 Okay, I'm gonna go through something that I Soon to see find a lot of students struggle with it's this whole idea of motor efficiencies And I've got students that are writing a test this weekend and this was basically this is for you boys I would in that the Surrey Foundation class for the rest of you Make sure you're watching this too because this is one of those things that kind of trips people up And I know it's I've got two videos coming out like one bang right after the other But I just really wanted to make sure that there's something out there So my students can go through and check it out now what I mean by this when I talk about motor efficiencies is We have motors that come with a certain horsepower rating and then they have a certain efficiency And then how we go about calculating all the electrical stuff we need out of that So I'm gonna pop into my I'm using a new app here called explain everything You've seen me use this a ton of times before it's just I'm trying this new hybrid model where I've got me on The screen as well as this pops in every once in a while, so let's take a look what I'm talking about here so I've got this motor and It's let's I mean it looks like an old cheap gross motor, but let's just say let me move it out of the way and give it some Context here that I've got Let's see here. Let's say it's 10 horsepower and let's say it's got an efficiency of 75% Then let's say that it's hooked up to 240 volts and I want to know exactly how many amps it's going to draw based off the information that I have here So there's a couple things that we really need to take into account Okay, so pay very close attention come come closer here number one that horsepower that is our output power Okay, that's our output. So that's that is something that as electricians. We're not so concerned with we need to use it To do a calculation But what we do is we have to convert it to watts first and then we use the efficiency formula To change it into input power. So let's just jump on to the whiteboard here and see what I mean So the first thing we're gonna do is I'm gonna go 10 times 746 That's easy 7,460 watts That's my output power. That is what is coming off of the shaft of the motor. So over here What we're concerned with as electricians is how much power electrically does it take in here this cable? How much how much electrical power is it supplying? Not necessarily what it's supplying on the outside or the shaft side So what we need to do is we have to look at the actual power for the efficiency formula And the efficiency formula is n is equal to output Over input. That's our efficiency formula. It plays out for everything Efficiency that little funky n is always output over input again The output is something that is the mechanical power that's being put out Maybe a mill right would be concerned with that as electricians But we're concerned with is what size cable do we need to connect to this motor in order for us to power it properly? We know that there's no such thing as a hundred percent efficient machine There's gonna be some loss on the motor bearings and the power the heat being dissipated So whatever you're never gonna have the exact power that horsepower is not gonna be what the actual electrical power is So what we're gonna do is we're gonna hop into this formula plug in what we know and calculate out what we need So we do that. Let me just change the color of my pen here By saying and let's change all this actually. Let me just move this out of the moving that over to there Let me just oh everything's kind of locked in there There we go making that a little smaller So what I'm gonna do now is we're gonna say, okay, we know that efficiency here is output over input So we're gonna plug the efficiency in so let's go with block. We know that efficiency is 75 percent We know that our output we calculated that out to be seven thousand six four hundred and sixty watts We don't know what our input is So what we'll do from there is we're gonna cross multiply point seven five X Is equal to seven four six zero X is equal to and if I calculate this out on my calculator seven four six zero divided by point seven five gets me Nine thousand nine hundred and forty six point seven watts. That is my input power That's what this is here my input power. That's what we are concerned with So what we've got now is we've got the electrical power This is what we are concerned with nine thousand nine hundred and forty six point seven watts What we can do now is take this power With this voltage to figure out the current because we know in what slaw P P oops, sorry, I didn't mean to move the screen around like that P is equal to E times I We have the P. Let me just move this over here is nine thousand nine hundred and forty six point seven watts We have the Voltage in this case, which is two hundred and forty volts So there's our P. There's our V So let's plug in what we know nine nine four six point seven is equal to E or the same as be same thing 240 times I I equals Punch this into the calculator divide that by 240 I equals 41.4 amps All right, just to refresh again what you do is you take your horsepower you multiply that by 746 That gives you your output power you take your output power You divide that by your motor efficiency that gives you your input power as Electricians that is the thing that we are concerned with we can take that input power And if we have voltage we can figure out current if we have current we can figure out voltage using watt slaw It's that easy doesn't need to over complicate things, but I find people get tripped up Just remember that your horsepower is your output and then you use that Efficiency formula to figure out what your input power is and from there you've got it golden