The Trainer #96: Master THIS to Accelerate Your Electrical Diag!

you know if you're like me diagnosing electrical problems it's one of your biggest challenges but what if I told you that after just taking a few simple measurements you can isolate the cause of the problem in 90% of the cases stick around that's the topic for today's edition of the trainer you know many technicians including yours truly often struggle with isolating the cause of an electrical problem now there are several reasons I think for this one is not really understanding what voltage is and the role it plays in the electrical circuit especially when it comes to understanding the concept of voltage drop and using that as a testing method to isolate the problem well I recently learned a new way to look at voltage and like to share that with you today I think it's a pretty safe bet that everyone watching understands what intake manifold vacuum is this low-pressure area in the intake is caused by the Pistons as they descend on their respective intake strokes on the other side of the throttle plate is atmospheric pressure higher than the pressure area in the intake manifold when the throttle plate is open that high pressure area will stream in to fill the low-pressure area and will continue to do so until the to equalize now if we compare atmospheric pressure to the amount of intake manifold vacuum achieved well that pressure difference is a number you should all be familiar with as well manifold absolute pressure getting current to flow is not all that much different the battery has a high number of electrons gathered around the positive post and a lower number at the negative post now the question is which way do the electrons flow well if we stick with our existing analogy it would seem to make sense that they would flow from the abundance on the positive side to the shortage on the negative side kind of that high pressure to low pressure concept that we've been talking about and that's called conventional current theory the only problem is it's not accurate CV electrons are negatively charged and the flow is actually reversed from negative to positive is it important to know in order for me to fix the car do I really care whether the electrons are going this way or that no all I know is that if I put my positive meter lead on the positive side of the battery and my negative meter lead on the negative side of the battery I'm measuring the voltage potential between the two leads or what's in the battery and I can take that one step further anywhere I place my meter leads in the circuit whether it's across the load or a section of wiring it's going to tell me any electro-motive potential or pressure or difference any voltage between those two leads if I haven't read a negative number well my orientation is backward to get an accurate reading all I have to do is swap leads when the circuit is on electrical pressure that is voltage causes the electrons to move through the circuit that's current and that is measured in terms of amperage or amps the energy carried by the electron flow is used to perform the work in the circuit the work may be illuminating a light bulb or turning a motor or creating the magnetic field that opens the fuel injector or fires the spark plug and the device our component in the circuit that is responsible for doing the work it's called the load okay let's see if I can explain this in a way that makes sense electrons don't move willingly in fact the more electrons there are in the outer ring of the atom of the material that we're trying to cause them to move in the harder it is which is why some materials make good conductors like copper for example with only I think one electron in the outer ring it's compared to other insulated materials that have say more than three or four in the outer ring more three than you really need to fix the car but what you do need to understand to fix the car is that that opposition to flow is called resistance and statically we can measure it in units called ohms but I'm not too interested in static resistance I'm more interested in what's happening when the circuits actually trying to function when it's turned on dynamic resistance and that's a big difference when the current is flowing through this circuit and we are able to use voltage to push the electrons through the circuit once it passes the major sources of resistance usually the load whether that be a headlight or motor or whatever that pressure will fall away to nothing so if we take a look at it with our bull meter we should be able to see the voltage potential the pressure present on the positive side of the load and once that pressure has managed to push the electrons through it should have all fallen off there should be zero or very little pressure left on the other side make sense hang on we're not done quite yet let's start with this fundamental principle all available voltage is used to overcome the resistance in the circuit okay so let's think about that for a minute in a perfect world the load the device doing the work the lightbulb the motor the solenoid whatever the case might be should be the only real source of resistance that we need to concern ourselves with but we have to keep in mind that everything in the circuit has some resistance it's small but everything else has some resistance so everything in the pathway from the beginning of the battery all the way through to the load and back to the battery again is offering sources of resistance to current flow that has to be overcome and that means there's going to be some voltage drop across each and every one of them the main source though should only be the load let's go back to that fundamental principle that we've been talking about all voltage applied will be used to overcome the resistances in the circuit is more accurately stated as all voltage applied will be used to overcome all sources of resistance in the circuit proportionally if one resistor has 10 ohms of resistance and we measured the drop in pressure or voltage across it we'll get nearly source voltage at the positive side of the resistor and almost a perfect 0 volts on the other side the resistor any minor variations can be accounted for by the wiring and other components that make up the circuit path now add a second 10 ohm resistor in series with the first what do you think will happen when we go down the line and take our measurements at the first resistor we should still measure the source voltage we started with just as we did earlier moving to the ground side of the first resistor will now measure roughly half of the source voltage that's because the voltage is being shared between the two just as the rule we just learned explained with no other major sources of resistance between the ground side the first resistor and the positive side of the second we should read the same amount of electrical pressure when we measure here when we move our meter lead to the ground side of the second resistor it should now return to a more normal level of close to zero volts now this whole concept of how different resistance sources in the circuit will take their share of voltage is very important it's critical for you to understand and if you're going to apply voltage drop testing to help you find electrical problems so let's go recap real really quick two resistors in the circuit each of them in this case were 10 ohms so they were equal in resistance because they were equal the voltage was split equally in hack between the two now yeah we had a little bit short going in from what we started at the battery with that the battery and we had a little bit left over at the end what was this attributable to well there's still some minor sources of resistance in the circuit isn't there there's the wiring there's the connectors switches fuses all of these apply some resistance to the circuit but it's minor compared to what the loads apply in this case we had two loads in the circuit wired in series now that's not the Norn right that's not the norm usually a load is not wired in series with another load so that single load as we went back to our first example that single load should be the only real source of resistance and we should see in a normal test saying on a light bulb or a motor or anything else for that matter if I measure the voltage going in it should be darn close to what I started with and when I measured the load on the of ol tidge on the other side there should be very very little left over again why because all of the voltage applied will be used to overcome the sources of resistance in the circuit proportionally in proportion and here's another thing that I really want you to lock in and make sure you understand it's probably something that you've heard more than you care to hear it and that's Ohm's law it seems that every electrical presentation or class I give I bring up the idea of Ohm's law and I'm not gonna ask you to do any any math here to figure out anything but what I do want to understand is that Ohm's law is a great way to understand how voltage resistance and current interact more importantly how changes in either of the first two voltage resistance is going to affect current flow in the circuit remember for example what Ohm's law has to say about the relationship between voltage and current flow if voltage decreases current flow also decreases take a moment about that two resistor circuit we had just over 12 volts going in but is that how much voltage was actually being applied to each resistor and we can use our voltmeter to help us answer that question you remember what I said about how the voltmeter works it's measuring the difference in electro-motive potential pressure between the two test leads just if if we had stuck one side nanosphere pressure and the other end of the intake manifold to get manifold absolute pressure by placing our meter leads on two points across the circuit we can measure the electro-motive potential between those two leads in this case just like we suspected about half of our source voltage now let's just take a moment to consider what we learned so far and think about in terms of something real-world something easy like a headlight bulb what if the first resistor was a headlight ball and that second resistor represents some form of resistance in the circuit that isn't supposed to be there that can be caused by a lot of things can it connector that's loose or corroded a weak ground a damaged connector a host of other possibilities comes to mind but the whole concept though is that that extra source of resistance is doing what it's taking its fair share of the total available voltage remember all the voltage is going to be used to overcome all all the sources of resistance in the circuit proportionally whether they were designed there and existing from the day the car was built to something that happened to it in the years that has been on the road all the sources of resistance are going to take their fair share and what happens when they well as we just showed you all the other resistances in the circuit are getting a much reduced level of voltage than they should be getting and that circles us back to where owns law voltage decreases what happens to current flow decreases and if there's less current flowing through that headlight bulb what's the light going to look like you bet you dim or not functioning at all now when a customer brings you a complaint that turns out to be electrically related very rarely does he or she tell you that from the outset usually it's in the form of something that isn't working the way it should maybe a headlights out or the horn sounds funny or the power seat won't move or something along those lines has to do with the work that the shirk is designed to do and what does the work in the circuit the load and that's where we're going to start our investigation the first step is to take a look at the wiring diagram and identify the load and its connections specifically we want to identify where the voltage is coming in and where it's going back out to ground this is where we're going to take two out of our three measurements now before we dive in to troubleshooting our customers complaint the very first thing I want you to do is test the battery make sure that it's healthy there's no need to go out after an electrical problem when we have a bad source to begin with so make sure that's working the way it should it's good and healthy before you proceed now once you confirm that the battery is okay I want you to take a voltage measurement at the battery that's your source voltage and I want you to measure it under the same conditions that the circuit that's having a problem needs to operate for example if you're doing an AC compressor clutch diagnosis well that AC is not going to turn on unless the engine is running is it so measure your source voltage with the engine running and the AC on headlight for example I don't need the engine running to check the headlight so I'm just going to turn the key on turn the headlights on and measure my source voltage under those conditions you understand why in a moment now move your positive meter lead to the positive side of the load in the circuit that you're testing and get as close to the load as you can while leaving your negative meter lead at the battery now keep in mind voltage drop is a dynamic measurement and current must be flowing for voltage drop to occur by leaving your negative meter lead at the battery you're also testing the entire circuit path at one time again the circuit has to be on in order for this test to be accurate that means if you're testing the horn circuit you've got to blow the horn and if it's a brake light circuit you got to step on the brakes so make sure that the circuit is operating while performing these tests the reading you took at the battery earlier and the reading that you just measured at the load should be relatively the same give or take a few tenths of a volt any small difference is caused by everything else in the circuit path the wire the connections switches and fuses for example remember the rule now if we don't measure very close to source voltage if we only measure say 1/2 then that's our indication that there's a problem and the problem exists between we're measuring now and where we measured last somewhere between the positive side the battery and the positive side of the load but let's just assume for a moment that all is okay so far and we're reading what we should be remember the rule now if I move my positive meter lead to the ground side of the load I should read what if you said close to zero you're absolutely right because all the voltage potential is used to overcome the resistances in the circuit and what's the only real source of resistance that should exist in our circuit the load a few tents that are left over well that's the wiring the connections and so forth in the path remaining between the ground point of the load and the negative side of the battery just like the example we looked at earlier when we use that single 10 ohm resistor so with only three measurements you're able to check the integrity of the entire electrical circuit that your customer has an issue with if the readings are not what we expect them to be then that's the side of the circuit that has the issue let me share some more specific examples of the types of readings you just might see and what they mean [Music] I want to really kind of hammer in a little bit more in that very last example that I just shared number one it's because that's the one you're gonna see most of the time when you're looking for problems on your customers vehicles it's usually ground related and a lot of people get thrown off when they see a voltage reading doing this test they're thinking both my meter leads on grounds how can I be reading a voltage all voltage is going to be used to overcome all the sources of resistance in proportion remember that rule remember that two resistor example a second resistor is that unplanned unwanted thief that's on the ground side of my primary load and it's just waiting to take its fair share it's not even waiting it's demanding and it's taking it right off the top and it's splitting it in proportion with the load so if you're getting a voltage reading on the ground side more than a few tenths then your problem is on the ground side and it's because there's another source a major source of resistance somewhere between your two test leads because what does that meter do it measures the potential between its leads these are all key things that I want you to think about and I want you to practice with until you make them your own believe me when you do when you work with this you're just gonna have that aha moment and all this is gonna seem so simple to you that I promise so anyway I hope that you found today's video helpful please review it as much as you need to in order to grasp those concepts take some wiring take a few light bulbs take a battery take some time and try these things for yourself build a little simple circuit measure the difference of voltages at different points in the circuit so you can see for yourself the impact the voltage drop has on the circuit more importantly how you can use it to find the problems that you're not finding today I paid Myer thanks for watching you

Channel: Motor Age

Views: 45,128

Rating: 4.9512196 out of 5

Keywords: motor age, the trainer, automotive repair, car repair, auto how to, how to fix my car, auto tech, auto technician, auto service professional

Id: jxKco2D9i-0

Length: 21min 49sec (1309 seconds)

Published: Wed Dec 11 2019