Common House Hold Batteries?

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2 Common House Hold Batteries? A. What does a battery do? B. What is the Same? C. What is Different? D. Why does it matter? A=Stores Chemical Energy, B= Voltage, C= Amount of Energy Stored, D= do not have infinite power 2

3 Water Analogies to Electricity Battery Voltage (Water Pressure = Height of Water) Resistance (Size of the hole) Electrical current ( Water Flow) 3

4 Water Experiment Two different size cylinders Same height of water Same size hole What happens when you pull both stoppers at the same time? Which water stream will go out farther? Stopper 4

5 Water Experiment Flow will initially be the same Why? The pressure has to do with the height of the water not the amount of water 5

6 Water Experiment Same hole size = Same resistance Height of water no longer the same Voltages not equal Flows will no longer be the same Current not equal Smaller one runs out first Why? The bigger Cylinder like the bigger battery holds more stored energy and can provide more power (watts) for a longer period of time 6

7 Water Analogies to Electricity Battery WATER There is a relationship between water pressure, hole size, and water flow If you keep the hole the same size (resistance) but increase the water pressure what happens? If you keep the water pressure the same but increase the hole size what happens? Water Pressure = Height of Water= Voltage Water Flow = Electrical current Resistance (Size of the hole) 7

8 Water Analogies to Electricity Electricity There is a relationship Between Voltage, Current, and Resistance If you keep the resistance the same (hole size) but increase the Voltage (water pressure) what happens? If you keep the Voltage (water pressure )the same but increase the Resistance (hole size what happens)? Voltage (Water Pressure = Height of Water) Battery Electrical current ( Water Flow) Resistance (Size of the hole) 8

9 Water Analogies to Electricity There is relationship between Volts (height of water=water pressure) Resistance (the size of the hole) = OHMS Current (the water flow) = AMPS OR AMERAGE Power (how long the flow will last = the amount of energy consumed over time) = WATTS These are called Watts Law and Ohms Law 9

10 Watts and Ohms Laws (DCV) Watts Law for Electrical Power Power (called watts) = Current * Volts P = I * E or P = I * V I like PIE better.. Ohms Law Voltage = Current * Resistance (called Ohms for DC) E = I * R or V = I * R And I have always remember EIR. 10

11 Bringing it Home Your ROV does not have infinite Power available to it. This shows up as the Maximum Amount of current (amperage) the ROV can use for the volt power source supplied at the competition. Watts Law: Power (watts) = Current (Amps) X Volts Scout/Navigator Power limit = 15 amps X 12 Volts = 180 watts At the power source (battery) 11

12 ROV Implications Not all devices require the same amount of power Depends on the device and the conditions For a fixed voltage a device will DRAW the amount of current (amperage) it needs to achieve the power required to operate. P = I * E constant This is where the mechanical and electrical worlds can collide Can lead to some spectacular outcomes. 12

13 Implications Motor spinning freely in air draws about 1 amp (12 Watts) Stuck motor draws almost 10 amps (120 watts) Leads to why we have fuses! 13

14 What is a Fuse What happens when you put too much air in a balloon? What happens when a device tries to draw too much current? Remember OHMS Law E = I * R E Constant I * R constant CANNOT EXIST for very long.something is going to happen. For our ROVs, a fuse is a small piece of metal calibrated to burn up at a specific current level. Why do we care and where should the fuse be placed? Ideally we want the fuse to burn up or blow first before anything else is damaged 14

15 Resistance What happens when you stand on the garden hose? Standing on the hose is resistance in electrical terms. Resistance impedes the flow of electricity. High Pressure The pressure (voltage) up stream of the resistance is higher than the pressure (voltage) down stream. Lower Pressure We call the change in voltage the Voltage Drop across the résistance 15

16 What does Watts and Ohms Law have to do with My ROV 25 AMP Fuse Maximum Power (Watts Law) is at Pools side 25 amps * 12 Volts = 300 Watts 8-11 Volts POOL Volts V A Power at ROV is LESS than at poolside source Current is the same at ROV and poolside = 25 amps Resistance in the Tether and connections = voltage drop V drop = R * I constant Voltage at ROV = Voltage poolside Drop; can be 8-11 Volts Power = 8 volts *25 Amps = 200 Watts (66%) Power = 11volts * 25 Amps = 275 Watts (92%) and the ROV has not moved yet!!!! 16

17 So How do We get the ROV to go slow? Demonstration measuring RPM 17

18 Appendix for those who like Math Power, Voltage, Current, and Resistance are all easily related by simple math In this display P=I*V = Watts Law V=I*R = Ohms Law 18

19 Appendix Differences Between Water & Electricity Effective conceptual starting point buy there ARE differences Water Flows out one end of a hose. Flow speeds up as it goes through a nozzle and produces a force. For a fixed size pipe, maximum flow depends on pressure at the source. Electricity (DCV) Must have a complete loop to have current. Electrical current does not speed up. At a constant voltage and resistance a device will DRAW more and more current flow to try to reach energy equilibrium. 19