Week 2, Power and Batteries

Day 1

Summary of This Lesson

This lesson will focus on what power is, how you can find the amount of it in a circuit, and how it works in a circuit.

Lessons for Electrical Training on the website requires a Tinkercad account at www.Tinkercad.com, so if you haven't already, make an account on that website. Also, you can press the "Try Circuits" button in the circuits tab of Tinkercad to get an introduction of how to use Tinkercad's circuit simulation feature.

So, What is Power, Really?

To start off, let's use an analogy. If you pushed a table 10 feet in 1 second (somehow), compared to pushing a table 10 feet in 10 seconds, you would say that you had more power the first time you pushed the table. This is basically what power is. When you push a table, you do work, which is the force and distance that you had put into pushing the table. How fast you did that work determines the power, which is work per second. So power is essentially how much work can something do every second, or minute, or hour. You can push a whole semi-truck for 10 feet, which is a lot of work, but if you do it for 100 years, then of course, you can push the semi-truck some distance over a large amount of time. Not too impressive. But if you pushed the same semi-truck 10 feet in 1 second, well then you are essentially superman, very impressive and powerful.

What is Power in Terms of Electricity?

You've learned about voltage as well as current. A quick review: voltage is the energy, or work, that each electron can provide in a circuit due to the electron difference, and current is the amount of electrons flowing through the circuit per second. So, every flowing electron can do work, every electron can help power a light bulb or a motor. See where I am getting at here? What if we had more electrons flowing at a time? More electrons would be able to help out, since each electron can contribute work to powering a component. The more electrons flowing per second, the more total energy/work per second. What if we wanted to do the same rate of work per second, but with less electrons? Well, simple. You just need to give more energy/work to every electron to balance it out.

So what is power? This is the equation for power: P = I*V, where P is the power in watts, I is the current in amps, and V is the voltage in volts. You can see how an increase in current (I) with a constant voltage means more power. The same concept is true for voltage.

You might wonder how P = I*V came to be. You know that current is the electrons flowing by per second, and voltage is the amount of work that each electron can do. So, lets use math to prove P = I*V. Current is electrons/second, and voltage is work/electron. What happens if you multiply those two together? (electrons/second)*(work/electron) = work/second, since the electrons cancel out. What is work per second? Power! To cement the concept, let's translate that equation in English. Power is determined by how many electrons flow by per second, multiplied by how much work each electron can do, which will give us how much work can be done per second, in watts. In reality, we don't use the number of electrons, we use a coulomb, which is around 6.24*10^18 electrons, which is like 6 with 18 zeroes after it. So yeah, if we used the number of electrons instead of coulombs like in current, we would get huge numbers, which are not as easy to use compared to say, 2 coulombs, or 1.5 coulombs. The concept of power, voltage or current still stands though. They still deal with electrons, it's just that coulombs are used to group the huge number of electrons into a much more manageable unit, the coulomb.

Now that you've created your circuit, change the voltage outputted by the power supply by turning the knob, or typing in numbers into the voltage section, and resistance of the resistor while simulating it. Notice how increasing the voltage (energy per electron) or decreasing the resistance (restricting factor for the flow of electrons) makes the LED brighter. Also notice how voltage, as well as current rises from the multimeter readings. The voltage reading is the voltage drop, or energy used up by the component that the multimeter is getting it's voltage reading from. Logically, the more voltage you put into a circuit, the more voltage can be used by all of the components, since Kirchhoff's voltage law says that all the voltage needs to be used up in a circuit. Logically, decreasing the voltage or increasing the resistance, or both, would make the LED dimmer, since less voltage, or energy is put into the circuit as a whole, and less current flows through.

Now, about power in this circuit. To get how much power a component like an LED or resistor is getting, we need the voltage drop (energy/work used by a component) and current flowing through that component, since P = I*V. So, if our LED had a 2 volt voltage drop, and had around 0.015 amps flowing through it, we can figure out how much work every second that LED is doing (and technically consuming from the power supply too). The power is simply 2 volts * 0.015 amps = 0.030 watts.

What if you didn't know the voltage drop across the LED? Say, you didn't have any multimeters, and only left if the circuit. Well, since we know that P = I*V, and V = I*R from Ohm's law, we can combine the two equations by substituting V = I*R into the V of P = I*V, getting us to P = I*(I*R), or I*I*R. You can do this trick of using Ohm's law to rewrite the equation of power in a similar way, incase for example, you don't know current, then instead of using P = I*R, you know that from Ohm's law, I = V/R, so P = I*R can be P = (V/R)/R, or V/(R^2).

In this example, increasing the voltage from the power supply or decreasing the resistance of the resistor will make the motor spin faster (shown by the gear turning, and the rpm counter increasing). The opposite happens when decreasing the voltage or increasing the resistance. The results are similar to the previous circuit that you made. Increasing the voltage and/or decreasing the resistance results in more power, which means your LED is brighter, or your motor spins faster. Decreasing the voltage and/or increasing the resistance results in less power, which means your LED is dimmer, or your motor spins slower. Power has different affects on different components, like in a resistor where more power going into it means more heat, but there is a similarity, which is that more or less power makes those affects greater or smaller.

Specific situation for Motors

This will be more for the in-person people, but you can still read this section since it is still pretty important. If you have a motor that is on, and you apply a load onto the shaft of the motor, for example, by squeezing the shaft of it and trying to slow it down, the motor starts to heat up. The in-person people will get to feel the heat of a motor from the situation described above. Anyway, the reason why the motor heats up is because there is more power being outputted by the motor. The slowing down of the motor by mechanical force actually allows more current to run through the motor, and we know that more current can mean more power, since P = I*V. Why does the current increase? It deals with inductors which we'll learn about later. Essentially, inductors increase in current gradually (it's actually pretty quick but it's still relatively gradual), and inside a motor, there are multiple inductors. When a motor spins the shaft, the inductors also spin. The inductors get charged with electricity in a smaller amount of time the faster the motor spins. If the motor spins slowly or stops spinning, one of the inductors gets charged by electricity for longer, and it will have a chance to gradually increase the current more than normal. What happens if the load is so heavy, that the shaft stops moving entirely? What you get, is a very sad motor. This means that the motor burns out due to all the heat caused by the large increase in current, which increases the power which is converted into that heat, instead of spinning the shaft (mechanical power). So in general, it is not wise to power a motor while it is unable to rotate it's shaft, or else it does something called stalling, and burns out. Don't worry if you didn't get everything, especially the inductor and some of the motor parts, we'll learn about them in detail later on.

That is basically all of Today's Lesson, Now Play Around with Circuits!

Try to create different circuits, series, parallel, with LEDs, motors, etc. Since this lesson was on power, try to find out how much power each component in your circuit dissipates (meaning how much it releases). Start off by using multimeters to get voltage and current to get the amount of power, and then challenge yourself by using Ohm's law to find voltage and resistace! Good luck, and have fun! (yes, I am a gamer).

If you want, you can tinker around with these circuits to get you started.

Here's a video about power and watts that can help wrap everything up!

Day 2

Summary of This Lesson

This lesson will cover how batteries work in more detail as well as how to use batteries, such as the 12V FRC lead acid battery. At the end of the lesson, you will be put in an imaginary scenario where you need to power multiple components while having the least amount of current flowing out of it, to preserve the battery capacity.

Lessons for Electrical Training on the website requires a Tinkercad account at www.Tinkercad.com, so if you haven't already, make an account on that website. Also, you can press the "Try Circuits" button in the circuits tab of Tinkercad to get an introduction of how to use Tinkercad's circuit simulation feature.

Batteries in Essence

Batteries have electrons on one side, and a lack of electrons on the other. This creates voltage, which you have been dealing with for a bit by now. So you know that because of the difference in electrons, this creates voltage, which gives the electrons energy to flow through the circuit, light up a lightbulb, or turn a motor. But what actually happens inside the battery?

Inside of a battery

A battery has different elements inside of it that are used to create the one sided situation of having one side of the battery contain the electrons, while the other side does not have the electrons. This lesson won't go too in depth of what exactly goes on inside of battery, but it is going to help you get the gist of it.

Inside of a battery, chemical reactions happen

Different elements are put inside of a battery in a specific configuration to react to each other. Certain elements inside of the battery react with each other to create an excess of free electrons (free electrons meaning they escape an atom, so they don't orbit the atom/element anymore). Other elements inside of the battery react with each other which requires a free electron to be used within that reaction. So in general, one side of the battery has a reaction that "makes" free electrons, and the other side attracts those free electrons to be used in the reaction. A chemical reaction can't actually "make" an electron out of thin air, it uses whatever was there in the reaction in the first place.

Here's a great video that lays all that out in detail, as well as relating what you've learned previously. I really suggest watching it.

How do We Know the Capacity of an FRC battery?

Usually, an 12V FRC battery, and most batteries, would tell you the capacity that that battery has. The unit is in mAh, or milliAmp hours. Weird unit, I know, but don't worry, it'll be explained. So, the unit of mAh combines current (in milliamps) and time (in hours). Let's go to a relatable example, running. If you ran at a speed of 6 miles per hour, for 2 hours (dang), what is the total amount of miles that you ran? It would be 12 miles, since you multiple 2 m/h and 2 hours. The hours cancel out, but you can also think of it logically, that each hour of you running means you ran 6 miles, and if you do that for 2 hours, you run 12 miles. It's basically the same for current. Current remember, is the electrons passing by per second, and because of that it also means how many electrons exit the battery per second. Both the analogy and battery capacity concept have the unit of time in hours, so no need to explain much there. So, we have electrons per second multiplied by hours. If you changed the hours to seconds, then you are left with electrons after multiplying the current and time (in seconds) together. In the end, you are left with the number of electrons, which is capacity. Why don't we use the number of electrons (or coulombs to make things simple, since the number of electrons would be huge). It makes it easier for people like us to determine how long a battery would last for in a circuit. Since mAh already has the unit of milliamps in it, you can simply take how many milliamps a circuit needs then divide the mAh of the battery by the mA needed for the circuit, then you are left with the hours since the milliamps cancel out. Now in reality, the battery won't actually last that long, because a battery only has so much material, so eventually, the difference in electrons gets small enough that prevents the battery from pushing electrons to the other side since the voltage is not large enough.

Putting the Concept of Battery Capacity in action

Go to Tinkercad and create a circuit with a battery. I suggest you make multiple circuits with either a 9v battery or 1.5 (AA) battery so that one, get the hang of making circuits, and two, have a good variety of circuits to work with to apply this concept. After that, use a multimeter the measure the current in those circuits, or better yet, use ohm's law to figure out the total current used by the circuit. After you get the current from the battery, find how long that circuit will continuously work for. If you used a 1.5v (AA) battery, the typical battery capacity of that is 2,400 mAh. As for the 9v battery, it is 500 mAh.

You can also use the two examples in this imbedded link

You might notice that a parallel circuit like the one above needs more current from a battery, even if it has the exact same components compared to a series circuit, like the one in the example above. In a parallel circuit, the total effective resistance of the parallel circuit is actually lower than the lowest resistive path. So if you have three paths, one with 350 ohms, another with 100 ohms, and another with 50 ohms, the actual resistance will be lower than 50 ohms, so it is essentially a resistor with less than 50 ohms. In a series circuit with the same components, the resistance is added, so the total effective resistance would definately be bigger than the lowest resistance resistor, which is 50 ohms. That is why there is more current flowing through the left circuit compared to the right circuit, since the left circuit is parallel, and the right is series. Relating to FRC, the more components you have, which will probably be connected in parallel, means more current will flow out of the battery, making it run out of electrons faster. I won't get into how you can calculate the effective resistance in parallel circuits, but you can search it up.

Internal Resistance of a Battery

Internal resistance of a battery is probably what you guess it is. It is the resistance from inside of the battery. You have dealt with resistance before, like in resistors, or essentially any component. Batteries are not an exception. Electrons flow through a circuit by going from one atom to another, and there it takes some effort, caused by the resistance from the atoms.

The internal resistance of a battery can limit its ability to provide current, and you can see how this is true because one of the ohm's law equations is I = V/R. This internal resistance means that a battery has a limit on how much current it can source, or provide in other words. Making a battery provide too much current than it is rated for for a long amount of time can cause it to stop working early. You know that power is voltage multiplied by current. If there is too much current, there is too much power. That power can be dissipated as heat, so all in all, too much current means too much heat, which logically would mean it can break something within the battery, and in general, a component like an LED.

FRC Battery's are rechargeable

FRC battery's are great components for a robot, so having to throw one away after every use is a waste. So it is nice to be able to recharge it, but how does that work? You know that one side of a battery has a chemical reaction that "creates" free electrons, and the other side has a chemical reaction that takes those free electrons. This process is reversible depending on the type of battery, which depends on the elements used, and how the battery is designed. Usually, a battery would have a label that states that it is rechargible, so you would recharge those. Essentially, electrons are forced by an external voltage source, like an outlet, back into the side that "creates" the electrons, returning the battery almost back to the state that it was when it was new. Of course, things don't last forever, so with every recharge, the battery wouldn't allow electrons to flow out of it as easily as it once did. This is why when you use a battery beak on older batteries, they would have larger internal resistances compared to newer batteries, because the older batteries recharged for many many times. They got tired. I can't blame them, powering a FRC robot is hard work, especially if you do it again and again.

Here's a video on recharging batteries.

Speaking of Aging Batteries...

If you were to measure the voltage of a new battery and a battery that was used of the same type with a multimeter, chances are, the used battery would give a voltage reading lower than the new battery. This is again because of how electrons from one side of a battery go to the other, and as that happens, the difference in electrons between the two sides decrease, which means the voltage decreases as well. Keep in mind that this is for nonrechargable batteries. Rechargable batteries would display basically the same voltage on a multimeter if they were, of course, fully charged. If they weren't fully charged, then logically, the voltage would be lower for the not fully charged battery. However, you should still use a new battery over an old one if you have it since older rechargable batteries probably will have a higher internal resistance, limiting the current, and therefore power that the battery can output, since I = V/R, and P = I*V.

What to do if You Drop a 12v Lead Acid Battery

Here's a great video showing you what to do if you accidentally drop a 12v lead acid battery.

A Challenge I have for you

Now that you know more about batteries, specifically about how they work, battery capacities, as well as internal resistance, I challenge you to create an efficient circuit. What I mean by that is try to create a circuit that can power three LEDs so that each LED can light up (meaning you can see a decent difference in brightness compared to it being off), while limiting the amount of current flowing out of the battery. The purpose of this is to introduce you the concept of battery capacity conservation. Generally in FRC, having a battery just run out of battery power is rare, but it is always good to be efficient with your electrons. Good luck, and have fun!