Goals This module is to introduce basic electrical concepts as they apply to power systems. Volts, Amps, Ohms, Watts are discussed. Ohms Law is introduced and different types of power sources are also introduced.

Objectives Upon completion of this module, the student should be able to: Describe the safety hazards with power sources. Perform simple Ohms Law calculations. Select the proper meter for voltage and amperage measurements and connect it properly in the circuit. Fabricate industry standard wire splices that are properly soldered and insulated. (not sure this should be here and not in controls)

Objectives (cont.) Determine the appropriate type, size and capacity of battery or batteries for the ROV and their appropriate placement on the surface. Estimate the total amount of energy and the maximum instantaneous power that your vehicle will require to complete its mission Select over current protection as dictated by the device being powered.

High Voltage Electricity and Water are a Dangerous Combination and is one of the greatest hazards students will encounter in these projects, therefore, this section should be thoroughly taught, tested, and constantly reiterated.

AC versus DC AC (Alternating Current) DC (Direct Current) Alternates its current in a sine wave pattern Typically osculates between 50 and 60 HZ Typically found in all building wiring. Typically above 100V (varies from country to country)(varies from country to country Can be deadly! The current travels the same direction and the voltage is constant Most commonly comes in the form of Batteries and Power Adapters or Inverters that change AC to DC Typically low in voltage (1.5V – 32V Can be deadly! it-construction-kit-ac

A/C Electrical Power Safety 115 Volts AC can and does kill roughly 100 people each year Working around water GREATLY increases the risk of serious physical injury Although it is common for many commercial ROVs to use very high voltages, the people designing and operating them are trained and certified professionals – you are not! Therefore: A/C Power should never enter water at any time and Working with A/C power near water should be done minimally and with the highest regard of safety

If you must… …work with A/C Power around water, commit the following to memory or retype and post near outlets in the room as a reminder to all. NEVER touch a device that is plugged in if either you or the device is in contact with the water

CERTIFY that any device plugged into a wall socket around water is plugged into a working GFI Outlet GFI and GFCI are the highest rated quickest to respond to any short circuit The cord on the right uses an in-line circuit breaker, and should only be used in conjunction with a GFI wall outlet

NEVER Work on any electrical system while it is plugged in (this includes small DC wall adapters and Batteries of all types) Let your body become the electrical pathway to the ground

ALWAYS Have a responsible person with you (preferably trained in CPR and First Aid) Work in a dry uncluttered place Use tools with insulated handles Check and Double-check that everything is unplugged before working with hands or tools Ensure that there is no latent charge in components that may have stored voltage after the device has been unplugged

Energy Energy is the ability or capacity something has to affect change in another thing Forms of Energy heat electromagnetic radiation (light, radio waves etc) energy stored in chemical bonds mechanical energy (potential and kinetic) electrical mass

Quantifying Energy The Unit of Energy is the joule (J) One joule is roughly the amount of energy needed to lift one apple one meter from the floor It is the amount of energy it takes to lift an object one meter using one Newton of force. Sometimes it is expressed as Newton Meters where 1 joule = 1 Nm or Newton-meter

Quantifying Energy – Watt Hour Watt hours (Wh) Are very useful to use when calculating the amount of Energy each of the systems in our vehicles are each going to need and how much the entire vehicle will need. Therefore Watt Hours will be the most commonly used unit of Energy 1Wh = 3600 joules (an easy way to remember this is that an hour has 60 x 60 seconds and therefore 3600 seconds, why this is relevant will become clear when we talk about Units of Power)

Kilowatt hours (KWh) 1kWh = 1000 Wh = 3.6 million joules Kilowatt hours are typically how building electricity usage is measured when purchased from a power plant ft-lbs is the imperial equivalent 1 ft-lb = joules Notice how the ft-lb is a combination of distance and force, just like the Newton-meter calorie The amount of energy required to raise the temperature of one milliliter of water one degree Celsius BTU The standard by which natural gas is measured Quantifying Energy – Other common units

Power = The rate at which electrical energy is transferred in an electronic ciruit Notice that the power is a rate, which means that it forms a ratio over time therefore the formula for power is: Power = Power

Energy and Power: What’s the difference? When applied non-scientifically, these words seem to have similar meaning, but they have a constituent relationship, they are part of one another. One way to imagine the difference is in a car. The Energy of the car is represented by the amount of fuel in the car. The Power of the car is the ability of its engine to convert the fuel into movement. How well it does this determines how powerful is it.

Quantifying Power Watt - The watt is the most often encountered metric unit of power 1 Watt = 1 joule/second. (remember that power is a rate of energy consumed over time, joule is a unit for energy and second is obviously a unit of time) Kilowatt – A higher order unit of power 1 kW = 1000 W Horsepower - An often used imperial unit of power. 1 Horespower = 746 Watts

Criteria for determining a power system What are the considerations that we need to make when deciding which kind of Power To understand how all of this is going to work together, we need to know a little bit about how we talk, think and work with electronics

This section is to provide only general, practical introduction to electrical theory. Circuit design and system specific electronics will be considered in another module. The focus of this module is Supplying the appropriate amount of power and delivering that power to the systems of the ROV

The Basic terminology Charged particles – elements (usually protons and electrons) that have electrical attraction or repulsion Current – the flow of electrons from one location to another (represented with the letter “I”) Voltage – the energy per unit charged in or repulsion of charged particles (represented with the letter “V” or “E”) (joules per coulomb) Resistance – a friction like property within a wire or a component that generates a transfer of energy like heat and other forms of energy (represented with the letter “R”)

Voltage is the amount of “pressure” needed to “push” the current along, measured in volts (V) Current is the “rate” at which the charged particles are moving through a substance, measured in amperes (“amps” or A) Resistance is the electronic “friction” restricting the movement of the current: measured in ohms (Ω) The relationship between voltage, current and resistance Since Electricity is invisible, we often use analogies to help us understand the different interactions that occur in a circuit

So what? What is a circuit? A circuit is a configuration usually comprised of a power source, a conductor and something resistant ation/circuit-construction-kit-dc This is the schematic RoMtg&feature=relmfu Kahn Academy CU Physics simulations

Ohm’s Law The interaction between the constituent parts of electrical power form a mathematical relationship famously defined as Ohm’s Law, the most famous law in all of electronics V = I x R (or E = I x R)

Using Ohm’s Law This configuration, sometimes called Ohm’s triangle is a useful way of remembering how to find one element when you know the other two Examples: … Let’s practice seeing how this works in our own circuits it-construction-kit-dc law/ohms-law_en.html

What about Power and Energy? Power is directly proportionate to Voltage and Current, in other words we have another formula P = V x I (or P = E x I) Again a triangle is useful to help us derive what we want to know from two things that we know Remember that power is the Rate at which Energy is put to use or used up, therefore it makes sense that as the “pressure” or voltage increases and the “rate” of the movement of the current increases, then the rate of consumption must also increase

The Wheel If we substitute the constituent parts between the two triangles mathematically we come up with an entire array of different formulas This looks really complicated, but if you can simply remember the relationships represented in the triangles, memorizing this is not all that important. It is useful however to see all of the possible mathematical possibilities between the four properties of electricity and to realize that if any two properties are known, than the other two properties can be derived

Testing connections for proper voltage and current

Measuring Voltage, current and resistance Generally we use a multi-meter to measure the properties of a circuits. Here is a good video illustrating the basic use of a multimeter And here is a virtual place to practice it-construction-kit-dc UD-_s

Tips for checking voltage and current Checking the voltage of a battery may give you a sense of whether it is charged or not, but to be certain, it is critical that either… A load is applied to the battery while it is being tested. This is because the internal resistance of a battery increases as it loses its charge, which may not be obvious unless it is being discharged You use a car battery tester that has been designed to apply a large enough load to do this without a circuit Remember when measuring current, the meter must be placed “in-line” and the correct amperage port is being used with the meter’s leads, ask for permission to do this first, as it is common to blow the fuse if done incorrectly

Soldering, crimping and an insulating

Proper soldering techniques Proper soldering is very important, a “cold”, a weekly soldered connection, or a solder bridge can lead to a lot of frustration and worse damaged equipment These films offer a great series on soldering techniques which should be studied, practiced and strictly applied This you tube channel, the curious inventor, has dozens of excellent videos that do a fantastic job of demonstrating and describing the proper way to solder

Wire Gauges The thickness of a wire or its “gauge” is a standard unit known as the AWG (American Wire Gauge) The wire gauge number INCREASES as the wire gets smaller. Wires carry resistance: the thinner and longer the wire, the more resistance it will have The method you choose to connect wires to other wires, circuit boards and components will be determined greatly by the wire’s gauge

Wire Gauges It is the amount of copper that determines the gauge of the wire, not the insulation Typically wires are stranded or solid. When they are stranded, the total combined width of the strands determines the gauge

Using proper connections Special connectors have been designed for splicing wires with other wires and components. Gauges of wire under #22 AGW can use crimp – on terminal connecters as long as the correct size is used and the connectors are not ever meant to come in contact into contact with water

Other connectors For smaller wire, and other types of connections there are literally hundreds of connectors that can be used, depending on your application. A couple of resources that are good for finding the right type of connector:

When choosing a power source there are multiple considerations Safety Maximum Power Output Energy Capacity Size and Weight Depth of Discharge Type Cost

Battery Safety Any battery powerful enough to propel an underwater vehicle is powerful enough to set a fire. When batteries are not in use, the leads should be properly insulated The battery should always be stored in a place where it is not going to tip, fall, or otherwise come into contact with something that may cause a short

Content needed here NOTE to MATE: Jeremy and Scott recommended adding content here about the following and mentioned that they would contribute this content…I have forwarded the file to them: Safely containing batteries in an enclosure (Scott) Sulfuric Acid Safety (Scott & Jeremy) Potential Off-Gassing (Scott & Jeremy) Baking soda (Scott & Jeremy) Video of melting metal with a battery (Jeremy)

Content needed here NOTE to MATE: Scott recommended adding content here a direct power supply, I am going to defer to his expertise in this matter since it is not discussed much in the book:

Battery Safety continued Burns A short circuit can cause serious burns even if it doesn’t cause fire The chemicals in many batteries often include sulfuric acid which will cause burns to the skin, so always use gloves when dealing with any battery solution Poisonous Gasses Some batteries can give off gasses (even Sealed Lead Acid batteries) that can either be poisonous or explosive

Maximum Power Output How much Power will you need? An inventory of all of your electrical systems provides will give you this amount Use a spreadsheet to compose the inventory so that changes can be easily made DeviceNumber Current (amps) Total Maximum Current (amps) Maximum on time Total Energy (amp-hrs) Thruster Motor Video Light Wireless Ethernet Switch Network video camera Camera tilt motor Microcontroller Lasers Misc. Sensors and other electronics11122 Totals

Power Inventory The power per device is derived by reading the rating of the device and if the rating is in amps, multiply the amps and the volts to get the total power use We do the reverse to determine how many amps we will need at total Maximum power DeviceNumber Current (amps) Total Maximum Current (amps) Maximum on time Total Energy (amp-hrs) Thruster Motor Video Light Wireless Ethernet Switch Network video camera Camera tilt motor Microcontroller Lasers Misc. Sensors and other electronics11122 Totals

Sizing the battery for the machine Batteries are measured in Volts and amp hours which gives you a broad sense of what you will need. Voltage is generally determined by the requirements of your onboard electronics. Generally it is advisable to choose a voltage that is as large or larger than the device with the largest need Amp hours simply tells us that the battery is designed to produce a certain level of current at its voltage for one hour before losing significant voltage

Calculating the Maximum power output of a battery In this example the battery can provide 35 amps of current 12 Volts for 1 hour If your system is drawing 7 amps of power continuously, then the battery should perform for five hours (5 x 7 = 35) If it were to draw 70 Amps the battery will only last 30 minutes These are not exactly precise because of various factors, but they give us a minimum threshold and put us in the ballpark for what we need

So how much will we need? Remember that Power = Volts x amps The maximum power of the example above is 106 Watts. Divide this by 12 and we should expect, that at a maximum, our system will need 8.83 amps The battery in our example provides 18 amp hours worth of energy so 18 ÷ 8.83 = If everything were running continuously, we could operate for 2.03 hours DeviceNumber Current (amps) Total Maximum Current (amps) Maximum on time Total Energy (amp-hrs) Thruster Motor Video Light Wireless Ethernet Switch Network video camera Camera tilt motor Microcontroller Lasers Misc. Sensors and other electronics11122 Totals

So how much will we really need? After we determine that we have more than enough amperage to power our vehicle at its maximum, we can take a look at how much we will need for the specific mission and see if our battery is sufficient Notice the maximum on time for this 1.5 hour mission for some devices is 2 hours. Prior to actually beginning the mission there may be a half hour spent testing equipment and that has been factored in Now, taking the data from our battery: 12V x 18Ah = 216 Watt hours, which is half an hour longer than is needed for our mission, therefore this battery is sufficient enough for our needs DeviceNumber Current (amps) Total Maximum Current (amps) Maximum on time Total Energy (amp-hrs) Thruster Motor Video Light Wireless Ethernet Switch Network video camera Camera tilt motor Microcontroller Lasers Misc. Sensors and other electronics11122 Totals

Devilish details Data sheets for batteries tell us a little bit more about how we should expect them to perform and before making a large investment, it is critical to inspect these sheets to make sure that this is what we need The “C” is the C-rate which is essentially the factor of the amperage we intend to use. In our case we are using at most 8.83 Amps which is a little less than half of the rated Amp hours of the battery (18Ah), therefore to see how this battery would perform at maximum power we can follow the line for 0.6 C and plan accordingly Of course this is at Maximum Power so we could go back through the chart and estimate a more realistic usage and then apply our chart. Notice how the bottom scale is logarithmic and a C rate of.25 actually triples our workable time

Other Electrical Considerations Deep Cycle batteries are designed to withstand severe discharging and repeated recharging cycles. Marine batteries are often Deep cycle or hybrids between deep cycle and standard auto batteries RV and Electric Car batteries are also of this type Maximum Charge Rate Batteries us the C-rate to inform what the maximum charge rate is, therefore if our battery must be charged at 0.5 C than the most Amperage we should supply is 9 amps

Multiple Batteries Voltage can be increased by connecting batteries in series Energy can be increased by connecting batteries in parallel

Size Big batteries provide a lot of power, but if you have to travel far, they may prove to be more of a burden then they are worth Also, large batteries may be more expensive than necessary, so it is best to choose a size that is appropriate for your needs.

Battery Types Alkaline - typical drug store batteries, not rechargeable and therefore not often considered for submersible vehicles Sealed Lead-Acid – Exact same chemistry of the traditional Car battery, only sealed and therefore not vulnerable to spillage AGM – Essentially a Sealed Lead Acid, only the fluid has been captured into an Absorbed Glass Mat, thereby making them very durable and ideal for surface NiMH and Ni-Cad – Nickel based rechargeable batteries that have become the standard replacement for the alkaline as a rechargeable alternative, affordable and available, when stacked to create higher voltages they can provide a good alternative to more expensive types

Battery Types continued Lead Acid Car Batteries These are not ideal for many reasons: They leak if they are not handled properly They may not have the “depth” to provide constant current and be very inefficient vs. Deep cycle marine batteries Can often be purchased as AGM and therefore not prone to mishandling Are meant to handle small amounts of current for longer amounts of time and are thus much more ideal than the average car battery

Battery Types to avoid Lithium – Because of the volatility of lithium, especially in water, Lithium is not recommended Automobile (Starter) batteries – Although very popular and readily available, these are discouraged because of the lack of containment of the battery fluid, Sealed Lead Acid and AGM should be used as an alternative,

Battery Types continued Lead Acid Car Batteries Deep cycle marine batteries These are not ideal for many reasons: They leak if they are not handled properly They may not have the “depth” to provide constant current and be very inefficient Are suggested as an alternatives to Car batteries because they: Can often be purchased as AGM and therefore not as prone to mishandling Are meant to handle small amounts of current for longer amounts of time and are thus much more ideal than the average car battery

Charging batteries With Sealed Lead Acid, Lead Acid and AGM Consult the manufacturer about what charging amperages will work most effectively. This is a consideration that should occur as decisions are made about the battery, as batteries will be charged a lot! Nickel based batteries – Investing in a “Smart” charger will preserve the life of the battery and ensure that batteries are fully charged each time they are used.

Fusing In line fuses placed as close to the positive lead of the power supply must be present to prevent short circuiting The voltage must be higher than the voltage of your system, and can be as high as you wish The current rating must be chosen carefully, the standard is 1.25 times the maximum current your system will draw “Slow blow” fuses are recommended to accommodate quick surges in the circuit, but still provide safety if the high current persists

References ysics ysics