So we had calculated that we would have to point for two amps, but in actuality we only have 0.36, which means that Ohm's law is not a liar. We have some resistance, that's showing up somewhere and that resistance is what we call inductive reactance hey thanks for watching this video, which is about inductive reactance and really impedance, impedance, being total resistance, inductive reactance and in typical, measured ohms resistance that we can measure in a Resistive load, so it's really the effects of resistive loads and inductive loads together and how that all works out without being overly complicated. What this comes down to is that Ohm's law gets a little complicated when you're working with magnetic loads, and so a load is an electrical device. That does something so a motor is a load or a light bulb is a load.

It's the part that actually does something in a circuit, and so with something simple like a oven. Coil, for example, that is a resistive load or a lightbulb, is a resistive load. Even those can be difficult to apply Ohm's law, for example, with a light bulb once that filament heats up, which is usually tungsten once that fill tungsten, filament heats up the resistance and that filament actually increases quite a bit, and so what you measure with an ohm Meter and try to work, Ohm's law beforehand doesn't really work in practice and with inductive loads, it's even more extreme, and so I'm gon na demonstrate why you can't just take an ohm measurement, use Ohm's law and figure out what the amperage will be. Okay.

So, let's look at some inductive and one resistive load here and show kind of what the difference is so first off, let's identify what these are. This is a 9340 relay. It has a magnetic coil. This is a typical 40 amp compressor contactor.

It has a magnetic coil and this is a stack sequencer and a stack sequencer uses bimetallic disks. A lot of people call thermo discs, they're, actually two dissimilar metals that have different expansion and contraction rates. So, basically, if you imagine them kind of they kind of pop up in place, and so they make or break the switches using these thermo discs, but rather than a mag, there's actually just a little heater down here in the bottom. In fact, when you energize it, you can actually feel a little bit of that heat as the heat travels up into the sequencer.

It causes these thermo discs. These snap action discs to activate and deactivate open and close so because this is a resistive load, it's going to function much more closely to Ohm's law, based on the resistance that I can measure on a meter, then the other relays that use magnetic coils will - and I'm going to show you how that works, so, first off we're expecting everything to behave according to e equals. I times R. I like this little rector's thing equals I times.

R is volts, equals amps times ohms and so we're gon na start by measuring the ohms on all three and we're gon na keep a little tally here on the side. So you can remember it easily we're gon na put this on home scale. So we've got the meter on ohms scale and our relay coil is this beeping noise kind of annoying to our relay coil is 18.3 ohms. So relay coil.

Eighteen point: three: ohms contactor coil: let's see what we get here, eleven point: seven ohms, so we would expect this to draw a slightly more amperage, eleven point, seven and then our heat sequencer. While that really went up so now we have sixty eight point six. So you have sixty eight point. Six.

We have eleven point: seven. 18.3. Okay, so we work Ohm's law, Ohm's law is gon na, be pretty easy in this calculation. First thing we need to do, though, is we need to actually measure what our voltage is.

So that way we can plug that in so I'm gon na put my meter in here. Volt meter see what our applied voltage is. So thirty eight point three or twenty eight point three. I should say so: I'm going to take the volts part and replace that with twenty eight point.

Three, so there's twenty eight hi hey equals amps times resistance. So all we have to do now is take these three numbers. 18 point three for the relay eleven point: seven for the contactor in sixty eight point, six for the heat, sequencer plug them into this equation, and that should tell us what our resistance issue. So we got a calculator here, we're gon na start with our we'll start with our Heat sequencer.

So we'll take twenty eight point: three: we're going to divide that by sixty eight point, six equals point four. What's the point four one will say: okay, so we'll write that down here. 0.41. That's our sequencer! The eleven point: seven is our contactor, so we're gon na take twenty eight point.

Three divided by eleven point. Seven two point: four: two: we're gon na round up to point four: two amps you're, probably noticing that seems a little high and we'll take our relay twenty eight point. Three divided by our ohms 18.3 equals one point: we'll save one point: five, five roundup. One point: five: five, all right, so these are this - is our resistances up here.

Sixty eight point, six, eleven point: seven. Eighteen point: three: we know our volts are twenty eight point three: this is our formula e equals. I times R or some people prefer V equals a times R, so it's volts amps resistance based on our calculations, our amps for our relation, be one point: five, five for a contactor to be two point, four two and for our resistive load, which is our heater On our little stack, sequencer should be point four one. So, let's see what we actually get start with the contactor that shows that it was supposed to be the highest of them at point.

Our 2.42 just gon na plug it into the coil. This is our electromagnetic coil, then I'm plugging in two on both sides to a 24 volt transformer and flip. The switch on you heard. The contactor pull in and our amps are only 0.36 amps, which means that if we do the calculation, that means that we have an effective resistance.

That's quite a bit different than what we thought. So we had calculated that we would have 2.4 2 amps, but in actuality we only have 0.36, which means that Ohm's law is not a liar. We have some resistance, that's showing up somewhere and that resistance is what we call inductive reactance. So I can actually tell you what the total circuit impedance is.

All I have to do is plug in what the actual amperage is. So that is actually 3 6. So if we knew that our voltage is 28 point 3 and we know that our actual amperage is 0.36 28.3 - that's our voltage. We divide it by our actual amperage, which is 0.36, and that gives us what our true circuit ohms are, and that would be an impedance impedance is the combination of both the resistive ohms that you can measure with a meter while it's static plus the inductive reactance, That occurs within a electromagnet due to the expanding and collapsing electrical fields.

I'm not going to explain it any more than that, but just recognize with an electromagnet. You get this additional resistance that only shows up once you energize the load. Now, let's try the relay see what we get just for giggles, so the relay is also an electromagnet, so inductive reactance comes into play and now you can see we have 0.39 amps. When we anticipated, we would have 1.5 v based on just doing the math of Ohm's law.

So again, Ohm's law is not broken. It's just that you can't on a electromagnet. You can't measure that resistance beforehand and inspected to stay the same and even in a resistive load. There is some variance as the resistor heats up.

It's not going to be exactly the same either, but let's see, if we're closer or not now on the stack sequencer, which uses a heater, we're expecting it to be point 4, 1 and let's see what we get so we can see. Initially, it jumped up a little bit higher, but now that amperage is diving quite a bit, something about that resistor! That's in there cause that resists that amperage to be a little bit higher at first, but now it's diving down and that that amperage is actually even going below the target that we thought we would get. But as you can see, this is much closer to what we expected, then what we got when we were doing it with the inductive loads. So because now it's heated up the resistance of that heater inside our stack sequencer is actually now even greater than what it was before and so we're even seeing a little bit lower amperage due to the properties of the metal.

That's used in that heater, and so it varies a little bit even with resistive loads as those resistors heat up and cool down. But what you will notice is that we're just much closer to that target that we thought we would be and it continues to drop as that heater warms up even further in the case of a resistive load, all of the resistance comes from the resistor itself directly. In an inductive load, which just means magnetic like a motor compressor, the coil on a relay anything that uses magnetics, you can't directly just measure the ohms use Ohm's law to figure out what it's going to be. You have to know what effect inductive reactance will have on that electromagnet.

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