to note that TWELVE volts is just a nominal voltage. Although we always refer to the related circuits and components as "12 Volt", in reality a typical, fully charged automotive battery will produce 12.6 volts (with the engine off) and a car's charging circuit (alternator) will supply 13.2 to 14.4 volts under normal conditions. As such, when using any of the equations we have discussed that include voltage, standard practice is to use 14 Volts, NOT 12.

In a series circuit the devices are connected in a row, one after the other, daisy-chain fashion. When wiring batteries together in series (positive terminal to negative terminal) the result is the total voltage produced is the sum of the voltages of the individual batteries.

In a parallel circuit multiple devices have a common power wire which splits and branches out to supply each device. The voltage drop is equal across all components in the circuit. In other words, all devices share the same voltage. All components share the same voltage; resistance in the circuit is less than resistance in any one branch, and branch currents add together to equal a larger total-circuit current.

Another example of a parallel circuit is the wiring of two or more 12 Volt batteries in parallel to increase total battery capacity while retaining 12 Volts (effectively making one big 12V battery).

Battery

1) Converts chemical energy into electrical energy.

2) Stores electrical energy.

3) Rated in Amp-Hours.

4) Batteries in series multiply voltage.

5) Batteries in parallel multiply capacity (amount of current they can supply and/or length of time they can supply a given current).

Alternator

Or in my case "Wind turbine"; I use wind-power to drive my generator whereas your car uses mechanical energy to drive your alternator. An engine-driven belt spins a magnet (called the rotor) inside a coil of wires (called the stator) which, by the laws of electromagnetism, induces an AC electrical current in the wires. The AC current is then rectified (turned into DC current) by a series of "electrical one-way valves" called diodes, and is output as DC current to the vehicle's electrical system.

Now, does my wind-turbine generate AC or DC?

The output of any given alternator is primarily determined by the rotationalspeed (RPM) of the rotor …

Although we always refer to the related circuits and components as "12 Volt", in reality a typical, fully charged automotive battery will produce 12.6 volts (with the engine off) and the alternator's voltage regulator will be set to maintain system voltage at somewhere between 14.0 - 14.6 volts …

The faster the alternator spins, the more power it will make … the alternator's performance curve which is a graph of the alternator's output vs. its rpm.

Sow what are the performance curves of the various wind turbines.

The more power you make the more heat is created when doing so. – but then my turbines ought not overheat while wind is blowing past/through them. Thought: Can I automatically switch gearing as wind speed increases?

http://www.madelectrical.com/electrical-tech.shtml is a linked resource which led me to http://www.madelectrical.com/electricaltech/battery-charging.shtml

Friday, December 11, 2020

What do I think I know?

(1) My wind turbine generates electrical energy according to the wind speed (rpm). A controller governs delivery of 12vDC (actually 14.6v?) to a bank of batteries.

(2) A bank of car batteries hold electrical energy. The capacity of this energy must be measured in Watt-hours.

(3) Over two dozen applications draw power from the battery bank according to the wattage and duration of each application

(4) I need tools, equipment, materials and meters to join these three components.

Lessons In Electric Circuits, Volume I – DC

A battery with a capacity of 1 amp-hour should be able to continuously supply a current of 1 amp to a load for exactly 1 hour, or 2 amps for 1/ 2 hour, or 1/ 3 amp for 3 hours, etc., bef ore becoming completely discharged.

An average automotive battery might have a capacity of about 70 amp- hours, specified at a current of 3. 5 amps. This means that the amount of time this battery could continuously supply a current of 3. 5 amps to a load would be 20 hours

For example, the 70 amp-hour automotive battery in the previous example should take 10 hours to charge from a fully-discharged state at a constant charging current of 7 amps

consider connecting batteries in series for greater voltage

Next, we will consider connecting batteries in parallel for greater current capacity (lower internal resistance) , or greater amp-hour capacity:

Two distinct concerns of battery charging are cycling and overcharging. Cycling refers to the process of charging a battery to a ”full” condition and then discharging it to a lowerstate. All batteries have a finite(limited) cycle life,and the allowable ”depth” of cycle (how far it should be discharged at any time) varies from design to design. Overcharging is the condition where current continues to be forced backwards through a secondary cell beyond the point where the cell has reached full charge. With lead-acid cells in particular, overcharging leads to electrolysis of the water (”boiling” the water out of the battery) and shortenedl ife.

E=I*Ror"VoltageisCurrent(amps)multipliedbyResistance(ohms)"

P=I*Eor"PowerisCurrentmultipliedbyVoltage"

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