1 Electricity Basics

2 Electron The smallest particle caring electrical charge. Electrical charge is measured in Coulombs video

3 Electrical current Electrical current is flow of electrical charges (by water analogy) Electrical current is measured in amperes one ampere is an electrical current that one Coulomb of electric charge is transferred in one second Electrical current is denoted with letter “I”

4 Materials and electricity Conductive materials (conductors): Metals Non metals – Carbon, electrolytes etc. Non conductive materials (insulators): P lastics Glass Ceramic etc.

5 A circuit Circuit is a continuous electrical path Closed circuit – circuit is unbroken and electricity flows Open circuit – circuit is interrupted, preventing electricity to flow

6 The task Our main task is to control the electrical flow for useful purposes. To predict the flow of electrons through electrical circuits so to organize consumers and sources of electricity in a properly working circuits To prevent electrical system from failure To predict size of the sources of electricity To prevent people from accidents Etc.

7 Useful purposes on boats (consumers) ContinuousLong durationSort duration Standby power taken by VHF or the SSB Refrigerator Freezer Instruments: boat speed wind speed fuel available tachometer Navigation lights Depth finder Marine charging Autopilot Navigation: Radar, GPS Cabin lights Water maker Air conditioning Entertainment Engine starter Pumps Trim and tilt system Electric winches and capstan Bow thrusters Microwave Washing machine

8 Factors controls current (I) in a circuit are: The electrical driving forces, or voltage (V) (current increases when voltage increases) The resistance to flow of the circuit materials (R) (current decreases when resistance increases)

9 Ohm’s Law where I – Current measured in amperes [A] V – Voltage measured in volts [V] R – Resistance measured in ohms [  ] (Works only when electric current flaws)

10 Schematic of a circuit V=12v R=2 

11 Ohm’s Law Ohm’s Law can be rearranged:

12 Loads in series Resistive loads in series act like one continuous load of a total resistance equal to the sum on the individual resistance R 1 =2  R 2 =5  R 3 =3  I=? Example:V=12V V1V1

13 Answer

14 Loads in parallel The same voltage acts across each of the loads. The currents through the loads are: Total current is:

15 Continue from the previous slide In other words: Remember Ohm’ low?

16 Example: V=12 V R 1 =2  R 2 =5  R 3 =3  R=? I=?

17 Loads in series/parallel V=12 V; R 1 =2  R=? R 2 =5  I=? R 3 =3  I 1,I 2,I 3 =? Solution: V1V1

18 Monitoring electrical systems THE MULTIMETER (VOM) The multimeter may also known as the Volt-Ohm-Milliammeter or VOM, or the DMM (Digital Multi- Meter). Because other functions may be included; thus the name multi-function meter or more simply; multimeter The multimeter is an instrument used to measure: Voltage in volts, Current in amperes, Resistance in ohms

19 ANALOG MULTIMETERS The analogue multimeter is easily recognised by: 1. A needle-like pointer 2. The semicircular scale both of which appear on the front panel. The pointer travels the scale and indicates the measurement on the scale directly beneath it. The scales are related to the settings of the function and range switches.

20 DIGITAL MULTIMETERS The digital multimeter is easily identified by: 1. Numerical readout panel 2. Absence of a scale The measurement appears as an ordinary number within the panel so that anyone who can read numbers can read the indicated value. Reading errors (long associated with analogue meters) are mostly eliminated by digital multimeters.

21 OPERATING CONTROLS The multimeter has two main operating controls: 1. The function switch 2. The range switch.... These are sometimes combined into one dual-purpose switch

22 Measuring current The multimeter is connected to the circuit in series The function switch should be on correct function (amps) The range has to be chosen on expected range of the value

23 Measuring resistance A resistor or other load measured must be isolated from the circuit The multimeter is connected to both ends of the item The function switch should be on correct function (Ohms) The range has to be chosen on expected range of the value

24 Measuring voltage The multimeter is connected to the circuit in paralel The function switch should be on correct function (voltage) The range has to be chosen on expected range of the value

25 Sources in series Therefore: Example: V 1 =1.5VR=4  V 2 =1.5V V 3 =3.0V I=?

26 Sources in series Caution! Batteries work in series must have the same capacity and the same state of charge. Otherwise the battery with the greatest capacity may drive the voltage of the weakest battery negative, which will destroy the weaker battery

27 Sources in parallel Provided batteries are the same voltage. The net result is a single battery of capacity equal to the sum of the individual capacities.

28 Sources in parallel If they are not of the same voltage, the higher voltage battery will discharge into the lower voltage battery, possibly overcharging and destroying it

29 Energy Energy is the ability to do work Energy can be neither created nor destroyed. Energy can be only transformed form one form to another.

30 Power Power is the rate of doing work Work is done when a force applied on a body causes it to move. In electrical circuit the power can be easily calculated:

31 Electrical measurements and units: Voltage is measured in Volts (V) Current is measured in Amps (A) Power is measured in Watts (W)

32 Example: What is the power of a light bulb that draws 1.25 amps at 12 Volts? How many amps would a 20Watt lamp draw in a 12 Volt circuit?

Resolve the problem: What is the resistance of a light bulb with a label: 33 12V 15W